Websocket output received by browser, complains about "Invalid UTF-8 sequence in header value "

When I load the page in my browser, the page gets served correctly. When the javascript executes, Chrome's console output says:

Invalid UTF-8 sequence in header value 

I have searched for that string, and am unable to find any mention of it for golang.

How do I go about telling golang not to write unicode characters to web sockets?

I assume that this is the cause of the problem, as the "Network" tab only reveals an empty request and response for this.

CCSSE:

main.go:

package main

import (
  "fmt"
  "net/http"
  "log"
  "code.google.com/p/go.net/websocket"
  //"github.com/garyburd/go-websocket/websocket"
)

const listenAddress = "localhost:9999"

func wsHandler(webSck *websocket.Conn) {
  fmt.Fprint(webSck, "Rpy")
  fmt.Println("Sent \"Rpy\" to web socket", webSck)
  //more code here
}

func main() {
  http.Handle("/", http.FileServer(http.Dir("./static")))
  http.Handle("/ws", websocket.Handler(wsHandler))
  err := http.ListenAndServe(listenAddress, nil)
  if err != nil {
    log.Fatal(err)
  }
}

static/main.js

var socket = new WebSocket("ws://localhost:9999/ws");
socket.onopen = function() {
  socket.onmessage = function(m) {
    console.log("Received: " + m);
  };
  socket.send("Req\n");
};

EDIT:

As suggested by @Intermernet, I have set the Sec-WebSocket-Protocol header. To no avail, still getting Invalid UTF-8 sequence in header value.

Note also that the reason I need to do webSck.Config().Header = make(http.Header) is that it is nil - confirmed by the log statement on webSck.Config(). Tack on to this another question - why do I have to do this; is there an intialisation step that I have missed somewhere?

func wsHandler(webSck *websocket.Conn) {
  webSck.Config().Header = make(http.Header)
  webSck.Config().Header.Add("Sec-WebSocket-Protocol", "chat")
  fmt.Printf("ws.Config()  %#v\n", webSck.Config())
  var buf []byte;
  buf = []byte("Rpy")
  _, err := webSck.Write(buf)
  if err != nil {
    fmt.Println("Error:", err)
  } else {
    fmt.Printf("Sent \"Rpy\" to web socket  %#v\n", webSck)
  }
}

Can this issue be related to recent change in code.google.com/p/go.net/websocket ?

https://code.google.com/p/go/source/detail?r=1e65ca1b2499c473ec267ca1d6759b3dc920a599&repo=net

Sorry for the comment in the form of an answer, I can't comment yet...

Are you setting Sec-WebSocket-Protocol header on the websocket Config? (https://code.google.com/p/go/source/browse/websocket/websocket.go?repo=net#74 and https://www.rfc-editor.org/rfc/rfc6455#page-59)

That error message seems to crop up on Google many times relating to incompatibility or conflict with that header.

Something like:

func wsHandler(webSck *websocket.Conn) {
  webSck.Config.Header.Add("Sec-WebSocket-Protocol", "chat")
  fmt.Fprint(webSck, "Rpy")
  fmt.Println("Sent \"Rpy\" to web socket", webSck)
  //more code here
}

Also, I think it's preferred to use the Write function on the websocket (https://code.google.com/p/go/source/browse/websocket/websocket.go?repo=net#205) as it encapsulates/converts the written data into frames.

So more like:

func wsHandler(webSck *websocket.Conn) {
  webSck.Config.Header.Add("Sec-WebSocket-Protocol", "chat")
  _, _ = webSck.Write("Rpy")
  fmt.Println("Sent \"Rpy\" to web socket")
  //more code here
}

But obviously checking the error from Write!

Hope that helps.

EDIT: Remove the extraneous ", webSck" from the fmt.Println .