The relevant section in the RFC says the following:
> If the field-value is "*", the condition is false if the origin
> server has a current representation for the target resource.
> An origin server that evaluates an If-None-Match condition MUST NOT
> perform the requested method if the condition evaluates to false;
> instead, the origin server MUST respond with either a) the 304 (Not
> Modified) status code if the request method is GET or HEAD or b) the
> 412 (Precondition Failed) status code for all other request methods.
https://httpwg.org/specs/rfc9110.html
Bug: T319382
Change-Id: Ieb3269d61de42242602ec9c46e19c4f2c3b37f6e
This changes handling of the If-Match header so a weak ETag coming from
the client may match a strong ETag generated by the handler.
This is needed because ETags may get "weakened" on the way to the client
by proxies and middleware, e.g. Varnish applying compression, see
<https://varnish-cache.org/docs/6.0/users-guide/compression.html>.
This behavior is technically a violation of RFC 7232 section 3.1, but it
should actually be safe: A client sending a weak ETag is still ok with
getting a strong match, and a handler that generates a strong ETag knows
that it can rely on strong semantics holding, even if the tag sent by
the client is weak.
Bug: T310710
Bug: T238849
Change-Id: I2a604f2f46719a5f74ddac1b1fa58c8a36910240
* Added ConditionalHeaderUtil, a conditional request helper class meant
for composition into Handler. I evaluated the composer package
micheh/psr7-cache for this role but I decided that I prefer DIY
code rather than some rather ugly glue.
* Check conditional request headers prior to entry into
Handler::execute(). Contrary to what was previously documented, use
the results of getLastModified() and getETag() to set headers in the
response. This is convenient and can be overridden in the Handler if
desired by overriding a one-line function.
* Instead of locking up header parsing inside ConditionalHeaderUtil as
was done in micheh/psr7-cache, make a start on a new reusable header
parsing framework, with recursive descent parsers for HTTP-date and
IfNoneMatch.
Change-Id: I260809081cad7701df8620ab03834158670d4230
