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golang websocket to tcp forwarder

January 15, 2015, 4:49 am

I’ve been writing a simple websocket to tcp forwarder in golang for a project I’m working on.

I previously showed a simple echo example using Gorilla websockets. The echoing example blocks on the sockets until data is available, however that isn’t really going to work here. At first I tried to use the SetReadDeadLine, mirroring non-blocking IO in C. While this worked, it wasn’t really an ideal solution. What I ended up with was my first use of go routines! Basically breaking the code into two threads each of which blocks on reads from the 2 sockets. The code is below for reference (it currently forwards traffic to/from localhost, but the first 12bytes sent from the client should be the destination host port, I’ll update this post then that codes in place):

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package main
  
import (
    "github.com/gorilla/websocket"
    "net/http"
    "net"
    "fmt"
    "io"
)
 
var upgrader = websocket.Upgrader{
    ReadBufferSize:  1024,
    WriteBufferSize: 1024,
}
 
 
       
func print_binary(s []byte) {
  fmt.Printf("print b:");
  for n := 0;n < len(s);n++ {
    fmt.Printf("%d,",s[n]);
  }
  fmt.Printf("\n");
}
 
func address_decode(address_bin []byte) (string,string) {
   
  var host string = "127.0.0.1"
  var port string = "22";
 
  return host,port
}
  
 
func forwardtcp(wsconn *websocket.Conn,conn net.Conn) {
 
  for {
    // Receive and forward pending data from tcp socket to web socket
    tcpbuffer := make([]byte, 1024)
 
    n,err := conn.Read(tcpbuffer)
    if err == io.EOF { fmt.Printf("TCP Read failed"); break; }
    if err == nil {
      fmt.Printf("Forwarding from tcp to ws: %d bytes: %s\n",n,tcpbuffer)
      print_binary(tcpbuffer)
      wsconn.WriteMessage(websocket.BinaryMessage,tcpbuffer[:n])
    }
  }
}
 
func forwardws (wsconn *websocket.Conn,conn net.Conn) {
 
 for {
    // Send pending data to tcp socket
    n,buffer,err := wsconn.ReadMessage()
    if err == io.EOF { fmt.Printf("WS Read Failed"); break; }
    if err == nil {
      s := string(buffer[:len(buffer)])
      fmt.Printf("Received (from ws) forwarding to tcp: %d bytes: %s %d\n",len(buffer),s,n)
      print_binary(buffer)
      conn.Write(buffer)
    }
  }
}
 
func wsProxyHandler(w http.ResponseWriter, r *http.Request) {
 
  wsconn, err := upgrader.Upgrade(w, r, nil)
 
  if err != nil {
    //log.Println(err)
    return
  }
 
  // get connection address and port
  address := make([]byte, 16)
 
  n,address,err := wsconn.ReadMessage()
  if err != nil {
    fmt.Printf("address read error");
    fmt.Printf("read %d bytes",n); 
  }
 
  print_binary(address)
 
  host, port := address_decode(address)
 
  conn, err := net.Dial("tcp", host + ":" + port)
  if err != nil {
  // handle error
  }
 
  go forwardtcp(wsconn,conn)
  go forwardws(wsconn,conn)
 
  fmt.Printf("websocket closed");
}
  
func main() {
  http.HandleFunc("/echo", wsProxyHandler)
  http.Handle("/", http.FileServer(http.Dir(".")))
  err := http.ListenAndServe(":8080", nil)
  if err != nil {
    panic("Error: " + err.Error())
  }
}
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