1# Alt-Svc 2 3curl features support for the Alt-Svc: HTTP header. 4 5## Enable Alt-Svc in build 6 7`./configure --enable-alt-svc` 8 9(enabled by default since 7.73.0) 10 11## Standard 12 13[RFC 7838](https://datatracker.ietf.org/doc/html/rfc7838) 14 15# Alt-Svc cache file format 16 17This is a text based file with one line per entry and each line consists of nine 18space separated fields. 19 20## Example 21 22 h2 quic.tech 8443 h3-22 quic.tech 8443 "20190808 06:18:37" 0 0 23 24## Fields 25 261. The ALPN id for the source origin 272. The hostname for the source origin 283. The port number for the source origin 294. The ALPN id for the destination host 305. The hostname for the destination host 316. The host number for the destination host 327. The expiration date and time of this entry within double quotes. The date format is "YYYYMMDD HH:MM:SS" and the time zone is GMT. 338. Boolean (1 or 0) if "persist" was set for this entry 349. Integer priority value (not currently used) 35 36If the hostname is an IPv6 numerical address, it is stored with brackets such 37as `[::1]`. 38 39# TODO 40 41- handle multiple response headers, when one of them says `clear` (should 42 override them all) 43- using `Age:` value for caching age as per spec 44- `CURLALTSVC_IMMEDIATELY` support 45