CURLOPT_PRE_PROXY(3) Library Functions Manual CURLOPT_PRE_PROXY(3)
NAME
CURLOPT_PRE_PROXY - pre-proxy host to use
SYNOPSIS
#include <curl/curl.h>
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_PRE_PROXY, char *preproxy);
DESCRIPTION
Set the preproxy to use for the upcoming request. The parameter should
be a char * to a null-terminated string holding the hostname 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 defaults
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(3) 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) explicitly disables
the use of a pre proxy.
When you set a hostname to use, do not assume that there is any particu-
lar single port number used widely for proxies. Specify it.
The application does not have to keep the string around after setting
this option.
Using this option multiple times makes the last set string override the
previous ones. Set it to NULL to disable its use again.
DEFAULT
NULL
PROTOCOLS
This functionality affects all supported protocols
EXAMPLE
int main(void)
{
CURL *curl = curl_easy_init();
if(curl) {
curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/file.txt");
curl_easy_setopt(curl, CURLOPT_PRE_PROXY, "socks4://socks-proxy:1080");
curl_easy_setopt(curl, CURLOPT_PROXY, "http://proxy:80");
curl_easy_perform(curl);
}
}
AVAILABILITY
Added in curl 7.52.0
RETURN VALUE
curl_easy_setopt(3) returns a CURLcode indicating success or error.
CURLE_OK (0) means everything was OK, non-zero means an error occurred,
see libcurl-errors(3).
SEE ALSO
CURLOPT_HTTPPROXYTUNNEL(3), CURLOPT_PROXY(3)
libcurl 2026-07-12 CURLOPT_PRE_PROXY(3)
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