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Gorilla Websockets, golang simple websockets example

December 27, 2014, 7:19 pm

I previously posted a quick example of using the standard library websockets API in golang. Unfortunately there are a number of issues that make difficult to use in practice. Notably, it lacks support for PING/PONG packets which are often used to for KeepAlive functionality in websockets. This is particularly important, as browsers tend to be aggressive in killing off these connections.

So, here’s a quick complete example of Gorilla Websockets in golang, with similar functionality to that I posted previously. It simply echos everything it receives back to the client. First the golang code:

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package main
 
import (
        "github.com/gorilla/websocket"
        "net/http"
        "fmt"
)
 
var upgrader = websocket.Upgrader{
    ReadBufferSize:  1024,
    WriteBufferSize: 1024,
}
 
func print_binary(s []byte) {
  fmt.Printf("Received b:");
  for n := 0;n < len(s);n++ {
    fmt.Printf("%d,",s[n]);
  }
  fmt.Printf("\n");
}
 
func echoHandler(w http.ResponseWriter, r *http.Request) {
    conn, err := upgrader.Upgrade(w, r, nil)
    if err != nil {
        //log.Println(err)
        return
    }
 
    for {
        messageType, p, err := conn.ReadMessage()
        if err != nil {
            return
        }
 
        print_binary(p)
 
        err = conn.WriteMessage(messageType, p);
        if  err != nil {
            return
        }
    }
}
 
func main() {
  http.HandleFunc("/echo", echoHandler)
  http.Handle("/", http.FileServer(http.Dir(".")))
  err := http.ListenAndServe(":8080", nil)
  if err != nil {
    panic("Error: " + err.Error())
  }
}

And then the html used to interface with the websocket. Save it in the same directory as the golang program, and access it at: http://localhost:8080/filename.html

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<html>
<head>
<meta charset="UTF-8" />
<script>
        var serversocket = new WebSocket("ws://localhost:8080/echo");
 
        serversocket.onopen = function() {
                serversocket.send("Connection init");
        }
 
        // Write message on receive
        serversocket.onmessage = function(e) {
                document.getElementById('comms').innerHTML += "Received: " + e.data + "<br>";
        };
 
        function senddata() {
                var data = document.getElementById('sendtext').value;
                serversocket.send(data);
                document.getElementById('comms').innerHTML += "Sent: " + data + "<br>";
        }
 
</script>
</head>
 
<body>
        <input id="sendtext" type="text" />
        <input type="button" id="sendBtn" value="send" onclick="senddata()"></input>
        <div id='comms'></div>
</body>
</html>
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