RFR: 8371903: HttpClient: improve handling of HTTP/2 GOAWAY frames with error code [v7]

[EunHyunsu]

On Sat, 13 Dec 2025 05:12:33 GMT, Christoph Läubrich <duke at openjdk.org> wrote:

>> EunHyunsu has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   8371903: Use Utils.adjustTimeout() in GoAwayWithErrorTest
>
> test/jdk/java/net/httpclient/http2/GoAwayWithErrorTest.java line 162:
> 
>> 160:                         && goawayError.getMessage().contains("0x1")
>> 161:                         && goawayError.getMessage().contains(DEBUG_MESSAGE),
>> 162:                 "Failed request should contain GOAWAY error details: " + goawayError.getMessage());
> 
> I think this test assertion alone already shows that a client has only the chance to use String parsing what I think is bad (both for test and for production code).
> 
> If its not planned to have an own public type, can it at least be an internal exception type that can be used in the test?
> Maybe a Http2ProtocolError?

@laeubi I appreciate your suggestion about semantic error handling. I looked into how HTTP/3 handles similar cases for consistency.

HTTP/3 tests also use string parsing to verify error messages. For example, in `test/jdk/java/net/httpclient/http3/H3ErrorHandlingTest.java:954-955`:


assertTrue(cause.getMessage().contains(reason),
        cause.getMessage() + " does not contain " + reason);

This pattern is used throughout HTTP/3 tests (e.g., verifying "INTERNAL_ERROR", "CRYPTO_ERROR", "H3_EXCESSIVE_LOAD" in error messages).

As @djelinski mentioned, this PR brings HTTP/2 error handling to parity with HTTP/3's current approach. I agree that a specialized exception type would be valuable, but it would ideally be done consistently across both HTTP/2 and HTTP/3 as a future enhancement.

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PR Review Comment: https://git.openjdk.org/jdk/pull/28632#discussion_r2616948240