127 lines
3.7 KiB
Go
127 lines
3.7 KiB
Go
package util
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import (
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"errors"
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"golang.org/x/time/rate"
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"io"
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"sync"
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"time"
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)
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// ErrLimitReached is the error returned by the Limiter and LimitWriter when the predefined limit has been reached
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var ErrLimitReached = errors.New("limit reached")
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// Limiter is an interface that implements a rate limiting mechanism, e.g. based on time or a fixed value
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type Limiter interface {
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// Allow adds n to the limiters internal value, or returns ErrLimitReached if the limit has been reached
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Allow(n int64) error
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// Remaining returns the remaining count until the limit is reached; may return -1 if the implementation
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// does not support this operation.
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Remaining() int64
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}
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// FixedLimiter is a helper that allows adding values up to a well-defined limit. Once the limit is reached
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// ErrLimitReached will be returned. FixedLimiter may be used by multiple goroutines.
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type FixedLimiter struct {
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value int64
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limit int64
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mu sync.Mutex
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}
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// NewFixedLimiter creates a new Limiter
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func NewFixedLimiter(limit int64) *FixedLimiter {
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return &FixedLimiter{
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limit: limit,
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}
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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
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// exceeded after adding n, ErrLimitReached is returned.
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func (l *FixedLimiter) Allow(n int64) error {
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l.mu.Lock()
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defer l.mu.Unlock()
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if l.value+n > l.limit {
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return ErrLimitReached
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}
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l.value += n
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return nil
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}
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// Remaining returns the remaining count until the limit is reached
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func (l *FixedLimiter) Remaining() int64 {
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l.mu.Lock()
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defer l.mu.Unlock()
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return l.limit - l.value
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}
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// RateLimiter is a Limiter that wraps a rate.Limiter, allowing a floating time-based limit.
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type RateLimiter struct {
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limiter *rate.Limiter
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}
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// NewRateLimiter creates a new RateLimiter
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func NewRateLimiter(r rate.Limit, b int) *RateLimiter {
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return &RateLimiter{
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limiter: rate.NewLimiter(r, b),
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}
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}
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// NewBytesLimiter creates a RateLimiter that is meant to be used for a bytes-per-interval limit,
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// e.g. 250 MB per day. And example of the underlying idea can be found here: https://go.dev/play/p/0ljgzIZQ6dJ
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func NewBytesLimiter(bytes int, interval time.Duration) *RateLimiter {
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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
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// exceeded after adding n, ErrLimitReached is returned.
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func (l *RateLimiter) Allow(n int64) error {
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if n <= 0 {
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return nil // No-op. Can't take back bytes you're written!
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}
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if !l.limiter.AllowN(time.Now(), int(n)) {
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return ErrLimitReached
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}
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return nil
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}
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// Remaining is not implemented for RateLimiter. It always returns -1.
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func (l *RateLimiter) Remaining() int64 {
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return -1
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}
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// LimitWriter implements an io.Writer that will pass through all Write calls to the underlying
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// writer w until any of the limiter's limit is reached, at which point a Write will return ErrLimitReached.
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// Each limiter's value is increased with every write.
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type LimitWriter struct {
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w io.Writer
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written int64
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limiters []Limiter
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mu sync.Mutex
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}
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// NewLimitWriter creates a new LimitWriter
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func NewLimitWriter(w io.Writer, limiters ...Limiter) *LimitWriter {
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return &LimitWriter{
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w: w,
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limiters: limiters,
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}
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}
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// Write passes through all writes to the underlying writer until any of the given limiter's limit is reached
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func (w *LimitWriter) Write(p []byte) (n int, err error) {
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w.mu.Lock()
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defer w.mu.Unlock()
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for i := 0; i < len(w.limiters); i++ {
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if err := w.limiters[i].Allow(int64(len(p))); err != nil {
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for j := i - 1; j >= 0; j-- {
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w.limiters[j].Allow(-int64(len(p))) // Revert limiters limits if allowed
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}
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return 0, ErrLimitReached
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}
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}
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n, err = w.w.Write(p)
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w.written += int64(n)
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return
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}
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