Long Polling in GO, Server Not Responding Appropriately?

StackOverflow https://stackoverflow.com/questions/19761549

  •  03-07-2022
  •  | 
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Domanda

I am trying to implement a simple "global" counter that updates based on every user that clicks the button on their browsers button. For example, if you go to the website and click the button, I will see the counter increase on my side if I'm on the same website. I sought to do this with long polling, but am facing some issues. Mainly the server variable is not coming back as I think it should.

The server:

package main

import (
    "net/http"
    "log"
    "io"
    "io/ioutil"
)

var messages chan string = make(chan string, 100)

var counter = 0

func PushHandler(w http.ResponseWriter, req *http.Request) {

    body, err := ioutil.ReadAll(req.Body)

    if err != nil {
        w.WriteHeader(400)
    }
    counter += 1
    messages <- string(counter)
}


func PollResponse(w http.ResponseWriter, req *http.Request) {

    io.WriteString(w, <-messages)
}

func main() {
    http.Handle("/", http.FileServer(http.Dir("./")))
    http.HandleFunc("/poll", PollResponse)
    http.HandleFunc("/push", PushHandler)
    err := http.ListenAndServe(":8005", nil)
    if err != nil {
        log.Fatal("ListenAndServe: ", err)
    }
}

The client:

<html>
<script language=javascript>

function longpoll(url, callback) {

    var req = new XMLHttpRequest (); 
    req.open ('GET', url, true); 

    req.onreadystatechange = function (aEvt) {
        if (req.readyState == 4) { 
            if (req.status == 200) {
                callback(req.responseText);
                longpoll(url, callback);
            } else {
                alert ("long-poll connection lost");
            }
        }
    };

    req.send(null);
}

function recv(msg) {

    var box = document.getElementById("counter");

    box.value += msg + "\n";
}
function send() {


    var box = document.getElementById("counter");

  var req = new XMLHttpRequest (); 
    req.open ('POST', "/push?rcpt=", true); 

    req.onreadystatechange = function (aEvt) {
        if (req.readyState == 4) { 
            if (req.status == 200) {
            } else {
                alert ("failed to send!");
            }
        }
  };
  req.send("hi")

  //box.innerHTML += "test" ;  
}
</script>
<body onload="longpoll('/poll', recv);">

<h1> Long-Poll Chat Demo </h1>

<p id="counter"></p>
<button onclick="send()" id="test">Test Button</button>
</body>
</html>

The counter variable is not coming back from the server for some reason. I believe I am changing the state every time the button is clicked and so the longpolling function should get the newly updated counter variable. If you have any suggestions, please let me know!

È stato utile?

Soluzione

I see two issues in you program: 1. In the server:

messages <- string(counter)

You should use "strconv" package

messages <- strconv.Itoa(counter)

string(0) will return something like []byte{0} not a "0"
2. In your client:

function recv(msg) {
    var box = document.getElementById("counter");
    box.value += msg + "\n";
}

Should be:

function recv(msg) {
    var box = document.getElementById("counter");
    box.innerHTML += msg + "\n";
}

I don't think the p element have value property

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