Simple GO TCP proxy

netfwd.go

// can be run in go 1.0.3
// build : go build netfwd.go

package main 
import ( 
        "net" 
        "fmt" 
        "io" 
        "os" 
) 
func main() { 
        if len(os.Args) != 3 { 
                fatal("usage: netfwd localIp:localPort remoteIp:remotePort") 
        } 
        localAddr := os.Args[1] 
        remoteAddr := os.Args[2] 
        local, err := net.Listen("tcp", localAddr) 
        if local == nil { 
                fatal("cannot listen: %v", err) 
        } 
        for { 
                conn, err := local.Accept() 
                if conn == nil { 
                        fatal("accept failed: %v", err) 
                } 
                go forward(conn, remoteAddr) 
        } 
} 

func forward(local net.Conn, remoteAddr string) { 
        remote, err := net.Dial("tcp",remoteAddr) 
        if remote == nil { 
                fmt.Fprintf(os.Stderr, "remote dial failed: %v\n", err) 
                return 
        } 
        go io.Copy(local, remote) 
        go io.Copy(remote, local) 
} 

func fatal(s string, a ... interface{}) { 
        fmt.Fprintf(os.Stderr, "netfwd: %s\n", fmt.Sprintf(s, a)) 
        os.Exit(2) 
} 
 

    go io.Copy(local, remote) 
    go io.Copy(remote, local) 

key point