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.TH CURLOPT_ALTSVC 3 "January 02, 2023" "libcurl 7.88.1" "curl_easy_setopt options"

.SH NAME
CURLOPT_ALTSVC \- alt-svc cache file name
.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 a after a transfer, unless \fBCURLALTSVC_READONLYFILE\fP is set in
\fICURLOPT_ALTSVC_CTRL(3)\fP.

Specify a blank file name ("") 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
HTTPS
.SH EXAMPLE
.nf
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

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

The fields of that line are:

.IP h2
ALPN id for the source origin
.IP www.example
Host name for the source origin
.IP 8443
Port number for the source origin
.IP h3
ALPN id for the destination host
.IP second.example
Host name 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 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), " CURLOPT_CONNECT_TO "(3), " CURLOPT_RESOLVE "(3), "
.BR CURLOPT_COOKIEFILE "(3), "