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CURLOPT_PRE_PROXY(3) curl_easy_setopt options CURLOPT_PRE_PROXY(3)


CURLOPT_PRE_PROXY - pre-proxy host to use


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


Set the preproxy to use for the upcoming request. The parameter should be a char * to a null-terminated string holding the host name or dotted numerical IP address. A numerical IPv6 address must be written within [brackets].

To specify port number in this string, append :[port] to the end of the host name. The proxy's port number may optionally be specified with the separate option CURLOPT_PROXYPORT(3). If not specified, libcurl will default to using port 1080 for proxies.

A pre proxy is a SOCKS proxy that curl connects to before it connects to the HTTP(S) proxy specified in the CURLOPT_PROXY option. The pre proxy can only be a SOCKS proxy.

The pre proxy string should be prefixed with [scheme]:// to specify which kind of socks is used. Use socks4://, socks4a://, socks5:// or socks5h:// (the last one to enable socks5 and asking the proxy to do the resolving, also known as CURLPROXY_SOCKS5_HOSTNAME type) to request the specific SOCKS version to be used. Otherwise SOCKS4 is used as default.

Setting the pre proxy string to "" (an empty string) will explicitly disable the use of a pre proxy.

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


Default is NULL, meaning no pre proxy is used.

When you set a host name to use, do not assume that there's any particular single port number used widely for proxies. Specify it!


All except file://. Note that some protocols do not work well over proxy.


CURL *curl = curl_easy_init();
if(curl) {

curl_easy_setopt(curl, CURLOPT_URL, "");
curl_easy_setopt(curl, CURLOPT_PRE_PROXY, "socks4://socks-proxy:1080");
curl_easy_setopt(curl, CURLOPT_PROXY, "http://proxy:80");
curl_easy_perform(curl); }


Added in 7.52.0


Returns CURLE_OK if proxies are supported, CURLE_UNKNOWN_OPTION if not, or CURLE_OUT_OF_MEMORY if there was insufficient heap space.



January 2, 2023 libcurl 7.88.1