websocket.c example: curl_ws_recv returns "Socket not ready for send/recv" (errno 81)

[untitaker]

I did this

1. copied this example into foo.c
2. edited the websocket URL in foo.c to be a valid websocket server. wss://ws.postman-echo.com/raw works, ws://localhost:8080 works as well, with websocat being invoked as websocat -s 8080
3. cloned curl master, moved foo.c into root folder
4. cmake -DENABLE_WEBSOCKETS=on
5. make
6. cc -L lib/ foo.c -lcurl
7. LD_LIBRARY_PATH=lib/ ./a.out

I expected the following

some kind of ping-pong demo, or a hanging connection, depending on which websocket server is being used.

instead the program immediately quits with this after sending the initial HTTP headers:

ws: curl_ws_recv returned 81, received 0

in the real-world application that is built based on that example code, I get (just posting the strerror for searchability):

code 81: "Socket not ready for send/recv"

curl/libcurl version

git sha 376cd67

I thought this was related to #11443, so I checked curl 7 as well. On tag curl-7_88_1 (046209e), foo.c hangs instead, though websocket.c does not exist on that commit at all anyway

operating system

Ubuntu 23.10

[untitaker]

Dug around a little, and I suspect that this is intended behavior due to #10625, and it's just the example that needs updating, similar to #10760

though I'm not sure a crude busy-loop is a good example to follow either