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.TH CURLOPT_INTERFACE 3 "September 16, 2020" "libcurl 7.73.0" "curl_easy_setopt options"

.SH NAME
CURLOPT_INTERFACE \- source interface for outgoing traffic
.SH SYNOPSIS
#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_INTERFACE, char *interface);
.SH DESCRIPTION
Pass a char * as parameter. This sets the \fIinterface\fP 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.
.SH DEFAULT
NULL, use whatever the TCP stack finds suitable
.SH PROTOCOLS
All
.SH EXAMPLE
.nf
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);
}
.fi
.SH AVAILABILITY
The "if!" and "host!" syntax was added in 7.24.0.
.SH RETURN VALUE
Returns CURLE_OK on success or
CURLE_OUT_OF_MEMORY if there was insufficient heap space.
.SH "SEE ALSO"
.BR CURLOPT_SOCKOPTFUNCTION "(3), " CURLOPT_TCP_NODELAY "(3), "