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75 lines
1.9 KiB
Go
75 lines
1.9 KiB
Go
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// Copyright 2013 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package netutil provides network utility functions, complementing the more
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// common ones in the net package.
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package netutil // import "golang.org/x/net/netutil"
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import (
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"net"
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"sync"
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)
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// LimitListener returns a Listener that accepts at most n simultaneous
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// connections from the provided Listener.
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func LimitListener(l net.Listener, n int) net.Listener {
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return &limitListener{
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Listener: l,
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sem: make(chan struct{}, n),
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done: make(chan struct{}),
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}
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}
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type limitListener 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 limiting semaphore. Returns true if successfully
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// accquired, false if the listener is closed and the semaphore is not
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// acquired.
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func (l *limitListener) 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 *limitListener) release() { <-l.sem }
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func (l *limitListener) Accept() (net.Conn, error) {
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acquired := l.acquire()
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// If the semaphore isn't acquired because the listener was closed, expect
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// that this call to accept won't block, but immediately return an error.
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c, err := l.Listener.Accept()
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if err != nil {
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if acquired {
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l.release()
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}
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return nil, err
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}
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return &limitListenerConn{Conn: c, release: l.release}, nil
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}
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func (l *limitListener) 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 limitListenerConn 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 *limitListenerConn) 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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