ntfy/util/limit.go
2022-01-08 15:47:08 -05:00

97 lines
2.4 KiB
Go

package util
import (
"errors"
"io"
"sync"
)
// 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 {
value int64
limit int64
mu sync.Mutex
}
// NewLimiter creates a new Limiter
func NewLimiter(limit int64) *Limiter {
return &Limiter{
limit: limit,
}
}
// Add 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 {
l.mu.Lock()
defer l.mu.Unlock()
if l.value+n > l.limit {
return ErrLimitReached
}
l.value += n
return nil
}
// Sub subtracts a value from the limiters internal value
func (l *Limiter) Sub(n int64) {
l.Add(-n)
}
// 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()
}
// Value returns the internal value of the limiter
func (l *Limiter) Value() int64 {
l.mu.Lock()
defer l.mu.Unlock()
return l.value
}
// Limit returns the defined limit
func (l *Limiter) Limit() int64 {
return l.limit
}
// LimitWriter implements an io.Writer that will pass through all Write calls to the underlying
// writer w until any of the limiter's limit is reached, at which point a Write will return ErrLimitReached.
// Each limiter's value is increased with every write.
type LimitWriter struct {
w io.Writer
written int64
limiters []*Limiter
mu sync.Mutex
}
// NewLimitWriter creates a new LimitWriter
func NewLimitWriter(w io.Writer, limiters ...*Limiter) *LimitWriter {
return &LimitWriter{
w: w,
limiters: limiters,
}
}
// Write passes through all writes to the underlying writer until any of the given limiter's limit is reached
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 {
for j := i - 1; j >= 0; j-- {
w.limiters[j].Sub(int64(len(p)))
}
return 0, ErrLimitReached
}
}
n, err = w.w.Write(p)
w.written += int64(n)
return
}