RFC 1123 Formatter does not pad zero as required by spec

[mikedawson]

RFC 1123 date format requires two digits for the day of the month as I understand from https://datatracker.ietf.org/doc/html/rfc822#section-5.1 . DateTimeComponents.Formats.RFC_1123 is not padding the day for days 1-9.

e.g.

val instant01Aug2025 = Instant.fromEpochSeconds(1754069088).format(DateTimeComponents.Formats.RFC_1123)        

Expected : Fri, 01 Aug 2025 17:24:48 GMT
Actual: Fri, 1 Aug 2025 17:24:48 GMT

I have a test for an http function that uses ktor server's ConditionalHeaders (to validate my component handles HTTP 304 correctly) . All of a sudden it started failing today (1/Aug), even though no code or versions had been changed. It seems to be failing because of the RFC_1123 formatter.

[DmitryNekrasov]

Hello @mikedawson!

According to RFC 822, as you indicated above, the following grammar is used for date:

date =  1*2DIGIT month 2DIGIT

RFC 1123 update (5.2.14):

5.2.14  RFC-822 Date and Time Specification: RFC-822 Section 5

The syntax for the date is hereby changed to:

date = 1*2DIGIT month 2*4DIGIT

According to the specification:

The character "*" preceding an element indicates repetition.
The full form is:

                         <l>*<m>element
                         
indicating at least <l> and at most <m> occurrences  of  element.
Default values are 0 and infinity so that "*(element)" allows any
number, including zero; "1*element" requires at  least  one;  and
"1*2element" allows one or two.

So both options, with one digit and with two, are considered acceptable.

[DmitryNekrasov]

@mikedawson Could you please provide a minimal reproducer of how ktor interacts with DateTimeComponents.Formats.RFC_1123 in your scenario? There may be a problem with ktor.