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.

SEE ALSO

       CURLOPT_ALTSVC(3), CURLOPT_CONNECT_TO(3), CURLOPT_RESOLVE(3)