Serving a websocket in Go

Question

I'm starting to play around with websockets + go and well I think I'm misunderstanding something quite basic with websockets in Go.

I'd like to simply listen for a websocket connection and process accordingly. However all examples I see in Go using websocket is serving the web page that then connects to the websocket, is this a requirement?

The following is a basic echo server I have setup:

package main

import (
  "fmt"
  "code.google.com/p/go.net/websocket"
  "net/http"
)

func webHandler(ws *websocket.Conn) {
  var s string
  fmt.Fscan(ws, &s)
  fmt.Println("Received: ", s)
}

func main() {
  fmt.Println("Starting websock server: ")
  http.Handle("/echo", websocket.Handler(webHandler))
  err := http.ListenAndServe(":8080", nil)
  if err != nil {
    panic("ListenAndServe: " + err.Error())
  }
}

This is the javascript used to connect:

ws = new WebSocket("ws://localhost:8080/echo");
ws.onmessage = function(e) {
    console.log("websock: " + e.data);
};

However this results in: WebSocket connection to 'ws://localhost:8080/echo' failed: Unexpected response code: 403

Answer 1

When working with websockets from Javascript, you will seldom have to read the frames directly. To be honest, I am not even sure how to do that.

Fortunately, the websocket package already has a type, Codec that does this for you. My suggestion is to use the predefined websocket.Message codec to Recieve and Send messages instead.

Message is a codec to send/receive text/binary data in a frame on WebSocket connection. To send/receive text frame, use string type. To send/receive binary frame, use []byte type.

Using websocket.Message, your webHandler would look something like this:

func webHandler(ws *websocket.Conn) {
    var in []byte
    if err := websocket.Message.Receive(ws, &in); err != nil {
        return
    }
    fmt.Printf("Received: %s\n", string(in))
    websocket.Message.Send(ws, in)      
}

And, no, it is not a requirement that Go serves the webpage. The 403 error you received does not have to do with Go or the websocket package.