CURLOPT_ALTSVC_CTRL(3)

1CURLOPT_ALTSVC_CTRL(3)              libcurl             CURLOPT_ALTSVC_CTRL(3)
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NAME

6       CURLOPT_ALTSVC_CTRL - control alt-svc behavior
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SYNOPSIS

9       #include <curl/curl.h>
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11       #define CURLALTSVC_READONLYFILE (1<<2)
12       #define CURLALTSVC_H1           (1<<3)
13       #define CURLALTSVC_H2           (1<<4)
14       #define CURLALTSVC_H3           (1<<5)
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16       CURLcode curl_easy_setopt(CURL *handle, CURLOPT_ALTSVC_CTRL, long bitmask);
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DESCRIPTION

19       Populate  the long bitmask with the correct set of features to instruct
20       libcurl how to handle Alt-Svc for the transfers using this handle.
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22       libcurl only accepts Alt-Svc headers over a secure  transport,  meaning
23       HTTPS. It will also only complete a request to an alternative origin if
24       that origin is properly hosted over HTTPS. These requirements are there
25       to make sure both the source and the destination are legitimate.
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27       Alternative  services are only used when setting up new connections. If
28       there exists an existing connection to the host in the connection pool,
29       then that will be preferred.
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31       Setting any bit will enable the alt-svc engine.
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33       CURLALTSVC_READONLYFILE
34              Do  not  write the alt-svc cache back to the file specified with
35              CURLOPT_ALTSVC(3) even if it gets updated.  By  default  a  file
36              specified with that option will be read and written to as deemed
37              necessary.
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39       CURLALTSVC_H1
40              Accept alternative services offered over HTTP/1.1.
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42       CURLALTSVC_H2
43              Accept alternative services offered over HTTP/2. This will  only
44              be  used  if  libcurl was also built to actually support HTTP/2,
45              otherwise this bit will be ignored.
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47       CURLALTSVC_H3
48              Accept alternative services offered over HTTP/3. This will  only
49              be  used  if  libcurl was also built to actually support HTTP/3,
50              otherwise this bit will be ignored.
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DEFAULT

53       Alt-Svc handling is disabled by default. If CURLOPT_ALTSVC(3)  is  set,
54       CURLOPT_ALTSVC_CTRL(3)   has   a   default   value   corresponding   to
55       CURLALTSVC_H1 | CURLALTSVC_H2 | CURLALTSVC_H3 - the HTTP/2  and  HTTP/3
56       bits are only set if libcurl was built with support for those versions.
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PROTOCOLS

59       HTTPS
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EXAMPLE

62       CURL *curl = curl_easy_init();
63       if(curl) {
64         curl_easy_setopt(curl, CURLOPT_ALTSVC_CTRL, (long)CURLALTSVC_H1);
65         curl_easy_setopt(curl, CURLOPT_ALTSVC, "altsvc-cache.txt");
66         curl_easy_perform(curl);
67       }
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AVAILABILITY

70       Added in 7.64.1
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RETURN VALUE

73       Returns  CURLE_OK  if the option is supported, and CURLE_UNKNOWN_OPTION
74       if not.
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