config timeout with CURLOPT_TIMEOUT_MS instead of CURLOPT_TIMEOUT for curl implementation

[lalitb]

Discussed in #1254

^{Originally posted by wxl374 March 10, 2022}
When configure OtlpHttpExporter's timeout less than 1s, it will set to 0 for the use of CURLOPT_TIMEOUT(

opentelemetry-cpp/ext/include/opentelemetry/ext/http/client/curl/http_operation_curl.h

Line 189 in fd5a621

curl_easy_setopt(curl_, CURLOPT_TIMEOUT, http_conn_timeout_.count() / 1000);

), then never times out (sometimes limited by CURLOPT_LOW_SPEED_TIME). Why not use CURLOPT_TIMEOUT_MS instead？

[lalitb]

This is a good point. Would be good to see the libcurl version having CURLOPT_TIMEOUT_MS support before supporting this. Moving this to issue to investigate further.

[wxl374]

CURLOPT_TIMEOUT_MS was provided from 7.16.2
https:/curl/curl/blob/e87c53d7eadd52d2f18cf00241d6afef958fa881/docs/libcurl/symbols-in-versions#L666
how about selected CURLOPT_TIMEOUT_MS by checking libcurl version?
https:/curl/curl/blob/master/include/curl/curlver.h

[lalitb]

CURLOPT_TIMEOUT_MS was provided from 7.16.2

Thanks, 7.16.2 seems long back (~2007), I think we can safely use CURLOPT_TIMEOUT_MS