RFR: 8286171: HttpClient/2 : Expect:100-Continue blocks indefinitely when response is not 100 [v2]

[Daniel Fuchs]

On Thu, 9 Jun 2022 10:31:31 GMT, Conor Cleary <ccleary at openjdk.org> wrote:

>> **Issue**
>> It was observed that when the httpclient sends a POST request with the `Expect: 100 Continue` header set and the server replies with a response code `417 Expectation Failed` that the httpclient hangs indefinitely when the version of Http used is HTTP/2. However, it was also seen that the issue persisted with HTTP/1_1 with the same usage.
>> 
>> This was caused by an implementation in ExchangeImpl that resulted in two calls to readBodyAsync() in this case, where the second call causes the indefinite hanging (as if there was a respomse body, it has already been read).
>> 
>> **Solution**
>> When ExchangeImpl::expectContinue() detects that a response code 417 is received, two things occur. Firstly, a flag is set which ensures that the connection is closed locally in this case. Secondly, the response is returned to the client as a failed future, A unit test was added to ensure that this usage of the httpclient does not cause hanging.
>
> Conor Cleary has updated the pull request incrementally with one additional commit since the last revision:
> 
>   8286171: Added teardown method and comments

test/jdk/java/net/httpclient/ExpectContinueTest.java line 286:

> 284:         resp = cf.join();
> 285:         System.err.println("Response Headers: " + resp.headers());
> 286:         System.err.println("Response Status Code: " + resp.statusCode());

Would be good to add some `assertEquals` here to verify that the status codes we get are those that we expect. Thanks!

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PR: https://git.openjdk.java.net/jdk/pull/9093