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package ratelimit
import (
"context"
"fmt"
)
type rateToken struct {
tokenCost uint
bucket *TokenBucket
}
func (t rateToken) release() error {
t.bucket.Refund(t.tokenCost)
return nil
}
// TokenRateLimit provides a Token Bucket RateLimiter implementation
// that limits the overall number of retry attempts that can be made across
// operation invocations.
type TokenRateLimit struct {
bucket *TokenBucket
}
// NewTokenRateLimit returns an TokenRateLimit with default values.
// Functional options can configure the retry rate limiter.
func NewTokenRateLimit(tokens uint) *TokenRateLimit {
return &TokenRateLimit{
bucket: NewTokenBucket(tokens),
}
}
type canceledError struct {
Err error
}
func (c canceledError) CanceledError() bool { return true }
func (c canceledError) Unwrap() error { return c.Err }
func (c canceledError) Error() string {
return fmt.Sprintf("canceled, %v", c.Err)
}
// GetToken may cause a available pool of retry quota to be
// decremented. Will return an error if the decremented value can not be
// reduced from the retry quota.
func (l *TokenRateLimit) GetToken(ctx context.Context, cost uint) (func() error, error) {
select {
case <-ctx.Done():
return nil, canceledError{Err: ctx.Err()}
default:
}
if avail, ok := l.bucket.Retrieve(cost); !ok {
return nil, QuotaExceededError{Available: avail, Requested: cost}
}
return rateToken{
tokenCost: cost,
bucket: l.bucket,
}.release, nil
}
// AddTokens increments the token bucket by a fixed amount.
func (l *TokenRateLimit) AddTokens(v uint) error {
l.bucket.Refund(v)
return nil
}
// Remaining returns the number of remaining tokens in the bucket.
func (l *TokenRateLimit) Remaining() uint {
return l.bucket.Remaining()
}
// QuotaExceededError provides the SDK error when the retries for a given
// token bucket have been exhausted.
type QuotaExceededError struct {
Available uint
Requested uint
}
func (e QuotaExceededError) Error() string {
return fmt.Sprintf("retry quota exceeded, %d available, %d requested",
e.Available, e.Requested)
}
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