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rate: add limiter sentinel errors #15

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rate: add limiter sentinel errors #15

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15 changes: 13 additions & 2 deletions rate/rate.go
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,7 @@ package rate

import (
"context"
"errors"
"fmt"
"math"
"sync"
Expand All @@ -29,6 +30,16 @@ func Every(interval time.Duration) Limit {
return 1 / Limit(interval.Seconds())
}

var (
// ErrExceedsBurst is returned when the limiter's burst is exceeded. The
// error is wrapped with additional context.
ErrExceedsBurst = errors.New("exceeds limiter's burst")

// ErrWouldExceedDeadline is returned when the limiter's deadline would be
// exceeded. The error is wrapped with additional context.
ErrWouldExceedDeadline = errors.New("would exceed context deadline")
)

// A Limiter controls how frequently events are allowed to happen.
// It implements a "token bucket" of size b, initially full and refilled
// at rate r tokens per second.
Expand Down Expand Up @@ -230,7 +241,7 @@ func (lim *Limiter) WaitN(ctx context.Context, n int) (err error) {
lim.mu.Unlock()

if n > burst && limit != Inf {
return fmt.Errorf("rate: Wait(n=%d) exceeds limiter's burst %d", n, burst)
return fmt.Errorf("rate: Wait(n=%d) %w %d", n, ErrExceedsBurst, burst)
}
// Check if ctx is already cancelled
select {
Expand All @@ -247,7 +258,7 @@ func (lim *Limiter) WaitN(ctx context.Context, n int) (err error) {
// Reserve
r := lim.reserveN(now, n, waitLimit)
if !r.ok {
return fmt.Errorf("rate: Wait(n=%d) would exceed context deadline", n)
return fmt.Errorf("rate: Wait(n=%d) %w", n, ErrWouldExceedDeadline)
}
// Wait if necessary
delay := r.DelayFrom(now)
Expand Down