RFR: 8354276: Strict HTTP header validation [v7]

[Daniel Fuchs]

On Wed, 30 Apr 2025 09:30:05 GMT, Daniel Jeliński <djelinski at openjdk.org> wrote:

>> RFC 9113 HTTP/2 mandates certain validation for HTTP headers; the HttpClient don't fully implement the described requirements.
>> 
>> This PR adds the following validation:
>> - pseudo-headers defined for requests are rejected in responses and push streams
>> - pseudo-headers defined for responses are rejected in push promises
>> - connection headers are rejected in responses and push streams
>> 
>> Connection headers are still accepted in push promises; that's because some popular server implementations were found to echo the request headers in push promises, and when the original request was a HTTP/1 upgrade, the push promise could contain one or more headers that were prohibited in HTTP/2 but allowed in HTTP/1.
>> 
>> An existing test was adapted to verify the handling of response headers. The modified test passes with this the changes in this PR, fails without them. Other tier1-3 tests continue to pass.
>
> Daniel Jeliński has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Remove localhost usage

Marked as reviewed by dfuchs (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/24569#pullrequestreview-2806574506