MAX_RW_BUF_LEN not large enough for WebSocketConnection::WssHandshake

[sjmh3]

The WSS HTTP GET request formed in WebSocketConnection::WssHandshake can exceed 2048 bytes, which is the size of MAX_RW_BUF_LEN. The error traced out is that the WSS handshake fails because there are no SSL packets to read. In fact the request has only been partially written because the buffer wasn't large enough to hold all of it in one go, so the IoT service hasn't sent a response.

[vareddy-zz]

Hi @sjmh3 ,
Thank you for your interest in the AWS IoT SDK!
Were you able to increase the MAX_RW_BUF_LEN to successfully complete the WSS handshake? If yes, what was the value of the buffer that was required for it?
We will investigate this on our end and provide a fix for this.
Thanks!
Varun

[sjmh3]

Hi @vareddy,
Yes, increasing MAX_RW_BUF_LEN allowed me to successfully complete the WSS handshake. I should have said what buffer size was required - sorry. I increased the buffer size to 3072 and then in WebSocketConnection::WssHandshake() I saw the length of the request string stored in rw_buf range from 2048 to 2088 (as returned from strnlen), so that would require MAX_RW_BUF_LENto be up to 2089. I'm always connecting to the same endpoint, so the variable length comes from the canonical query string. I haven't investigated what causes its length to vary so can't say if 2089 would be sufficient for all situations.
The original buffer size of 2048 was large enough for my request string a couple of months ago with the same code; I only started hitting this problem when returning to the project this week. So something about the request is longer now than it was then.
Simon

[vareddy-zz]

Hi @sjmh3 ,
While connecting over WebSockets, did you fill in the "aws_session_token" in the configuration?
Thanks!
Varun

[sjmh3]

Hi @vareddy,

Yes, I did fill in the session token - do I not need to?

Thanks,
Simon

[vareddy-zz]

Hi @sjmh3 ,
That would explain the overshoot as it can easily be over 2k if you fill in the session token. That is more like oversight on our part. I have made a fix and will be pushing to master after our internal testing.
Thanks!
Varun