CURLOPT_PROTOCOLS_STR - allowed protocols

Added in curl 7.85.0

All protocols built-in

Pass a pointer to a string that holds a comma-separated list of case insensitive protocol names (URL schemes) to allow in the transfer. This option allows applications to use libcurl built to support a wide range of protocols but still limit specific transfers to only be allowed to use a subset of them. By default, libcurl accepts all protocols it was built with support for. See also CURLOPT_REDIR_PROTOCOLS_STR(3). If trying to set a non-existing protocol or if no matching protocol at all is set, it returns error. These are the available protocols: DICT, FILE, FTP, FTPS, GOPHER, GOPHERS, HTTP, HTTPS, IMAP, IMAPS, LDAP, LDAPS, MQTT, POP3, POP3S, RTMP, RTMPE, RTMPS, RTMPT, RTMPTE, RTMPTS, RTSP, SCP, SFTP, SMB, SMBS, SMTP, SMTPS, TELNET, TFTP, WS, WSS You can set "ALL" as a short-cut to enable all protocols. Note that by setting all, you may enable protocols that were not supported the day you write this but are introduced in a future libcurl version. curl_version_info(3) can be used to get a list of all supported protocols in the current libcurl. CURLINFO_SCHEME(3) is the recommended way to figure out the protocol used in a previous transfer. Using this option multiple times makes the last set string override the previous ones. Set it to NULL to restore to the internal default.

int main(int argc, char **argv) { CURL *curl = curl_easy_init(); if(curl) { /* pass in the URL from an external source */ curl_easy_setopt(curl, CURLOPT_URL, argv[1]); /* only allow HTTP, TFTP and SFTP */ curl_easy_setopt(curl, CURLOPT_PROTOCOLS_STR, "http,tftp,sftp"); /* Perform the request */ curl_easy_perform(curl); } }

CURLOPT_PROTOCOLS_STR - allowed protocols

This functionality affects all supported protocols

Returns CURLE_UNKNOWN_OPTION if the option is not implemented, CURLE_UNSUPPORTED_PROTOCOL if a listed protocol is not supported or disabled, CURLE_BAD_FUNCTION_ARGUMENT if no protocol is listed else CURLE_OK.

CURLINFO_SCHEME(3), CURLOPT_DEFAULT_PROTOCOL(3), CURLOPT_REDIR_PROTOCOLS_STR(3), CURLOPT_URL(3), curl_version_info(3) libcurl 2025-06-16 CURLOPT_PROTOCOLS_STR(3)

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