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 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.

       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 will be preferred.

       Setting any bit will enable 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 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  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

       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 7.81.0                                  November 04, 2021                         CURLOPT_ALTSVC_CTRL(3)