CURLOPT_ALTSVC - Man Page

alt-svc cache filename

Synopsis

#include <curl/curl.h>

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

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.

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)