.\" generated by cd2nroff 0.1 from CURLOPT_ALTSVC.md
.TH CURLOPT_ALTSVC 3 "2024-07-29" libcurl
.SH NAME
CURLOPT_ALTSVC \- alt\-svc cache filename
.SH SYNOPSIS
.nf
#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_ALTSVC, char *filename);
.fi
.SH DESCRIPTION
Pass in a pointer to a \fIfilename\fP 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 \fBCURLALTSVC_READONLYFILE\fP is set in
\fICURLOPT_ALTSVC_CTRL(3)\fP.

Specify a blank filename ("") to make libcurl not load from a file at all.
.SH DEFAULT
NULL. The alt\-svc cache is not read nor written to file.
.SH PROTOCOLS
This functionality affects http only
.SH EXAMPLE
.nf
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);
  }
}
.fi
.SH 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

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

The fields of that line are:
.IP h2
ALPN id for the source origin
.IP www.example.comp
Hostname for the source origin
.IP 8443
Port number for the source origin
.IP h3
ALPN id for the destination host
.IP second.example.com
Hostname for the destination host
.IP 443
Port number for the destination host
.IP 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.
.IP 1
Boolean (1 or 0) if "persist" was set for this entry
.IP 0
Integer priority value (not currently used)
.SH AVAILABILITY
Added in curl 7.64.1
.SH RETURN VALUE
Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.
.SH SEE ALSO
.BR CURLOPT_ALTSVC_CTRL (3),
.BR CURLOPT_CONNECT_TO (3),
.BR CURLOPT_COOKIEFILE (3),
.BR CURLOPT_RESOLVE (3)