ServeDir lacks the `Last-Modified` response header

[photino]

Bug Report

Version

0.4.4

Platform

64-bit (Windows)

Crates

Description

The ServeDir lacks the Last-Modified response header even when it returns a 304 response.

[nathaniel-daniel]

To my understanding, it isn't strictly required to send a Last-Modified header for 304 responses: https://datatracker.ietf.org/doc/html/rfc9110#section-15.4.5

[photino]

It is also OK to return an ETag header. Without either Last-Modified or ETag, it is difficult for us to ensure that the content is unchanged.

[nathaniel-daniel]

It is also OK to return an ETag header. Without either Last-Modified or ETag, it is difficult for us to ensure that the content is unchanged.

Well, you would know it's unchanged because of the 304 response. An ETag header seems necessary for 304s, but a Last-Modified isn't. Also note that ServeDir doesn't use ETags at all. It is also explicitly stated that a Last-Modified header may be useful for responses without an ETag, but it isn't required.

I was just trying to note that the current behavior isn't technically wrong, but it might still be worthwhile to send a Last-Modified header for 304 responses.