RFR: 8299015: Ensure that HttpResponse.BodySubscribers.ofFile writes all bytes

[Dawid Weiss]

On Mon, 19 Dec 2022 14:02:41 GMT, Chris Hegarty <chegar at openjdk.org> wrote:

> The implementation of `BodySubscribers.ofFile` does not correctly handle the case of a short gathering write. The write should be retried until all the bytes have been written to the underlying file.
> 
> This is generally not an issue that would occur very frequently, since the `IOV_MAX` is commonly 1024 on Mac/Linux, and 16 on Windows. However, it is clearly a bug, and should be fixed.

LGTM (not a reviewer). Thanks for adding a proper test, @ChrisHegarty .

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PR: https://git.openjdk.org/jdk/pull/11722