Im trying to get SSE working. I have a simple web with two buttons. Each one send a POST request to the server that adds a message to a list.
When the eventsource is listening, the server checks the list once each second and sends all the available messages to the client, at the same time that it marks them as readed so they won't be sent again to that client.
It kind of works but does all sorts of weird stuff:
Sometimes the button POST requests are delayed for no apparent reason and then sent all at once.
Sometimes the EventSource restarts itself making a GET request to the server.
Sometimes the server generates an exception when calling Response.Flush() after spamming the buttons: "The remote host closed the connection. The error code is 0x800704CD"
After pressing the buttons a few times, when I try to reload the page, it stays "loading" forever.
After starting the EventSource in javascript it generates a GET request that stays open and after that, any POST request that the buttons send is never sent until the event source GET request ends. Once the EventSource connection ends, all POST requests from the buttons are sent.
I know a lot of things from this code can be improved but I simplified it a lot by leaving just the essential for it to "work".
Also note that:
NotificationSystem.GetNotifications() gets all messages available for the user in a thread safe way.
NotificationSystem.AddNotification() adds the messages.
So here is the server code:
public void GetNotifs() {
try {
Response.ContentType = "text/event-stream";
while(true) {
List<string> Notifs = NotificationSystem.GetNotifications( GetUserId() );
if(Notifs != null && Notifs.Count > 0) {
foreach(var Text in Notifs) {
Response.Write( string.Format( "data: {0}\n\n", Text ) );
}
Response.Flush();
}
Thread.Sleep( 1000 );
}
} catch(Exception ex) {
Response.Close();
}
}
public ActionResult AddButton1() {
NotificationSystem.AddNotification( GetUserId(), "BTN1 (" + GetUserId() + ")" );
return Json( "OK" );
}
public ActionResult AddButton2() {
NotificationSystem.AddNotification( GetUserId(), "BTN2 (" + GetUserId() + ")" );
return Json( "OK" );
}
And the client JS code:
var urlMessages = "/Notifs/GetNotifs";
var urlButton1 = "/Notifs/AddButton1";
var urlButton2 = "/Notifs/AddButton2";
function PushBtn1() {
$.post(urlButton1);
}
function PushBtn2() {
$.post(urlButton2);
}
var myEventSource;
$(document).ready(function () {
myEventSource = new EventSource(urlMessages);
myEventSource.onmessage = function (e) {
console.log(e.data);
$('#EventLog').append("<li>Received: " + e.data + "<li>");
}
});
Related
I'm trying to use server-side events (SSE) in Javascript and Node.JS to push updates to a web client.
To keep things simple, I have a function which will generate the time every second:
setTimeout(function time() {
sendEvent('time', + new Date);
setTimeout(time, uptimeTimeout);
}, 1000);
The sendEvent function puts together the event in the expected format and sends it to the client.
var clientRes;
var lastMessageId = 0;
function sendEvent(event, message) {
message = JSON.stringify(message);
++lastMessageId;
sendSSE(clientRes, lastMessageId, event, message);
}
The clientRes value comes from the server function to handle the route from the base URL.
app.use('/', function (req, res) {
clientRes = res;
...
}
What I want to achieve at the client UI is a simple page which shows:
> <h1>The current time is {event.data}</h1>
where I derive the current time from the latest message data received from the server.
I have created an index.html file to have the client listen for these server-sent messages:
<!DOCTYPE html>
<html>
<body>
<h1>Getting server updates</h1>
<div id="result"></div>
<script>
if(typeof(EventSource) !== "undefined") {
console.log("Event source is supported");
var source = new EventSource("localhost:3000");
source.onmessage = function(event) {
document.getElementById("result").innerHTML += "=>" + event.data + "<br>";
};
} else {
console.log("Event source not supported");
document.getElementById("result").innerHTML = "Sorry, your browser does not support server-sent events...";
}
evtSource.addEventListener("time", function(event) {
const newElement = document.createElement("li");
const time = JSON.parse(event.data).time;
console.log("Time listener found time " + time);
newElement.innerHTML = "ping at " + time;
eventList.appendChild(newElement);
});
</script>
</body>
</html>
If I respond to a GET request with this index.html, I don't see any of the time messages.
That is, this server code does not work:
app.use("/", function(request, response) {
response.sendFile(__dirname + "/index.html");
clientRes = response;
});
However if I don't respond with the index.html file and allow the server to push timestamps to the client, they to show up in the browser:
event: time
id: 104
data: 1587943717153
event: time
id: 105
data: 1587943727161
...
Here's is where I'm stuck.
It appears I have successfully gotten the server to push new timestamps every second.
And the browser is seeing them and displaying the text.
But the arrival of the message from the server is not triggering the listener and the message is not being rendered based on the index.html.
Most of the examples I've seen for use of SSE involves a PHP data source. I need for the server to both generate the data and to provide the HTML to display it.
I've been successful in one or the other, but not both at the same time.
I figured out what I was missing.
I did not specify the endpoints correctly.
For the root endpoint, the server code needs to deliver the index.html file.
app.use("/", function(request, response) {
console.log("In root handler");
response.sendFile(__dirname + "/index.html");
});
Index.html contains the script that creates the event source:
var source = new EventSource("http://localhost:3000/time");
But the URL that gets passed in as the input to the EventSource constructor must be a different endpoint (not root). It needs to be the endpoint that generates the timestamps.
So in the server, the handler for the /time endpoint is the one which pushes the data.
app.use('/time', function (req, res) {
res.writeHead(200, {
'content-type': 'text/event-stream',
'cache-control': 'no-cache',
'connection': 'keep-alive'
});
// Save the response
clientRes = res;
});
so, below is a code snippet from my server.js file. When running, and I send a URL with a message, the res.end() causes the view to render a blank page.
When I comment out the res.end() command, the view displays all of the messages, but the browser waits and waits for the signal that the response from the server is complete.
I get that you can use res.end() and put data in the parens, to be transmitted and rendered by the view.
What I expect to happen is that with no args, it will just leave the view alone, but the empty args in the parens is manifesting as an empty view.
How do I indicate that the response is complete without deleting the data on the view?
server.js
var http = require('http'),
url = require('url'),
fs = require('fs');
var messages = ["testing"];
var clients = [];
http.createServer(function(req,res) {
var url_parts = url.parse(req.url);
console.log(url_parts);
if(url_parts.pathname == '/') {
// file serving
fs.readFile('./index.html', function(err, data) {
// console.log(data);
res.end(data);
});
} else if(url_parts.pathname.substr(0,5) == '/poll'){
//polling code
var count = url_parts.pathname.replace(/[^0-9]*/,'');
console.log(count);
if(messages.length > count){
res.end(JSON.stringify({
count: messages.length,
append: messages.slice(count).join("\n")+"\n"
}));
} else {
clients.push(res);
}
} else if(url_parts.pathname.substr(0, 5) == '/msg/') {
// message receiving
var msg = unescape(url_parts.pathname.substr(5));
messages.push(msg);
while(clients.length > 0) {
var client = clients.pop();
client.end(JSON.stringify({
count: messages.length,
append: msg+"\n"
}));
}
// res.end(); //if left in, this renders an empty page, if removed,
// client keeps waiting....
}
}).listen(8080, 'localhost');
console.log('server running!');
index.html
<html>
<head>
<script src="http://code.jquery.com/jquery-1.6.4.min.js"></script>
<script>
var counter = 0;
var poll = function() {
$.getJSON('/poll/'+counter, function(response) {
counter = response.count;
var elem = $('#output');
elem.text(elem.text() + response.append);
//elem.text(counter);
poll();
});
}
poll();
</script>
</head>
<body>
<textarea id="output" style="width: 90%; height: 90%;">
</textarea>
</body>
</html>
I have looked in the docs, but I don't see anything specific about using .end() method with empty args to signify and end without passing data to be rendered. I have googled this, but I don't have an answer yet.
Do a res.json({success:"true"}) instead. The reason being is because res.end inherently thinks the client was sent a view prior to the stream being closed. With res.json() you can send any generic data, without an implied view being expected as well as close out the stream on client and server side.
Move res.end() inside while loop
while (clients.length > 0) {
var client = clients.pop();
client.end(JSON.stringify({
count : messages.length,
append : msg + "\n"
}));
if(!clients.length) {
res.end();
}
}
My understand of your problem is:
You have an HTML page (index.html), which has a textarea displaying all messages submitted by user. After one message is received and displayed, it will send the request for next message immediately (/poll/<n>).
To accept user's input for latest message, you open an API (/msg/<message>). When an HTTP request is sent to this API, server will extract the message, and return this message to /poll/<n> sent in step 1.
However, as HTML page (index.html) and the request to /msg/<message> happens in the same browser window, you can't let the http handler of /msg/<message> in node.js invoke res.end(), because in that case, the browser window will render the HTTP response of /msg/<message> request (blank page). Actually, you can't make the res return 200 OK, whatever data it returns. You can't make res fail the /msg/<message> request either (using req.destroy()), because in that case the browser window will render a failure/broken page, which is worse.
Unfortunately, you can't make res of /msg/<message> in node.js keep pending either. Although it will update index.html, the browser window will keep waiting...
The root cause of your problem is: browser window resource conflict between index.html and /msg/<message> response -- as long as /msg/<message> request is sent by using index.html window's URL bar, whenever its response is sent back, the window content (index.html) will be cleaned.
One solution is: using Ajax to send /msg/<message>. In this way, there would be no conflict for window resource. Example code is listed below:
<body>
<textarea id="output" style="width: 90%; height: 90%;">
</textarea>
<div>
<input type="text" id="msg">
<button type="button" onclick="submitMsg()">Submit</button>
</div>
</body>
window.submitMsg = function() {
var msg = $('#msg').val();
$.getJSON('/msg/' + msg, function(res) {
$('#msg').val('');
console.log('message sent.');
});
}
EDIT:
Another simpler solution is: open index.html in one browser window, and open /msg/<message> in another one (use res.end('message received successfully') to indicate message receiving result).
I have used the Asp.Net Identity framework in my app.There is a need, when the session expires give a prompt message, and then jump to the login page instead of directly jump to the login page.Prompt information using custom styles.
Because my app's left menus load the view with ajax,so I overried the AuthorizeAttribute.HandleUnauthorizedRequest methord to return a json.Now when users click left menus, it can work properly.But if users refresh the page by click F5,the page will still jump directly to the login page.
I have already overrided AuthorizeAttribute.HandleUnauthorizedRequest
protected override void HandleUnauthorizedRequest(AuthorizationContext filterContext)
{
var httpContext = filterContext.HttpContext;
string sintab = httpContext.Request["inTab"];
if (!string.IsNullOrEmpty(sintab) && bool.Parse(sintab))
{
var result = new JsonResult();
result.Data = new
{
Authorize = false,
Url = LOGIN_URL
};
result.JsonRequestBehavior = JsonRequestBehavior.AllowGet;
filterContext.Result =result;
return;
}
if (filterContext.Controller.GetType() != typeof(Controllers.HomeController) &&
!filterContext.ActionDescriptor.ActionName.Equals("Index", StringComparison.OrdinalIgnoreCase))
{
string returnUrl = "/" + filterContext.Controller.GetType().Name.Replace("Controller","") + "/Index" ;
returnUrl = httpContext.Server.UrlEncode(returnUrl);
httpContext.Response.Redirect("~/Account/Login?ReturnUrl="+returnUrl);
return;
}
base.HandleUnauthorizedRequest(filterContext);
}
The code of left menus' loadView js
$.get(url, null, function (html) {
html = html.replace(/#%/g, "\"").replace(/%#/g, "\"");
var json;
try {
json = eval("(" + html + ")");
} catch (e) {
}
if (json && !json.Authorize) {
// give an message
layer.alert("Session timeout, please re login.", function (index) {
window.location.href = json.Url + "?returnurl=" + encodeURI(hash);
});
}
else {
$("#content").empty().html(html);
_initModalButton();
$("#content").show();
}
}, 'html');
The page looks like this image
I want to know if there are some better ways to do this because there are a lot of other button need to check authorize status and show message before jump to the login page,and how to give the message when users refresh the page?
Thanks very much!
I think you're looking for are Global Ajax Events.
Please, check this, I think this make your job easier.
In my response, I have a function that load a model-data of point (Google point) and serialize it, sending to the client when finish.
The code looks like:
IList<PuntoMappa> punti = new List<PuntoMappa>();
foreach (Ricettivito Struttura in StruttureFinali)
{
PuntoMappa punto = new PuntoMappa();
punto.Titolo = Struttura.Titolo;
punto.Lat = Struttura.Geo.Latitudine;
punto.Lng = Struttura.Geo.Longitudine;
punto.Categoria = Struttura.Categoria;
punti.Add(punto);
}
}
m_strPunti = jsonSerializer.Serialize(punti);
if (m_strPunti == "")
{
m_strPunti = "{ }";
}
ScriptManager.RegisterClientScriptBlock(this, this.GetType(), "puntiLocalizzati", "var puntiLocalizzati = " + m_strPunti + ";", true);
the problem is that I have 200/300 object inside StruttureFinali, and it took somethings like 10 seconds to load this function and serialize it.
The webpage won't show until all functions in the .cs on the WebForm is finished.
Is there a way to load this content asynch? So display the code normally, and return "this function" asynch? Client side I can manage the whole operation with ready/load events.
P.S.
StruttureFinali is a List<Ricettivito>.ToList();
Here is what I am working with:
webserver.py:
import sys
from twisted.internet import reactor
from twisted.python import log
from autobahn.websocket import WebSocketServerFactory, \
WebSocketServerProtocol, \
listenWS
class EchoServerProtocol(WebSocketServerProtocol):
def onMessage(self, msg, binary):
print "sending echo:", msg
self.sendMessage(msg, binary)
if __name__ == '__main__':
log.startLogging(sys.stdout)
factory = WebSocketServerFactory("ws://localhost:9000", debug = False)
factory.protocol = EchoServerProtocol
listenWS(factory)
reactor.run()
background.js:
function updateCookies(info) {
send();
console.log(info.cookie.domain);
}
function send() {
msg = "TEST";
sock.send(msg);
};
var sock = null;
sock = new WebSocket("ws://localhost:9000");
console.log("Websocket created...");
sock.onopen = function() {
console.log("connected to server");
sock.send("CONNECTED TO YOU");
}
sock.onclose = function(e) {
console.log("connection closed (" + e.code + ")");
}
sock.onmessage = function(e) {
console.log("message received: " + e.data);
}
chrome.cookies.onChanged.addListener(updateCookies);
Now, upon running webserver.py and running background.js, nothing happens. The client see's no echo and the server doesn't report any connections or messages. However, if I reload background.js, all the sudden the previous message of "CONNECTED TO YOU" is shown by the server. Reloading again produces the same effect, showing the delayed "CONNECTED TO YOU" message. I've tried running sock.close() after sending the message, but that still produces nothing. I'm really confused at what is causing this random delay. Leaving the server running for 10 - 15 minutes also produces nothing, I must manually refresh the page before I see any messages. Any idea what might be causing this?