RFR: 7036144: GZIPInputStream readTrailer uses faulty available() test for end-of-stream [v6]

[Jaikiran Pai]

On Mon, 5 Feb 2024 23:53:06 GMT, Archie Cobbs <acobbs at openjdk.org> wrote:

>> `GZIPInputStream`, when looking for a concatenated stream, relies on what the underlying `InputStream` says is how many bytes are `available()`. But this is inappropriate because `InputStream.available()` is just an estimate and is allowed (for example) to always return zero.
>> 
>> The fix is to ignore what's `available()` and just proceed and see what happens. If fewer bytes are available than required, the attempt to extend to another stream is canceled just as it was before, e.g., when the next stream header couldn't be read.
>
> Archie Cobbs has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains six additional commits since the last revision:
> 
>  - Merge branch 'master' into JDK-7036144
>  - Merge branch 'master' into JDK-7036144
>  - Address third round of review comments.
>  - Address second round of review comments.
>  - Address review comments.
>  - Fix bug in GZIPInputStream when underlying available() returns short.

Hello Archie,

> Edited to add: I said "already a problem in the current code" but should clarify: what I mean is, suppose some clever InputStream were never letting available() return more than the number of compressed bytes remaining. That strategy would not be reliable, because not all reads from the underlying stream are gated with a check of what's available() (for example, see InflaterInputStream.fill()). So I don't think we need to worry about breaking such a case because it's already broken for other reasons.

I think what you note is reasonable and accurate. I'll run some experiments against existing corpus of artifacts to see if this proposed change could cause  more issues than the current state of GZIPInputStream.

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PR Comment: https://git.openjdk.org/jdk/pull/17113#issuecomment-1968364298