Large message support in C (> 65535 bytes)

[novnc]

Large message support in C (> 65535 bytes)

[WhiteRavenTechnology]

Quick followup: I managed to get the websockify.js library to work, and now I'm getting a different message from the proxy:
0: Receiving frames larger than 65535 bytes not supported
0: decoding error
0: handler exit

I suppose the obvious question, then, is do you anticipate adding support for frames larger than 65535 bytes? :)

I appreciate any advice you might have for me.

• John

[kanaka]

@JFitzDela any chance you can post enough code to reproduce the problem you are seeing? I have no problem supporting frames larger than 65535 bytes from the browser, however, this never happens with noVNC (client to server traffic is usually only a few dozens bytes at a time). If you can provide a reproducer/test case, then I should be able to fix it pretty quickly. Otherwise, it might be a while before I get around to this (since I'll have to code up the test case in addition to the fix). Thanks.

[WhiteRavenTechnology]

Happy to! If the attachment doesn't work (replying by e-mail, and I'm new to github), the source for the example that breaks is available at http://whiteraventechnology.com/websockify_test.zip.

The data in the example is actually closer to 300kb -- I didn't realize it was SO large, but for the sake of testing, that's what's breaking the C version of the server on my end (the python version works fine).

My code basically breaks the large string into 8192 byte chunks and sends them as individual messages (a requirement of my target server in this case). Interestingly, it's only after a final message is sent some few seconds AFTER all of the parts have been sent that the server kills the connection with the "Receiving frames larger than 65535 bytes not supported" message.

I appreciate your help!

• John

P.S. - Only difference in the included websock.js and yours is that I replaced the Util functions with console.logs -- they were causing an odd conflict somewhere in my code, so I removed the library.

[kanaka]

Thanks, I've replicated the problem. The C version is not as well designed as the python version and has some stack buffer size assumptions. Getting it to support larger frames isn't too hard and I've started working on it, but my spare time is limited so guarantee when I'll get to this.

BTW, one way you might be able to work around this is by setting a very short timeout (setTimeout) between sends of less than 65536 bytes. The reason you are running into frames larger than 65536 even when you are only sending 8192 at a time is because you are doing all of them within the same Javascript execution path/context. If you set a slight delay between each one then you will give the browser the opportunity to send a separate frame and websockify a chance to process it in smaller chunks.