Websocket Client

[paul_cardinale]

Has anyone here ever successfully used the LabVIEW WebSockets Library to create a websocket client in LabVIEW?

If so, can you share an example?

[mikeporter]

Look here:

http://www.notatamelion.com/2015/12/07/if-the-socket-fits-wear-it/

Mike...

[paul_cardinale]

That's all very nice, but it only describes a websocket server, not a websocket client.

[Sam_Sharp]

Hi Paul - I created the WebSockets library - I don't think I have any examples from applications of a WebSocket Client and I have never fully tested that functionality (I got it work well enough for my application) against the WebSocket Spec. It should be pretty straightforward though - open a TCP connection, use the SendHandshake VI and then you are free to use the read/write VIs to send/receive data from the server. I think for the client, you need to Mask the data - it's one of the inputs to the write VI, I think.

Here is a very simple example:

[paul_cardinale]

I could only get the handshake to work by modifying your "InitiateClientHandshake.vi" (see attachment).  But I haven't been able to get past that.  After the handshake, the 'Read' function always times out.

[Sam_Sharp]

You probably also need to change the end of line constant with a \r\n as this can change depending on the target you're running the code on.

As for the read - is your websocket server actually sending out data?

My test code works fine with a LabVIEW WebSockets server, but like I said - I haven't done extensive testing on it with other websockets services.

[paul_cardinale]

I can only get "InitiateClientHandshake" to work when the line break is \n.

I'm sure the server is sending data because I can get a browser to see it.

[Sam_Sharp]

Weird - the issue with the line breaks is because a LabVIEW string has \n as termination, but on different targets, an EOL constant could be \n or \r\n or something else - HTTP specifies \r\n - it's fixed in the server handshake but didn't see it on the client side.

Is it a public server you're communicating with? Can you post your code?

[paul_cardinale]

I was mistaken about the server sending data (after the handshake, additional messaging is required before it starts sending).

After I get the server to start sending data, the Read function throws error 66.  The actual data that comes out is "ˆ&êClients may not send unmasked frames".  If I try masking the payload for the messages that tell the server to start sending, then I get no response.

It's not a public server, it's inside an instrument.

Attached it the test code (Note: I'm using the modified version of "InitiateClientHandshake.vi")

[paul_cardinale]

I managed to get a websocket client working with my instrument.

Attached is the modified version of the WebSockets API.