curl_multi_poll hangs forever on negative timeout

[hamstergene]

This program hangs forever

#include <curl/curl.h>

int main(int narg, char**argv) {
    curl_global_init( CURL_GLOBAL_ALL );
    CURLM* mh = curl_multi_init();
    curl_multi_poll( mh, 0, 0, /*timeout_ms*/-1, 0 );
}

I expected the following

The function interface takes signed integer (int) it must be ready to handle negative numbers.

curl/libcurl version

7.68.0-20191218

operating system

macOS 10.14.6

[dfandrich]

Using a negative timeout is undocumented, so you're hitting undefined behaviour. Don't do undefined things if you don't want to be surprised by what happens.

[hamstergene]

Positive and zero are also undocumented. The is simply no documentation on which values are valid. One has to document something first before claiming that everything else is undocumented.

[jay]

It's implied though we should error if negative. I couldn't find a good error code for it so I've added one in #4765 and if approved that will address this issue in the release after next.

[tomalakgeretkal]

I don't understand why we cannot accept -1 for "forever" so that this functions like POSIX poll(). It's easy to make it behave properly with expiry timeouts: I'd submitted a PR for it before realising that this new validation had been added, which breaks my fix. #4932