Sync outliers with the rest of the code.
Also:
- return error in some failed init cases, instead of `CURLE_OK`:
1908, 1910, 1913, 2082, 3010
- lib1541: delete unused struct member.
Closes#19515
- 'CURL *' handles are called 'curl'
- 'CURLM *' handles are called 'multi'
- write callbacks are called 'write_cb'
- read callbacs are called 'read_cb'
- CURLcode variables are called 'res'
It makes the examples look and feel more consistent. It allows for
easier copy and pasting between examples.
Closes#19299
- add `curl_global_init()` and `curl_global_cleanup()` where missing.
- check the result of `curl_global_init()` where missing.
- return the last curl error from `main()`.
- drop Win32-specific socket initialization in favor of `curl_global_init()`.
- rename some outliers to `res` for curl result code.
- fix cleanup in some error cases.
Inspired by Joshua's report on examples.
Closes#19053
Add support for CURLOPT_READFUNCTION with WebSocket urls when *not* in
connect-only mode, e.g. when using curl_multi_perform.
Install the callback function and set CURLOPT_UPLOAD. Return
CURL_READFUNC_PAUSE when having nothing more to send and unpause the
transfer when more data is ready.
This will send the read bytes in a WebSocket BINARY frame.
Add support for this mode in the pytest "ws_data" client and have all
tests run in 'curl_ws_send/recv' and 'peform' mode as well.
Add `curl_ws_start_frame()`. Document, cover in libcurl-ws.md and
explain the READFUNCTION mode for websockets.
Add example `websocket-updown` for this.
Closes#17683
