Why am I getting CURLE_NOT_BUILT_IN when using libcurl with CURLOPT_PROXY?

Question

I'm debugging some HTTP request, using a proxy (Burp).

Let's say we have this command, running OK. Burp is capturing everything:

curl --proxy localhost:8080 -k https://www.ipchicken.com/

Now I'm trying to do the same, programmatically:

CURL     *curlHandle;
CURLcode curlErrorCode;
curlHandle=curl_easy_init();
curlErrorCode=curl_easy_setopt(curlHandle,CURLOPT_URL,"https://www.ipchicken.com/");
curlErrorCode=curl_easy_setopt(curlHandle,CURLOPT_PROXY,"https://127.0.0.1:8080");
curlErrorCode=curl_easy_setopt(curlHandle,CURLOPT_SSL_VERIFYPEER,0);
curlErrorCode=curl_easy_setopt(curlHandle,CURLOPT_HTTPGET,1L);
// ...
curlErrorCode=curl_easy_perform(curlHandle);
// ...
curl_easy_cleanup(curlHandle);

All the curl_easy_setopt() calls return CURLE_OK. But curl_easy_perform() is returning CURLE_NOT_BUILT_IN.

This does not make sense, since the curl executable was made in the same build as the library I'm using.

Any idea about what could be happening?

Thanks.

Answer 1

I had to replace https:// with http:// for the CURLOPT_PROXY option:

curlErrorCode=curl_easy_setopt(curlHandle,CURLOPT_PROXY,"http://127.0.0.1:8080");

It works now.

For the record, even building libcurl with all features/packages did not allow me to use HTTPS for the proxy type.