CURLOPT_DEFAULT_PROTOCOL - default protocol to use if the URL is missing a scheme name

#include <curl/curl.h>
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_DEFAULT_PROTOCOL,
                          char *protocol);

This option tells libcurl to use protocol if the URL is missing a scheme name.

Use one of these protocol (scheme) names:

dict, file, ftp, ftps, gopher, http, https, imap, imaps, ldap, ldaps, pop3, pop3s, rtsp, scp, sftp, smb, smbs, smtp, smtps, telnet, tftp

An unknown or unsupported protocol causes error CURLE_UNSUPPORTED_PROTOCOL when libcurl parses a URL without a scheme. Parsing happens when curl_easy_perform(3) or curl_multi_perform(3) is called. The protocol set supported by libcurl vary depending on how it was built. Use curl_version_info(3) if you need a list of protocol names supported by the build of libcurl that you are using.

This option does not change the default proxy protocol (http).

Without this option libcurl would make a guess based on the host, see CURLOPT_URL(3) for details.

The application does not have to keep the string around after setting this option.

NULL (make a guess based on the host)


int main(void)
  CURL *curl = curl_easy_init();
  if(curl) {
    /* set a URL without a scheme */
    curl_easy_setopt(curl, CURLOPT_URL, "");
    /* set the default protocol (scheme) for schemeless URLs */
    curl_easy_setopt(curl, CURLOPT_DEFAULT_PROTOCOL, "https");
    /* Perform the request */

Added in 7.45.0

CURLE_OK if the option is supported.

CURLE_OUT_OF_MEMORY if there was insufficient heap space.

CURLE_UNKNOWN_OPTION if the option is not supported.


2024-05-22 libcurl