HttpDate

reads and writes HTTP-date values (RFC 9110 §5.6.7), the timestamp form used by Date, Expires, Last-Modified, If-Modified-Since and the Expires attribute of a Set-Cookie header.

format

defn

(Fn [(Ref Datetime a)] String) 

                        (format dt)

renders dt as an IMF-fixdate, e.g. Sun, 06 Nov 1994 08:49:37 GMT. It is the only format RFC 9110 §5.6.7 permits a sender to generate.

dt is converted to UTC first, so a Datetime carrying a local timezone names the same instant once labelled GMT.

parse

defn

(Fn [(Ref String a)] (Result Datetime String)) 

                        (parse s)

parses an HTTP-date, returning the Datetime it names in UTC.

All three formats RFC 9110 §5.6.7 obliges a recipient to accept are recognized — IMF-fixdate (Sun, 06 Nov 1994 08:49:37 GMT), rfc850-date (Sunday, 06-Nov-94 08:49:37 GMT) and asctime-date (Sun Nov 6 08:49:37 1994) — as are two dashed cookie-date forms RFC 6265 §5.1.1 accepts, both spelling the day name in its abbreviated form: with a four-digit year (Thu, 01-Jan-1970 00:00:01 GMT) and with a two-digit one (Sun, 06-Nov-94 08:49:37 GMT).

A two-digit year is windowed as 69–99 → 1969–1999 and 00–68 → 2000–2068.