LabVIEW
Web Services: Implementing Server-Side Events (SSE)
Hi all,
I have been trying to implement SSE in LabView. I don't know if this is even possible, but it would be really awesome if it was.
So far, this is what I've done in my Web Service project:
And this is my implementation in the client side:
var urlSSE = 'http://127.0.0.1:8001/RIP/SSE';
// Register to the SSE:
var source = new EventSource(urlSSE);
// Manage SSE Events
source.onopen = function(e) {
// Connection was opened.
console.log('Open');
};
source.onmessage = function(e) {
console.log('data:'+e.data);
if (e.id == "CLOSE") {
console.log('Closing');
source.close();
}
};
When I look at the network traffic in my browser's console I can see that the SSE connection is recognized and established:
However, as you can see from above, the SSE only receives the data one time, then the connection ends and, after the timeout (set to 1000 miliseconds in the Vi), the client makes a new connection. This is happening, I guess, because the web service Vi is only executed once per each client request.
What I would like to obtain is a constant flow of data from the LabView server to the client, without having to ask for data from the client. It looks like I'm really close, actually. I would just need to keep the Vi running, particularly the Write Response.vi and the Flush Output.vi. I tried to put those inside a while loop but this didn't work.
Does anyone know how could I do this?
Thanks!
Hi Milan,
I already tried your example. Thanks again for that!
The solution you implemented is basicaly the one I described at the end of my original message: adding the while loop in the Write Response.vi and the Flush Output.vi. It works perfectly fine BUT I have my concerns about it. By adding the while loop, the LabView web server stays inside the loop and never finishes the response request to the web client. Therefore, the web browser never gets to identify the connection as a SSE communication. This happens because the communication is still going and the LabView web server never sends the end of the first message.
The problem with this is that LabView's web service gets caught in the execution of this Vi and it is incapable of doing other things (attending to POST requests, for example). You said I can change the max simultaneous connection to the SSE by modifying the reentrency configuration of the Vi, but what happens if I have a different HTTP Method Vi (for attending POST requests, for example)? Also, is it possible that this solution may affect in some negative way the web client too?
EDIT: I just thought about a possible solution: If you use a for loop instead of a while loop and run it, let's say, 10 or 50 times, you get the end of the SSE (which will then reconnect after the specified timeout) and the web server is therefore free to attend POST requests every once in a while. Still, I just feel like there should be a better way to handle this... Ideas? I tried to set the SSE as one web service (listening in one port) and the POST Method Vi in a different web service (listening in a different port) but it looks like LabView only allows publishing web services in port 8080.
Regards.
