What date formats does the HTTP protocol support?

The latest HTTP protocol version 1.1 is the most common version currently in use, and the standard text in RFC 2068 clarifies many things in the original HTTP 1.0 specification. I was today looking into the standard text as I needed to investigate how date/time formats are handled.

The current version supports three separate date formats to remain compatible with HTTP/1.0. The RFC document uses these examples:

Sun, 06 Nov 1994 08:49:37 GMT

Sunday, 06-Nov-94 08:49:37 GMT

Sun Nov  6 08:49:37 1994

The first one is the one suggested for use (RFC 822), but the two later format (last is from the ANSI C language) are supported too. Note that the two first formats use a time zone indicator. This must always be "GMT" for Greenwich Mean Time.

From programming perspective, pick the first format and stick to it. If you are not using a framework to write the HTTP headers, create a function that converts a date/time value in your programming language to a correctly formatted string. Then, you can also test this date generation work independent of the HTTP logic.

Hope this helps!