ntfy/util/limit.go

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package util
import (
"errors"
"golang.org/x/time/rate"
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"io"
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"sync"
"time"
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)
// 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 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 {
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value int64
limit int64
mu sync.Mutex
}
// NewFixedLimiter creates a new Limiter
func NewFixedLimiter(limit int64) *FixedLimiter {
return &FixedLimiter{
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limit: limit,
}
}
// Allow adds n to the limiters internal value, but only if the limit has not been reached. If the limit was
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// exceeded after adding n, ErrLimitReached is returned.
func (l *FixedLimiter) Allow(n int64) error {
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l.mu.Lock()
defer l.mu.Unlock()
if l.value+n > l.limit {
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return ErrLimitReached
}
l.value += n
return nil
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}
// RateLimiter is a Limiter that wraps a rate.Limiter, allowing a floating time-based limit.
type RateLimiter struct {
limiter *rate.Limiter
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}
// NewRateLimiter creates a new RateLimiter
func NewRateLimiter(r rate.Limit, b int) *RateLimiter {
return &RateLimiter{
limiter: rate.NewLimiter(r, b),
}
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}
// 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)
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}
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// 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
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}
// 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
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mu sync.Mutex
}
// NewLimitWriter creates a new LimitWriter
func NewLimitWriter(w io.Writer, limiters ...Limiter) *LimitWriter {
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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 {
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for j := i - 1; j >= 0; j-- {
w.limiters[j].Allow(-int64(len(p))) // Revert limiters limits if allowed
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}
return 0, ErrLimitReached
}
}
n, err = w.w.Write(p)
w.written += int64(n)
return
}