CURLOPT_INTERFACE(3)

NAME
CURLOPT_INTERFACE - source interface for outgoing traffic

SYNOPSIS
#include <curl/curl.h>
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_INTERFACE, char *interface);

DESCRIPTION
Pass a char * as parameter. This sets the interface name to use as outgoing network interface. The name can be an interface name, an IP address, or a host name. If the parameter starts with "if!" then it is treated as only as interface name and no attempt will ever be named to do treat it as an IP address or to do name resolution on it. If the parameter starts with "host!" it is treated as either an IP address or a hostname. If "if!" is specified but the parameter does not match an existing interface, CURLE_INTERFACE_FAILED is returned from the libcurl function used to perform the transfer. libcurl does not support using network interface names for this option on Windows. We strongly advise against specifying the interface with a hostname, as it causes libcurl to do a blocking name resolve call to retrieve the IP address. That name resolve operation will not use DNS-over-HTTPS even if CURLOPT_DOH_URL(3) is set. The application does not have to keep the string around after setting this option.

DEFAULT
NULL, use whatever the TCP stack finds suitable

PROTOCOLS
All

EXAMPLE
CURL *curl = curl_easy_init();
if(curl) {
  curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/foo.bin");
  curl_easy_setopt(curl, CURLOPT_INTERFACE, "eth0");
  ret = curl_easy_perform(curl);
  curl_easy_cleanup(curl);
}

AVAILABILITY
The "if!" and "host!" syntax was added in 7.24.0.

RETURN VALUE
Returns CURLE_OK on success or CURLE_OUT_OF_MEMORY if there was insufficient heap space.

SEE ALSO
CURLOPT_SOCKOPTFUNCTION(3), CURLOPT_TCP_NODELAY(3),