CURLOPT_INTERFACE(3) Library Functions Manual CURLOPT_INTERFACE(3)

CURLOPT_INTERFACE - source interface for outgoing traffic

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

Pass a char pointer 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 hostname.

If the parameter starts with "if!" then it is treated only as an interface name. 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 does 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.

NULL, use whatever the TCP stack finds suitable

All

int main(void)
{
  CURL *curl = curl_easy_init();
  if(curl) {
    CURLcode res;
    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/foo.bin");
    curl_easy_setopt(curl, CURLOPT_INTERFACE, "eth0");
    res = curl_easy_perform(curl);
    curl_easy_cleanup(curl);
  }
}

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

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

CURLOPT_LOCALPORT(3), CURLOPT_SOCKOPTFUNCTION(3), CURLOPT_TCP_NODELAY(3)

2024-05-22 libcurl