a proxy with go,supports tcp,http,socks4/5
go get github.com/ejunjsh/goproxy
$GOPATH/bin/goproxy -a :8090 -t tcp -b [backend_ip:port]
$GOPATH/bin/goproxy -a :8090 -t http
$GOPATH/bin/goproxy -a :8090 -t socks4
$GOPATH/bin/goproxy -a :8090 -t socks5