Older asynchronous messages overwriting newer ones - asp.net

Question

We are developing a document collaboration tool in SignalR where multiple users can update one single WYSIWYG form.
We are struggling getting the app to work using the KeyUp method to send the changes back to the server. This causes the system to overwrite what the user wrote after his first key stroke when it sends the message back.
Is there anyway to work around this problem?
For the moment I tried to set up a 2 seconds timeout but this delays all updates not only the "writer" page.
public class ChatHub : Hub
{
public ChatHub()
{
}
public void Send(int id,string message)
{
// Call the broadcastMessage method to update clients.
Clients.All.broadcastMessage(id,message); //id is for the document id where to update the content
}
}
and the client:
$(function () {
// Declare a proxy to reference the hub.
var chat = $.connection.chatHub;
//console.log("Declare a proxy to reference the hub.");
// Create a function that the hub can call to broadcast messages.
chat.client.broadcastMessage = function (id, message) {
var encodedValue = $('<div />').text(id).html();
// Add the message to the page.
if (encodedValue == $('#hdnDocId').val()) {
$('#DiaplayMsg').text(message);
tinyMCE.activeEditor.setContent("");
tinyMCE.get('txtContent').execCommand('insertHTML', false, message); //!!!
}
};
// Start the connection.
$.connection.hub.start().done(function (e) {
//console.log("Start the connection.");
if ($('#hdnDocId').val() != '') {
tinyMCE.activeEditor.onKeyUp.add(function (ed, e) {
var elelist = $(tinyMCE.activeEditor.getBody()).text();
var content = tinyMCE.get('txtContent').getContent();
function Chat() {
var content = tinyMCE.get('txtContent').getContent();
chat.server.send($('#hdnDocId').val(), content); //send a push to server
}
typewatch(Chat, 2000);
});
}
});
});
var typewatch = function () {
var timer = 0;
return function (Chat, ms) {
clearTimeout(timer);
timer = setTimeout(Chat, ms);
}
} ();
</script>
Hello, here is an update of the client KeyUp code. It seems to be working but I would like your opinion. I've used a global variable to store the timeout, see below:
<script type="text/javascript">
$(function () {
// Declare a proxy to reference the hub.
var chat = $.connection.chatHub;
//console.log("Declare a proxy to reference the hub.");
// Create a function that the hub can call to broadcast messages.
chat.client.broadcastMessage = function (id, message) {
var encodedValue = $('<div />').text(id).html();
var currenttime = new Date().getTime() / 1000 - 2
if (typeof window.istyping == 'undefined') {
window.istyping = 0;
}
if (encodedValue == $('#hdnDocId').val() && window.istyping == 0 && window.istyping < currenttime) {
function Update() {
$('#DiaplayMsg').text(message);
tinyMCE.activeEditor.setContent("");
tinyMCE.get('txtContent').execCommand('insertHTML', false, message); //!!!
// tinyMCE.get('txtContent').setContent(message);
window.istyping = 0
}
Update();
}
};
// Start the connection.
$.connection.hub.start().done(function (e) {
//console.log("Start the connection.");
if ($('#hdnDocId').val() != '') {
tinyMCE.activeEditor.onKeyUp.add(function (ed, e) {
var elelist = $(tinyMCE.activeEditor.getBody()).text();
var content = tinyMCE.get('txtContent').getContent();
function Chat() {
//alert("Call");
var content = tinyMCE.get('txtContent').getContent();
chat.server.send($('#hdnDocId').val(), content);
window.istyping = new Date().getTime() / 1000;
}
Chat();
});
}
});
});
var typewatch = function () {
var timer = 0;
return function (Chat, ms) {
clearTimeout(timer);
timer = setTimeout(Chat, ms);
}
} ();
Thanks,
Roberto.

Answer 1

Is there anyway to work around this problem?
Yes, by not sending the entire document to the server, but document elements like paragraphs, table cells, and so on. You can synchronize these after the user has stopped typing for a period, or when focus is lost for example.
Otherwise add some incrementing counter to the messages, so older return values don't overwrite newer ones arriving earlier.
But you're basically asking us to solve a non-trivial problem regarding collaborated document editing. What have you tried?

Answer 2

"This causes the system to overwrite what the user wrote"
that's because this code isn't making any effort to merge changes. it is just blindly overwriting whatever is there.
tinyMCE.activeEditor.setContent("");
tinyMCE.get('txtContent').execCommand('insertHTML', false, message);
as #CodeCaster hinted, you need to be more precise in the messages you send - pass specific changes back and forth rather re-sending the entire document - so that changes can be carefully merged on the receiving side