CURLOPT_ALTSVC_CTRL(3)     curl_easy_setopt options     CURLOPT_ALTSVC_CTRL(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 will only accept Alt-Svc headers over a secure transport,
       meaning HTTPS. It will also only complete 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.

       Setting any bit will enable the alt-svc engine.

       CURLALTSVC_READONLYFILE
              Do not write the alt-svc cache back to the file specified with
              _ALTSVC&section=3">CURLOPT_ALTSVC(3) even if it gets updated. By default a file
              specified with that option will be 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 will only
              be used if libcurl was also built to actually support HTTP/2,
              otherwise this bit will be ignored.

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

DEFAULT
       Alt-Svc handling is disabled by default. If _ALTSVC&section=3">CURLOPT_ALTSVC(3) is set,
       _ALTSVC_CTRL&section=3">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
       CURL *curl = curl_easy_init();
       if(curl) {
         curl_easy_setopt(curl, CURLOPT_ALTSVC_CTRL, 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.

SEE ALSO
       CURLOPT_ALTSVC(3), CURLOPT_CONNECT_TO(3), CURLOPT_RESOLVE(3),

libcurl 7.77.0                 November 4, 2020         CURLOPT_ALTSVC_CTRL(3)