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 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.

DEFAULT

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

PROTOCOLS

HTTPS

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 7.64.1

RETURN VALUE

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