What does this websocket url “ws://{{$}}/ws” mean?

Question

I work with websocket in go. And I got a websocket url format from a trivial example that I google like this:

ws://{{$}}/ws

Relatively complete code below:

home.html:

<html>
<head>
<title>Chat Example</title>
<script type="text/javascript">
    $(function() {
        ......
        if (window["WebSocket"]) {
            conn = new WebSocket("ws://{{$}}/ws");
            conn.onclose = function(evt) {
                appendLog($("<div><b>Connection closed.</b></div>"))
            }
            conn.onmessage = function(evt) {
                appendLog($("<div/>").text(evt.data))
            }
        } else {
            appendLog($("<div><b>Your browser does not support WebSockets.</b></div>"))
        }
        ......
    });
</script>
</head>
</html>

And wsServer.go:

package main

import (
    "flag"
    "log"
    "net/http"
    "text/template"
)
var addr = flag.String("addr", ":8080", "http service address")
var homeTempl = template.Must(template.ParseFiles("home.html"))

func serveHome(w http.ResponseWriter, r *http.Request) {
    ......
    w.Header().Set("Content-Type", "text/html; charset=utf-8")
    homeTempl.Execute(w, r.Host)
}

func main() {
    http.HandleFunc("/", serveHome)
    http.HandleFunc("/ws", serveWs)
    err := http.ListenAndServe(:8080, nil)
    if err != nil {
        log.Fatal("ListenAndServe: ", err)
    }
}

I thought it would be a regular expression while actually I can't explain it.

I test it on my own PC browser, and connect success with:

http://localhost:8080

but

http://ip:8080 (which ip is my computer's also the litsening server's ip)

not. And why?

Of course it works when I change "ws://{{$}}/ws" to a certain url. But I want to know why?And what can this expression matching for?

The complete example code is large, I think above is enough to the question. If I miss something you can find out complete example in this page : https://github.com/garyburd/go-websocket/tree/master/examples/chat

Answer 1

I'm guessing you are using the template package of Go. The template package supports {{ placeholders }} that are annotated by those curly brackets. Those curly brackets might contain statements like range , if etc, and variable names. The variable name $ is a special name that points to the root element that was passed to the template.Execute method.

Please add the code of your wsServe method so that we can see what value your are passing to your template. I will extend my answer afterwards.

What does this websocket url “ws://{{$}}/ws” mean?

Question

1 answers

solution1
1 ACCPTED 2013-08-17 18:21:16

What does this websocket url “ws://{{$}}/ws” mean?

Question

1 answers

solution1 1 ACCPTED 2013-08-17 18:21:16

solution1
1 ACCPTED 2013-08-17 18:21:16