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98 lines
2.6 KiB
98 lines
2.6 KiB
3 months ago
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// Copyright 2024 The Prometheus Authors
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// Based on golang.org/x/net/netutil:
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// Copyright 2013 The Go Authors
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// Package netconnlimit provides network utility functions for limiting
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// simultaneous connections across multiple listeners.
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package netconnlimit
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import (
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"net"
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"sync"
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)
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// NewSharedSemaphore creates and returns a new semaphore channel that can be used
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// to limit the number of simultaneous connections across multiple listeners.
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func NewSharedSemaphore(n int) chan struct{} {
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return make(chan struct{}, n)
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}
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// SharedLimitListener returns a listener that accepts at most n simultaneous
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// connections across multiple listeners using the provided shared semaphore.
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func SharedLimitListener(l net.Listener, sem chan struct{}) net.Listener {
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return &sharedLimitListener{
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Listener: l,
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sem: sem,
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done: make(chan struct{}),
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}
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}
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type sharedLimitListener struct {
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net.Listener
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sem chan struct{}
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closeOnce sync.Once // Ensures the done chan is only closed once.
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done chan struct{} // No values sent; closed when Close is called.
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}
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// Acquire acquires the shared semaphore. Returns true if successfully
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// acquired, false if the listener is closed and the semaphore is not
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// acquired.
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func (l *sharedLimitListener) acquire() bool {
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select {
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case <-l.done:
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return false
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case l.sem <- struct{}{}:
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return true
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}
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}
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func (l *sharedLimitListener) release() { <-l.sem }
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func (l *sharedLimitListener) Accept() (net.Conn, error) {
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if !l.acquire() {
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for {
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c, err := l.Listener.Accept()
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if err != nil {
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return nil, err
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}
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c.Close()
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}
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}
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c, err := l.Listener.Accept()
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if err != nil {
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l.release()
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return nil, err
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}
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return &sharedLimitListenerConn{Conn: c, release: l.release}, nil
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}
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func (l *sharedLimitListener) Close() error {
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err := l.Listener.Close()
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l.closeOnce.Do(func() { close(l.done) })
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return err
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}
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type sharedLimitListenerConn struct {
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net.Conn
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releaseOnce sync.Once
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release func()
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}
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func (l *sharedLimitListenerConn) Close() error {
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err := l.Conn.Close()
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l.releaseOnce.Do(l.release)
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return err
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}
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