NAME

       CURLOPT_ALTSVC - alt-svc cache filename

SYNOPSIS

       #include <curl/curl.h>

       CURLcode curl_easy_setopt(CURL *handle, CURLOPT_ALTSVC, char *filename);

DESCRIPTION

       Pass  in  a  pointer  to  a  filename  to  instruct libcurl to use that file as the Alt-Svc cache to read
       existing  cache  contents  from  and  possibly  also  write  it  back  to  after   a   transfer,   unless
       CURLALTSVC_READONLYFILE is set in CURLOPT_ALTSVC_CTRL(3).

       Specify a blank filename ("") to make libcurl not load from a file at all.

       The application does not have to keep the string around after setting this option.

       Using  this option multiple times makes the last set string override the previous ones. Set it to NULL to
       disable its use again.

SECURITY CONCERNS

       libcurl cannot fully protect against attacks where an attacker has write access  to  the  same  directory
       where  it  is  directed  to  save  files. This is particularly sensitive if you save files using elevated
       privileges.

DEFAULT

       NULL. The alt-svc cache is not read nor written to file.

PROTOCOLS

       This functionality affects http only

EXAMPLE

       int main(void)
       {
         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);
         }
       }

FILE FORMAT

       A text based file with one line per alt-svc entry and each line consists of nine space-separated fields.

       An example line could look like

       h2 www.example.com 8443 h3 second.example.com 443 "20190808 06:18:37" 1 0

       The fields of that line are:

       h2     ALPN id for the source origin

       www.example.comp
              Hostname for the source origin

       8443   Port number for the source origin

       h3     ALPN id for the destination host

       second.example.com
              Hostname for the destination host

       443    Port number for the destination host

       2019*  Expiration date and time of this  entry  within  double  quotes.  The  date  format  is  "YYYYMMDD
              HH:MM:SS" and the time zone is GMT.

       1      Boolean (1 or 0) if "persist" was set for this entry

       0      Integer priority value (not currently used)

AVAILABILITY

       Added in curl 7.64.1

RETURN VALUE

       curl_easy_setopt(3) returns a CURLcode indicating success or error.

       CURLE_OK (0) means everything was OK, non-zero means an error occurred, see libcurl-errors(3).

SEE ALSO

       CURLOPT_ALTSVC_CTRL(3), CURLOPT_CONNECT_TO(3), CURLOPT_COOKIEFILE(3), CURLOPT_RESOLVE(3)

libcurl                                            2025-03-05                                  CURLOPT_ALTSVC(3)