Merge pull request #82 from binwiederhier/attachments

Attachments
2022-01-13 15:47:58 -05:00 · 2022-01-13 15:47:58 -05:00 · bc16ef8480
parent 014b561b29 6a7b20e4e3
commit bc16ef8480
36 changed files with 2161 additions and 341 deletions
--- a/.gitignore
+++ b/.gitignore
@ -3,4 +3,5 @@ build/
 .idea/
 server/docs/
 tools/fbsend/fbsend
+playground/
 *.iml
--- a/client/client.go
+++ b/client/client.go
@ -67,6 +67,12 @@ func New(config *Config) *Client {
 }

 // Publish sends a message to a specific topic, optionally using options.
+// See PublishReader for details.
+func (c *Client) Publish(topic, message string, options ...PublishOption) (*Message, error) {
+	return c.PublishReader(topic, strings.NewReader(message), options...)
+}
+
+// PublishReader sends a message to a specific topic, optionally using options.
 //
 // A topic can be either a full URL (e.g. https://myhost.lan/mytopic), a short URL which is then prepended https://
 // (e.g. myhost.lan -> https://myhost.lan), or a short name which is expanded using the default host in the
@ -74,9 +80,9 @@ func New(config *Config) *Client {
 //
 // To pass title, priority and tags, check out WithTitle, WithPriority, WithTagsList, WithDelay, WithNoCache,
 // WithNoFirebase, and the generic WithHeader.
-func (c *Client) Publish(topic, message string, options ...PublishOption) (*Message, error) {
+func (c *Client) PublishReader(topic string, body io.Reader, options ...PublishOption) (*Message, error) {
 	topicURL := c.expandTopicURL(topic)
-	req, _ := http.NewRequest("POST", topicURL, strings.NewReader(message))
+	req, _ := http.NewRequest("POST", topicURL, body)
 	for _, option := range options {
 		if err := option(req); err != nil {
 			return nil, err
--- a/client/options.go
+++ b/client/options.go
@ -16,6 +16,11 @@ type PublishOption = RequestOption
 // SubscribeOption is an option that can be passed to a Client.Subscribe or Client.Poll call
 type SubscribeOption = RequestOption

+// WithMessage sets the notification message. This is an alternative way to passing the message body.
+func WithMessage(message string) PublishOption {
+	return WithHeader("X-Message", message)
+}
+
 // WithTitle adds a title to a message
 func WithTitle(title string) PublishOption {
 	return WithHeader("X-Title", title)
@ -50,6 +55,16 @@ func WithClick(url string) PublishOption {
 	return WithHeader("X-Click", url)
 }

+// WithAttach sets a URL that will be used by the client to download an attachment
+func WithAttach(attach string) PublishOption {
+	return WithHeader("X-Attach", attach)
+}
+
+// WithFilename sets a filename for the attachment, and/or forces the HTTP body to interpreted as an attachment
+func WithFilename(filename string) PublishOption {
+	return WithHeader("X-Filename", filename)
+}
+
 // WithEmail instructs the server to also send the message to the given e-mail address
 func WithEmail(email string) PublishOption {
 	return WithHeader("X-Email", email)
--- a/cmd/publish.go
+++ b/cmd/publish.go
@ -5,6 +5,9 @@ import (
 	"fmt"
 	"github.com/urfave/cli/v2"
 	"heckel.io/ntfy/client"
+	"io"
+	"os"
+	"path/filepath"
 	"strings"
 )

@ -21,6 +24,9 @@ var cmdPublish = &cli.Command{
 		&cli.StringFlag{Name: "tags", Aliases: []string{"tag", "T"}, Usage: "comma separated list of tags and emojis"},
 		&cli.StringFlag{Name: "delay", Aliases: []string{"at", "in", "D"}, Usage: "delay/schedule message"},
 		&cli.StringFlag{Name: "click", Aliases: []string{"U"}, Usage: "URL to open when notification is clicked"},
+		&cli.StringFlag{Name: "attach", Aliases: []string{"a"}, Usage: "URL to send as an external attachment"},
+		&cli.StringFlag{Name: "filename", Aliases: []string{"name", "n"}, Usage: "Filename for the attachment"},
+		&cli.StringFlag{Name: "file", Aliases: []string{"f"}, Usage: "File to upload as an attachment"},
 		&cli.StringFlag{Name: "email", Aliases: []string{"e-mail", "mail", "e"}, Usage: "also send to e-mail address"},
 		&cli.BoolFlag{Name: "no-cache", Aliases: []string{"C"}, Usage: "do not cache message server-side"},
 		&cli.BoolFlag{Name: "no-firebase", Aliases: []string{"F"}, Usage: "do not forward message to Firebase"},
@ -37,6 +43,9 @@ Examples:
  ntfy pub --at=8:30am delayed_topic Laterzz              # Send message at 8:30am
  ntfy pub -e phil@example.com alerts 'App is down!'      # Also send email to phil@example.com
  ntfy pub --click="https://reddit.com" redd 'New msg'    # Opens Reddit when notification is clicked
+  ntfy pub --attach="http://some.tld/file.zip" files      # Send ZIP archive from URL as attachment
+  ntfy pub --file=flower.jpg flowers 'Nice!'              # Send image.jpg as attachment
+  cat flower.jpg | ntfy pub --file=- flowers 'Nice!'      # Same as above, send image.jpg as attachment
  ntfy trigger mywebhook                                  # Sending without message, useful for webhooks

 Please also check out the docs on publishing messages. Especially for the --tags and --delay options, 
@ -59,6 +68,9 @@ func execPublish(c *cli.Context) error {
 	tags := c.String("tags")
 	delay := c.String("delay")
 	click := c.String("click")
+	attach := c.String("attach")
+	filename := c.String("filename")
+	file := c.String("file")
 	email := c.String("email")
 	noCache := c.Bool("no-cache")
 	noFirebase := c.Bool("no-firebase")
@ -82,7 +94,13 @@ func execPublish(c *cli.Context) error {
 		options = append(options, client.WithDelay(delay))
 	}
 	if click != "" {
-		options = append(options, client.WithClick(email))
+		options = append(options, client.WithClick(click))
+	}
+	if attach != "" {
+		options = append(options, client.WithAttach(attach))
+	}
+	if filename != "" {
+		options = append(options, client.WithFilename(filename))
 	}
 	if email != "" {
 		options = append(options, client.WithEmail(email))
@ -93,8 +111,30 @@ func execPublish(c *cli.Context) error {
 	if noFirebase {
 		options = append(options, client.WithNoFirebase())
 	}
+	var body io.Reader
+	if file == "" {
+		body = strings.NewReader(message)
+	} else {
+		if message != "" {
+			options = append(options, client.WithMessage(message))
+		}
+		if file == "-" {
+			if filename == "" {
+				options = append(options, client.WithFilename("stdin"))
+			}
+			body = c.App.Reader
+		} else {
+			if filename == "" {
+				options = append(options, client.WithFilename(filepath.Base(file)))
+			}
+			body, err = os.Open(file)
+			if err != nil {
+				return err
+			}
+		}
+	}
 	cl := client.New(conf)
-	m, err := cl.Publish(topic, message, options...)
+	m, err := cl.PublishReader(topic, body, options...)
 	if err != nil {
 		return err
 	}
--- a/cmd/serve.go
+++ b/cmd/serve.go
@ -2,11 +2,13 @@ package cmd

 import (
 	"errors"
+	"fmt"
 	"github.com/urfave/cli/v2"
 	"github.com/urfave/cli/v2/altsrc"
 	"heckel.io/ntfy/server"
 	"heckel.io/ntfy/util"
 	"log"
+	"math"
 	"time"
 )

@ -20,6 +22,10 @@ var flagsServe = []cli.Flag{
 	altsrc.NewStringFlag(&cli.StringFlag{Name: "firebase-key-file", Aliases: []string{"F"}, EnvVars: []string{"NTFY_FIREBASE_KEY_FILE"}, Usage: "Firebase credentials file; if set additionally publish to FCM topic"}),
 	altsrc.NewStringFlag(&cli.StringFlag{Name: "cache-file", Aliases: []string{"C"}, EnvVars: []string{"NTFY_CACHE_FILE"}, Usage: "cache file used for message caching"}),
 	altsrc.NewDurationFlag(&cli.DurationFlag{Name: "cache-duration", Aliases: []string{"b"}, EnvVars: []string{"NTFY_CACHE_DURATION"}, Value: server.DefaultCacheDuration, Usage: "buffer messages for this time to allow `since` requests"}),
+	altsrc.NewStringFlag(&cli.StringFlag{Name: "attachment-cache-dir", EnvVars: []string{"NTFY_ATTACHMENT_CACHE_DIR"}, Usage: "cache directory for attached files"}),
+	altsrc.NewStringFlag(&cli.StringFlag{Name: "attachment-total-size-limit", Aliases: []string{"A"}, EnvVars: []string{"NTFY_ATTACHMENT_TOTAL_SIZE_LIMIT"}, DefaultText: "5G", Usage: "limit of the on-disk attachment cache"}),
+	altsrc.NewStringFlag(&cli.StringFlag{Name: "attachment-file-size-limit", Aliases: []string{"Y"}, EnvVars: []string{"NTFY_ATTACHMENT_FILE_SIZE_LIMIT"}, DefaultText: "15M", Usage: "per-file attachment size limit (e.g. 300k, 2M, 100M)"}),
+	altsrc.NewDurationFlag(&cli.DurationFlag{Name: "attachment-expiry-duration", Aliases: []string{"X"}, EnvVars: []string{"NTFY_ATTACHMENT_EXPIRY_DURATION"}, Value: server.DefaultAttachmentExpiryDuration, DefaultText: "3h", Usage: "duration after which uploaded attachments will be deleted (e.g. 3h, 20h)"}),
 	altsrc.NewDurationFlag(&cli.DurationFlag{Name: "keepalive-interval", Aliases: []string{"k"}, EnvVars: []string{"NTFY_KEEPALIVE_INTERVAL"}, Value: server.DefaultKeepaliveInterval, Usage: "interval of keepalive messages"}),
 	altsrc.NewDurationFlag(&cli.DurationFlag{Name: "manager-interval", Aliases: []string{"m"}, EnvVars: []string{"NTFY_MANAGER_INTERVAL"}, Value: server.DefaultManagerInterval, Usage: "interval of for message pruning and stats printing"}),
 	altsrc.NewStringFlag(&cli.StringFlag{Name: "smtp-sender-addr", EnvVars: []string{"NTFY_SMTP_SENDER_ADDR"}, Usage: "SMTP server address (host:port) for outgoing emails"}),
@ -29,8 +35,10 @@ var flagsServe = []cli.Flag{
 	altsrc.NewStringFlag(&cli.StringFlag{Name: "smtp-server-listen", EnvVars: []string{"NTFY_SMTP_SERVER_LISTEN"}, Usage: "SMTP server address (ip:port) for incoming emails, e.g. :25"}),
 	altsrc.NewStringFlag(&cli.StringFlag{Name: "smtp-server-domain", EnvVars: []string{"NTFY_SMTP_SERVER_DOMAIN"}, Usage: "SMTP domain for incoming e-mail, e.g. ntfy.sh"}),
 	altsrc.NewStringFlag(&cli.StringFlag{Name: "smtp-server-addr-prefix", EnvVars: []string{"NTFY_SMTP_SERVER_ADDR_PREFIX"}, Usage: "SMTP email address prefix for topics to prevent spam (e.g. 'ntfy-')"}),
-	altsrc.NewIntFlag(&cli.IntFlag{Name: "global-topic-limit", Aliases: []string{"T"}, EnvVars: []string{"NTFY_GLOBAL_TOPIC_LIMIT"}, Value: server.DefaultGlobalTopicLimit, Usage: "total number of topics allowed"}),
+	altsrc.NewIntFlag(&cli.IntFlag{Name: "global-topic-limit", Aliases: []string{"T"}, EnvVars: []string{"NTFY_GLOBAL_TOPIC_LIMIT"}, Value: server.DefaultTotalTopicLimit, Usage: "total number of topics allowed"}),
 	altsrc.NewIntFlag(&cli.IntFlag{Name: "visitor-subscription-limit", EnvVars: []string{"NTFY_VISITOR_SUBSCRIPTION_LIMIT"}, Value: server.DefaultVisitorSubscriptionLimit, Usage: "number of subscriptions per visitor"}),
+	altsrc.NewStringFlag(&cli.StringFlag{Name: "visitor-attachment-total-size-limit", EnvVars: []string{"NTFY_VISITOR_ATTACHMENT_TOTAL_SIZE_LIMIT"}, Value: "100M", Usage: "total storage limit used for attachments per visitor"}),
+	altsrc.NewStringFlag(&cli.StringFlag{Name: "visitor-attachment-daily-bandwidth-limit", EnvVars: []string{"NTFY_VISITOR_ATTACHMENT_DAILY_BANDWIDTH_LIMIT"}, Value: "500M", Usage: "total daily attachment download/upload bandwidth limit per visitor"}),
 	altsrc.NewIntFlag(&cli.IntFlag{Name: "visitor-request-limit-burst", EnvVars: []string{"NTFY_VISITOR_REQUEST_LIMIT_BURST"}, Value: server.DefaultVisitorRequestLimitBurst, Usage: "initial limit of requests per visitor"}),
 	altsrc.NewDurationFlag(&cli.DurationFlag{Name: "visitor-request-limit-replenish", EnvVars: []string{"NTFY_VISITOR_REQUEST_LIMIT_REPLENISH"}, Value: server.DefaultVisitorRequestLimitReplenish, Usage: "interval at which burst limit is replenished (one per x)"}),
 	altsrc.NewIntFlag(&cli.IntFlag{Name: "visitor-email-limit-burst", EnvVars: []string{"NTFY_VISITOR_EMAIL_LIMIT_BURST"}, Value: server.DefaultVisitorEmailLimitBurst, Usage: "initial limit of e-mails per visitor"}),
@ -69,6 +77,10 @@ func execServe(c *cli.Context) error {
 	firebaseKeyFile := c.String("firebase-key-file")
 	cacheFile := c.String("cache-file")
 	cacheDuration := c.Duration("cache-duration")
+	attachmentCacheDir := c.String("attachment-cache-dir")
+	attachmentTotalSizeLimitStr := c.String("attachment-total-size-limit")
+	attachmentFileSizeLimitStr := c.String("attachment-file-size-limit")
+	attachmentExpiryDuration := c.Duration("attachment-expiry-duration")
 	keepaliveInterval := c.Duration("keepalive-interval")
 	managerInterval := c.Duration("manager-interval")
 	smtpSenderAddr := c.String("smtp-sender-addr")
@ -78,8 +90,10 @@ func execServe(c *cli.Context) error {
 	smtpServerListen := c.String("smtp-server-listen")
 	smtpServerDomain := c.String("smtp-server-domain")
 	smtpServerAddrPrefix := c.String("smtp-server-addr-prefix")
-	globalTopicLimit := c.Int("global-topic-limit")
+	totalTopicLimit := c.Int("global-topic-limit")
 	visitorSubscriptionLimit := c.Int("visitor-subscription-limit")
+	visitorAttachmentTotalSizeLimitStr := c.String("visitor-attachment-total-size-limit")
+	visitorAttachmentDailyBandwidthLimitStr := c.String("visitor-attachment-daily-bandwidth-limit")
 	visitorRequestLimitBurst := c.Int("visitor-request-limit-burst")
 	visitorRequestLimitReplenish := c.Duration("visitor-request-limit-replenish")
 	visitorEmailLimitBurst := c.Int("visitor-email-limit-burst")
@ -105,6 +119,28 @@ func execServe(c *cli.Context) error {
 		return errors.New("if smtp-sender-addr is set, base-url, smtp-sender-user, smtp-sender-pass and smtp-sender-from must also be set")
 	} else if smtpServerListen != "" && smtpServerDomain == "" {
 		return errors.New("if smtp-server-listen is set, smtp-server-domain must also be set")
+	} else if attachmentCacheDir != "" && baseURL == "" {
+		return errors.New("if attachment-cache-dir is set, base-url must also be set")
+	}
+
+	// Convert sizes to bytes
+	attachmentTotalSizeLimit, err := parseSize(attachmentTotalSizeLimitStr, server.DefaultAttachmentTotalSizeLimit)
+	if err != nil {
+		return err
+	}
+	attachmentFileSizeLimit, err := parseSize(attachmentFileSizeLimitStr, server.DefaultAttachmentFileSizeLimit)
+	if err != nil {
+		return err
+	}
+	visitorAttachmentTotalSizeLimit, err := parseSize(visitorAttachmentTotalSizeLimitStr, server.DefaultVisitorAttachmentTotalSizeLimit)
+	if err != nil {
+		return err
+	}
+	visitorAttachmentDailyBandwidthLimit, err := parseSize(visitorAttachmentDailyBandwidthLimitStr, server.DefaultVisitorAttachmentDailyBandwidthLimit)
+	if err != nil {
+		return err
+	} else if visitorAttachmentDailyBandwidthLimit > math.MaxInt {
+		return fmt.Errorf("config option visitor-attachment-daily-bandwidth-limit must be lower than %d", math.MaxInt)
 	}

 	// Run server
@ -117,6 +153,10 @@ func execServe(c *cli.Context) error {
 	conf.FirebaseKeyFile = firebaseKeyFile
 	conf.CacheFile = cacheFile
 	conf.CacheDuration = cacheDuration
+	conf.AttachmentCacheDir = attachmentCacheDir
+	conf.AttachmentTotalSizeLimit = attachmentTotalSizeLimit
+	conf.AttachmentFileSizeLimit = attachmentFileSizeLimit
+	conf.AttachmentExpiryDuration = attachmentExpiryDuration
 	conf.KeepaliveInterval = keepaliveInterval
 	conf.ManagerInterval = managerInterval
 	conf.SMTPSenderAddr = smtpSenderAddr
@ -126,8 +166,10 @@ func execServe(c *cli.Context) error {
 	conf.SMTPServerListen = smtpServerListen
 	conf.SMTPServerDomain = smtpServerDomain
 	conf.SMTPServerAddrPrefix = smtpServerAddrPrefix
-	conf.GlobalTopicLimit = globalTopicLimit
+	conf.TotalTopicLimit = totalTopicLimit
 	conf.VisitorSubscriptionLimit = visitorSubscriptionLimit
+	conf.VisitorAttachmentTotalSizeLimit = visitorAttachmentTotalSizeLimit
+	conf.VisitorAttachmentDailyBandwidthLimit = int(visitorAttachmentDailyBandwidthLimit)
 	conf.VisitorRequestLimitBurst = visitorRequestLimitBurst
 	conf.VisitorRequestLimitReplenish = visitorRequestLimitReplenish
 	conf.VisitorEmailLimitBurst = visitorEmailLimitBurst
@ -143,3 +185,14 @@ func execServe(c *cli.Context) error {
 	log.Printf("Exiting.")
 	return nil
 }
+
+func parseSize(s string, defaultValue int64) (v int64, err error) {
+	if s == "" {
+		return defaultValue, nil
+	}
+	v, err = util.ParseSize(s)
+	if err != nil {
+		return 0, err
+	}
+	return v, nil
+}
--- a/docs/config.md
+++ b/docs/config.md
@ -35,6 +35,43 @@ the message to the subscribers.
 Subscribers can retrieve cached messaging using the [`poll=1` parameter](subscribe/api.md#poll-for-messages), as well as the
 [`since=` parameter](subscribe/api.md#fetch-cached-messages).

+## Attachments
+If desired, you may allow users to upload and [attach files to notifications](publish.md#attachments). To enable
+this feature, you have to simply configure an attachment cache directory and a base URL (`attachment-cache-dir`, `base-url`). 
+Once these options are set and the directory is writable by the server user, you can upload attachments via PUT.
+
+By default, attachments are stored in the disk-cache **for only 3 hours**. The main reason for this is to avoid legal issues
+and such when hosting user controlled content. Typically, this is more than enough time for the user (or the auto download 
+feature) to download the file. The following config options are relevant to attachments:
+
+* `base-url` is the root URL for the ntfy server; this is needed for the generated attachment URLs
+* `attachment-cache-dir` is the cache directory for attached files
+* `attachment-total-size-limit` is the size limit of the on-disk attachment cache (default: 5G)
+* `attachment-file-size-limit` is the per-file attachment size limit (e.g. 300k, 2M, 100M, default: 15M)
+* `attachment-expiry-duration` is the duration after which uploaded attachments will be deleted (e.g. 3h, 20h, default: 3h)
+
+Here's an example config using mostly the defaults (except for the cache directory, which is empty by default): 
+
+=== "/etc/ntfy/server.yml (minimal)"
+    ``` yaml
+    base-url: "https://ntfy.sh"
+    attachment-cache-dir: "/var/cache/ntfy/attachments"
+    ```
+
+=== "/etc/ntfy/server.yml (all options)"
+    ``` yaml
+    base-url: "https://ntfy.sh"
+    attachment-cache-dir: "/var/cache/ntfy/attachments"
+    attachment-total-size-limit: "5G"
+    attachment-file-size-limit: "15M"
+    attachment-expiry-duration: "3h"
+    visitor-attachment-total-size-limit: "100M"
+    visitor-attachment-daily-bandwidth-limit: "500M"
+    ```
+
+Please also refer to the [rate limiting](#rate-limiting) settings below, specifically `visitor-attachment-total-size-limit`
+and `visitor-attachment-daily-bandwidth-limit`. Setting these conservatively is necessary to avoid abuse.
+
 ## E-mail notifications
 To allow forwarding messages via e-mail, you can configure an **SMTP server for outgoing messages**. Once configured, 
 you can set the `X-Email` header to [send messages via e-mail](publish.md#e-mail-notifications) (e.g. 
@ -124,7 +161,7 @@ which lets you use [AWS Route 53](https://aws.amazon.com/route53/) as the challe
 HTTP challenge. I've found [this guide](https://nandovieira.com/using-lets-encrypt-in-development-with-nginx-and-aws-route53) to
 be incredibly helpful.

-### nginx/Apache2
+### nginx/Apache2/caddy
 For your convenience, here's a working config that'll help configure things behind a proxy. In this 
 example, ntfy runs on `:2586` and we proxy traffic to it. We also redirect HTTP to HTTPS for GET requests against a topic
 or the root domain:
@ -153,6 +190,7 @@ or the root domain:
        proxy_http_version 1.1;
    
        proxy_buffering off;
+        proxy_request_buffering off;
        proxy_redirect off;
     
        proxy_set_header Host $http_host;
@ -161,6 +199,8 @@ or the root domain:
        proxy_connect_timeout 3m;
        proxy_send_timeout 3m;
        proxy_read_timeout 3m;
+
+        client_max_body_size 20m; # Must be >= attachment-file-size-limit in /etc/ntfy/server.yml
      }
    }
    
@ -179,8 +219,9 @@ or the root domain:
      location / {
        proxy_pass http://127.0.0.1:2586;
        proxy_http_version 1.1;
-    
+
        proxy_buffering off;
+        proxy_request_buffering off;
        proxy_redirect off;
     
        proxy_set_header Host $http_host;
@ -189,6 +230,8 @@ or the root domain:
        proxy_connect_timeout 3m;
        proxy_send_timeout 3m;
        proxy_read_timeout 3m;
+        
+        client_max_body_size 20m; # Must be >= attachment-file-size-limit in /etc/ntfy/server.yml
      }
    }
    ```
@ -239,6 +282,19 @@ or the root domain:
    </VirtualHost>
    ```

+=== "caddy"
+    ```
+    # Note that this config is most certainly incomplete. Please help out and let me know what's missing
+    # via Discord/Matrix or in a GitHub issue.
+
+    ntfy.sh {
+        reverse_proxy 127.0.0.1:2586
+    }
+    http://nfty.sh {
+        reverse_proxy 127.0.0.1:2586
+    }
+    ```
+
 ## Firebase (FCM)
 !!! info
    Using Firebase is **optional** and only works if you modify and [build your own Android .apk](develop.md#android-app).
@ -272,14 +328,23 @@ firebase-key-file: "/etc/ntfy/ntfy-sh-firebase-adminsdk-ahnce-9f4d6f14b5.json"
    Otherwise, all visitors are rate limited as if they are one.

 By default, ntfy runs without authentication, so it is vitally important that we protect the server from abuse or overload.
-There are various limits and rate limits in place that you can use to configure the server. Let's do the easy ones first:
+There are various limits and rate limits in place that you can use to configure the server:

-* `global-topic-limit` defines the total number of topics before the server rejects new topics. It defaults to 5000.
+* **Global limit**: A global limit applies across all visitors (IPs, clients, users)
+* **Visitor limit**: A visitor limit only applies to a certain visitor. A **visitor** is identified by its IP address 
+  (or the `X-Forwarded-For` header if `behind-proxy` is set). All config options that start with the word `visitor` apply 
+  only on a per-visitor basis.
+
+During normal usage, you shouldn't encounter these limits at all, and even if you burst a few requests or emails
+(e.g. when you reconnect after a connection drop), it shouldn't have any effect.
+
+### General limits
+Let's do the easy limits first:
+
+* `global-topic-limit` defines the total number of topics before the server rejects new topics. It defaults to 15,000.
 * `visitor-subscription-limit` is the number of subscriptions (open connections) per visitor. This value defaults to 30.

-A **visitor** is identified by its IP address (or the `X-Forwarded-For` header if `behind-proxy` is set). All config 
-options that start with the word `visitor` apply only on a per-visitor basis.   
-
+### Request limits
 In addition to the limits above, there is a requests/second limit per visitor for all sensitive GET/PUT/POST requests.
 This limit uses a [token bucket](https://en.wikipedia.org/wiki/Token_bucket) (using Go's [rate package](https://pkg.go.dev/golang.org/x/time/rate)):

@ -290,15 +355,24 @@ request every 10s (defined by `visitor-request-limit-replenish`)
 * `visitor-request-limit-burst` is the initial bucket of requests each visitor has. This defaults to 60.
 * `visitor-request-limit-replenish` is the rate at which the bucket is refilled (one request per x). Defaults to 10s.

+### Attachment limits
+Aside from the global file size and total attachment cache limits (see [above](#attachments)), there are two relevant 
+per-visitor limits:
+
+* `visitor-attachment-total-size-limit` is the total storage limit used for attachments per visitor. It defaults to 100M.
+  The per-visitor storage is automatically decreased as attachments expire. External attachments (attached via `X-Attach`, 
+  see [publishing docs](publish.md#attachments)) do not count here. 
+* `visitor-attachment-daily-bandwidth-limit` is the total daily attachment download/upload bandwidth limit per visitor, 
+  including PUT and GET requests. This is to protect your precious bandwidth from abuse, since egress costs money in
+  most cloud providers. This defaults to 500M.
+
+### E-mail limits
 Similarly to the request limit, there is also an e-mail limit (only relevant if [e-mail notifications](#e-mail-notifications) 
 are enabled):

 * `visitor-email-limit-burst` is the initial bucket of emails each visitor has. This defaults to 16.
 * `visitor-email-limit-replenish` is the rate at which the bucket is refilled (one email per x). Defaults to 1h.

-During normal usage, you shouldn't encounter these limits at all, and even if you burst a few requests or emails
-(e.g. when you reconnect after a connection drop), it shouldn't have any effect.
-
 ## Tuning for scale
 If you're running ntfy for your home server, you probably don't need to worry about scale at all. In its default config,
 if it's not behind a proxy, the ntfy server can keep about **as many connections as the open file limit allows**.
@ -309,7 +383,7 @@ Depending on *how you run it*, here are a few limits that are relevant:

 ### For systemd services
 If you're running ntfy in a systemd service (e.g. for .deb/.rpm packages), the main limiting factor is the
-`LimitNOFILE` setting in the systemd unit. The default open files limit for `ntfy.service` is 10000. You can override it
+`LimitNOFILE` setting in the systemd unit. The default open files limit for `ntfy.service` is 10,000. You can override it
 by creating a `/etc/systemd/system/ntfy.service.d/override.conf` file. As far as I can tell, `/etc/security/limits.conf`
 is not relevant.

@ -322,7 +396,7 @@ is not relevant.

 ### Outside of systemd
 If you're running outside systemd, you may want to adjust your `/etc/security/limits.conf` file to
-increase the `nofile` setting. Here's an example that increases the limit to 5000. You can find out the current setting
+increase the `nofile` setting. Here's an example that increases the limit to 5,000. You can find out the current setting
 by running `ulimit -n`, or manually override it temporarily by running `ulimit -n 50000`.

 === "/etc/security/limits.conf"
@ -403,34 +477,41 @@ Each config option can be set in the config file `/etc/ntfy/server.yml` (e.g. `l
 CLI option (e.g. `--listen-http :80`. Here's a list of all available options. Alternatively, you can set an environment
 variable before running the `ntfy` command (e.g. `export NTFY_LISTEN_HTTP=:80`).

-| Config option | Env variable | Format | Default | Description |
-|---|---|---|---|---|
-| `base-url` | `NTFY_BASE_URL` | *URL* | - | Public facing base URL of the service (e.g. `https://ntfy.sh`) |
-| `listen-http` | `NTFY_LISTEN_HTTP` | `[host]:port` | `:80` | Listen address for the HTTP web server |
-| `listen-https` | `NTFY_LISTEN_HTTPS` | `[host]:port` | - | Listen address for the HTTPS web server. If set, you also need to set `key-file` and `cert-file`. |
-| `key-file` | `NTFY_KEY_FILE` | *filename* | - | HTTPS/TLS private key file, only used if `listen-https` is set. |
-| `cert-file` | `NTFY_CERT_FILE` | *filename* | - | HTTPS/TLS certificate file, only used if `listen-https` is set. |
-| `firebase-key-file` | `NTFY_FIREBASE_KEY_FILE` | *filename* | - | If set, also publish messages to a Firebase Cloud Messaging (FCM) topic for your app. This is optional and only required to save battery when using the Android app. See [Firebase (FCM](#firebase-fcm). |
-| `cache-file` | `NTFY_CACHE_FILE` | *filename* | - | If set, messages are cached in a local SQLite database instead of only in-memory. This allows for service restarts without losing messages in support of the since= parameter. See [message cache](#message-cache). |
-| `cache-duration` | `NTFY_CACHE_DURATION` | *duration* | 12h | Duration for which messages will be buffered before they are deleted. This is required to support the `since=...` and `poll=1` parameter. Set this to `0` to disable the cache entirely. |
-| `behind-proxy` | `NTFY_BEHIND_PROXY` | *bool* | false | If set, the X-Forwarded-For header is used to determine the visitor IP address instead of the remote address of the connection. |
-| `smtp-sender-addr` | `NTFY_SMTP_SENDER_ADDR` | `host:port` | - | SMTP server address to allow email sending |
-| `smtp-sender-user` | `NTFY_SMTP_SENDER_USER` | *string* | - | SMTP user; only used if e-mail sending is enabled |
-| `smtp-sender-pass` | `NTFY_SMTP_SENDER_PASS` | *string* | - | SMTP password; only used if e-mail sending is enabled |
-| `smtp-sender-from` | `NTFY_SMTP_SENDER_FROM` | *e-mail address* | - | SMTP sender e-mail address; only used if e-mail sending is enabled |
-| `smtp-server-listen` | `NTFY_SMTP_SERVER_LISTEN` | `[ip]:port` | - | Defines the IP address and port the SMTP server will listen on, e.g. `:25` or `1.2.3.4:25` |
-| `smtp-server-domain` | `NTFY_SMTP_SERVER_DOMAIN` | *domain name* | - | SMTP server e-mail domain, e.g. `ntfy.sh` |
-| `smtp-server-addr-prefix` | `NTFY_SMTP_SERVER_ADDR_PREFIX` | `[ip]:port` | - |  Optional prefix for the e-mail addresses to prevent spam, e.g. `ntfy-` |
-| `keepalive-interval` | `NTFY_KEEPALIVE_INTERVAL` | *duration* | 55s | Interval in which keepalive messages are sent to the client. This is to prevent intermediaries closing the connection for inactivity. Note that the Android app has a hardcoded timeout at 77s, so it should be less than that. |
-| `manager-interval` | `$NTFY_MANAGER_INTERVAL` | *duration* | 1m | Interval in which the manager prunes old messages, deletes topics and prints the stats. |
-| `global-topic-limit` | `NTFY_GLOBAL_TOPIC_LIMIT` | *number* | 5000 | Rate limiting: Total number of topics before the server rejects new topics. |
-| `visitor-subscription-limit` | `NTFY_VISITOR_SUBSCRIPTION_LIMIT` | *number* | 30 | Rate limiting: Number of subscriptions per visitor (IP address) |
-| `visitor-request-limit-burst` | `NTFY_VISITOR_REQUEST_LIMIT_BURST` | *number* | 60 | Allowed GET/PUT/POST requests per second, per visitor. This setting is the initial bucket of requests each visitor has |
-| `visitor-request-limit-replenish` | `NTFY_VISITOR_REQUEST_LIMIT_REPLENISH` | *duration* | 10s | Strongly related to `visitor-request-limit-burst`: The rate at which the bucket is refilled |
-| `visitor-email-limit-burst` | `NTFY_VISITOR_EMAIL_LIMIT_BURST` | *number* | 16 |Initial limit of e-mails per visitor |
-| `visitor-email-limit-replenish` | `NTFY_VISITOR_EMAIL_LIMIT_REPLENISH` | *duration* | 1h | Strongly related to `visitor-email-limit-burst`: The rate at which the bucket is refilled |
+| Config option                              | Env variable                                    | Format           | Default | Description                                                                                                                                                                                                                     |
+|--------------------------------------------|-------------------------------------------------|------------------|---------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| `base-url`                                 | `NTFY_BASE_URL`                                 | *URL*            | -       | Public facing base URL of the service (e.g. `https://ntfy.sh`)                                                                                                                                                                  |
+| `listen-http`                              | `NTFY_LISTEN_HTTP`                              | `[host]:port`    | `:80`   | Listen address for the HTTP web server                                                                                                                                                                                          |
+| `listen-https`                             | `NTFY_LISTEN_HTTPS`                             | `[host]:port`    | -       | Listen address for the HTTPS web server. If set, you also need to set `key-file` and `cert-file`.                                                                                                                               |
+| `key-file`                                 | `NTFY_KEY_FILE`                                 | *filename*       | -       | HTTPS/TLS private key file, only used if `listen-https` is set.                                                                                                                                                                 |
+| `cert-file`                                | `NTFY_CERT_FILE`                                | *filename*       | -       | HTTPS/TLS certificate file, only used if `listen-https` is set.                                                                                                                                                                 |
+| `firebase-key-file`                        | `NTFY_FIREBASE_KEY_FILE`                        | *filename*       | -       | If set, also publish messages to a Firebase Cloud Messaging (FCM) topic for your app. This is optional and only required to save battery when using the Android app. See [Firebase (FCM](#firebase-fcm).                        |
+| `cache-file`                               | `NTFY_CACHE_FILE`                               | *filename*       | -       | If set, messages are cached in a local SQLite database instead of only in-memory. This allows for service restarts without losing messages in support of the since= parameter. See [message cache](#message-cache).             |
+| `cache-duration`                           | `NTFY_CACHE_DURATION`                           | *duration*       | 12h     | Duration for which messages will be buffered before they are deleted. This is required to support the `since=...` and `poll=1` parameter. Set this to `0` to disable the cache entirely.                                        |
+| `behind-proxy`                             | `NTFY_BEHIND_PROXY`                             | *bool*           | false   | If set, the X-Forwarded-For header is used to determine the visitor IP address instead of the remote address of the connection.                                                                                                 |
+| `attachment-cache-dir`                     | `NTFY_ATTACHMENT_CACHE_DIR`                     | *directory*      | -       | Cache directory for attached files. To enable attachments, this has to be set.                                                                                                                                                  |
+| `attachment-total-size-limit`              | `NTFY_ATTACHMENT_TOTAL_SIZE_LIMIT`              | *size*           | 5G      | Limit of the on-disk attachment cache directory. If the limits is exceeded, new attachments will be rejected.                                                                                                                   |
+| `attachment-file-size-limit`               | `NTFY_ATTACHMENT_FILE_SIZE_LIMIT`               | *size*           | 15M     | Per-file attachment size limit (e.g. 300k, 2M, 100M). Larger attachment will be rejected.                                                                                                                                       |
+| `attachment-expiry-duration`               | `NTFY_ATTACHMENT_EXPIRY_DURATION`               | *duration*       | 3h      | Duration after which uploaded attachments will be deleted (e.g. 3h, 20h). Strongly affects `visitor-attachment-total-size-limit`.                                                                                               |
+| `smtp-sender-addr`                         | `NTFY_SMTP_SENDER_ADDR`                         | `host:port`      | -       | SMTP server address to allow email sending                                                                                                                                                                                      |
+| `smtp-sender-user`                         | `NTFY_SMTP_SENDER_USER`                         | *string*         | -       | SMTP user; only used if e-mail sending is enabled                                                                                                                                                                               |
+| `smtp-sender-pass`                         | `NTFY_SMTP_SENDER_PASS`                         | *string*         | -       | SMTP password; only used if e-mail sending is enabled                                                                                                                                                                           |
+| `smtp-sender-from`                         | `NTFY_SMTP_SENDER_FROM`                         | *e-mail address* | -       | SMTP sender e-mail address; only used if e-mail sending is enabled                                                                                                                                                              |
+| `smtp-server-listen`                       | `NTFY_SMTP_SERVER_LISTEN`                       | `[ip]:port`      | -       | Defines the IP address and port the SMTP server will listen on, e.g. `:25` or `1.2.3.4:25`                                                                                                                                      |
+| `smtp-server-domain`                       | `NTFY_SMTP_SERVER_DOMAIN`                       | *domain name*    | -       | SMTP server e-mail domain, e.g. `ntfy.sh`                                                                                                                                                                                       |
+| `smtp-server-addr-prefix`                  | `NTFY_SMTP_SERVER_ADDR_PREFIX`                  | `[ip]:port`      | -       | Optional prefix for the e-mail addresses to prevent spam, e.g. `ntfy-`                                                                                                                                                          |
+| `keepalive-interval`                       | `NTFY_KEEPALIVE_INTERVAL`                       | *duration*       | 55s     | Interval in which keepalive messages are sent to the client. This is to prevent intermediaries closing the connection for inactivity. Note that the Android app has a hardcoded timeout at 77s, so it should be less than that. |
+| `manager-interval`                         | `$NTFY_MANAGER_INTERVAL`                        | *duration*       | 1m      | Interval in which the manager prunes old messages, deletes topics and prints the stats.                                                                                                                                         |
+| `global-topic-limit`                       | `NTFY_GLOBAL_TOPIC_LIMIT`                       | *number*         | 15,000  | Rate limiting: Total number of topics before the server rejects new topics.                                                                                                                                                     |
+| `visitor-subscription-limit`               | `NTFY_VISITOR_SUBSCRIPTION_LIMIT`               | *number*         | 30      | Rate limiting: Number of subscriptions per visitor (IP address)                                                                                                                                                                 |
+| `visitor-attachment-total-size-limit`      | `NTFY_VISITOR_ATTACHMENT_TOTAL_SIZE_LIMIT`      | *size*           | 100M    | Rate limiting: Total storage limit used for attachments per visitor, for all attachments combined. Storage is freed after attachments expire. See `attachment-expiry-duration`.                                                 |
+| `visitor-attachment-daily-bandwidth-limit` | `NTFY_VISITOR_ATTACHMENT_DAILY_BANDWIDTH_LIMIT` | *size*           | 500M    | Rate limiting: Total daily attachment download/upload traffic limit per visitor. This is to protect your bandwidth costs from exploding.                                                                                        |
+| `visitor-request-limit-burst`              | `NTFY_VISITOR_REQUEST_LIMIT_BURST`              | *number*         | 60      | Rate limiting: Allowed GET/PUT/POST requests per second, per visitor. This setting is the initial bucket of requests each visitor has                                                                                           |
+| `visitor-request-limit-replenish`          | `NTFY_VISITOR_REQUEST_LIMIT_REPLENISH`          | *duration*       | 10s     | Rate limiting: Strongly related to `visitor-request-limit-burst`: The rate at which the bucket is refilled                                                                                                                      |
+| `visitor-email-limit-burst`                | `NTFY_VISITOR_EMAIL_LIMIT_BURST`                | *number*         | 16      | Rate limiting:Initial limit of e-mails per visitor                                                                                                                                                                              |
+| `visitor-email-limit-replenish`            | `NTFY_VISITOR_EMAIL_LIMIT_REPLENISH`            | *duration*       | 1h      | Rate limiting: Strongly related to `visitor-email-limit-burst`: The rate at which the bucket is refilled                                                                                                                        |

-The format for a *duration* is: `<number>(smh)`, e.g. 30s, 20m or 1h.
+The format for a *duration* is: `<number>(smh)`, e.g. 30s, 20m or 1h.   
+The format for a *size* is: `<number>(GMK)`, e.g. 1G, 200M or 4000k.

 ## Command line options
 ```
@ -452,31 +533,37 @@ DESCRIPTION:
     ntfy serve --listen-http :8080  # Starts server with alternate port

 OPTIONS:
-   --config value, -c value                 config file (default: /etc/ntfy/server.yml) [$NTFY_CONFIG_FILE]
-   --base-url value, -B value               externally visible base URL for this host (e.g. https://ntfy.sh) [$NTFY_BASE_URL]
-   --listen-http value, -l value            ip:port used to as HTTP listen address (default: ":80") [$NTFY_LISTEN_HTTP]
-   --listen-https value, -L value           ip:port used to as HTTPS listen address [$NTFY_LISTEN_HTTPS]
-   --key-file value, -K value               private key file, if listen-https is set [$NTFY_KEY_FILE]
-   --cert-file value, -E value              certificate file, if listen-https is set [$NTFY_CERT_FILE]
-   --firebase-key-file value, -F value      Firebase credentials file; if set additionally publish to FCM topic [$NTFY_FIREBASE_KEY_FILE]
-   --cache-file value, -C value             cache file used for message caching [$NTFY_CACHE_FILE]
-   --cache-duration since, -b since         buffer messages for this time to allow since requests (default: 12h0m0s) [$NTFY_CACHE_DURATION]
-   --keepalive-interval value, -k value     interval of keepalive messages (default: 55s) [$NTFY_KEEPALIVE_INTERVAL]
-   --manager-interval value, -m value       interval of for message pruning and stats printing (default: 1m0s) [$NTFY_MANAGER_INTERVAL]
-   --smtp-sender-addr value                 SMTP server address (host:port) for outgoing emails [$NTFY_SMTP_SENDER_ADDR]
-   --smtp-sender-user value                 SMTP user (if e-mail sending is enabled) [$NTFY_SMTP_SENDER_USER]
-   --smtp-sender-pass value                 SMTP password (if e-mail sending is enabled) [$NTFY_SMTP_SENDER_PASS]
-   --smtp-sender-from value                 SMTP sender address (if e-mail sending is enabled) [$NTFY_SMTP_SENDER_FROM]
-   --smtp-server-listen value               SMTP server address (ip:port) for incoming emails, e.g. :25 [$NTFY_SMTP_SERVER_LISTEN]
-   --smtp-server-domain value               SMTP domain for incoming e-mail, e.g. ntfy.sh [$NTFY_SMTP_SERVER_DOMAIN]
-   --smtp-server-addr-prefix value          SMTP email address prefix for topics to prevent spam (e.g. 'ntfy-') [$NTFY_SMTP_SERVER_ADDR_PREFIX]
-   --global-topic-limit value, -T value     total number of topics allowed (default: 5000) [$NTFY_GLOBAL_TOPIC_LIMIT]
-   --visitor-subscription-limit value       number of subscriptions per visitor (default: 30) [$NTFY_VISITOR_SUBSCRIPTION_LIMIT]
-   --visitor-request-limit-burst value      initial limit of requests per visitor (default: 60) [$NTFY_VISITOR_REQUEST_LIMIT_BURST]
-   --visitor-request-limit-replenish value  interval at which burst limit is replenished (one per x) (default: 10s) [$NTFY_VISITOR_REQUEST_LIMIT_REPLENISH]
-   --visitor-email-limit-burst value        initial limit of e-mails per visitor (default: 16) [$NTFY_VISITOR_EMAIL_LIMIT_BURST]
-   --visitor-email-limit-replenish value    interval at which burst limit is replenished (one per x) (default: 1h0m0s) [$NTFY_VISITOR_EMAIL_LIMIT_REPLENISH]
-   --behind-proxy, -P                       if set, use X-Forwarded-For header to determine visitor IP address (for rate limiting) (default: false) [$NTFY_BEHIND_PROXY]
-   --help, -h                               show help (default: false)
+   --config value, -c value                          config file (default: /etc/ntfy/server.yml) [$NTFY_CONFIG_FILE]
+   --base-url value, -B value                        externally visible base URL for this host (e.g. https://ntfy.sh) [$NTFY_BASE_URL]
+   --listen-http value, -l value                     ip:port used to as HTTP listen address (default: ":80") [$NTFY_LISTEN_HTTP]
+   --listen-https value, -L value                    ip:port used to as HTTPS listen address [$NTFY_LISTEN_HTTPS]
+   --key-file value, -K value                        private key file, if listen-https is set [$NTFY_KEY_FILE]
+   --cert-file value, -E value                       certificate file, if listen-https is set [$NTFY_CERT_FILE]
+   --firebase-key-file value, -F value               Firebase credentials file; if set additionally publish to FCM topic [$NTFY_FIREBASE_KEY_FILE]
+   --cache-file value, -C value                      cache file used for message caching [$NTFY_CACHE_FILE]
+   --cache-duration since, -b since                  buffer messages for this time to allow since requests (default: 12h0m0s) [$NTFY_CACHE_DURATION]
+   --attachment-cache-dir value                      cache directory for attached files [$NTFY_ATTACHMENT_CACHE_DIR]
+   --attachment-total-size-limit value, -A value     limit of the on-disk attachment cache (default: 5G) [$NTFY_ATTACHMENT_TOTAL_SIZE_LIMIT]
+   --attachment-file-size-limit value, -Y value      per-file attachment size limit (e.g. 300k, 2M, 100M) (default: 15M) [$NTFY_ATTACHMENT_FILE_SIZE_LIMIT]
+   --attachment-expiry-duration value, -X value      duration after which uploaded attachments will be deleted (e.g. 3h, 20h) (default: 3h) [$NTFY_ATTACHMENT_EXPIRY_DURATION]
+   --keepalive-interval value, -k value              interval of keepalive messages (default: 55s) [$NTFY_KEEPALIVE_INTERVAL]
+   --manager-interval value, -m value                interval of for message pruning and stats printing (default: 1m0s) [$NTFY_MANAGER_INTERVAL]
+   --smtp-sender-addr value                          SMTP server address (host:port) for outgoing emails [$NTFY_SMTP_SENDER_ADDR]
+   --smtp-sender-user value                          SMTP user (if e-mail sending is enabled) [$NTFY_SMTP_SENDER_USER]
+   --smtp-sender-pass value                          SMTP password (if e-mail sending is enabled) [$NTFY_SMTP_SENDER_PASS]
+   --smtp-sender-from value                          SMTP sender address (if e-mail sending is enabled) [$NTFY_SMTP_SENDER_FROM]
+   --smtp-server-listen value                        SMTP server address (ip:port) for incoming emails, e.g. :25 [$NTFY_SMTP_SERVER_LISTEN]
+   --smtp-server-domain value                        SMTP domain for incoming e-mail, e.g. ntfy.sh [$NTFY_SMTP_SERVER_DOMAIN]
+   --smtp-server-addr-prefix value                   SMTP email address prefix for topics to prevent spam (e.g. 'ntfy-') [$NTFY_SMTP_SERVER_ADDR_PREFIX]
+   --global-topic-limit value, -T value              total number of topics allowed (default: 15000) [$NTFY_GLOBAL_TOPIC_LIMIT]
+   --visitor-subscription-limit value                number of subscriptions per visitor (default: 30) [$NTFY_VISITOR_SUBSCRIPTION_LIMIT]
+   --visitor-attachment-total-size-limit value       total storage limit used for attachments per visitor (default: "100M") [$NTFY_VISITOR_ATTACHMENT_TOTAL_SIZE_LIMIT]
+   --visitor-attachment-daily-bandwidth-limit value  total daily attachment download/upload bandwidth limit per visitor (default: "500M") [$NTFY_VISITOR_ATTACHMENT_DAILY_BANDWIDTH_LIMIT]
+   --visitor-request-limit-burst value               initial limit of requests per visitor (default: 60) [$NTFY_VISITOR_REQUEST_LIMIT_BURST]
+   --visitor-request-limit-replenish value           interval at which burst limit is replenished (one per x) (default: 10s) [$NTFY_VISITOR_REQUEST_LIMIT_REPLENISH]
+   --visitor-email-limit-burst value                 initial limit of e-mails per visitor (default: 16) [$NTFY_VISITOR_EMAIL_LIMIT_BURST]
+   --visitor-email-limit-replenish value             interval at which burst limit is replenished (one per x) (default: 1h0m0s) [$NTFY_VISITOR_EMAIL_LIMIT_REPLENISH]
+   --behind-proxy, -P                                if set, use X-Forwarded-For header to determine visitor IP address (for rate limiting) (default: false) [$NTFY_BEHIND_PROXY]
+   --help, -h                                        show help (default: false)
 ```

--- a/docs/publish.md
+++ b/docs/publish.md
@ -659,6 +659,166 @@ Here's an example that will open Reddit when the notification is clicked:
    ]));
    ```

+## Attachments
+You can **send images and other files to your phone** as attachments to a notification. The attachments are then downloaded
+onto your phone (depending on size and setting automatically), and can be used from the Downloads folder.
+
+There are two different ways to send attachments: 
+
+* sending [a local file](#attach-local-file) via PUT, e.g. from `~/Flowers/flower.jpg` or `ringtone.mp3`
+* or by [passing an external URL](#attach-file-from-a-url) as an attachment, e.g. `https://f-droid.org/F-Droid.apk` 
+
+### Attach local file
+To **send a file from your computer** as an attachment, you can send it as the PUT request body. If a message is greater 
+than the maximum message size (4,096 bytes) or consists of non UTF-8 characters, the ntfy server will automatically 
+detect the mime type and size, and send the message as an attachment file. To send smaller text-only messages or files 
+as attachments, you must pass a filename by passing the `X-Filename` header or query parameter (or any of its aliases 
+`Filename`, `File` or `f`). 
+
+By default, and how ntfy.sh is configured, the **max attachment size is 15 MB** (with 100 MB total per visitor). 
+Attachments **expire after 3 hours**, which typically is plenty of time for the user to download it, or for the Android app
+to auto-download it. Please also check out the [other limits below](#limitations).
+
+Here's an example showing how to upload an image:
+
+=== "Command line (curl)"
+    ```
+    curl \
+        -T flower.jpg \
+        -H "Filename: flower.jpg" \
+        ntfy.sh/flowers
+    ```
+
+=== "ntfy CLI"
+    ```
+    ntfy publish \
+        --file=flower.jpg \
+        flowers
+    ```
+
+=== "HTTP"
+    ``` http
+    PUT /flowers HTTP/1.1
+    Host: ntfy.sh
+    Filename: flower.jpg
+    Content-Type: 52312
+
+    <binary JPEG data>
+    ```
+
+=== "JavaScript"
+    ``` javascript
+    fetch('https://ntfy.sh/flowers', {
+        method: 'PUT',
+        body: document.getElementById("file").files[0],
+        headers: { 'Filename': 'flower.jpg' }
+    })
+    ```
+
+=== "Go"
+    ``` go
+    file, _ := os.Open("flower.jpg")
+    req, _ := http.NewRequest("PUT", "https://ntfy.sh/flowers", file)
+    req.Header.Set("Filename", "flower.jpg")
+    http.DefaultClient.Do(req)
+    ```
+
+=== "Python"
+    ``` python
+    requests.put("https://ntfy.sh/flowers",
+        data=open("flower.jpg", 'rb'),
+        headers={ "Filename": "flower.jpg" })
+    ```
+
+=== "PHP"
+    ``` php-inline
+    file_get_contents('https://ntfy.sh/flowers', false, stream_context_create([
+        'http' => [
+            'method' => 'PUT',
+            'header' =>
+                "Content-Type: application/octet-stream\r\n" . // Does not matter
+                "Filename: flower.jpg",
+            'content' => file_get_contents('flower.jpg') // Dangerous for large files 
+        ]
+    ]));
+    ```
+
+Here's what that looks like on Android:
+
+<figure markdown>
+  ![image attachment](static/img/android-screenshot-attachment-image.png){ width=500 }
+  <figcaption>Image attachment sent from a local file</figcaption>
+</figure>
+
+### Attach file from a URL
+Instead of sending a local file to your phone, you can use **an external URL** to specify where the attachment is hosted.
+This could be a Google Drive or Dropbox link, or any other publicly available URL. The ntfy server will briefly probe
+the URL to retrieve type and size for you. Since the files are externally hosted, the expiration or size limits from 
+above do not apply here.
+
+To attach an external file, simple pass the `X-Attach` header or query parameter (or any of its aliases `Attach` or `a`)
+to specify the attachment URL. It can be any type of file. Here's an example showing how to upload an image:
+
+=== "Command line (curl)"
+    ```
+    curl \
+        -X POST \
+        -H "Attach: https://f-droid.org/F-Droid.apk" \
+        ntfy.sh/mydownloads
+    ```
+
+=== "ntfy CLI"
+    ```
+    ntfy publish \
+        --attach="https://f-droid.org/F-Droid.apk" \
+        mydownloads
+    ```
+
+=== "HTTP"
+    ``` http
+    POST /mydownloads HTTP/1.1
+    Host: ntfy.sh
+    Attach: https://f-droid.org/F-Droid.apk
+    ```
+
+=== "JavaScript"
+    ``` javascript
+    fetch('https://ntfy.sh/mydownloads', {
+        method: 'POST',
+        headers: { 'Attach': 'https://f-droid.org/F-Droid.apk' }
+    })
+    ```
+
+=== "Go"
+    ``` go
+    req, _ := http.NewRequest("POST", "https://ntfy.sh/mydownloads", file)
+    req.Header.Set("Attach", "https://f-droid.org/F-Droid.apk")
+    http.DefaultClient.Do(req)
+    ```
+
+=== "Python"
+    ``` python
+    requests.put("https://ntfy.sh/mydownloads",
+        headers={ "Attach": "https://f-droid.org/F-Droid.apk" })
+    ```
+
+=== "PHP"
+    ``` php-inline
+    file_get_contents('https://ntfy.sh/mydownloads', false, stream_context_create([
+        'http' => [
+        'method' => 'PUT',
+        'header' =>
+            "Content-Type: text/plain\r\n" . // Does not matter
+            "Attach: https://f-droid.org/F-Droid.apk",
+        ]
+    ]));
+    ```
+
+<figure markdown>
+  ![file attachment](static/img/android-screenshot-attachment-file.png){ width=500 }
+  <figcaption>File attachment sent from an external URL</figcaption>
+</figure>
+
 ## E-mail notifications
 You can forward messages to e-mail by specifying an address in the header. This can be useful for messages that 
 you'd like to persist longer, or to blast-notify yourself on all possible channels. 
@ -927,17 +1087,33 @@ to `no`. This will instruct the server not to forward messages to Firebase.
    ]));
    ```

+### UnifiedPush
+!!! info
+    This setting is not relevant to users, only to app developers and people interested in [UnifiedPush](https://unifiedpush.org). 
+
+[UnifiedPush](https://unifiedpush.org) is a standard for receiving push notifications without using the Google-owned
+[Firebase Cloud Messaging (FCM)](https://firebase.google.com/docs/cloud-messaging) service. It puts push notifications
+in the control of the user. ntfy can act as a **UnifiedPush distributor**, forwarding messages to apps that support it.
+
+When publishing messages to a topic, apps using ntfy as a UnifiedPush distributor can set the `X-UnifiedPush` header or query
+parameter (or any of its aliases `unifiedpush` or `up`) to `1` to [disable Firebase](#disable-firebase). As of today, this
+option is equivalent to `Firebase: no`, but was introduced to allow future flexibility.
+
 ## Limitations
-There are a few limitations to the API to prevent abuse and to keep the server healthy. Most of them you won't run into,
+There are a few limitations to the API to prevent abuse and to keep the server healthy. Almost all of these settings 
+are configurable via the server side [rate limiting settings](config.md#rate-limiting). Most of these limits you won't run into,
 but just in case, let's list them all:

-| Limit | Description |
-|---|---|
-| **Message length** | Each message can be up to 4096 bytes long. Longer messages are truncated. |
-| **Requests** | By default, the server is configured to allow 60 requests at once, and then refills the your allowed requests bucket at a rate of one request per 10 seconds. You can read more about this in the [rate limiting](config.md#rate-limiting) section. |
-| **E-mails** | By default, the server is configured to allow sending 16 e-mails at once, and then refills the your allowed e-mail bucket at a rate of one per hour. You can read more about this in the [rate limiting](config.md#rate-limiting) section. |
-| **Subscription limits** | By default, the server allows each visitor to keep 30 connections to the server open. |
-| **Total number of topics** | By default, the server is configured to allow 5,000 topics. The ntfy.sh server has higher limits though. |
+| Limit                     | Description                                                                                                                                                               |
+|---------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| **Message length**        | Each message can be up to 4,096 bytes long. Longer messages are treated as [attachments](#attachments).                                                                   |
+| **Requests**              | By default, the server is configured to allow 60 requests per visitor at once, and then refills the your allowed requests bucket at a rate of one request per 10 seconds. |
+| **E-mails**               | By default, the server is configured to allow sending 16 e-mails per visitor at once, and then refills the your allowed e-mail bucket at a rate of one per hour.          |
+| **Subscription limit**    | By default, the server allows each visitor to keep 30 connections to the server open.                                                                                     |
+| **Attachment size limit** | By default, the server allows attachments up to 15 MB in size, up to 100 MB in total per visitor and up to 5 GB across all visitors.                                      |
+| **Attachment expiry**     | By default, the server deletes attachments after 3 hours and thereby frees up space from the total visitor attachment limit.                                              |
+| **Attachment bandwidth**  | By default, the server allows 500 MB of GET/PUT/POST traffic for attachments per visitor in a 24 hour period. Traffic exceeding that is rejected.                         |
+| **Total number of topics** | By default, the server is configured to allow 15,000 topics. The ntfy.sh server has higher limits though.                                                                 |

 ## List of all parameters
 The following is a list of all parameters that can be passed when publishing a message. Parameter names are **case-insensitive**,
@ -951,6 +1127,9 @@ and can be passed as **HTTP headers** or **query parameters in the URL**. They a
 | `X-Tags` | `Tags`, `Tag`, `ta` | [Tags and emojis](#tags-emojis) |
 | `X-Delay` | `Delay`, `X-At`, `At`, `X-In`, `In` | Timestamp or duration for [delayed delivery](#scheduled-delivery) |
 | `X-Click` | `Click` | URL to open when [notification is clicked](#click-action) |
+| `X-Attach` | `Attach`, `a` | URL to send as an [attachment](#attachments), as an alternative to PUT/POST-ing an attachment |
+| `X-Filename` | `Filename`, `file`, `f` | Optional [attachment](#attachments) filename, as it appears in the client |
 | `X-Email` | `X-E-Mail`, `Email`, `E-Mail`, `mail`, `e` | E-mail address for [e-mail notifications](#e-mail-notifications) |
 | `X-Cache` | `Cache` | Allows disabling [message caching](#message-caching) |
 | `X-Firebase` | `Firebase` | Allows disabling [sending to Firebase](#disable-firebase) |
+| `X-UnifiedPush` | `UnifiedPush`, `up` | [UnifiedPush](#unifiedpush) publish option, currently equivalent to `Firebase: no` |
--- a/docs/static/img/android-screenshot-attachment-file.png
+++ b/docs/static/img/android-screenshot-attachment-file.png
--- a/docs/static/img/android-screenshot-attachment-image.png
+++ b/docs/static/img/android-screenshot-attachment-image.png
--- a/go.mod
+++ b/go.mod
@ -30,6 +30,7 @@ require (
 	github.com/emersion/go-sasl v0.0.0-20200509203442-7bfe0ed36a21 // indirect
 	github.com/envoyproxy/go-control-plane v0.10.1 // indirect
 	github.com/envoyproxy/protoc-gen-validate v0.6.2 // indirect
+	github.com/gabriel-vasile/mimetype v1.4.0 // indirect
 	github.com/golang/groupcache v0.0.0-20210331224755-41bb18bfe9da // indirect
 	github.com/golang/protobuf v1.5.2 // indirect
 	github.com/google/go-cmp v0.5.6 // indirect
--- a/go.sum
+++ b/go.sum
@ -106,6 +106,8 @@ github.com/envoyproxy/go-control-plane v0.10.1/go.mod h1:AY7fTTXNdv/aJ2O5jwpxAPO
 github.com/envoyproxy/protoc-gen-validate v0.1.0/go.mod h1:iSmxcyjqTsJpI2R4NaDN7+kN2VEUnK/pcBlmesArF7c=
 github.com/envoyproxy/protoc-gen-validate v0.6.2 h1:JiO+kJTpmYGjEodY7O1Zk8oZcNz1+f30UtwtXoFUPzE=
 github.com/envoyproxy/protoc-gen-validate v0.6.2/go.mod h1:2t7qjJNvHPx8IjnBOzl9E9/baC+qXE/TeeyBRzgJDws=
+github.com/gabriel-vasile/mimetype v1.4.0 h1:Cn9dkdYsMIu56tGho+fqzh7XmvY2YyGU0FnbhiOsEro=
+github.com/gabriel-vasile/mimetype v1.4.0/go.mod h1:fA8fi6KUiG7MgQQ+mEWotXoEOvmxRtOJlERCzSmRvr8=
 github.com/ghodss/yaml v1.0.0/go.mod h1:4dBDuWmgqj2HViK6kFavaiC9ZROes6MMH2rRYeMEF04=
 github.com/go-gl/glfw v0.0.0-20190409004039-e6da0acd62b1/go.mod h1:vR7hzQXu2zJy9AVAgeJqvqgH9Q5CA+iKCZ2gyEVpxRU=
 github.com/go-gl/glfw/v3.3/glfw v0.0.0-20191125211704-12ad95a8df72/go.mod h1:tQ2UAYgL5IevRw8kRxooKSPJfGvJ9fJQFa0TUsXzTg8=
@ -323,6 +325,7 @@ golang.org/x/net v0.0.0-20210226172049-e18ecbb05110/go.mod h1:m0MpNAwzfU5UDzcl9v
 golang.org/x/net v0.0.0-20210316092652-d523dce5a7f4/go.mod h1:RBQZq4jEuRlivfhVLdyRGr576XBO4/greRjx4P4O3yc=
 golang.org/x/net v0.0.0-20210405180319-a5a99cb37ef4/go.mod h1:p54w0d4576C0XHj96bSt6lcn1PtDYWL6XObtHCRCNQM=
 golang.org/x/net v0.0.0-20210503060351-7fd8e65b6420/go.mod h1:9nx3DQGgdP8bBQD5qxJ1jj9UTztislL4KSBs9R2vV5Y=
+golang.org/x/net v0.0.0-20210505024714-0287a6fb4125/go.mod h1:9nx3DQGgdP8bBQD5qxJ1jj9UTztislL4KSBs9R2vV5Y=
 golang.org/x/net v0.0.0-20210813160813-60bc85c4be6d h1:LO7XpTYMwTqxjLcGWPijK3vRXg1aWdlNOVOHRq45d7c=
 golang.org/x/net v0.0.0-20210813160813-60bc85c4be6d/go.mod h1:9nx3DQGgdP8bBQD5qxJ1jj9UTztislL4KSBs9R2vV5Y=
 golang.org/x/oauth2 v0.0.0-20180821212333-d2e6202438be/go.mod h1:N/0e6XlmueqKjAGxoOufVs8QHGRruUQn6yWY3a++T0U=
--- a/scripts/postinst.sh
+++ b/scripts/postinst.sh
@ -4,8 +4,6 @@ set -e
 # Restart systemd service if it was already running. Note that "deb-systemd-invoke try-restart" will
 # only act if the service is already running. If it's not running, it's a no-op.
 #
-# TODO: This is only tested on Debian.
-#
 if [ "$1" = "configure" ] || [ "$1" -ge 1 ]; then
  if [ -d /run/systemd/system ]; then
    # Create ntfy user/group
--- a/server/cache.go
+++ b/server/cache.go
@ -20,4 +20,6 @@ type cache interface {
 	Topics() (map[string]*topic, error)
 	Prune(olderThan time.Time) error
 	MarkPublished(m *message) error
+	AttachmentsSize(owner string) (int64, error)
+	AttachmentsExpired() ([]string, error)
 }
--- a/server/cache_mem.go
+++ b/server/cache_mem.go
@ -125,6 +125,35 @@ func (c *memCache) Prune(olderThan time.Time) error {
 	return nil
 }

+func (c *memCache) AttachmentsSize(owner string) (int64, error) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	var size int64
+	for topic := range c.messages {
+		for _, m := range c.messages[topic] {
+			counted := m.Attachment != nil && m.Attachment.Owner == owner && m.Attachment.Expires > time.Now().Unix()
+			if counted {
+				size += m.Attachment.Size
+			}
+		}
+	}
+	return size, nil
+}
+
+func (c *memCache) AttachmentsExpired() ([]string, error) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	ids := make([]string, 0)
+	for topic := range c.messages {
+		for _, m := range c.messages[topic] {
+			if m.Attachment != nil && m.Attachment.Expires > 0 && m.Attachment.Expires < time.Now().Unix() {
+				ids = append(ids, m.ID)
+			}
+		}
+	}
+	return ids, nil
+}
+
 func (c *memCache) pruneTopic(topic string, olderThan time.Time) {
 	messages := make([]*message, 0)
 	for _, m := range c.messages[topic] {
--- a/server/cache_mem_test.go
+++ b/server/cache_mem_test.go
@ -25,6 +25,10 @@ func TestMemCache_Prune(t *testing.T) {
 	testCachePrune(t, newMemCache())
 }

+func TestMemCache_Attachments(t *testing.T) {
+	testCacheAttachments(t, newMemCache())
+}
+
 func TestMemCache_NopCache(t *testing.T) {
 	c := newNopCache()
 	assert.Nil(t, c.AddMessage(newDefaultMessage("mytopic", "my message")))
--- a/server/cache_sqlite.go
+++ b/server/cache_sqlite.go
@ -23,27 +23,36 @@ const (
 			priority INT NOT NULL,
 			tags TEXT NOT NULL,
 			click TEXT NOT NULL,
+			attachment_name TEXT NOT NULL,
+			attachment_type TEXT NOT NULL,
+			attachment_size INT NOT NULL,
+			attachment_expires INT NOT NULL,
+			attachment_url TEXT NOT NULL,
+			attachment_owner TEXT NOT NULL,
 			published INT NOT NULL
 		);
 		CREATE INDEX IF NOT EXISTS idx_topic ON messages (topic);
 		COMMIT;
 	`
-	insertMessageQuery           = `INSERT INTO messages (id, time, topic, message, title, priority, tags, click, published) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?)`
+	insertMessageQuery = `
+		INSERT INTO messages (id, time, topic, message, title, priority, tags, click, attachment_name, attachment_type, attachment_size, attachment_expires, attachment_url, attachment_owner, published) 
+		VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
+	`
 	pruneMessagesQuery           = `DELETE FROM messages WHERE time < ? AND published = 1`
 	selectMessagesSinceTimeQuery = `
-		SELECT id, time, topic, message, title, priority, tags, click
+		SELECT id, time, topic, message, title, priority, tags, click, attachment_name, attachment_type, attachment_size, attachment_expires, attachment_url, attachment_owner
 		FROM messages 
 		WHERE topic = ? AND time >= ? AND published = 1
 		ORDER BY time ASC
 	`
 	selectMessagesSinceTimeIncludeScheduledQuery = `
-		SELECT id, time, topic, message, title, priority, tags, click
+		SELECT id, time, topic, message, title, priority, tags, click, attachment_name, attachment_type, attachment_size, attachment_expires, attachment_url, attachment_owner
 		FROM messages 
 		WHERE topic = ? AND time >= ?
 		ORDER BY time ASC
 	`
 	selectMessagesDueQuery = `
-		SELECT id, time, topic, message, title, priority, tags, click
+		SELECT id, time, topic, message, title, priority, tags, click, attachment_name, attachment_type, attachment_size, attachment_expires, attachment_url, attachment_owner
 		FROM messages 
 		WHERE time <= ? AND published = 0
 	`
@ -51,6 +60,8 @@ const (
 	selectMessagesCountQuery        = `SELECT COUNT(*) FROM messages`
 	selectMessageCountForTopicQuery = `SELECT COUNT(*) FROM messages WHERE topic = ?`
 	selectTopicsQuery               = `SELECT topic FROM messages GROUP BY topic`
+	selectAttachmentsSizeQuery      = `SELECT IFNULL(SUM(attachment_size), 0) FROM messages WHERE attachment_owner = ? AND attachment_expires >= ?`
+	selectAttachmentsExpiredQuery   = `SELECT id FROM messages WHERE attachment_expires > 0 AND attachment_expires < ?`
 )

 // Schema management queries
@ -82,7 +93,15 @@ const (

 	// 2 -> 3
 	migrate2To3AlterMessagesTableQuery = `
+		BEGIN;
 		ALTER TABLE messages ADD COLUMN click TEXT NOT NULL DEFAULT('');
+		ALTER TABLE messages ADD COLUMN attachment_name TEXT NOT NULL DEFAULT('');
+		ALTER TABLE messages ADD COLUMN attachment_type TEXT NOT NULL DEFAULT('');
+		ALTER TABLE messages ADD COLUMN attachment_size INT NOT NULL DEFAULT('0');
+		ALTER TABLE messages ADD COLUMN attachment_expires INT NOT NULL DEFAULT('0');
+		ALTER TABLE messages ADD COLUMN attachment_owner TEXT NOT NULL DEFAULT('');
+		ALTER TABLE messages ADD COLUMN attachment_url TEXT NOT NULL DEFAULT('');
+		COMMIT;
 	`
 )

@ -110,7 +129,35 @@ func (c *sqliteCache) AddMessage(m *message) error {
 		return errUnexpectedMessageType
 	}
 	published := m.Time <= time.Now().Unix()
-	_, err := c.db.Exec(insertMessageQuery, m.ID, m.Time, m.Topic, m.Message, m.Title, m.Priority, strings.Join(m.Tags, ","), m.Click, published)
+	tags := strings.Join(m.Tags, ",")
+	var attachmentName, attachmentType, attachmentURL, attachmentOwner string
+	var attachmentSize, attachmentExpires int64
+	if m.Attachment != nil {
+		attachmentName = m.Attachment.Name
+		attachmentType = m.Attachment.Type
+		attachmentSize = m.Attachment.Size
+		attachmentExpires = m.Attachment.Expires
+		attachmentURL = m.Attachment.URL
+		attachmentOwner = m.Attachment.Owner
+	}
+	_, err := c.db.Exec(
+		insertMessageQuery,
+		m.ID,
+		m.Time,
+		m.Topic,
+		m.Message,
+		m.Title,
+		m.Priority,
+		tags,
+		m.Click,
+		attachmentName,
+		attachmentType,
+		attachmentSize,
+		attachmentExpires,
+		attachmentURL,
+		attachmentOwner,
+		published,
+	)
 	return err
 }

@ -187,30 +234,80 @@ func (c *sqliteCache) Prune(olderThan time.Time) error {
 	return err
 }

+func (c *sqliteCache) AttachmentsSize(owner string) (int64, error) {
+	rows, err := c.db.Query(selectAttachmentsSizeQuery, owner, time.Now().Unix())
+	if err != nil {
+		return 0, err
+	}
+	defer rows.Close()
+	var size int64
+	if !rows.Next() {
+		return 0, errors.New("no rows found")
+	}
+	if err := rows.Scan(&size); err != nil {
+		return 0, err
+	} else if err := rows.Err(); err != nil {
+		return 0, err
+	}
+	return size, nil
+}
+
+func (c *sqliteCache) AttachmentsExpired() ([]string, error) {
+	rows, err := c.db.Query(selectAttachmentsExpiredQuery, time.Now().Unix())
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	ids := make([]string, 0)
+	for rows.Next() {
+		var id string
+		if err := rows.Scan(&id); err != nil {
+			return nil, err
+		}
+		ids = append(ids, id)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return ids, nil
+}
+
 func readMessages(rows *sql.Rows) ([]*message, error) {
 	defer rows.Close()
 	messages := make([]*message, 0)
 	for rows.Next() {
-		var timestamp int64
+		var timestamp, attachmentSize, attachmentExpires int64
 		var priority int
-		var id, topic, msg, title, tagsStr, click string
-		if err := rows.Scan(&id, &timestamp, &topic, &msg, &title, &priority, &tagsStr, &click); err != nil {
+		var id, topic, msg, title, tagsStr, click, attachmentName, attachmentType, attachmentURL, attachmentOwner string
+		if err := rows.Scan(&id, &timestamp, &topic, &msg, &title, &priority, &tagsStr, &click, &attachmentName, &attachmentType, &attachmentSize, &attachmentExpires, &attachmentURL, &attachmentOwner); err != nil {
 			return nil, err
 		}
 		var tags []string
 		if tagsStr != "" {
 			tags = strings.Split(tagsStr, ",")
 		}
+		var att *attachment
+		if attachmentName != "" && attachmentURL != "" {
+			att = &attachment{
+				Name:    attachmentName,
+				Type:    attachmentType,
+				Size:    attachmentSize,
+				Expires: attachmentExpires,
+				URL:     attachmentURL,
+				Owner:   attachmentOwner,
+			}
+		}
 		messages = append(messages, &message{
-			ID:       id,
-			Time:     timestamp,
-			Event:    messageEvent,
-			Topic:    topic,
-			Message:  msg,
-			Title:    title,
-			Priority: priority,
-			Tags:     tags,
-			Click:    click,
+			ID:         id,
+			Time:       timestamp,
+			Event:      messageEvent,
+			Topic:      topic,
+			Message:    msg,
+			Title:      title,
+			Priority:   priority,
+			Tags:       tags,
+			Click:      click,
+			Attachment: att,
 		})
 	}
 	if err := rows.Err(); err != nil {
--- a/server/cache_sqlite_test.go
+++ b/server/cache_sqlite_test.go
@ -29,6 +29,10 @@ func TestSqliteCache_Prune(t *testing.T) {
 	testCachePrune(t, newSqliteTestCache(t))
 }

+func TestSqliteCache_Attachments(t *testing.T) {
+	testCacheAttachments(t, newSqliteTestCache(t))
+}
+
 func TestSqliteCache_Migration_From0(t *testing.T) {
 	filename := newSqliteTestCacheFile(t)
 	db, err := sql.Open("sqlite3", filename)
--- a/server/cache_test.go
+++ b/server/cache_test.go
@ -1,7 +1,7 @@
 package server

 import (
-	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 	"testing"
 	"time"
 )
@ -13,71 +13,71 @@ func testCacheMessages(t *testing.T, c cache) {
 	m2 := newDefaultMessage("mytopic", "my other message")
 	m2.Time = 2

-	assert.Nil(t, c.AddMessage(m1))
-	assert.Nil(t, c.AddMessage(newDefaultMessage("example", "my example message")))
-	assert.Nil(t, c.AddMessage(m2))
+	require.Nil(t, c.AddMessage(m1))
+	require.Nil(t, c.AddMessage(newDefaultMessage("example", "my example message")))
+	require.Nil(t, c.AddMessage(m2))

 	// Adding invalid
-	assert.Equal(t, errUnexpectedMessageType, c.AddMessage(newKeepaliveMessage("mytopic"))) // These should not be added!
-	assert.Equal(t, errUnexpectedMessageType, c.AddMessage(newOpenMessage("example")))      // These should not be added!
+	require.Equal(t, errUnexpectedMessageType, c.AddMessage(newKeepaliveMessage("mytopic"))) // These should not be added!
+	require.Equal(t, errUnexpectedMessageType, c.AddMessage(newOpenMessage("example")))      // These should not be added!

 	// mytopic: count
 	count, err := c.MessageCount("mytopic")
-	assert.Nil(t, err)
-	assert.Equal(t, 2, count)
+	require.Nil(t, err)
+	require.Equal(t, 2, count)

 	// mytopic: since all
 	messages, _ := c.Messages("mytopic", sinceAllMessages, false)
-	assert.Equal(t, 2, len(messages))
-	assert.Equal(t, "my message", messages[0].Message)
-	assert.Equal(t, "mytopic", messages[0].Topic)
-	assert.Equal(t, messageEvent, messages[0].Event)
-	assert.Equal(t, "", messages[0].Title)
-	assert.Equal(t, 0, messages[0].Priority)
-	assert.Nil(t, messages[0].Tags)
-	assert.Equal(t, "my other message", messages[1].Message)
+	require.Equal(t, 2, len(messages))
+	require.Equal(t, "my message", messages[0].Message)
+	require.Equal(t, "mytopic", messages[0].Topic)
+	require.Equal(t, messageEvent, messages[0].Event)
+	require.Equal(t, "", messages[0].Title)
+	require.Equal(t, 0, messages[0].Priority)
+	require.Nil(t, messages[0].Tags)
+	require.Equal(t, "my other message", messages[1].Message)

 	// mytopic: since none
 	messages, _ = c.Messages("mytopic", sinceNoMessages, false)
-	assert.Empty(t, messages)
+	require.Empty(t, messages)

 	// mytopic: since 2
 	messages, _ = c.Messages("mytopic", sinceTime(time.Unix(2, 0)), false)
-	assert.Equal(t, 1, len(messages))
-	assert.Equal(t, "my other message", messages[0].Message)
+	require.Equal(t, 1, len(messages))
+	require.Equal(t, "my other message", messages[0].Message)

 	// example: count
 	count, err = c.MessageCount("example")
-	assert.Nil(t, err)
-	assert.Equal(t, 1, count)
+	require.Nil(t, err)
+	require.Equal(t, 1, count)

 	// example: since all
 	messages, _ = c.Messages("example", sinceAllMessages, false)
-	assert.Equal(t, "my example message", messages[0].Message)
+	require.Equal(t, "my example message", messages[0].Message)

 	// non-existing: count
 	count, err = c.MessageCount("doesnotexist")
-	assert.Nil(t, err)
-	assert.Equal(t, 0, count)
+	require.Nil(t, err)
+	require.Equal(t, 0, count)

 	// non-existing: since all
 	messages, _ = c.Messages("doesnotexist", sinceAllMessages, false)
-	assert.Empty(t, messages)
+	require.Empty(t, messages)
 }

 func testCacheTopics(t *testing.T, c cache) {
-	assert.Nil(t, c.AddMessage(newDefaultMessage("topic1", "my example message")))
-	assert.Nil(t, c.AddMessage(newDefaultMessage("topic2", "message 1")))
-	assert.Nil(t, c.AddMessage(newDefaultMessage("topic2", "message 2")))
-	assert.Nil(t, c.AddMessage(newDefaultMessage("topic2", "message 3")))
+	require.Nil(t, c.AddMessage(newDefaultMessage("topic1", "my example message")))
+	require.Nil(t, c.AddMessage(newDefaultMessage("topic2", "message 1")))
+	require.Nil(t, c.AddMessage(newDefaultMessage("topic2", "message 2")))
+	require.Nil(t, c.AddMessage(newDefaultMessage("topic2", "message 3")))

 	topics, err := c.Topics()
 	if err != nil {
 		t.Fatal(err)
 	}
-	assert.Equal(t, 2, len(topics))
-	assert.Equal(t, "topic1", topics["topic1"].ID)
-	assert.Equal(t, "topic2", topics["topic2"].ID)
+	require.Equal(t, 2, len(topics))
+	require.Equal(t, "topic1", topics["topic1"].ID)
+	require.Equal(t, "topic2", topics["topic2"].ID)
 }

 func testCachePrune(t *testing.T, c cache) {
@ -90,23 +90,23 @@ func testCachePrune(t *testing.T, c cache) {
 	m3 := newDefaultMessage("another_topic", "and another one")
 	m3.Time = 1

-	assert.Nil(t, c.AddMessage(m1))
-	assert.Nil(t, c.AddMessage(m2))
-	assert.Nil(t, c.AddMessage(m3))
-	assert.Nil(t, c.Prune(time.Unix(2, 0)))
+	require.Nil(t, c.AddMessage(m1))
+	require.Nil(t, c.AddMessage(m2))
+	require.Nil(t, c.AddMessage(m3))
+	require.Nil(t, c.Prune(time.Unix(2, 0)))

 	count, err := c.MessageCount("mytopic")
-	assert.Nil(t, err)
-	assert.Equal(t, 1, count)
+	require.Nil(t, err)
+	require.Equal(t, 1, count)

 	count, err = c.MessageCount("another_topic")
-	assert.Nil(t, err)
-	assert.Equal(t, 0, count)
+	require.Nil(t, err)
+	require.Equal(t, 0, count)

 	messages, err := c.Messages("mytopic", sinceAllMessages, false)
-	assert.Nil(t, err)
-	assert.Equal(t, 1, len(messages))
-	assert.Equal(t, "my other message", messages[0].Message)
+	require.Nil(t, err)
+	require.Equal(t, 1, len(messages))
+	require.Equal(t, "my other message", messages[0].Message)
 }

 func testCacheMessagesTagsPrioAndTitle(t *testing.T, c cache) {
@ -114,12 +114,12 @@ func testCacheMessagesTagsPrioAndTitle(t *testing.T, c cache) {
 	m.Tags = []string{"tag1", "tag2"}
 	m.Priority = 5
 	m.Title = "some title"
-	assert.Nil(t, c.AddMessage(m))
+	require.Nil(t, c.AddMessage(m))

 	messages, _ := c.Messages("mytopic", sinceAllMessages, false)
-	assert.Equal(t, []string{"tag1", "tag2"}, messages[0].Tags)
-	assert.Equal(t, 5, messages[0].Priority)
-	assert.Equal(t, "some title", messages[0].Title)
+	require.Equal(t, []string{"tag1", "tag2"}, messages[0].Tags)
+	require.Equal(t, 5, messages[0].Priority)
+	require.Equal(t, "some title", messages[0].Title)
 }

 func testCacheMessagesScheduled(t *testing.T, c cache) {
@ -130,20 +130,93 @@ func testCacheMessagesScheduled(t *testing.T, c cache) {
 	m3.Time = time.Now().Add(time.Minute).Unix() // earlier than m2!
 	m4 := newDefaultMessage("mytopic2", "message 4")
 	m4.Time = time.Now().Add(time.Minute).Unix()
-	assert.Nil(t, c.AddMessage(m1))
-	assert.Nil(t, c.AddMessage(m2))
-	assert.Nil(t, c.AddMessage(m3))
+	require.Nil(t, c.AddMessage(m1))
+	require.Nil(t, c.AddMessage(m2))
+	require.Nil(t, c.AddMessage(m3))

 	messages, _ := c.Messages("mytopic", sinceAllMessages, false) // exclude scheduled
-	assert.Equal(t, 1, len(messages))
-	assert.Equal(t, "message 1", messages[0].Message)
+	require.Equal(t, 1, len(messages))
+	require.Equal(t, "message 1", messages[0].Message)

 	messages, _ = c.Messages("mytopic", sinceAllMessages, true) // include scheduled
-	assert.Equal(t, 3, len(messages))
-	assert.Equal(t, "message 1", messages[0].Message)
-	assert.Equal(t, "message 3", messages[1].Message) // Order!
-	assert.Equal(t, "message 2", messages[2].Message)
+	require.Equal(t, 3, len(messages))
+	require.Equal(t, "message 1", messages[0].Message)
+	require.Equal(t, "message 3", messages[1].Message) // Order!
+	require.Equal(t, "message 2", messages[2].Message)

 	messages, _ = c.MessagesDue()
-	assert.Empty(t, messages)
+	require.Empty(t, messages)
+}
+
+func testCacheAttachments(t *testing.T, c cache) {
+	expires1 := time.Now().Add(-4 * time.Hour).Unix()
+	m := newDefaultMessage("mytopic", "flower for you")
+	m.ID = "m1"
+	m.Attachment = &attachment{
+		Name:    "flower.jpg",
+		Type:    "image/jpeg",
+		Size:    5000,
+		Expires: expires1,
+		URL:     "https://ntfy.sh/file/AbDeFgJhal.jpg",
+		Owner:   "1.2.3.4",
+	}
+	require.Nil(t, c.AddMessage(m))
+
+	expires2 := time.Now().Add(2 * time.Hour).Unix() // Future
+	m = newDefaultMessage("mytopic", "sending you a car")
+	m.ID = "m2"
+	m.Attachment = &attachment{
+		Name:    "car.jpg",
+		Type:    "image/jpeg",
+		Size:    10000,
+		Expires: expires2,
+		URL:     "https://ntfy.sh/file/aCaRURL.jpg",
+		Owner:   "1.2.3.4",
+	}
+	require.Nil(t, c.AddMessage(m))
+
+	expires3 := time.Now().Add(1 * time.Hour).Unix() // Future
+	m = newDefaultMessage("another-topic", "sending you another car")
+	m.ID = "m3"
+	m.Attachment = &attachment{
+		Name:    "another-car.jpg",
+		Type:    "image/jpeg",
+		Size:    20000,
+		Expires: expires3,
+		URL:     "https://ntfy.sh/file/zakaDHFW.jpg",
+		Owner:   "1.2.3.4",
+	}
+	require.Nil(t, c.AddMessage(m))
+
+	messages, err := c.Messages("mytopic", sinceAllMessages, false)
+	require.Nil(t, err)
+	require.Equal(t, 2, len(messages))
+
+	require.Equal(t, "flower for you", messages[0].Message)
+	require.Equal(t, "flower.jpg", messages[0].Attachment.Name)
+	require.Equal(t, "image/jpeg", messages[0].Attachment.Type)
+	require.Equal(t, int64(5000), messages[0].Attachment.Size)
+	require.Equal(t, expires1, messages[0].Attachment.Expires)
+	require.Equal(t, "https://ntfy.sh/file/AbDeFgJhal.jpg", messages[0].Attachment.URL)
+	require.Equal(t, "1.2.3.4", messages[0].Attachment.Owner)
+
+	require.Equal(t, "sending you a car", messages[1].Message)
+	require.Equal(t, "car.jpg", messages[1].Attachment.Name)
+	require.Equal(t, "image/jpeg", messages[1].Attachment.Type)
+	require.Equal(t, int64(10000), messages[1].Attachment.Size)
+	require.Equal(t, expires2, messages[1].Attachment.Expires)
+	require.Equal(t, "https://ntfy.sh/file/aCaRURL.jpg", messages[1].Attachment.URL)
+	require.Equal(t, "1.2.3.4", messages[1].Attachment.Owner)
+
+	size, err := c.AttachmentsSize("1.2.3.4")
+	require.Nil(t, err)
+	require.Equal(t, int64(30000), size)
+
+	size, err = c.AttachmentsSize("5.6.7.8")
+	require.Nil(t, err)
+	require.Equal(t, int64(0), size)
+
+	ids, err := c.AttachmentsExpired()
+	require.Nil(t, err)
+	require.Equal(t, []string{"m1"}, ids)
 }
--- a/server/config.go
+++ b/server/config.go
@ -4,7 +4,7 @@ import (
 	"time"
 )

-// Defines default config settings
+// Defines default config settings (excluding limits, see below)
 const (
 	DefaultListenHTTP                = ":80"
 	DefaultCacheDuration             = 12 * time.Hour
@ -13,81 +13,107 @@ const (
 	DefaultAtSenderInterval          = 10 * time.Second
 	DefaultMinDelay                  = 10 * time.Second
 	DefaultMaxDelay                  = 3 * 24 * time.Hour
-	DefaultMessageLimit              = 4096
 	DefaultFirebaseKeepaliveInterval = 3 * time.Hour // Not too frequently to save battery
 )

-// Defines all the limits
-// - global topic limit: max number of topics overall
+// Defines all global and per-visitor limits
+// - message size limit: the max number of bytes for a message
+// - total topic limit: max number of topics overall
+// - various attachment limits
+const (
+	DefaultMessageLengthLimit       = 4096 // Bytes
+	DefaultTotalTopicLimit          = 15000
+	DefaultAttachmentTotalSizeLimit = int64(5 * 1024 * 1024 * 1024) // 5 GB
+	DefaultAttachmentFileSizeLimit  = int64(15 * 1024 * 1024)       // 15 MB
+	DefaultAttachmentExpiryDuration = 3 * time.Hour
+)
+
+// Defines all per-visitor limits
+// - per visitor subscription limit: max number of subscriptions (active HTTP connections) per per-visitor/IP
 // - per visitor request limit: max number of PUT/GET/.. requests (here: 60 requests bucket, replenished at a rate of one per 10 seconds)
 // - per visitor email limit: max number of emails (here: 16 email bucket, replenished at a rate of one per hour)
-// - per visitor subscription limit: max number of subscriptions (active HTTP connections) per per-visitor/IP
+// - per visitor attachment size limit: total per-visitor attachment size in bytes to be stored on the server
+// - per visitor attachment daily bandwidth limit: number of bytes that can be transferred to/from the server
 const (
-	DefaultGlobalTopicLimit             = 5000
-	DefaultVisitorRequestLimitBurst     = 60
-	DefaultVisitorRequestLimitReplenish = 10 * time.Second
-	DefaultVisitorEmailLimitBurst       = 16
-	DefaultVisitorEmailLimitReplenish   = time.Hour
-	DefaultVisitorSubscriptionLimit     = 30
+	DefaultVisitorSubscriptionLimit             = 30
+	DefaultVisitorRequestLimitBurst             = 60
+	DefaultVisitorRequestLimitReplenish         = 10 * time.Second
+	DefaultVisitorEmailLimitBurst               = 16
+	DefaultVisitorEmailLimitReplenish           = time.Hour
+	DefaultVisitorAttachmentTotalSizeLimit      = 100 * 1024 * 1024 // 100 MB
+	DefaultVisitorAttachmentDailyBandwidthLimit = 500 * 1024 * 1024 // 500 MB
 )

 // Config is the main config struct for the application. Use New to instantiate a default config struct.
 type Config struct {
-	BaseURL                      string
-	ListenHTTP                   string
-	ListenHTTPS                  string
-	KeyFile                      string
-	CertFile                     string
-	FirebaseKeyFile              string
-	CacheFile                    string
-	CacheDuration                time.Duration
-	KeepaliveInterval            time.Duration
-	ManagerInterval              time.Duration
-	AtSenderInterval             time.Duration
-	FirebaseKeepaliveInterval    time.Duration
-	SMTPSenderAddr               string
-	SMTPSenderUser               string
-	SMTPSenderPass               string
-	SMTPSenderFrom               string
-	SMTPServerListen             string
-	SMTPServerDomain             string
-	SMTPServerAddrPrefix         string
-	MessageLimit                 int
-	MinDelay                     time.Duration
-	MaxDelay                     time.Duration
-	GlobalTopicLimit             int
-	VisitorRequestLimitBurst     int
-	VisitorRequestLimitReplenish time.Duration
-	VisitorEmailLimitBurst       int
-	VisitorEmailLimitReplenish   time.Duration
-	VisitorSubscriptionLimit     int
-	BehindProxy                  bool
+	BaseURL                              string
+	ListenHTTP                           string
+	ListenHTTPS                          string
+	KeyFile                              string
+	CertFile                             string
+	FirebaseKeyFile                      string
+	CacheFile                            string
+	CacheDuration                        time.Duration
+	AttachmentCacheDir                   string
+	AttachmentTotalSizeLimit             int64
+	AttachmentFileSizeLimit              int64
+	AttachmentExpiryDuration             time.Duration
+	KeepaliveInterval                    time.Duration
+	ManagerInterval                      time.Duration
+	AtSenderInterval                     time.Duration
+	FirebaseKeepaliveInterval            time.Duration
+	SMTPSenderAddr                       string
+	SMTPSenderUser                       string
+	SMTPSenderPass                       string
+	SMTPSenderFrom                       string
+	SMTPServerListen                     string
+	SMTPServerDomain                     string
+	SMTPServerAddrPrefix                 string
+	MessageLimit                         int
+	MinDelay                             time.Duration
+	MaxDelay                             time.Duration
+	TotalTopicLimit                      int
+	TotalAttachmentSizeLimit             int64
+	VisitorSubscriptionLimit             int
+	VisitorAttachmentTotalSizeLimit      int64
+	VisitorAttachmentDailyBandwidthLimit int
+	VisitorRequestLimitBurst             int
+	VisitorRequestLimitReplenish         time.Duration
+	VisitorEmailLimitBurst               int
+	VisitorEmailLimitReplenish           time.Duration
+	BehindProxy                          bool
 }

 // NewConfig instantiates a default new server config
 func NewConfig() *Config {
 	return &Config{
-		BaseURL:                      "",
-		ListenHTTP:                   DefaultListenHTTP,
-		ListenHTTPS:                  "",
-		KeyFile:                      "",
-		CertFile:                     "",
-		FirebaseKeyFile:              "",
-		CacheFile:                    "",
-		CacheDuration:                DefaultCacheDuration,
-		KeepaliveInterval:            DefaultKeepaliveInterval,
-		ManagerInterval:              DefaultManagerInterval,
-		MessageLimit:                 DefaultMessageLimit,
-		MinDelay:                     DefaultMinDelay,
-		MaxDelay:                     DefaultMaxDelay,
-		AtSenderInterval:             DefaultAtSenderInterval,
-		FirebaseKeepaliveInterval:    DefaultFirebaseKeepaliveInterval,
-		GlobalTopicLimit:             DefaultGlobalTopicLimit,
-		VisitorRequestLimitBurst:     DefaultVisitorRequestLimitBurst,
-		VisitorRequestLimitReplenish: DefaultVisitorRequestLimitReplenish,
-		VisitorEmailLimitBurst:       DefaultVisitorEmailLimitBurst,
-		VisitorEmailLimitReplenish:   DefaultVisitorEmailLimitReplenish,
-		VisitorSubscriptionLimit:     DefaultVisitorSubscriptionLimit,
-		BehindProxy:                  false,
+		BaseURL:                              "",
+		ListenHTTP:                           DefaultListenHTTP,
+		ListenHTTPS:                          "",
+		KeyFile:                              "",
+		CertFile:                             "",
+		FirebaseKeyFile:                      "",
+		CacheFile:                            "",
+		CacheDuration:                        DefaultCacheDuration,
+		AttachmentCacheDir:                   "",
+		AttachmentTotalSizeLimit:             DefaultAttachmentTotalSizeLimit,
+		AttachmentFileSizeLimit:              DefaultAttachmentFileSizeLimit,
+		AttachmentExpiryDuration:             DefaultAttachmentExpiryDuration,
+		KeepaliveInterval:                    DefaultKeepaliveInterval,
+		ManagerInterval:                      DefaultManagerInterval,
+		MessageLimit:                         DefaultMessageLengthLimit,
+		MinDelay:                             DefaultMinDelay,
+		MaxDelay:                             DefaultMaxDelay,
+		AtSenderInterval:                     DefaultAtSenderInterval,
+		FirebaseKeepaliveInterval:            DefaultFirebaseKeepaliveInterval,
+		TotalTopicLimit:                      DefaultTotalTopicLimit,
+		VisitorSubscriptionLimit:             DefaultVisitorSubscriptionLimit,
+		VisitorAttachmentTotalSizeLimit:      DefaultVisitorAttachmentTotalSizeLimit,
+		VisitorAttachmentDailyBandwidthLimit: DefaultVisitorAttachmentDailyBandwidthLimit,
+		VisitorRequestLimitBurst:             DefaultVisitorRequestLimitBurst,
+		VisitorRequestLimitReplenish:         DefaultVisitorRequestLimitReplenish,
+		VisitorEmailLimitBurst:               DefaultVisitorEmailLimitBurst,
+		VisitorEmailLimitReplenish:           DefaultVisitorEmailLimitReplenish,
+		BehindProxy:                          false,
 	}
 }
--- a/server/file_cache.go
+++ b/server/file_cache.go
@ -0,0 +1,121 @@
+package server
+
+import (
+	"errors"
+	"heckel.io/ntfy/util"
+	"io"
+	"os"
+	"path/filepath"
+	"regexp"
+	"sync"
+)
+
+var (
+	fileIDRegex      = regexp.MustCompile(`^[-_A-Za-z0-9]+$`)
+	errInvalidFileID = errors.New("invalid file ID")
+	errFileExists    = errors.New("file exists")
+)
+
+type fileCache struct {
+	dir              string
+	totalSizeCurrent int64
+	totalSizeLimit   int64
+	fileSizeLimit    int64
+	mu               sync.Mutex
+}
+
+func newFileCache(dir string, totalSizeLimit int64, fileSizeLimit int64) (*fileCache, error) {
+	if err := os.MkdirAll(dir, 0700); err != nil {
+		return nil, err
+	}
+	size, err := dirSize(dir)
+	if err != nil {
+		return nil, err
+	}
+	return &fileCache{
+		dir:              dir,
+		totalSizeCurrent: size,
+		totalSizeLimit:   totalSizeLimit,
+		fileSizeLimit:    fileSizeLimit,
+	}, nil
+}
+
+func (c *fileCache) Write(id string, in io.Reader, limiters ...util.Limiter) (int64, error) {
+	if !fileIDRegex.MatchString(id) {
+		return 0, errInvalidFileID
+	}
+	file := filepath.Join(c.dir, id)
+	if _, err := os.Stat(file); err == nil {
+		return 0, errFileExists
+	}
+	f, err := os.OpenFile(file, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0600)
+	if err != nil {
+		return 0, err
+	}
+	defer f.Close()
+	limiters = append(limiters, util.NewFixedLimiter(c.Remaining()), util.NewFixedLimiter(c.fileSizeLimit))
+	limitWriter := util.NewLimitWriter(f, limiters...)
+	size, err := io.Copy(limitWriter, in)
+	if err != nil {
+		os.Remove(file)
+		return 0, err
+	}
+	if err := f.Close(); err != nil {
+		os.Remove(file)
+		return 0, err
+	}
+	c.mu.Lock()
+	c.totalSizeCurrent += size
+	c.mu.Unlock()
+	return size, nil
+}
+
+func (c *fileCache) Remove(ids ...string) error {
+	for _, id := range ids {
+		if !fileIDRegex.MatchString(id) {
+			return errInvalidFileID
+		}
+		file := filepath.Join(c.dir, id)
+		_ = os.Remove(file) // Best effort delete
+	}
+	size, err := dirSize(c.dir)
+	if err != nil {
+		return err
+	}
+	c.mu.Lock()
+	c.totalSizeCurrent = size
+	c.mu.Unlock()
+	return nil
+}
+
+func (c *fileCache) Size() int64 {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	return c.totalSizeCurrent
+}
+
+func (c *fileCache) Remaining() int64 {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	remaining := c.totalSizeLimit - c.totalSizeCurrent
+	if remaining < 0 {
+		return 0
+	}
+	return remaining
+}
+
+func dirSize(dir string) (int64, error) {
+	entries, err := os.ReadDir(dir)
+	if err != nil {
+		return 0, err
+	}
+	var size int64
+	for _, e := range entries {
+		info, err := e.Info()
+		if err != nil {
+			return 0, err
+		}
+		size += info.Size()
+	}
+	return size, nil
+}
--- a/server/file_cache_test.go
+++ b/server/file_cache_test.go
@ -0,0 +1,83 @@
+package server
+
+import (
+	"bytes"
+	"fmt"
+	"github.com/stretchr/testify/require"
+	"heckel.io/ntfy/util"
+	"os"
+	"strings"
+	"testing"
+)
+
+var (
+	oneKilobyteArray = make([]byte, 1024)
+)
+
+func TestFileCache_Write_Success(t *testing.T) {
+	dir, c := newTestFileCache(t)
+	size, err := c.Write("abc", strings.NewReader("normal file"), util.NewFixedLimiter(999))
+	require.Nil(t, err)
+	require.Equal(t, int64(11), size)
+	require.Equal(t, "normal file", readFile(t, dir+"/abc"))
+	require.Equal(t, int64(11), c.Size())
+	require.Equal(t, int64(10229), c.Remaining())
+}
+
+func TestFileCache_Write_Remove_Success(t *testing.T) {
+	dir, c := newTestFileCache(t) // max = 10k (10240), each = 1k (1024)
+	for i := 0; i < 10; i++ {     // 10x999 = 9990
+		size, err := c.Write(fmt.Sprintf("abc%d", i), bytes.NewReader(make([]byte, 999)))
+		require.Nil(t, err)
+		require.Equal(t, int64(999), size)
+	}
+	require.Equal(t, int64(9990), c.Size())
+	require.Equal(t, int64(250), c.Remaining())
+	require.FileExists(t, dir+"/abc1")
+	require.FileExists(t, dir+"/abc5")
+
+	require.Nil(t, c.Remove("abc1", "abc5"))
+	require.NoFileExists(t, dir+"/abc1")
+	require.NoFileExists(t, dir+"/abc5")
+	require.Equal(t, int64(7992), c.Size())
+	require.Equal(t, int64(2248), c.Remaining())
+}
+
+func TestFileCache_Write_FailedTotalSizeLimit(t *testing.T) {
+	dir, c := newTestFileCache(t)
+	for i := 0; i < 10; i++ {
+		size, err := c.Write(fmt.Sprintf("abc%d", i), bytes.NewReader(oneKilobyteArray))
+		require.Nil(t, err)
+		require.Equal(t, int64(1024), size)
+	}
+	_, err := c.Write("abc11", bytes.NewReader(oneKilobyteArray))
+	require.Equal(t, util.ErrLimitReached, err)
+	require.NoFileExists(t, dir+"/abc11")
+}
+
+func TestFileCache_Write_FailedFileSizeLimit(t *testing.T) {
+	dir, c := newTestFileCache(t)
+	_, err := c.Write("abc", bytes.NewReader(make([]byte, 1025)))
+	require.Equal(t, util.ErrLimitReached, err)
+	require.NoFileExists(t, dir+"/abc")
+}
+
+func TestFileCache_Write_FailedAdditionalLimiter(t *testing.T) {
+	dir, c := newTestFileCache(t)
+	_, err := c.Write("abc", bytes.NewReader(make([]byte, 1001)), util.NewFixedLimiter(1000))
+	require.Equal(t, util.ErrLimitReached, err)
+	require.NoFileExists(t, dir+"/abc")
+}
+
+func newTestFileCache(t *testing.T) (dir string, cache *fileCache) {
+	dir = t.TempDir()
+	cache, err := newFileCache(dir, 10*1024, 1*1024)
+	require.Nil(t, err)
+	return dir, cache
+}
+
+func readFile(t *testing.T, f string) string {
+	b, err := os.ReadFile(f)
+	require.Nil(t, err)
+	return string(b)
+}
--- a/server/message.go
+++ b/server/message.go
@ -18,15 +18,25 @@ const (

 // message represents a message published to a topic
 type message struct {
-	ID       string   `json:"id"`    // Random message ID
-	Time     int64    `json:"time"`  // Unix time in seconds
-	Event    string   `json:"event"` // One of the above
-	Topic    string   `json:"topic"`
-	Priority int      `json:"priority,omitempty"`
-	Tags     []string `json:"tags,omitempty"`
-	Click    string   `json:"click,omitempty"`
-	Title    string   `json:"title,omitempty"`
-	Message  string   `json:"message,omitempty"`
+	ID         string      `json:"id"`    // Random message ID
+	Time       int64       `json:"time"`  // Unix time in seconds
+	Event      string      `json:"event"` // One of the above
+	Topic      string      `json:"topic"`
+	Priority   int         `json:"priority,omitempty"`
+	Tags       []string    `json:"tags,omitempty"`
+	Click      string      `json:"click,omitempty"`
+	Attachment *attachment `json:"attachment,omitempty"`
+	Title      string      `json:"title,omitempty"`
+	Message    string      `json:"message,omitempty"`
+}
+
+type attachment struct {
+	Name    string `json:"name"`
+	Type    string `json:"type,omitempty"`
+	Size    int64  `json:"size,omitempty"`
+	Expires int64  `json:"expires,omitempty"`
+	URL     string `json:"url"`
+	Owner   string `json:"-"` // IP address of uploader, used for rate limiting
 }

 // messageEncoder is a function that knows how to encode a message
--- a/server/server.go
+++ b/server/server.go
@ -18,11 +18,14 @@ import (
 	"net"
 	"net/http"
 	"net/http/httptest"
+	"os"
+	"path/filepath"
 	"regexp"
 	"strconv"
 	"strings"
 	"sync"
 	"time"
+	"unicode/utf8"
 )

 // TODO add "max messages in a topic" limit
@ -41,6 +44,7 @@ type Server struct {
 	mailer      mailer
 	messages    int64
 	cache       cache
+	fileCache   *fileCache
 	closeChan   chan bool
 	mu          sync.Mutex
 }
@ -96,7 +100,9 @@ var (

 	staticRegex      = regexp.MustCompile(`^/static/.+`)
 	docsRegex        = regexp.MustCompile(`^/docs(|/.*)$`)
-	disallowedTopics = []string{"docs", "static"}
+	fileRegex        = regexp.MustCompile(`^/file/([-_A-Za-z0-9]{1,64})(?:\.[A-Za-z0-9]{1,16})?$`)
+	disallowedTopics = []string{"docs", "static", "file"}
+	attachURLRegex   = regexp.MustCompile(`^https?://`)

 	templateFnMap = template.FuncMap{
 		"durationToHuman": util.DurationToHuman,
@ -117,28 +123,38 @@ var (
 	docsStaticFs     embed.FS
 	docsStaticCached = &util.CachingEmbedFS{ModTime: time.Now(), FS: docsStaticFs}

-	errHTTPNotFound                          = &errHTTP{40401, http.StatusNotFound, "page not found", ""}
-	errHTTPTooManyRequestsLimitRequests      = &errHTTP{42901, http.StatusTooManyRequests, "limit reached: too many requests, please be nice", "https://ntfy.sh/docs/publish/#limitations"}
-	errHTTPTooManyRequestsLimitEmails        = &errHTTP{42902, http.StatusTooManyRequests, "limit reached: too many emails, please be nice", "https://ntfy.sh/docs/publish/#limitations"}
-	errHTTPTooManyRequestsLimitSubscriptions = &errHTTP{42903, http.StatusTooManyRequests, "limit reached: too many active subscriptions, please be nice", "https://ntfy.sh/docs/publish/#limitations"}
-	errHTTPTooManyRequestsLimitGlobalTopics  = &errHTTP{42904, http.StatusTooManyRequests, "limit reached: the total number of topics on the server has been reached, please contact the admin", "https://ntfy.sh/docs/publish/#limitations"}
-	errHTTPBadRequestEmailDisabled           = &errHTTP{40001, http.StatusBadRequest, "e-mail notifications are not enabled", "https://ntfy.sh/docs/config/#e-mail-notifications"}
-	errHTTPBadRequestDelayNoCache            = &errHTTP{40002, http.StatusBadRequest, "cannot disable cache for delayed message", ""}
-	errHTTPBadRequestDelayNoEmail            = &errHTTP{40003, http.StatusBadRequest, "delayed e-mail notifications are not supported", ""}
-	errHTTPBadRequestDelayCannotParse        = &errHTTP{40004, http.StatusBadRequest, "invalid delay parameter: unable to parse delay", "https://ntfy.sh/docs/publish/#scheduled-delivery"}
-	errHTTPBadRequestDelayTooSmall           = &errHTTP{40005, http.StatusBadRequest, "invalid delay parameter: too small, please refer to the docs", "https://ntfy.sh/docs/publish/#scheduled-delivery"}
-	errHTTPBadRequestDelayTooLarge           = &errHTTP{40006, http.StatusBadRequest, "invalid delay parameter: too large, please refer to the docs", "https://ntfy.sh/docs/publish/#scheduled-delivery"}
-	errHTTPBadRequestPriorityInvalid         = &errHTTP{40007, http.StatusBadRequest, "invalid priority parameter", "https://ntfy.sh/docs/publish/#message-priority"}
-	errHTTPBadRequestSinceInvalid            = &errHTTP{40008, http.StatusBadRequest, "invalid since parameter", "https://ntfy.sh/docs/subscribe/api/#fetch-cached-messages"}
-	errHTTPBadRequestTopicInvalid            = &errHTTP{40009, http.StatusBadRequest, "invalid topic: path invalid", ""}
-	errHTTPBadRequestTopicDisallowed         = &errHTTP{40010, http.StatusBadRequest, "invalid topic: topic name is disallowed", ""}
-	errHTTPInternalError                     = &errHTTP{50001, http.StatusInternalServerError, "internal server error", ""}
+	errHTTPBadRequestEmailDisabled                   = &errHTTP{40001, http.StatusBadRequest, "e-mail notifications are not enabled", "https://ntfy.sh/docs/config/#e-mail-notifications"}
+	errHTTPBadRequestDelayNoCache                    = &errHTTP{40002, http.StatusBadRequest, "cannot disable cache for delayed message", ""}
+	errHTTPBadRequestDelayNoEmail                    = &errHTTP{40003, http.StatusBadRequest, "delayed e-mail notifications are not supported", ""}
+	errHTTPBadRequestDelayCannotParse                = &errHTTP{40004, http.StatusBadRequest, "invalid delay parameter: unable to parse delay", "https://ntfy.sh/docs/publish/#scheduled-delivery"}
+	errHTTPBadRequestDelayTooSmall                   = &errHTTP{40005, http.StatusBadRequest, "invalid delay parameter: too small, please refer to the docs", "https://ntfy.sh/docs/publish/#scheduled-delivery"}
+	errHTTPBadRequestDelayTooLarge                   = &errHTTP{40006, http.StatusBadRequest, "invalid delay parameter: too large, please refer to the docs", "https://ntfy.sh/docs/publish/#scheduled-delivery"}
+	errHTTPBadRequestPriorityInvalid                 = &errHTTP{40007, http.StatusBadRequest, "invalid priority parameter", "https://ntfy.sh/docs/publish/#message-priority"}
+	errHTTPBadRequestSinceInvalid                    = &errHTTP{40008, http.StatusBadRequest, "invalid since parameter", "https://ntfy.sh/docs/subscribe/api/#fetch-cached-messages"}
+	errHTTPBadRequestTopicInvalid                    = &errHTTP{40009, http.StatusBadRequest, "invalid topic: path invalid", ""}
+	errHTTPBadRequestTopicDisallowed                 = &errHTTP{40010, http.StatusBadRequest, "invalid topic: topic name is disallowed", ""}
+	errHTTPBadRequestMessageNotUTF8                  = &errHTTP{40011, http.StatusBadRequest, "invalid message: message must be UTF-8 encoded", ""}
+	errHTTPBadRequestAttachmentTooLarge              = &errHTTP{40012, http.StatusBadRequest, "invalid request: attachment too large, or bandwidth limit reached", ""}
+	errHTTPBadRequestAttachmentURLInvalid            = &errHTTP{40013, http.StatusBadRequest, "invalid request: attachment URL is invalid", ""}
+	errHTTPBadRequestAttachmentURLPeakGeneral        = &errHTTP{40014, http.StatusBadRequest, "invalid request: attachment URL peak failed", ""}
+	errHTTPBadRequestAttachmentURLPeakNon2xx         = &errHTTP{40015, http.StatusBadRequest, "invalid request: attachment URL peak failed with non-2xx status code", ""}
+	errHTTPBadRequestAttachmentsDisallowed           = &errHTTP{40016, http.StatusBadRequest, "invalid request: attachments not allowed", ""}
+	errHTTPBadRequestAttachmentsExpiryBeforeDelivery = &errHTTP{40017, http.StatusBadRequest, "invalid request: attachment expiry before delayed delivery date", ""}
+	errHTTPNotFound                                  = &errHTTP{40401, http.StatusNotFound, "page not found", ""}
+	errHTTPTooManyRequestsLimitRequests              = &errHTTP{42901, http.StatusTooManyRequests, "limit reached: too many requests, please be nice", "https://ntfy.sh/docs/publish/#limitations"}
+	errHTTPTooManyRequestsLimitEmails                = &errHTTP{42902, http.StatusTooManyRequests, "limit reached: too many emails, please be nice", "https://ntfy.sh/docs/publish/#limitations"}
+	errHTTPTooManyRequestsLimitSubscriptions         = &errHTTP{42903, http.StatusTooManyRequests, "limit reached: too many active subscriptions, please be nice", "https://ntfy.sh/docs/publish/#limitations"}
+	errHTTPTooManyRequestsLimitTotalTopics           = &errHTTP{42904, http.StatusTooManyRequests, "limit reached: the total number of topics on the server has been reached, please contact the admin", "https://ntfy.sh/docs/publish/#limitations"}
+	errHTTPTooManyRequestsAttachmentBandwidthLimit   = &errHTTP{42905, http.StatusTooManyRequests, "too many requests: daily bandwidth limit reached", "https://ntfy.sh/docs/publish/#limitations"}
+	errHTTPInternalError                             = &errHTTP{50001, http.StatusInternalServerError, "internal server error", ""}
+	errHTTPInternalErrorInvalidFilePath              = &errHTTP{50002, http.StatusInternalServerError, "internal server error: invalid file path", ""}
 )

 const (
-	firebaseControlTopic = "~control" // See Android if changed
-	emptyMessageBody     = "triggered"
-	fcmMessageLimit      = 4000 // see maybeTruncateFCMMessage for details
+	firebaseControlTopic     = "~control"                // See Android if changed
+	emptyMessageBody         = "triggered"               // Used if message body is empty
+	defaultAttachmentMessage = "You received a file: %s" // Used if message body is empty, and there is an attachment
+	fcmMessageLimit          = 4000                      // see maybeTruncateFCMMessage for details
 )

 // New instantiates a new Server. It creates the cache and adds a Firebase
@ -164,13 +180,21 @@ func New(conf *Config) (*Server, error) {
 	if err != nil {
 		return nil, err
 	}
+	var fileCache *fileCache
+	if conf.AttachmentCacheDir != "" {
+		fileCache, err = newFileCache(conf.AttachmentCacheDir, conf.AttachmentTotalSizeLimit, conf.AttachmentFileSizeLimit)
+		if err != nil {
+			return nil, err
+		}
+	}
 	return &Server{
-		config:   conf,
-		cache:    cache,
-		firebase: firebaseSubscriber,
-		mailer:   mailer,
-		topics:   topics,
-		visitors: make(map[string]*visitor),
+		config:    conf,
+		cache:     cache,
+		fileCache: fileCache,
+		firebase:  firebaseSubscriber,
+		mailer:    mailer,
+		topics:    topics,
+		visitors:  make(map[string]*visitor),
 	}, nil
 }

@ -214,6 +238,13 @@ func createFirebaseSubscriber(conf *Config) (subscriber, error) {
 				"title":    m.Title,
 				"message":  m.Message,
 			}
+			if m.Attachment != nil {
+				data["attachment_name"] = m.Attachment.Name
+				data["attachment_type"] = m.Attachment.Type
+				data["attachment_size"] = fmt.Sprintf("%d", m.Attachment.Size)
+				data["attachment_expires"] = fmt.Sprintf("%d", m.Attachment.Expires)
+				data["attachment_url"] = m.Attachment.URL
+			}
 		}
 		var androidConfig *messaging.AndroidConfig
 		if m.Priority >= 4 {
@ -270,7 +301,7 @@ func (s *Server) Run() error {
 		errChan <- s.httpServer.ListenAndServe()
 	}()
 	if s.config.ListenHTTPS != "" {
-		s.httpsServer = &http.Server{Addr: s.config.ListenHTTP, Handler: mux}
+		s.httpsServer = &http.Server{Addr: s.config.ListenHTTPS, Handler: mux}
 		go func() {
 			errChan <- s.httpsServer.ListenAndServeTLS(s.config.CertFile, s.config.KeyFile)
 		}()
@ -311,7 +342,7 @@ func (s *Server) handle(w http.ResponseWriter, r *http.Request) {
 		if e, ok = err.(*errHTTP); !ok {
 			e = errHTTPInternalError
 		}
-		log.Printf("[%s] %s - %d - %s", r.RemoteAddr, r.Method, e.HTTPCode, err.Error())
+		log.Printf("[%s] %s - %d - %d - %s", r.RemoteAddr, r.Method, e.HTTPCode, e.Code, err.Error())
 		w.Header().Set("Content-Type", "application/json")
 		w.Header().Set("Access-Control-Allow-Origin", "*") // CORS, allow cross-origin requests
 		w.WriteHeader(e.HTTPCode)
@ -330,6 +361,8 @@ func (s *Server) handleInternal(w http.ResponseWriter, r *http.Request) error {
 		return s.handleStatic(w, r)
 	} else if r.Method == http.MethodGet && docsRegex.MatchString(r.URL.Path) {
 		return s.handleDocs(w, r)
+	} else if r.Method == http.MethodGet && fileRegex.MatchString(r.URL.Path) && s.config.AttachmentCacheDir != "" {
+		return s.withRateLimit(w, r, s.handleFile)
 	} else if r.Method == http.MethodOptions {
 		return s.handleOptions(w, r)
 	} else if r.Method == http.MethodGet && topicPathRegex.MatchString(r.URL.Path) {
@ -385,28 +418,52 @@ func (s *Server) handleDocs(w http.ResponseWriter, r *http.Request) error {
 	return nil
 }

+func (s *Server) handleFile(w http.ResponseWriter, r *http.Request, v *visitor) error {
+	if s.config.AttachmentCacheDir == "" {
+		return errHTTPInternalError
+	}
+	matches := fileRegex.FindStringSubmatch(r.URL.Path)
+	if len(matches) != 2 {
+		return errHTTPInternalErrorInvalidFilePath
+	}
+	messageID := matches[1]
+	file := filepath.Join(s.config.AttachmentCacheDir, messageID)
+	stat, err := os.Stat(file)
+	if err != nil {
+		return errHTTPNotFound
+	}
+	if err := v.BandwidthLimiter().Allow(stat.Size()); err != nil {
+		return errHTTPTooManyRequestsAttachmentBandwidthLimit
+	}
+	w.Header().Set("Content-Length", fmt.Sprintf("%d", stat.Size()))
+	f, err := os.Open(file)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+	_, err = io.Copy(util.NewContentTypeWriter(w, r.URL.Path), f)
+	return err
+}
+
 func (s *Server) handlePublish(w http.ResponseWriter, r *http.Request, v *visitor) error {
 	t, err := s.topicFromPath(r.URL.Path)
 	if err != nil {
 		return err
 	}
-	reader := io.LimitReader(r.Body, int64(s.config.MessageLimit))
-	b, err := io.ReadAll(reader)
+	body, err := util.Peak(r.Body, s.config.MessageLimit)
 	if err != nil {
 		return err
 	}
-	m := newDefaultMessage(t.ID, strings.TrimSpace(string(b)))
-	cache, firebase, email, err := s.parsePublishParams(r, m)
+	m := newDefaultMessage(t.ID, "")
+	cache, firebase, email, err := s.parsePublishParams(r, v, m)
 	if err != nil {
 		return err
 	}
-	if email != "" {
-		if err := v.EmailAllowed(); err != nil {
-			return errHTTPTooManyRequestsLimitEmails
-		}
+	if err := maybePeakAttachmentURL(m); err != nil {
+		return err
 	}
-	if s.mailer == nil && email != "" {
-		return errHTTPBadRequestEmailDisabled
+	if err := s.handlePublishBody(r, v, m, body); err != nil {
+		return err
 	}
 	if m.Message == "" {
 		m.Message = emptyMessageBody
@ -445,12 +502,34 @@ func (s *Server) handlePublish(w http.ResponseWriter, r *http.Request, v *visito
 	return nil
 }

-func (s *Server) parsePublishParams(r *http.Request, m *message) (cache bool, firebase bool, email string, err error) {
+func (s *Server) parsePublishParams(r *http.Request, v *visitor, m *message) (cache bool, firebase bool, email string, err error) {
 	cache = readParam(r, "x-cache", "cache") != "no"
 	firebase = readParam(r, "x-firebase", "firebase") != "no"
-	email = readParam(r, "x-email", "x-e-mail", "email", "e-mail", "mail", "e")
 	m.Title = readParam(r, "x-title", "title", "t")
 	m.Click = readParam(r, "x-click", "click")
+	attach := readParam(r, "x-attach", "attach", "a")
+	filename := readParam(r, "x-filename", "filename", "file", "f")
+	if attach != "" || filename != "" {
+		m.Attachment = &attachment{}
+	}
+	if attach != "" {
+		if !attachURLRegex.MatchString(attach) {
+			return false, false, "", errHTTPBadRequestAttachmentURLInvalid
+		}
+		m.Attachment.URL = attach
+	}
+	if filename != "" {
+		m.Attachment.Name = filename
+	}
+	email = readParam(r, "x-email", "x-e-mail", "email", "e-mail", "mail", "e")
+	if email != "" {
+		if err := v.EmailAllowed(); err != nil {
+			return false, false, "", errHTTPTooManyRequestsLimitEmails
+		}
+	}
+	if s.mailer == nil && email != "" {
+		return false, false, "", errHTTPBadRequestEmailDisabled
+	}
 	messageStr := readParam(r, "x-message", "message", "m")
 	if messageStr != "" {
 		m.Message = messageStr
@ -507,6 +586,81 @@ func readParam(r *http.Request, names ...string) string {
 	return ""
 }

+// handlePublishBody consumes the PUT/POST body and decides whether the body is an attachment or the message.
+//
+// 1. curl -H "Attach: http://example.com/file.jpg" ntfy.sh/mytopic
+//    Body must be a message, because we attached an external URL
+// 2. curl -T short.txt -H "Filename: short.txt" ntfy.sh/mytopic
+//    Body must be attachment, because we passed a filename
+// 3. curl -T file.txt ntfy.sh/mytopic
+//    If file.txt is <= 4096 (message limit) and valid UTF-8, treat it as a message
+// 4. curl -T file.txt ntfy.sh/mytopic
+//    If file.txt is > message limit, treat it as an attachment
+func (s *Server) handlePublishBody(r *http.Request, v *visitor, m *message, body *util.PeakedReadCloser) error {
+	if m.Attachment != nil && m.Attachment.URL != "" {
+		return s.handleBodyAsMessage(m, body) // Case 1
+	} else if m.Attachment != nil && m.Attachment.Name != "" {
+		return s.handleBodyAsAttachment(r, v, m, body) // Case 2
+	} else if !body.LimitReached && utf8.Valid(body.PeakedBytes) {
+		return s.handleBodyAsMessage(m, body) // Case 3
+	}
+	return s.handleBodyAsAttachment(r, v, m, body) // Case 4
+}
+
+func (s *Server) handleBodyAsMessage(m *message, body *util.PeakedReadCloser) error {
+	if !utf8.Valid(body.PeakedBytes) {
+		return errHTTPBadRequestMessageNotUTF8
+	}
+	if len(body.PeakedBytes) > 0 { // Empty body should not override message (publish via GET!)
+		m.Message = strings.TrimSpace(string(body.PeakedBytes)) // Truncates the message to the peak limit if required
+	}
+	if m.Attachment != nil && m.Attachment.Name != "" && m.Message == "" {
+		m.Message = fmt.Sprintf(defaultAttachmentMessage, m.Attachment.Name)
+	}
+	return nil
+}
+
+func (s *Server) handleBodyAsAttachment(r *http.Request, v *visitor, m *message, body *util.PeakedReadCloser) error {
+	if s.fileCache == nil || s.config.BaseURL == "" || s.config.AttachmentCacheDir == "" {
+		return errHTTPBadRequestAttachmentsDisallowed
+	} else if m.Time > time.Now().Add(s.config.AttachmentExpiryDuration).Unix() {
+		return errHTTPBadRequestAttachmentsExpiryBeforeDelivery
+	}
+	visitorAttachmentsSize, err := s.cache.AttachmentsSize(v.ip)
+	if err != nil {
+		return err
+	}
+	remainingVisitorAttachmentSize := s.config.VisitorAttachmentTotalSizeLimit - visitorAttachmentsSize
+	contentLengthStr := r.Header.Get("Content-Length")
+	if contentLengthStr != "" { // Early "do-not-trust" check, hard limit see below
+		contentLength, err := strconv.ParseInt(contentLengthStr, 10, 64)
+		if err == nil && (contentLength > remainingVisitorAttachmentSize || contentLength > s.config.AttachmentFileSizeLimit) {
+			return errHTTPBadRequestAttachmentTooLarge
+		}
+	}
+	if m.Attachment == nil {
+		m.Attachment = &attachment{}
+	}
+	var ext string
+	m.Attachment.Owner = v.ip // Important for attachment rate limiting
+	m.Attachment.Expires = time.Now().Add(s.config.AttachmentExpiryDuration).Unix()
+	m.Attachment.Type, ext = util.DetectContentType(body.PeakedBytes, m.Attachment.Name)
+	m.Attachment.URL = fmt.Sprintf("%s/file/%s%s", s.config.BaseURL, m.ID, ext)
+	if m.Attachment.Name == "" {
+		m.Attachment.Name = fmt.Sprintf("attachment%s", ext)
+	}
+	if m.Message == "" {
+		m.Message = fmt.Sprintf(defaultAttachmentMessage, m.Attachment.Name)
+	}
+	m.Attachment.Size, err = s.fileCache.Write(m.ID, body, v.BandwidthLimiter(), util.NewFixedLimiter(remainingVisitorAttachmentSize))
+	if err == util.ErrLimitReached {
+		return errHTTPBadRequestAttachmentTooLarge
+	} else if err != nil {
+		return err
+	}
+	return nil
+}
+
 func (s *Server) handleSubscribeJSON(w http.ResponseWriter, r *http.Request, v *visitor) error {
 	encoder := func(msg *message) (string, error) {
 		var buf bytes.Buffer
@ -720,8 +874,8 @@ func (s *Server) topicsFromIDs(ids ...string) ([]*topic, error) {
 			return nil, errHTTPBadRequestTopicDisallowed
 		}
 		if _, ok := s.topics[id]; !ok {
-			if len(s.topics) >= s.config.GlobalTopicLimit {
-				return nil, errHTTPTooManyRequestsLimitGlobalTopics
+			if len(s.topics) >= s.config.TotalTopicLimit {
+				return nil, errHTTPTooManyRequestsLimitTotalTopics
 			}
 			s.topics[id] = newTopic(id)
 		}
@ -741,6 +895,18 @@ func (s *Server) updateStatsAndPrune() {
 		}
 	}

+	// Delete expired attachments
+	if s.fileCache != nil {
+		ids, err := s.cache.AttachmentsExpired()
+		if err == nil {
+			if err := s.fileCache.Remove(ids...); err != nil {
+				log.Printf("error while deleting attachments: %s", err.Error())
+			}
+		} else {
+			log.Printf("error retrieving expired attachments: %s", err.Error())
+		}
+	}
+
 	// Prune message cache
 	olderThan := time.Now().Add(-1 * s.config.CacheDuration)
 	if err := s.cache.Prune(olderThan); err != nil {
@ -857,12 +1023,11 @@ func (s *Server) sendDelayedMessages() error {
 			if err := t.Publish(m); err != nil {
 				log.Printf("unable to publish message %s to topic %s: %v", m.ID, m.Topic, err.Error())
 			}
-			if s.firebase != nil {
-				if err := s.firebase(m); err != nil {
-					log.Printf("unable to publish to Firebase: %v", err.Error())
-				}
+		}
+		if s.firebase != nil { // Firebase subscribers may not show up in topics map
+			if err := s.firebase(m); err != nil {
+				log.Printf("unable to publish to Firebase: %v", err.Error())
 			}
-			// TODO delayed email sending
 		}
 		if err := s.cache.MarkPublished(m); err != nil {
 			return err
--- a/server/server.yml
+++ b/server/server.yml
@ -36,7 +36,7 @@
 #
 # You can disable the cache entirely by setting this to 0.
 #
-# cache-duration: 12h
+# cache-duration: "12h"

 # If set, the X-Forwarded-For header is used to determine the visitor IP address
 # instead of the remote address of the connection.
@ -46,6 +46,19 @@
 #
 # behind-proxy: false

+# If enabled, clients can attach files to notifications as attachments. Minimum settings to enable attachments
+# are "attachment-cache-dir" and "base-url".
+#
+# - attachment-cache-dir is the cache directory for attached files
+# - attachment-total-size-limit is the limit of the on-disk attachment cache directory (total size)
+# - attachment-file-size-limit is the per-file attachment size limit (e.g. 300k, 2M, 100M)
+# - attachment-expiry-duration is the duration after which uploaded attachments will be deleted (e.g. 3h, 20h)
+#
+# attachment-cache-dir:
+# attachment-total-size-limit: "5G"
+# attachment-file-size-limit: "15M"
+# attachment-expiry-duration: "3h"
+
 # If enabled, allow outgoing e-mail notifications via the 'X-Email' header. If this header is set,
 # messages will additionally be sent out as e-mail using an external SMTP server. As of today, only
 # SMTP servers with plain text auth and STARTLS are supported. Please also refer to the rate limiting settings
@ -78,16 +91,16 @@
 #
 # Note that the Android app has a hardcoded timeout at 77s, so it should be less than that.
 #
-# keepalive-interval: 30s
+# keepalive-interval: "30s"

 # Interval in which the manager prunes old messages, deletes topics
 # and prints the stats.
 #
-# manager-interval: 1m
+# manager-interval: "1m"

 # Rate limiting: Total number of topics before the server rejects new topics.
 #
-# global-topic-limit: 5000
+# global-topic-limit: 15000

 # Rate limiting: Number of subscriptions per visitor (IP address)
 #
@ -98,11 +111,18 @@
 # - visitor-request-limit-replenish is the rate at which the bucket is refilled
 #
 # visitor-request-limit-burst: 60
-# visitor-request-limit-replenish: 10s
+# visitor-request-limit-replenish: "10s"

 # Rate limiting: Allowed emails per visitor:
 # - visitor-email-limit-burst is the initial bucket of emails each visitor has
 # - visitor-email-limit-replenish is the rate at which the bucket is refilled
 #
 # visitor-email-limit-burst: 16
-# visitor-email-limit-replenish: 1h
+# visitor-email-limit-replenish: "1h"
+
+# Rate limiting: Attachment size and bandwidth limits per visitor:
+# - visitor-attachment-total-size-limit is the total storage limit used for attachments per visitor
+# - visitor-attachment-daily-bandwidth-limit is the total daily attachment download/upload traffic limit per visitor
+#
+# visitor-attachment-total-size-limit: "100M"
+# visitor-attachment-daily-bandwidth-limit: "500M"
--- a/server/server_test.go
+++ b/server/server_test.go
@ -7,6 +7,7 @@ import (
 	"firebase.google.com/go/messaging"
 	"fmt"
 	"github.com/stretchr/testify/require"
+	"heckel.io/ntfy/util"
 	"net/http"
 	"net/http/httptest"
 	"os"
@ -163,20 +164,13 @@ func TestServer_StaticSites(t *testing.T) {
 }

 func TestServer_PublishLargeMessage(t *testing.T) {
-	s := newTestServer(t, newTestConfig(t))
+	c := newTestConfig(t)
+	c.AttachmentCacheDir = "" // Disable attachments
+	s := newTestServer(t, c)

 	body := strings.Repeat("this is a large message", 5000)
-	truncated := body[0:4096]
 	response := request(t, s, "PUT", "/mytopic", body, nil)
-	msg := toMessage(t, response.Body.String())
-	require.NotEmpty(t, msg.ID)
-	require.Equal(t, truncated, msg.Message)
-	require.Equal(t, 4096, len(msg.Message))
-
-	response = request(t, s, "GET", "/mytopic/json?poll=1", "", nil)
-	messages := toMessages(t, response.Body.String())
-	require.Equal(t, 1, len(messages))
-	require.Equal(t, truncated, messages[0].Message)
+	require.Equal(t, 400, response.Code)
 }

 func TestServer_PublishPriority(t *testing.T) {
@ -205,6 +199,9 @@ func TestServer_PublishPriority(t *testing.T) {

 	response = request(t, s, "GET", "/mytopic/trigger?priority=urgent", "test", nil)
 	require.Equal(t, 5, toMessage(t, response.Body.String()).Priority)
+
+	response = request(t, s, "GET", "/mytopic/trigger?priority=INVALID", "test", nil)
+	require.Equal(t, 40007, toHTTPError(t, response.Body.String()).Code)
 }

 func TestServer_PublishNoCache(t *testing.T) {
@ -268,13 +265,28 @@ func TestServer_PublishAtTooShortDelay(t *testing.T) {

 func TestServer_PublishAtTooLongDelay(t *testing.T) {
 	s := newTestServer(t, newTestConfig(t))
-
 	response := request(t, s, "PUT", "/mytopic", "a message", map[string]string{
 		"In": "99999999h",
 	})
 	require.Equal(t, 400, response.Code)
 }

+func TestServer_PublishAtInvalidDelay(t *testing.T) {
+	s := newTestServer(t, newTestConfig(t))
+	response := request(t, s, "PUT", "/mytopic?delay=INVALID", "a message", nil)
+	err := toHTTPError(t, response.Body.String())
+	require.Equal(t, 400, response.Code)
+	require.Equal(t, 40004, err.Code)
+}
+
+func TestServer_PublishAtTooLarge(t *testing.T) {
+	s := newTestServer(t, newTestConfig(t))
+	response := request(t, s, "PUT", "/mytopic?x-in=99999h", "a message", nil)
+	err := toHTTPError(t, response.Body.String())
+	require.Equal(t, 400, response.Code)
+	require.Equal(t, 40006, err.Code)
+}
+
 func TestServer_PublishAtAndPrune(t *testing.T) {
 	s := newTestServer(t, newTestConfig(t))

@ -356,6 +368,19 @@ func TestServer_PublishAndPollSince(t *testing.T) {
 	messages := toMessages(t, response.Body.String())
 	require.Equal(t, 1, len(messages))
 	require.Equal(t, "test 2", messages[0].Message)
+
+	response = request(t, s, "GET", "/mytopic/json?poll=1&since=10s", "", nil)
+	messages = toMessages(t, response.Body.String())
+	require.Equal(t, 2, len(messages))
+	require.Equal(t, "test 1", messages[0].Message)
+
+	response = request(t, s, "GET", "/mytopic/json?poll=1&since=100ms", "", nil)
+	messages = toMessages(t, response.Body.String())
+	require.Equal(t, 1, len(messages))
+	require.Equal(t, "test 2", messages[0].Message)
+
+	response = request(t, s, "GET", "/mytopic/json?poll=1&since=INVALID", "", nil)
+	require.Equal(t, 40008, toHTTPError(t, response.Body.String()).Code)
 }

 func TestServer_PublishViaGET(t *testing.T) {
@ -396,6 +421,13 @@ func TestServer_PublishFirebase(t *testing.T) {
 	time.Sleep(500 * time.Millisecond) // Time for sends
 }

+func TestServer_PublishInvalidTopic(t *testing.T) {
+	s := newTestServer(t, newTestConfig(t))
+	s.mailer = &testMailer{}
+	response := request(t, s, "PUT", "/docs", "fail", nil)
+	require.Equal(t, 40010, toHTTPError(t, response.Body.String()).Code)
+}
+
 func TestServer_PollWithQueryFilters(t *testing.T) {
 	s := newTestServer(t, newTestConfig(t))

@ -649,9 +681,241 @@ func TestServer_MaybeTruncateFCMMessage_NotTooLong(t *testing.T) {
 	require.Equal(t, "", notTruncatedFCMMessage.Data["truncated"])
 }

+func TestServer_PublishAttachment(t *testing.T) {
+	content := util.RandomString(5000) // > 4096
+	s := newTestServer(t, newTestConfig(t))
+	response := request(t, s, "PUT", "/mytopic", content, nil)
+	msg := toMessage(t, response.Body.String())
+	require.Equal(t, "attachment.txt", msg.Attachment.Name)
+	require.Equal(t, "text/plain; charset=utf-8", msg.Attachment.Type)
+	require.Equal(t, int64(5000), msg.Attachment.Size)
+	require.GreaterOrEqual(t, msg.Attachment.Expires, time.Now().Add(3*time.Hour).Unix())
+	require.Contains(t, msg.Attachment.URL, "http://127.0.0.1:12345/file/")
+	require.Equal(t, "", msg.Attachment.Owner) // Should never be returned
+	require.FileExists(t, filepath.Join(s.config.AttachmentCacheDir, msg.ID))
+
+	path := strings.TrimPrefix(msg.Attachment.URL, "http://127.0.0.1:12345")
+	response = request(t, s, "GET", path, "", nil)
+	require.Equal(t, 200, response.Code)
+	require.Equal(t, "5000", response.Header().Get("Content-Length"))
+	require.Equal(t, content, response.Body.String())
+
+	// Slightly unrelated cross-test: make sure we add an owner for internal attachments
+	size, err := s.cache.AttachmentsSize("9.9.9.9") // See request()
+	require.Nil(t, err)
+	require.Equal(t, int64(5000), size)
+}
+
+func TestServer_PublishAttachmentShortWithFilename(t *testing.T) {
+	c := newTestConfig(t)
+	c.BehindProxy = true
+	s := newTestServer(t, c)
+	content := "this is an ATTACHMENT"
+	response := request(t, s, "PUT", "/mytopic?f=myfile.txt", content, map[string]string{
+		"X-Forwarded-For": "1.2.3.4",
+	})
+	msg := toMessage(t, response.Body.String())
+	require.Equal(t, "myfile.txt", msg.Attachment.Name)
+	require.Equal(t, "text/plain; charset=utf-8", msg.Attachment.Type)
+	require.Equal(t, int64(21), msg.Attachment.Size)
+	require.GreaterOrEqual(t, msg.Attachment.Expires, time.Now().Add(3*time.Hour).Unix())
+	require.Contains(t, msg.Attachment.URL, "http://127.0.0.1:12345/file/")
+	require.Equal(t, "", msg.Attachment.Owner) // Should never be returned
+	require.FileExists(t, filepath.Join(s.config.AttachmentCacheDir, msg.ID))
+
+	path := strings.TrimPrefix(msg.Attachment.URL, "http://127.0.0.1:12345")
+	response = request(t, s, "GET", path, "", nil)
+	require.Equal(t, 200, response.Code)
+	require.Equal(t, "21", response.Header().Get("Content-Length"))
+	require.Equal(t, content, response.Body.String())
+
+	// Slightly unrelated cross-test: make sure we add an owner for internal attachments
+	size, err := s.cache.AttachmentsSize("1.2.3.4")
+	require.Nil(t, err)
+	require.Equal(t, int64(21), size)
+}
+
+func TestServer_PublishAttachmentExternalWithoutFilename(t *testing.T) {
+	s := newTestServer(t, newTestConfig(t))
+	response := request(t, s, "PUT", "/mytopic", "", map[string]string{
+		"Attach": "https://upload.wikimedia.org/wikipedia/commons/f/fd/Pink_flower.jpg",
+	})
+	msg := toMessage(t, response.Body.String())
+	require.Equal(t, "You received a file: Pink_flower.jpg", msg.Message)
+	require.Equal(t, "Pink_flower.jpg", msg.Attachment.Name)
+	require.Equal(t, "image/jpeg", msg.Attachment.Type)
+	require.Equal(t, int64(190173), msg.Attachment.Size)
+	require.Equal(t, int64(0), msg.Attachment.Expires)
+	require.Equal(t, "https://upload.wikimedia.org/wikipedia/commons/f/fd/Pink_flower.jpg", msg.Attachment.URL)
+	require.Equal(t, "", msg.Attachment.Owner)
+
+	// Slightly unrelated cross-test: make sure we don't add an owner for external attachments
+	size, err := s.cache.AttachmentsSize("127.0.0.1")
+	require.Nil(t, err)
+	require.Equal(t, int64(0), size)
+}
+
+func TestServer_PublishAttachmentExternalWithFilename(t *testing.T) {
+	s := newTestServer(t, newTestConfig(t))
+	response := request(t, s, "PUT", "/mytopic", "This is a custom message", map[string]string{
+		"X-Attach": "https://upload.wikimedia.org/wikipedia/commons/f/fd/Pink_flower.jpg",
+		"File":     "some file.jpg",
+	})
+	msg := toMessage(t, response.Body.String())
+	require.Equal(t, "This is a custom message", msg.Message)
+	require.Equal(t, "some file.jpg", msg.Attachment.Name)
+	require.Equal(t, "image/jpeg", msg.Attachment.Type)
+	require.Equal(t, int64(190173), msg.Attachment.Size)
+	require.Equal(t, int64(0), msg.Attachment.Expires)
+	require.Equal(t, "https://upload.wikimedia.org/wikipedia/commons/f/fd/Pink_flower.jpg", msg.Attachment.URL)
+	require.Equal(t, "", msg.Attachment.Owner)
+}
+
+func TestServer_PublishAttachmentBadURL(t *testing.T) {
+	s := newTestServer(t, newTestConfig(t))
+	response := request(t, s, "PUT", "/mytopic?a=not+a+URL", "", nil)
+	err := toHTTPError(t, response.Body.String())
+	require.Equal(t, 400, response.Code)
+	require.Equal(t, 400, err.HTTPCode)
+	require.Equal(t, 40013, err.Code)
+}
+
+func TestServer_PublishAttachmentTooLargeContentLength(t *testing.T) {
+	content := util.RandomString(5000) // > 4096
+	s := newTestServer(t, newTestConfig(t))
+	response := request(t, s, "PUT", "/mytopic", content, map[string]string{
+		"Content-Length": "20000000",
+	})
+	err := toHTTPError(t, response.Body.String())
+	require.Equal(t, 400, response.Code)
+	require.Equal(t, 400, err.HTTPCode)
+	require.Equal(t, 40012, err.Code)
+}
+
+func TestServer_PublishAttachmentTooLargeBodyAttachmentFileSizeLimit(t *testing.T) {
+	content := util.RandomString(5001) // > 5000, see below
+	c := newTestConfig(t)
+	c.AttachmentFileSizeLimit = 5000
+	s := newTestServer(t, c)
+	response := request(t, s, "PUT", "/mytopic", content, nil)
+	err := toHTTPError(t, response.Body.String())
+	require.Equal(t, 400, response.Code)
+	require.Equal(t, 400, err.HTTPCode)
+	require.Equal(t, 40012, err.Code)
+}
+
+func TestServer_PublishAttachmentExpiryBeforeDelivery(t *testing.T) {
+	c := newTestConfig(t)
+	c.AttachmentExpiryDuration = 10 * time.Minute
+	s := newTestServer(t, c)
+	response := request(t, s, "PUT", "/mytopic", util.RandomString(5000), map[string]string{
+		"Delay": "11 min", // > AttachmentExpiryDuration
+	})
+	err := toHTTPError(t, response.Body.String())
+	require.Equal(t, 400, response.Code)
+	require.Equal(t, 400, err.HTTPCode)
+	require.Equal(t, 40017, err.Code)
+}
+
+func TestServer_PublishAttachmentTooLargeBodyVisitorAttachmentTotalSizeLimit(t *testing.T) {
+	c := newTestConfig(t)
+	c.VisitorAttachmentTotalSizeLimit = 10000
+	s := newTestServer(t, c)
+
+	response := request(t, s, "PUT", "/mytopic", util.RandomString(5000), nil)
+	msg := toMessage(t, response.Body.String())
+	require.Equal(t, 200, response.Code)
+	require.Equal(t, "You received a file: attachment.txt", msg.Message)
+	require.Equal(t, int64(5000), msg.Attachment.Size)
+
+	content := util.RandomString(5001) // 5000+5001 > , see below
+	response = request(t, s, "PUT", "/mytopic", content, nil)
+	err := toHTTPError(t, response.Body.String())
+	require.Equal(t, 400, response.Code)
+	require.Equal(t, 400, err.HTTPCode)
+	require.Equal(t, 40012, err.Code)
+}
+
+func TestServer_PublishAttachmentAndPrune(t *testing.T) {
+	content := util.RandomString(5000) // > 4096
+
+	c := newTestConfig(t)
+	c.AttachmentExpiryDuration = time.Millisecond // Hack
+	s := newTestServer(t, c)
+
+	// Publish and make sure we can retrieve it
+	response := request(t, s, "PUT", "/mytopic", content, nil)
+	msg := toMessage(t, response.Body.String())
+	require.Contains(t, msg.Attachment.URL, "http://127.0.0.1:12345/file/")
+	file := filepath.Join(s.config.AttachmentCacheDir, msg.ID)
+	require.FileExists(t, file)
+
+	path := strings.TrimPrefix(msg.Attachment.URL, "http://127.0.0.1:12345")
+	response = request(t, s, "GET", path, "", nil)
+	require.Equal(t, 200, response.Code)
+	require.Equal(t, content, response.Body.String())
+
+	// Prune and makes sure it's gone
+	time.Sleep(time.Second) // Sigh ...
+	s.updateStatsAndPrune()
+	require.NoFileExists(t, file)
+	response = request(t, s, "GET", path, "", nil)
+	require.Equal(t, 404, response.Code)
+}
+
+func TestServer_PublishAttachmentBandwidthLimit(t *testing.T) {
+	content := util.RandomString(5000) // > 4096
+
+	c := newTestConfig(t)
+	c.VisitorAttachmentDailyBandwidthLimit = 5*5000 + 123 // A little more than 1 upload and 3 downloads
+	s := newTestServer(t, c)
+
+	// Publish attachment
+	response := request(t, s, "PUT", "/mytopic", content, nil)
+	msg := toMessage(t, response.Body.String())
+	require.Contains(t, msg.Attachment.URL, "http://127.0.0.1:12345/file/")
+
+	// Get it 4 times successfully
+	path := strings.TrimPrefix(msg.Attachment.URL, "http://127.0.0.1:12345")
+	for i := 1; i <= 4; i++ { // 4 successful downloads
+		response = request(t, s, "GET", path, "", nil)
+		require.Equal(t, 200, response.Code)
+		require.Equal(t, content, response.Body.String())
+	}
+
+	// And then fail with a 429
+	response = request(t, s, "GET", path, "", nil)
+	err := toHTTPError(t, response.Body.String())
+	require.Equal(t, 429, response.Code)
+	require.Equal(t, 42905, err.Code)
+}
+
+func TestServer_PublishAttachmentBandwidthLimitUploadOnly(t *testing.T) {
+	content := util.RandomString(5000) // > 4096
+
+	c := newTestConfig(t)
+	c.VisitorAttachmentDailyBandwidthLimit = 5*5000 + 500 // 5 successful uploads
+	s := newTestServer(t, c)
+
+	// 5 successful uploads
+	for i := 1; i <= 5; i++ {
+		response := request(t, s, "PUT", "/mytopic", content, nil)
+		msg := toMessage(t, response.Body.String())
+		require.Contains(t, msg.Attachment.URL, "http://127.0.0.1:12345/file/")
+	}
+
+	// And a failed one
+	response := request(t, s, "PUT", "/mytopic", content, nil)
+	err := toHTTPError(t, response.Body.String())
+	require.Equal(t, 400, response.Code)
+	require.Equal(t, 40012, err.Code)
+}
+
 func newTestConfig(t *testing.T) *Config {
 	conf := NewConfig()
+	conf.BaseURL = "http://127.0.0.1:12345"
 	conf.CacheFile = filepath.Join(t.TempDir(), "cache.db")
+	conf.AttachmentCacheDir = t.TempDir()
 	return conf
 }

@ -669,6 +933,7 @@ func request(t *testing.T, s *Server, method, url, body string, headers map[stri
 	if err != nil {
 		t.Fatal(err)
 	}
+	req.RemoteAddr = "9.9.9.9" // Used for tests
 	for k, v := range headers {
 		req.Header.Set(k, v)
 	}
--- a/server/util.go
+++ b/server/util.go
@ -0,0 +1,69 @@
+package server
+
+import (
+	"fmt"
+	"heckel.io/ntfy/util"
+	"io"
+	"net/http"
+	"net/url"
+	"path"
+	"strconv"
+	"time"
+)
+
+const (
+	peakAttachmentTimeout   = 2500 * time.Millisecond
+	peakAttachmentReadBytes = 128
+)
+
+func maybePeakAttachmentURL(m *message) error {
+	return maybePeakAttachmentURLInternal(m, peakAttachmentTimeout)
+}
+
+func maybePeakAttachmentURLInternal(m *message, timeout time.Duration) error {
+	if m.Attachment == nil || m.Attachment.URL == "" {
+		return nil
+	}
+	client := http.Client{
+		Timeout: timeout,
+		Transport: &http.Transport{
+			DisableCompression: true, // Disable "Accept-Encoding: gzip", otherwise we won't get the Content-Length
+			Proxy:              http.ProxyFromEnvironment,
+		},
+	}
+	req, err := http.NewRequest(http.MethodGet, m.Attachment.URL, nil)
+	if err != nil {
+		return err
+	}
+	req.Header.Set("User-Agent", "ntfy")
+	resp, err := client.Do(req)
+	if err != nil {
+		return errHTTPBadRequestAttachmentURLPeakGeneral
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode < 200 || resp.StatusCode > 299 {
+		return errHTTPBadRequestAttachmentURLPeakNon2xx
+	}
+	if size, err := strconv.ParseInt(resp.Header.Get("Content-Length"), 10, 64); err == nil {
+		m.Attachment.Size = size
+	}
+	buf := make([]byte, peakAttachmentReadBytes)
+	io.ReadFull(resp.Body, buf) // Best effort: We don't care about the error
+	mimeType, ext := util.DetectContentType(buf, m.Attachment.URL)
+	m.Attachment.Type = resp.Header.Get("Content-Type")
+	if m.Attachment.Type == "" {
+		m.Attachment.Type = mimeType
+	}
+	if m.Attachment.Name == "" {
+		u, err := url.Parse(m.Attachment.URL)
+		if err != nil {
+			m.Attachment.Name = fmt.Sprintf("attachment%s", ext)
+		} else {
+			m.Attachment.Name = path.Base(u.Path)
+			if m.Attachment.Name == "." || m.Attachment.Name == "/" {
+				m.Attachment.Name = fmt.Sprintf("attachment%s", ext)
+			}
+		}
+	}
+	return nil
+}
--- a/server/util_test.go
+++ b/server/util_test.go
@ -0,0 +1,19 @@
+package server
+
+import (
+	"github.com/stretchr/testify/require"
+	"testing"
+)
+
+func TestMaybePeakAttachmentURL_Success(t *testing.T) {
+	m := &message{
+		Attachment: &attachment{
+			URL: "https://ntfy.sh/static/img/ntfy.png",
+		},
+	}
+	require.Nil(t, maybePeakAttachmentURL(m))
+	require.Equal(t, "ntfy.png", m.Attachment.Name)
+	require.Equal(t, int64(3627), m.Attachment.Size)
+	require.Equal(t, "image/png", m.Attachment.Type)
+	require.Equal(t, int64(0), m.Attachment.Expires)
+}
--- a/server/visitor.go
+++ b/server/visitor.go
@ -25,7 +25,8 @@ type visitor struct {
 	ip            string
 	requests      *rate.Limiter
 	emails        *rate.Limiter
-	subscriptions *util.Limiter
+	subscriptions util.Limiter
+	bandwidth     util.Limiter
 	seen          time.Time
 	mu            sync.Mutex
 }
@ -36,7 +37,8 @@ func newVisitor(conf *Config, ip string) *visitor {
 		ip:            ip,
 		requests:      rate.NewLimiter(rate.Every(conf.VisitorRequestLimitReplenish), conf.VisitorRequestLimitBurst),
 		emails:        rate.NewLimiter(rate.Every(conf.VisitorEmailLimitReplenish), conf.VisitorEmailLimitBurst),
-		subscriptions: util.NewLimiter(int64(conf.VisitorSubscriptionLimit)),
+		subscriptions: util.NewFixedLimiter(int64(conf.VisitorSubscriptionLimit)),
+		bandwidth:     util.NewBytesLimiter(conf.VisitorAttachmentDailyBandwidthLimit, 24*time.Hour),
 		seen:          time.Now(),
 	}
 }
@ -62,7 +64,7 @@ func (v *visitor) EmailAllowed() error {
 func (v *visitor) SubscriptionAllowed() error {
 	v.mu.Lock()
 	defer v.mu.Unlock()
-	if err := v.subscriptions.Add(1); err != nil {
+	if err := v.subscriptions.Allow(1); err != nil {
 		return errVisitorLimitReached
 	}
 	return nil
@ -71,7 +73,7 @@ func (v *visitor) SubscriptionAllowed() error {
 func (v *visitor) RemoveSubscription() {
 	v.mu.Lock()
 	defer v.mu.Unlock()
-	v.subscriptions.Sub(1)
+	v.subscriptions.Allow(-1)
 }

 func (v *visitor) Keepalive() {
@ -80,6 +82,10 @@ func (v *visitor) Keepalive() {
 	v.seen = time.Now()
 }

+func (v *visitor) BandwidthLimiter() util.Limiter {
+	return v.bandwidth
+}
+
 func (v *visitor) Stale() bool {
 	v.mu.Lock()
 	defer v.mu.Unlock()
--- a/util/content_type_writer.go
+++ b/util/content_type_writer.go
@ -0,0 +1,42 @@
+package util
+
+import (
+	"net/http"
+	"strings"
+)
+
+// ContentTypeWriter is an implementation of http.ResponseWriter that will detect the content type and set the
+// Content-Type and (optionally) Content-Disposition headers accordingly.
+//
+// It will always set a Content-Type based on http.DetectContentType, but will never send the "text/html"
+// content type.
+type ContentTypeWriter struct {
+	w        http.ResponseWriter
+	filename string
+	sniffed  bool
+}
+
+// NewContentTypeWriter creates a new ContentTypeWriter
+func NewContentTypeWriter(w http.ResponseWriter, filename string) *ContentTypeWriter {
+	return &ContentTypeWriter{w, filename, false}
+}
+
+func (w *ContentTypeWriter) Write(p []byte) (n int, err error) {
+	if w.sniffed {
+		return w.w.Write(p)
+	}
+	// Detect and set Content-Type header
+	// Fix content types that we don't want to inline-render in the browser. In particular,
+	// we don't want to render HTML in the browser for security reasons.
+	contentType, _ := DetectContentType(p, w.filename)
+	if strings.HasPrefix(contentType, "text/html") {
+		contentType = strings.ReplaceAll(contentType, "text/html", "text/plain")
+	} else if contentType == "application/octet-stream" {
+		contentType = "" // Reset to let downstream http.ResponseWriter take care of it
+	}
+	if contentType != "" {
+		w.w.Header().Set("Content-Type", contentType)
+	}
+	w.sniffed = true
+	return w.w.Write(p)
+}
--- a/util/content_type_writer_test.go
+++ b/util/content_type_writer_test.go
@ -0,0 +1,57 @@
+package util
+
+import (
+	"crypto/rand"
+	"github.com/stretchr/testify/require"
+	"net/http/httptest"
+	"testing"
+)
+
+func TestSniffWriter_WriteHTML(t *testing.T) {
+	rr := httptest.NewRecorder()
+	sw := NewContentTypeWriter(rr, "")
+	sw.Write([]byte("<script>alert('hi')</script>"))
+	require.Equal(t, "text/plain; charset=utf-8", rr.Header().Get("Content-Type"))
+}
+
+func TestSniffWriter_WriteTwoWriteCalls(t *testing.T) {
+	rr := httptest.NewRecorder()
+	sw := NewContentTypeWriter(rr, "")
+	sw.Write([]byte{0x25, 0x50, 0x44, 0x46, 0x2d, 0x11, 0x22, 0x33})
+	sw.Write([]byte("<script>alert('hi')</script>"))
+	require.Equal(t, "application/pdf", rr.Header().Get("Content-Type"))
+}
+
+func TestSniffWriter_NoSniffWriterWriteHTML(t *testing.T) {
+	// This test just makes sure that without the sniff-w, we would get text/html
+
+	rr := httptest.NewRecorder()
+	rr.Write([]byte("<script>alert('hi')</script>"))
+	require.Equal(t, "text/html; charset=utf-8", rr.Header().Get("Content-Type"))
+}
+
+func TestSniffWriter_WriteHTMLSplitIntoTwoWrites(t *testing.T) {
+	// This test shows how splitting the HTML into two Write() calls will still yield text/plain
+
+	rr := httptest.NewRecorder()
+	sw := NewContentTypeWriter(rr, "")
+	sw.Write([]byte("<scr"))
+	sw.Write([]byte("ipt>alert('hi')</script>"))
+	require.Equal(t, "text/plain; charset=utf-8", rr.Header().Get("Content-Type"))
+}
+
+func TestSniffWriter_WriteUnknownMimeType(t *testing.T) {
+	rr := httptest.NewRecorder()
+	sw := NewContentTypeWriter(rr, "")
+	randomBytes := make([]byte, 199)
+	rand.Read(randomBytes)
+	sw.Write(randomBytes)
+	require.Equal(t, "application/octet-stream", rr.Header().Get("Content-Type"))
+}
+
+func TestSniffWriter_WriteWithFilenameAPK(t *testing.T) {
+	rr := httptest.NewRecorder()
+	sw := NewContentTypeWriter(rr, "https://example.com/ntfy.apk")
+	sw.Write([]byte{0x50, 0x4B, 0x03, 0x04})
+	require.Equal(t, "application/vnd.android.package-archive", rr.Header().Get("Content-Type"))
+}
--- a/util/limit.go
+++ b/util/limit.go
@ -2,59 +2,109 @@ package util

 import (
 	"errors"
+	"golang.org/x/time/rate"
+	"io"
 	"sync"
+	"time"
 )

 // ErrLimitReached is the error returned by the Limiter and LimitWriter when the predefined limit has been reached
 var ErrLimitReached = errors.New("limit reached")

-// Limiter is a helper that allows adding values up to a well-defined limit. Once the limit is reached
-// ErrLimitReached will be returned. Limiter may be used by multiple goroutines.
-type Limiter struct {
+// Limiter is an interface that implements a rate limiting mechanism, e.g. based on time or a fixed value
+type Limiter interface {
+	// Allow adds n to the limiters internal value, or returns ErrLimitReached if the limit has been reached
+	Allow(n int64) error
+}
+
+// FixedLimiter is a helper that allows adding values up to a well-defined limit. Once the limit is reached
+// ErrLimitReached will be returned. FixedLimiter may be used by multiple goroutines.
+type FixedLimiter struct {
 	value int64
 	limit int64
 	mu    sync.Mutex
 }

-// NewLimiter creates a new Limiter
-func NewLimiter(limit int64) *Limiter {
-	return &Limiter{
+// NewFixedLimiter creates a new Limiter
+func NewFixedLimiter(limit int64) *FixedLimiter {
+	return &FixedLimiter{
 		limit: limit,
 	}
 }

-// Add adds n to the limiters internal value, but only if the limit has not been reached. If the limit would be
+// Allow adds n to the limiters internal value, but only if the limit has not been reached. If the limit was
 // exceeded after adding n, ErrLimitReached is returned.
-func (l *Limiter) Add(n int64) error {
+func (l *FixedLimiter) Allow(n int64) error {
 	l.mu.Lock()
 	defer l.mu.Unlock()
-	if l.limit == 0 {
-		l.value += n
-		return nil
-	} else if l.value+n <= l.limit {
-		l.value += n
-		return nil
-	} else {
+	if l.value+n > l.limit {
 		return ErrLimitReached
 	}
+	l.value += n
+	return nil
+}
+
+// RateLimiter is a Limiter that wraps a rate.Limiter, allowing a floating time-based limit.
+type RateLimiter struct {
+	limiter *rate.Limiter
+}
+
+// NewRateLimiter creates a new RateLimiter
+func NewRateLimiter(r rate.Limit, b int) *RateLimiter {
+	return &RateLimiter{
+		limiter: rate.NewLimiter(r, b),
+	}
 }

-// Sub subtracts a value from the limiters internal value
-func (l *Limiter) Sub(n int64) {
-	l.Add(-n)
+// NewBytesLimiter creates a RateLimiter that is meant to be used for a bytes-per-interval limit,
+// e.g. 250 MB per day. And example of the underlying idea can be found here: https://go.dev/play/p/0ljgzIZQ6dJ
+func NewBytesLimiter(bytes int, interval time.Duration) *RateLimiter {
+	return NewRateLimiter(rate.Limit(bytes)*rate.Every(interval), bytes)
 }

-// Set sets the value of the limiter to n. This function ignores the limit. It is meant to set the value
-// based on reality.
-func (l *Limiter) Set(n int64) {
-	l.mu.Lock()
-	l.value = n
-	l.mu.Unlock()
+// Allow adds n to the limiters internal value, but only if the limit has not been reached. If the limit was
+// exceeded after adding n, ErrLimitReached is returned.
+func (l *RateLimiter) Allow(n int64) error {
+	if n <= 0 {
+		return nil // No-op. Can't take back bytes you're written!
+	}
+	if !l.limiter.AllowN(time.Now(), int(n)) {
+		return ErrLimitReached
+	}
+	return nil
 }

-// Value returns the internal value of the limiter
-func (l *Limiter) Value() int64 {
-	l.mu.Lock()
-	defer l.mu.Unlock()
-	return l.value
+// LimitWriter implements an io.Writer that will pass through all Write calls to the underlying
+// writer w until any of the limiter's limit is reached, at which point a Write will return ErrLimitReached.
+// Each limiter's value is increased with every write.
+type LimitWriter struct {
+	w        io.Writer
+	written  int64
+	limiters []Limiter
+	mu       sync.Mutex
+}
+
+// NewLimitWriter creates a new LimitWriter
+func NewLimitWriter(w io.Writer, limiters ...Limiter) *LimitWriter {
+	return &LimitWriter{
+		w:        w,
+		limiters: limiters,
+	}
+}
+
+// Write passes through all writes to the underlying writer until any of the given limiter's limit is reached
+func (w *LimitWriter) Write(p []byte) (n int, err error) {
+	w.mu.Lock()
+	defer w.mu.Unlock()
+	for i := 0; i < len(w.limiters); i++ {
+		if err := w.limiters[i].Allow(int64(len(p))); err != nil {
+			for j := i - 1; j >= 0; j-- {
+				w.limiters[j].Allow(-int64(len(p))) // Revert limiters limits if allowed
+			}
+			return 0, ErrLimitReached
+		}
+	}
+	n, err = w.w.Write(p)
+	w.written += int64(n)
+	return
 }
--- a/util/limit_test.go
+++ b/util/limit_test.go
@ -1,30 +1,139 @@
 package util

 import (
+	"bytes"
+	"github.com/stretchr/testify/require"
 	"testing"
+	"time"
 )

-func TestLimiter_Add(t *testing.T) {
-	l := NewLimiter(10)
-	if err := l.Add(5); err != nil {
+func TestFixedLimiter_Add(t *testing.T) {
+	l := NewFixedLimiter(10)
+	if err := l.Allow(5); err != nil {
 		t.Fatal(err)
 	}
-	if err := l.Add(5); err != nil {
+	if err := l.Allow(5); err != nil {
 		t.Fatal(err)
 	}
-	if err := l.Add(5); err != ErrLimitReached {
+	if err := l.Allow(5); err != ErrLimitReached {
 		t.Fatalf("expected ErrLimitReached, got %#v", err)
 	}
 }

-func TestLimiter_AddSub(t *testing.T) {
-	l := NewLimiter(10)
-	l.Add(5)
-	if l.Value() != 5 {
-		t.Fatalf("expected value to be %d, got %d", 5, l.Value())
+func TestFixedLimiter_AddSub(t *testing.T) {
+	l := NewFixedLimiter(10)
+	l.Allow(5)
+	if l.value != 5 {
+		t.Fatalf("expected value to be %d, got %d", 5, l.value)
 	}
-	l.Sub(2)
-	if l.Value() != 3 {
-		t.Fatalf("expected value to be %d, got %d", 3, l.Value())
+	l.Allow(-2)
+	if l.value != 3 {
+		t.Fatalf("expected value to be %d, got %d", 7, l.value)
 	}
 }
+
+func TestBytesLimiter_Add_Simple(t *testing.T) {
+	l := NewBytesLimiter(250*1024*1024, 24*time.Hour) // 250 MB per 24h
+	require.Nil(t, l.Allow(100*1024*1024))
+	require.Nil(t, l.Allow(100*1024*1024))
+	require.Equal(t, ErrLimitReached, l.Allow(300*1024*1024))
+}
+
+func TestBytesLimiter_Add_Wait(t *testing.T) {
+	l := NewBytesLimiter(250*1024*1024, 24*time.Hour) // 250 MB per 24h (~ 303 bytes per 100ms)
+	require.Nil(t, l.Allow(250*1024*1024))
+	require.Equal(t, ErrLimitReached, l.Allow(400))
+	time.Sleep(200 * time.Millisecond)
+	require.Nil(t, l.Allow(400))
+}
+
+func TestLimitWriter_WriteNoLimiter(t *testing.T) {
+	var buf bytes.Buffer
+	lw := NewLimitWriter(&buf)
+	if _, err := lw.Write(make([]byte, 10)); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := lw.Write(make([]byte, 1)); err != nil {
+		t.Fatal(err)
+	}
+	if buf.Len() != 11 {
+		t.Fatalf("expected buffer length to be %d, got %d", 11, buf.Len())
+	}
+}
+
+func TestLimitWriter_WriteOneLimiter(t *testing.T) {
+	var buf bytes.Buffer
+	l := NewFixedLimiter(10)
+	lw := NewLimitWriter(&buf, l)
+	if _, err := lw.Write(make([]byte, 10)); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := lw.Write(make([]byte, 1)); err != ErrLimitReached {
+		t.Fatalf("expected ErrLimitReached, got %#v", err)
+	}
+	if buf.Len() != 10 {
+		t.Fatalf("expected buffer length to be %d, got %d", 10, buf.Len())
+	}
+	if l.value != 10 {
+		t.Fatalf("expected limiter value to be %d, got %d", 10, l.value)
+	}
+}
+
+func TestLimitWriter_WriteTwoLimiters(t *testing.T) {
+	var buf bytes.Buffer
+	l1 := NewFixedLimiter(11)
+	l2 := NewFixedLimiter(9)
+	lw := NewLimitWriter(&buf, l1, l2)
+	if _, err := lw.Write(make([]byte, 8)); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := lw.Write(make([]byte, 2)); err != ErrLimitReached {
+		t.Fatalf("expected ErrLimitReached, got %#v", err)
+	}
+	if buf.Len() != 8 {
+		t.Fatalf("expected buffer length to be %d, got %d", 8, buf.Len())
+	}
+	if l1.value != 8 {
+		t.Fatalf("expected limiter 1 value to be %d, got %d", 8, l1.value)
+	}
+	if l2.value != 8 {
+		t.Fatalf("expected limiter 2 value to be %d, got %d", 8, l2.value)
+	}
+}
+
+func TestLimitWriter_WriteTwoDifferentLimiters(t *testing.T) {
+	var buf bytes.Buffer
+	l1 := NewFixedLimiter(32)
+	l2 := NewBytesLimiter(8, 200*time.Millisecond)
+	lw := NewLimitWriter(&buf, l1, l2)
+	_, err := lw.Write(make([]byte, 8))
+	require.Nil(t, err)
+	_, err = lw.Write(make([]byte, 4))
+	require.Equal(t, ErrLimitReached, err)
+}
+
+func TestLimitWriter_WriteTwoDifferentLimiters_Wait(t *testing.T) {
+	var buf bytes.Buffer
+	l1 := NewFixedLimiter(32)
+	l2 := NewBytesLimiter(8, 200*time.Millisecond)
+	lw := NewLimitWriter(&buf, l1, l2)
+	_, err := lw.Write(make([]byte, 8))
+	require.Nil(t, err)
+	time.Sleep(250 * time.Millisecond)
+	_, err = lw.Write(make([]byte, 8))
+	require.Nil(t, err)
+	_, err = lw.Write(make([]byte, 4))
+	require.Equal(t, ErrLimitReached, err)
+}
+
+func TestLimitWriter_WriteTwoDifferentLimiters_Wait_FixedLimiterFail(t *testing.T) {
+	var buf bytes.Buffer
+	l1 := NewFixedLimiter(11) // <<< This fails below
+	l2 := NewBytesLimiter(8, 200*time.Millisecond)
+	lw := NewLimitWriter(&buf, l1, l2)
+	_, err := lw.Write(make([]byte, 8))
+	require.Nil(t, err)
+	time.Sleep(250 * time.Millisecond)
+	_, err = lw.Write(make([]byte, 8)) // <<< FixedLimiter fails
+	require.Equal(t, ErrLimitReached, err)
+}
--- a/util/peak.go
+++ b/util/peak.go
@ -0,0 +1,61 @@
+package util
+
+import (
+	"bytes"
+	"io"
+	"strings"
+)
+
+// PeakedReadCloser is a ReadCloser that allows peaking into a stream and buffering it in memory.
+// It can be instantiated using the Peak function. After a stream has been peaked, it can still be fully
+// read by reading the PeakedReadCloser. It first drained from the memory buffer, and then from the remaining
+// underlying reader.
+type PeakedReadCloser struct {
+	PeakedBytes  []byte
+	LimitReached bool
+	peaked       io.Reader
+	underlying   io.ReadCloser
+	closed       bool
+}
+
+// Peak reads the underlying ReadCloser into memory up until the limit and returns a PeakedReadCloser
+func Peak(underlying io.ReadCloser, limit int) (*PeakedReadCloser, error) {
+	if underlying == nil {
+		underlying = io.NopCloser(strings.NewReader(""))
+	}
+	peaked := make([]byte, limit)
+	read, err := io.ReadFull(underlying, peaked)
+	if err != nil && err != io.ErrUnexpectedEOF && err != io.EOF {
+		return nil, err
+	}
+	return &PeakedReadCloser{
+		PeakedBytes:  peaked[:read],
+		LimitReached: read == limit,
+		underlying:   underlying,
+		peaked:       bytes.NewReader(peaked[:read]),
+		closed:       false,
+	}, nil
+}
+
+// Read reads from the peaked bytes and then from the underlying stream
+func (r *PeakedReadCloser) Read(p []byte) (n int, err error) {
+	if r.closed {
+		return 0, io.EOF
+	}
+	n, err = r.peaked.Read(p)
+	if err == io.EOF {
+		return r.underlying.Read(p)
+	} else if err != nil {
+		return 0, err
+	}
+	return
+}
+
+// Close closes the underlying stream
+func (r *PeakedReadCloser) Close() error {
+	if r.closed {
+		return io.EOF
+	}
+	r.closed = true
+	return r.underlying.Close()
+}
--- a/util/peak_test.go
+++ b/util/peak_test.go
@ -0,0 +1,55 @@
+package util
+
+import (
+	"github.com/stretchr/testify/require"
+	"io"
+	"strings"
+	"testing"
+)
+
+func TestPeak_LimitReached(t *testing.T) {
+	underlying := io.NopCloser(strings.NewReader("1234567890"))
+	peaked, err := Peak(underlying, 5)
+	if err != nil {
+		t.Fatal(err)
+	}
+	require.Equal(t, []byte("12345"), peaked.PeakedBytes)
+	require.Equal(t, true, peaked.LimitReached)
+
+	all, err := io.ReadAll(peaked)
+	if err != nil {
+		t.Fatal(err)
+	}
+	require.Equal(t, []byte("1234567890"), all)
+	require.Equal(t, []byte("12345"), peaked.PeakedBytes)
+	require.Equal(t, true, peaked.LimitReached)
+}
+
+func TestPeak_LimitNotReached(t *testing.T) {
+	underlying := io.NopCloser(strings.NewReader("1234567890"))
+	peaked, err := Peak(underlying, 15)
+	if err != nil {
+		t.Fatal(err)
+	}
+	all, err := io.ReadAll(peaked)
+	if err != nil {
+		t.Fatal(err)
+	}
+	require.Equal(t, []byte("1234567890"), all)
+	require.Equal(t, []byte("1234567890"), peaked.PeakedBytes)
+	require.Equal(t, false, peaked.LimitReached)
+}
+
+func TestPeak_Nil(t *testing.T) {
+	peaked, err := Peak(nil, 15)
+	if err != nil {
+		t.Fatal(err)
+	}
+	all, err := io.ReadAll(peaked)
+	if err != nil {
+		t.Fatal(err)
+	}
+	require.Equal(t, []byte(""), all)
+	require.Equal(t, []byte(""), peaked.PeakedBytes)
+	require.Equal(t, false, peaked.LimitReached)
+}
--- a/util/util.go
+++ b/util/util.go
@ -3,8 +3,11 @@ package util
 import (
 	"errors"
 	"fmt"
+	"github.com/gabriel-vasile/mimetype"
 	"math/rand"
 	"os"
+	"regexp"
+	"strconv"
 	"strings"
 	"sync"
 	"time"
@ -15,9 +18,9 @@ const (
 )

 var (
-	random      = rand.New(rand.NewSource(time.Now().UnixNano()))
-	randomMutex = sync.Mutex{}
-
+	random             = rand.New(rand.NewSource(time.Now().UnixNano()))
+	randomMutex        = sync.Mutex{}
+	sizeStrRegex       = regexp.MustCompile(`(?i)^(\d+)([gmkb])?$`)
 	errInvalidPriority = errors.New("invalid priority")
 )

@ -163,3 +166,39 @@ func ExpandHome(path string) string {
 func ShortTopicURL(s string) string {
 	return strings.TrimPrefix(strings.TrimPrefix(s, "https://"), "http://")
 }
+
+// DetectContentType probes the byte array b and returns mime type and file extension.
+// The filename is only used to override certain special cases.
+func DetectContentType(b []byte, filename string) (mimeType string, ext string) {
+	if strings.HasSuffix(strings.ToLower(filename), ".apk") {
+		return "application/vnd.android.package-archive", ".apk"
+	}
+	m := mimetype.Detect(b)
+	mimeType, ext = m.String(), m.Extension()
+	if ext == "" {
+		ext = ".bin"
+	}
+	return
+}
+
+// ParseSize parses a size string like 2K or 2M into bytes. If no unit is found, e.g. 123, bytes is assumed.
+func ParseSize(s string) (int64, error) {
+	matches := sizeStrRegex.FindStringSubmatch(s)
+	if matches == nil {
+		return -1, fmt.Errorf("invalid size %s", s)
+	}
+	value, err := strconv.Atoi(matches[1])
+	if err != nil {
+		return -1, fmt.Errorf("cannot convert number %s", matches[1])
+	}
+	switch strings.ToUpper(matches[2]) {
+	case "G":
+		return int64(value) * 1024 * 1024 * 1024, nil
+	case "M":
+		return int64(value) * 1024 * 1024, nil
+	case "K":
+		return int64(value) * 1024, nil
+	default:
+		return int64(value), nil
+	}
+}
--- a/util/util_test.go
+++ b/util/util_test.go
@ -121,3 +121,34 @@ func TestShortTopicURL(t *testing.T) {
 	require.Equal(t, "ntfy.sh/mytopic", ShortTopicURL("http://ntfy.sh/mytopic"))
 	require.Equal(t, "lalala", ShortTopicURL("lalala"))
 }
+
+func TestParseSize_10GSuccess(t *testing.T) {
+	s, err := ParseSize("10G")
+	if err != nil {
+		t.Fatal(err)
+	}
+	require.Equal(t, int64(10*1024*1024*1024), s)
+}
+
+func TestParseSize_10MUpperCaseSuccess(t *testing.T) {
+	s, err := ParseSize("10M")
+	if err != nil {
+		t.Fatal(err)
+	}
+	require.Equal(t, int64(10*1024*1024), s)
+}
+
+func TestParseSize_10kLowerCaseSuccess(t *testing.T) {
+	s, err := ParseSize("10k")
+	if err != nil {
+		t.Fatal(err)
+	}
+	require.Equal(t, int64(10*1024), s)
+}
+
+func TestParseSize_FailureInvalid(t *testing.T) {
+	_, err := ParseSize("not a size")
+	if err == nil {
+		t.Fatalf("expected error, but got none")
+	}
+}