RFR: 8286171: HttpClient/2 : Expect:100-Continue blocks indefinitely when response is not 100 [v3]

[Jaikiran Pai]

On Thu, 9 Jun 2022 11:27:47 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 two additional commits since the last revision:
> 
>  - 8286171: Package-protected access for method
>  - 8286171: Added checks for correct response codes

test/jdk/java/net/httpclient/ExpectContinueTest.java line 102:

> 100:         // Due to limitations of the above Http1 Server, a manual approach is taken to test the hanging with the
> 101:         // httpclient using Http1 so that the correct response header can be returned for the test case
> 102:         http1HangServer = new Http1HangServer(saHang);

It took me a while to understand why we have special server implementation for this. The comment helped :) It reminded me about the `ServerImpl` used by the `HttpServer`, which unconditionally sends a `100` response code when it sees a `Expect: 100-continue` in the request header.

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