RFR: 8347597: HttpClient: improve exception reporting when closing connection

[Jaikiran Pai]

On Mon, 13 Jan 2025 16:07:45 GMT, Daniel Fuchs <dfuchs at openjdk.org> wrote:

> There are a few places in the HttpClient code base where we close the connection when some error/exception happens. This can some time trigger a race condition where closing the connection in turns causes a "connection closed locally" exception to get reported instead of the original exception. This typically happens if another thread is attempting to read from / write to the connection concurrently when the original exception that caused the connection to get closed occurred. 
> 
> The fix makes sure that we store the first exception in the underlying connection before closing it, and that this is the exception that gets subsequently reported.
> 
> Some minor drive by test fixes. No new regression test.

src/java.net.http/share/classes/jdk/internal/net/http/Http1Response.java line 334:

> 332:                 if (cf.isCompletedExceptionally()) {
> 333:                     // if an error occurs during subscription
> 334:                     connection.close(cf.exceptionNow());

`Future.exceptionNow()` (among other things) states that it will throw a `IllegalStateException` if the Future was cancelled. We do have a check for `cf.isCompletedExceptionally()` before invoking this method. However, the `CompletableFuture.isCompletedExceptionally()` states that it returns `true` even in the case of cancellation:

> Returns {@code true} if this CompletableFuture completed exceptionally, in any way. Possible causes include cancellation ...

So I suspect this call to `exceptionNow()` might need a rethink or some additional checks?

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PR Review Comment: https://git.openjdk.org/jdk/pull/23080#discussion_r1914539627