dotcloud/docker

package main

import (
    "io"
    "log"
    "net"
    "sync"
)

// TCPProxy is a proxy for TCP connections. It implements the Proxy interface to
// handle TCP traffic forwarding between the frontend and backend addresses.
type TCPProxy struct {
    listener     *net.TCPListener
    frontendAddr *net.TCPAddr
    backendAddr  *net.TCPAddr
}

// NewTCPProxy creates a new TCPProxy.
func NewTCPProxy(frontendAddr, backendAddr *net.TCPAddr) (*TCPProxy, error) {
    // detect version of hostIP to bind only to correct version
    ipVersion := ipv4
    if frontendAddr.IP.To4() == nil {
        ipVersion = ipv6
    }
    listener, err := net.ListenTCP("tcp"+string(ipVersion), frontendAddr)
    if err != nil {
        return nil, err
    }
    // If the port in frontendAddr was 0 then ListenTCP will have a picked
    // a port to listen on, hence the call to Addr to get that actual port:
    return &TCPProxy{
        listener:     listener,
        frontendAddr: listener.Addr().(*net.TCPAddr),
        backendAddr:  backendAddr,
    }, nil
}

func (proxy *TCPProxy) clientLoop(client *net.TCPConn, quit chan bool) {
    backend, err := net.DialTCP("tcp", nil, proxy.backendAddr)
    if err != nil {
        log.Printf("Can't forward traffic to backend tcp/%v: %s\n", proxy.backendAddr, err)
        client.Close()
        return
    }

    var wg sync.WaitGroup
    broker := func(to, from *net.TCPConn) {
        io.Copy(to, from)
        from.CloseRead()
        to.CloseWrite()
        wg.Done()
    }

    wg.Add(2)
    go broker(client, backend)
    go broker(backend, client)

    finish := make(chan struct{})
    go func() {
        wg.Wait()
        close(finish)
    }()

    select {
    case <-quit:
    case <-finish:
    }
    client.Close()
    backend.Close()
    <-finish
}

// Run starts forwarding the traffic using TCP.
func (proxy *TCPProxy) Run() {
    quit := make(chan bool)
    defer close(quit)
    for {
        client, err := proxy.listener.Accept()
        if err != nil {
            log.Printf("Stopping proxy on tcp/%v for tcp/%v (%s)", proxy.frontendAddr, proxy.backendAddr, err)
            return
        }
        go proxy.clientLoop(client.(*net.TCPConn), quit)
    }
}

// Close stops forwarding the traffic.
func (proxy *TCPProxy) Close() { proxy.listener.Close() }

// FrontendAddr returns the TCP address on which the proxy is listening.
func (proxy *TCPProxy) FrontendAddr() net.Addr { return proxy.frontendAddr }

// BackendAddr returns the TCP proxied address.
func (proxy *TCPProxy) BackendAddr() net.Addr { return proxy.backendAddr }