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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
var 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 }
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