CURLOPT_ALTSVC_CTRL(3)     Library Functions Manual     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 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
       HTTP

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)

libcurl                          April 26 2024          CURLOPT_ALTSVC_CTRL(3)