Why does the default cache end with the Thu headline, 01 Dec 1994 16:00:00 GMT? What is the meaning of this date?

Question

When some requests are processed through the WebSphere application server, it determines that the cache ends with the Thu header, 01 Dec 1994 16:00:00 GMT. It seems that this date is presented in many documents as an example of a well-formed date for the expires header, but it also applies to actual answers all over the Internet. Where did this exact date come from (Thu, 01 Dec 1994 16:00:00 GMT)?

This is what happens when you do response.setHeader("Expires",0) , is this the default value?

Answer 1

I don’t think there is any special meaning besides its appearance as an example, the date in RFC 1945 "expires" : Hypertext Transfer Protocol - HTTP / 1.0 of May 1996. At least part of the text was written much earlier, in fact, RFC 1738: Uniform Resource Locators (URLs) are dated December 1994.

At the time of writing this would be a reasonable example. Similarly, an example of the 'date' header in the RFC 'Tue, November 15, 1994 08:12:31 GMT', is common on the Internet. The two values ​​together form a consistent example.

RFC 1945 does not mention a specific default value, however it does indicate

Note. Applications are encouraged to be tolerant of poor or misinformed implementations of the Expires header. A value of zero (0) or an invalid date format shall be considered equivalent to "expire immediately." Although these values ​​are not legal, HTTP / 1.0 always requires a reliable implementation.

Server implementers will read the RFC — they will need to know what to implement — and choose a date with a date and use it.

Answer 2

You can check these 30 seconds to see why this is so. This is mainly copying and pasting values ​​from technical documentation.