Tribblix: manual page: CURLOPT_ALTSVC

CURLOPT_ALTSVC_CTRL(3) Introduction to Library Functions

NAME

CURLOPT_ALTSVC_CTRL - control alt-svc behavior

SYNOPSIS

#include <curl/curl.h>

#define CURLALTSVC_READONLYFILE (1<<2)
#define CURLALTSVC_H1 (1<<3)
#define CURLALTSVC_H2 (1<<4)
#define CURLALTSVC_H3 (1<<5)

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_ALTSVC_CTRL, long bitmask);

DESCRIPTION

Populate the long bitmask with the correct set of features to
instruct libcurl how to handle Alt-Svc for the transfers using this
handle.

libcurl only accepts Alt-Svc headers over a Secure Transport, meaning
HTTPS. It also only completes a request to an alternative origin if
that origin is properly hosted over HTTPS. These requirements are
there to make sure both the source and the destination are
legitimate.

Alternative services are only used when setting up new connections.
If there exists an existing connection to the host in the connection
pool, then that is preferred.

If CURLOPT_ALTSVC(3) is set, CURLOPT_ALTSVC_CTRL(3) gets a default
value corresponding to CURLALTSVC_H1 | CURLALTSVC_H2 | CURLALTSVC_H3
- the HTTP/2 and HTTP/3 bits are only set if libcurl was built with
support for those versions.

Setting any bit enables the alt-svc engine.

CURLALTSVC_READONLYFILE
Do not write the alt-svc cache back to the file specified with
CURLOPT_ALTSVC(3) even if it gets updated. By default a file
specified with that option is read and written to as deemed
necessary.

CURLALTSVC_H1
Accept alternative services offered over HTTP/1.1.

CURLALTSVC_H2
Accept alternative services offered over HTTP/2. This is only
used if libcurl was also built to actually support HTTP/2,
otherwise this bit is ignored.

CURLALTSVC_H3
Accept alternative services offered over HTTP/3. This is only
used if libcurl was also built to actually support HTTP/3,
otherwise this bit is ignored.

DEFAULT

0 - Alt-Svc handling is disabled

PROTOCOLS

This functionality affects http only

EXAMPLE

int main(void)
{
CURL *curl = curl_easy_init();
if(curl) {
curl_easy_setopt(curl, CURLOPT_ALTSVC_CTRL, (long)CURLALTSVC_H1);
curl_easy_setopt(curl, CURLOPT_ALTSVC, "altsvc-cache.txt");
curl_easy_perform(curl);
}
}

AVAILABILITY

Added in curl 7.64.1

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).