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Making RateLimiter and FixedLimiter, so they can both work with LimitWriter

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This commit is contained in:
Philipp Heckel 2022-01-12 17:03:28 -05:00
parent f6b9ebb693
commit c76e55a1c8
7 changed files with 127 additions and 67 deletions

71
util/limit.go
View file

@ -2,31 +2,39 @@ 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 was
// 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.value+n > l.limit {
@ -36,29 +44,34 @@ func (l *Limiter) Add(n int64) error {
return nil
}
// Sub subtracts a value from the limiters internal value
func (l *Limiter) Sub(n int64) {
l.Add(-n)
// RateLimiter is a Limiter that wraps a rate.Limiter, allowing a floating time-based limit.
type RateLimiter struct {
limiter *rate.Limiter
}
// 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()
// NewRateLimiter creates a new RateLimiter
func NewRateLimiter(r rate.Limit, b int) *RateLimiter {
return &RateLimiter{
limiter: rate.NewLimiter(r, b),
}
}
// Value returns the internal value of the limiter
func (l *Limiter) Value() int64 {
l.mu.Lock()
defer l.mu.Unlock()
return l.value
// 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)
}
// Limit returns the defined limit
func (l *Limiter) Limit() int64 {
return l.limit
// 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
}
// LimitWriter implements an io.Writer that will pass through all Write calls to the underlying
@ -67,12 +80,12 @@ func (l *Limiter) Limit() int64 {
type LimitWriter struct {
w io.Writer
written int64
limiters []*Limiter
limiters []Limiter
mu sync.Mutex
}
// NewLimitWriter creates a new LimitWriter
func NewLimitWriter(w io.Writer, limiters ...*Limiter) *LimitWriter {
func NewLimitWriter(w io.Writer, limiters ...Limiter) *LimitWriter {
return &LimitWriter{
w: w,
limiters: limiters,
@ -84,9 +97,9 @@ 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].Add(int64(len(p))); err != nil {
if err := w.limiters[i].Allow(int64(len(p))); err != nil {
for j := i - 1; j >= 0; j-- {
w.limiters[j].Sub(int64(len(p)))
w.limiters[j].Allow(-int64(len(p))) // Revert limiters limits if allowed
}
return 0, ErrLimitReached
}

98
util/limit_test.go
View file

@ -2,34 +2,51 @@ 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_AddSet(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.Set(7)
if l.Value() != 7 {
t.Fatalf("expected value to be %d, got %d", 7, 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)
@ -46,7 +63,7 @@ func TestLimitWriter_WriteNoLimiter(t *testing.T) {
func TestLimitWriter_WriteOneLimiter(t *testing.T) {
var buf bytes.Buffer
l := NewLimiter(10)
l := NewFixedLimiter(10)
lw := NewLimitWriter(&buf, l)
if _, err := lw.Write(make([]byte, 10)); err != nil {
t.Fatal(err)
@ -57,15 +74,15 @@ func TestLimitWriter_WriteOneLimiter(t *testing.T) {
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())
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 := NewLimiter(11)
l2 := NewLimiter(9)
l1 := NewFixedLimiter(11)
l2 := NewFixedLimiter(9)
lw := NewLimitWriter(&buf, l1, l2)
if _, err := lw.Write(make([]byte, 8)); err != nil {
t.Fatal(err)
@ -76,10 +93,47 @@ func TestLimitWriter_WriteTwoLimiters(t *testing.T) {
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 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())
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)
}