CURLOPT_ALTSVC(3)

NAME
CURLOPT_ALTSVC - alt-svc cache file name

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 a after a transfer, unless CURLALTSVC_READONLYFILE is set in CURLOPT_ALTSVC_CTRL(3). Specify a blank file name ("") to make libcurl not load from a file at all.

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

PROTOCOLS
HTTPS

EXAMPLE
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 8443 h3 quic.example 443 "20190808 06:18:37" 1 0 The fields of that line are:

h2  ALPN id for the source origin

www.example
    Host name for the source origin

8443
    Port number for the source origin

h3  ALPN id for the destination host

quic.example
    Host name 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 7.64.1

RETURN VALUE
Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.

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