CURLOPT_INTERFACE - source interface for outgoing traffic
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_INTERFACE, char *interface);
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.
Hostnames are resolved synchronously. Using the if! format is highly
recommended when using the multi interfaces to avoid allowing the code to
block. 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.
The application does not have to keep the string around after
setting this option.
NULL, use whatever the TCP stack finds suitable
CURL *curl = curl_easy_init();
curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/foo.bin");
curl_easy_setopt(curl, CURLOPT_INTERFACE, "eth0");
ret = curl_easy_perform(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