ETAG-IN-304


Test ID	`CAP-ETAG-IN-304`
Category	Capabilities
Type	Sequence (2 steps)
Scored	No
RFC	RFC 9110 §15.4.5
RFC Level	SHOULD
Expected	`304` with ETag

What it does

This is a sequence test — it verifies that a 304 Not Modified response includes the ETag header, allowing clients to update their cached validators.

Step 1: Initial GET (capture ETag)

GET / HTTP/1.1\r\n
Host: localhost:8080\r\n
Connection: keep-alive\r\n
\r\n

Captures the ETag header from the response.

Step 2: Conditional GET (If-None-Match)

GET / HTTP/1.1\r\n
Host: localhost:8080\r\n
If-None-Match: {ETag from step 1}\r\n
\r\n

Replays the ETag value captured from step 1. If the server returns 304, this test checks whether the ETag header is present in that response.

What the RFC says

"A server generating a 304 response MUST generate any of the following header fields that would have been sent in a 200 (OK) response to the same request: ... ETag" — RFC 9110 §15.4.5

Why it matters

Including the ETag in a 304 response lets clients confirm which representation they have cached and update their stored validator. Without it, clients may lose track of the ETag and fall back to unconditional requests.

Verdicts

Pass — Step 2 returns 304 with an ETag header
Warn — Server does not support ETags, or returns 304 without an ETag header
Fail — Unexpected error (non-2xx/304 response)