RFR: 8354276: Strict HTTP header validation

[Daniel Fuchs]

On Thu, 10 Apr 2025 11:37:23 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.

> @dfuch has indicated that a [compatibility and specification](https://wiki.openjdk.org/display/csr/Main) (CSR) request is needed for this pull request.

There will be an observable change of behaviour for clients if for instance, a response contains a `connection: close` header added by custom code on the server side.

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PR Comment: https://git.openjdk.org/jdk/pull/24569#issuecomment-2792717783