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package ratelimit
import (
"sync"
)
// TokenBucket provides a concurrency safe utility for adding and removing
// tokens from the available token bucket.
type TokenBucket struct {
remainingTokens uint
maxCapacity uint
minCapacity uint
mu sync.Mutex
}
// NewTokenBucket returns an initialized TokenBucket with the capacity
// specified.
func NewTokenBucket(i uint) *TokenBucket {
return &TokenBucket{
remainingTokens: i,
maxCapacity: i,
minCapacity: 1,
}
}
// Retrieve attempts to reduce the available tokens by the amount requested. If
// there are tokens available true will be returned along with the number of
// available tokens remaining. If amount requested is larger than the available
// capacity, false will be returned along with the available capacity. If the
// amount is less than the available capacity, the capacity will be reduced by
// that amount, and the remaining capacity and true will be returned.
func (t *TokenBucket) Retrieve(amount uint) (available uint, retrieved bool) {
t.mu.Lock()
defer t.mu.Unlock()
if amount > t.remainingTokens {
return t.remainingTokens, false
}
t.remainingTokens -= amount
return t.remainingTokens, true
}
// Refund returns the amount of tokens back to the available token bucket, up
// to the initial capacity.
func (t *TokenBucket) Refund(amount uint) {
t.mu.Lock()
defer t.mu.Unlock()
// Capacity cannot exceed max capacity.
t.remainingTokens = uintMin(t.remainingTokens+amount, t.maxCapacity)
}
// Capacity returns the maximum capacity of tokens that the bucket could
// contain.
func (t *TokenBucket) Capacity() uint {
t.mu.Lock()
defer t.mu.Unlock()
return t.maxCapacity
}
// Remaining returns the number of tokens that remaining in the bucket.
func (t *TokenBucket) Remaining() uint {
t.mu.Lock()
defer t.mu.Unlock()
return t.remainingTokens
}
// Resize adjusts the size of the token bucket. Returns the capacity remaining.
func (t *TokenBucket) Resize(size uint) uint {
t.mu.Lock()
defer t.mu.Unlock()
t.maxCapacity = uintMax(size, t.minCapacity)
// Capacity needs to be capped at max capacity, if max size reduced.
t.remainingTokens = uintMin(t.remainingTokens, t.maxCapacity)
return t.remainingTokens
}
func uintMin(a, b uint) uint {
if a < b {
return a
}
return b
}
func uintMax(a, b uint) uint {
if a > b {
return a
}
return b
}
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