Gzip static responses

README.md

@@ -61,4 +61,5 @@ Third party libraries and resources:
 * [Firebase Admin SDK](https://github.com/firebase/firebase-admin-go) (Apache 2.0) is used to send FCM messages
 * [github/gemoji](https://github.com/github/gemoji) (MIT) is used for emoji support (specifically the [emoji.json](https://raw.githubusercontent.com/github/gemoji/master/db/emoji.json) file)
 * [Lightbox with vanilla JS](https://yossiabramov.com/blog/vanilla-js-lightbox) as a lightbox on the landing page 
+* [HTTP middleware for gzip compression](https://gist.github.com/CJEnright/bc2d8b8dc0c1389a9feeddb110f822d7) (MIT) is used for serving static files
 * [Statically linking go-sqlite3](https://www.arp242.net/static-go.html)

server/server.go

@@ -351,12 +351,12 @@ var config = {
 
 func (s *Server) handleStatic(w http.ResponseWriter, r *http.Request) error {
 	r.URL.Path = webSiteDir + r.URL.Path
-	http.FileServer(http.FS(webFsCached)).ServeHTTP(w, r)
+	util.Gzip(http.FileServer(http.FS(webFsCached))).ServeHTTP(w, r)
 	return nil
 }
 
 func (s *Server) handleDocs(w http.ResponseWriter, r *http.Request) error {
-	http.FileServer(http.FS(docsStaticCached)).ServeHTTP(w, r)
+	util.Gzip(http.FileServer(http.FS(docsStaticCached))).ServeHTTP(w, r)
 	return nil
 }
 

util/gzip_handler.go

@@ -0,0 +1,52 @@
+package util
+
+import (
+	"compress/gzip"
+	"io"
+	"io/ioutil"
+	"net/http"
+	"strings"
+	"sync"
+)
+
+// Gzip is a HTTP middleware to transparently compress responses using gzip.
+// Original code from https://gist.github.com/CJEnright/bc2d8b8dc0c1389a9feeddb110f822d7 (MIT)
+func Gzip(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if !strings.Contains(r.Header.Get("Accept-Encoding"), "gzip") {
+			next.ServeHTTP(w, r)
+			return
+		}
+		w.Header().Set("Content-Encoding", "gzip")
+
+		gz := gzPool.Get().(*gzip.Writer)
+		defer gzPool.Put(gz)
+
+		gz.Reset(w)
+		defer gz.Close()
+
+		r.Header.Del("Accept-Encoding") // prevent double-gzipping
+		next.ServeHTTP(&gzipResponseWriter{ResponseWriter: w, Writer: gz}, r)
+	})
+}
+
+var gzPool = sync.Pool{
+	New: func() interface{} {
+		w := gzip.NewWriter(ioutil.Discard)
+		return w
+	},
+}
+
+type gzipResponseWriter struct {
+	io.Writer
+	http.ResponseWriter
+}
+
+func (w *gzipResponseWriter) WriteHeader(status int) {
+	w.Header().Del("Content-Length")
+	w.ResponseWriter.WriteHeader(status)
+}
+
+func (w *gzipResponseWriter) Write(b []byte) (int, error) {
+	return w.Writer.Write(b)
+}

util/gzip_handler_test.go

@@ -0,0 +1,40 @@
+package util
+
+import (
+	"compress/gzip"
+	"github.com/stretchr/testify/require"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func TestGzipHandler(t *testing.T) {
+	s := Gzip(http.FileServer(http.FS(testFs)))
+
+	rr := httptest.NewRecorder()
+	req, _ := http.NewRequest("GET", "/embedfs/test.txt", nil)
+	req.Header.Set("Accept-Encoding", "gzip, deflate")
+	s.ServeHTTP(rr, req)
+	require.Equal(t, 200, rr.Code)
+	require.Equal(t, "gzip", rr.Header().Get("Content-Encoding"))
+	require.Equal(t, "", rr.Header().Get("Content-Length"))
+
+	gz, _ := gzip.NewReader(rr.Body)
+	b, _ := io.ReadAll(gz)
+	require.Equal(t, "This is a test file for embedfs_test.go\n", string(b))
+}
+
+func TestGzipHandler_NoGzip(t *testing.T) {
+	s := Gzip(http.FileServer(http.FS(testFs)))
+
+	rr := httptest.NewRecorder()
+	req, _ := http.NewRequest("GET", "/embedfs/test.txt", nil)
+	s.ServeHTTP(rr, req)
+	require.Equal(t, 200, rr.Code)
+	require.Equal(t, "", rr.Header().Get("Content-Encoding"))
+	require.Equal(t, "40", rr.Header().Get("Content-Length"))
+
+	b, _ := io.ReadAll(rr.Body)
+	require.Equal(t, "This is a test file for embedfs_test.go\n", string(b))
+}