Nginx: How to log the number of bytes sent over a websocket?

Question

I am using nginx as a websocket reverse-proxy. I would like to log the number of bytes sent (and ideally also received) over a websocket. If I use $body_bytes_sent in log_format, the entry in the access_log is always 0. As far as I can tell, a lot of data went through the websocket, so clearly $body_bytes_sent does not include data sent over a websocket.

I tried to use $bytes_sent, but it's just one or two hundred bytes (no matter how much data is sent over the websocket), which is clearly just the HTTP headers. I went through the list of available nginx variables, but I coulnd't find anything for me...

Any idea?

Answer 1

Problem solved!

The problem was that I was using an old version of nginx. With the latest one (1.14.0), $body_bytes_sent does log the amount of bytes sent over the websocket.