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CURLOPT_ALTSVC_CTRL(3)              libcurl             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 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, (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),

ibcurl 8.1.2                    April 26, 2023          CURLOPT_ALTSVC_CTRL(3)

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