curl/docs/libcurl/opts/CURLOPT_ALTSVC_CTRL.md
Daniel Stenberg eefcc1bda4
docs: introduce "curldown" for libcurl man page format
curldown is this new file format for libcurl man pages. It is markdown
inspired with differences:

- Each file has a set of leading headers with meta-data
- Supports a small subset of markdown
- Uses .md file extensions for editors/IDE/GitHub to treat them nicely
- Generates man pages very similar to the previous ones
- Generates man pages that still convert nicely to HTML on the website
- Detects and highlights mentions of curl symbols automatically (when
  their man page section is specified)

tools:

- cd2nroff: converts from curldown to nroff man page
- nroff2cd: convert an (old) nroff man page to curldown
- cdall: convert many nroff pages to curldown versions
- cd2cd: verifies and updates a curldown to latest curldown

This setup generates .3 versions of all the curldown versions at build time.

CI:

Since the documentation is now technically markdown in the eyes of many
things, the CI runs many more tests and checks on this documentation,
including proselint, link checkers and tests that make sure we capitalize the
first letter after a period...

Closes #12730
2024-01-23 00:29:02 +01:00

2.5 KiB

c SPDX-License-Identifier Title Section Source See-also
Copyright (C) Daniel Stenberg, <daniel.se>, et al. curl CURLOPT_ALTSVC_CTRL 3 libcurl
CURLOPT_ALTSVC (3)
CURLOPT_CONNECT_TO (3)
CURLOPT_RESOLVE (3)

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.

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

Alt-Svc handling is disabled by default. If CURLOPT_ALTSVC(3) is set, CURLOPT_ALTSVC_CTRL(3) has 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.

PROTOCOLS

HTTPS

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 7.64.1

RETURN VALUE

Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.