RFR: 8322256: Define and document GZIPInputStream concatenated stream semantics [v9]

[Lance Andersen]

On Sun, 11 Aug 2024 18:58:05 GMT, Archie Cobbs <acobbs at openjdk.org> wrote:

>> `GZIPInputStream` supports reading data from multiple concatenated GZIP data streams since [JDK-4691425](https://bugs.openjdk.org/browse/JDK-4691425). In order to do this, after a GZIP trailer frame is read, it attempts to read a GZIP header frame and, if successful, proceeds onward to decompress the new stream. If the attempt to decode a GZIP header frame fails, or happens to trigger an `IOException`, it just ignores the trailing garbage and/or the `IOException` and returns EOF.
>> 
>> There are several issues with this:
>> 
>> 1. The behaviors of (a) supporting concatenated streams and (b) ignoring trailing garbage are not documented, much less precisely specified.
>> 2. Ignoring trailing garbage is dubious because it could easily hide errors or other data corruption that an application would rather be notified about. Moreover, the API claims that a `ZipException` will be thrown when corrupt data is read, but obviously that doesn't happen in the trailing garbage scenario (so N concatenated streams where the last one has a corrupted header frame is indistinguishable from N-1 valid streams).
>> 3. There's no way to create a `GZIPInputStream` that does _not_ support stream concatenation.
>> 
>> On the other hand, `GZIPInputStream` is an old class with lots of existing usage, so it's important to preserve the existing behavior, warts and all (note: my the definition of "existing behavior" here includes the bug fix in [JDK-7036144](https://bugs.openjdk.org/browse/JDK-7036144)).
>> 
>> So this patch adds a new constructor that takes two new parameters `allowConcatenation` and `allowTrailingGarbage`. The legacy behavior is enabled by setting both to true; otherwise, they do what they sound like. In particular, when `allowTrailingGarbage` is false, then the underlying input must contain exactly one (if `allowConcatenation` is false) or exactly N (if `allowConcatenation` is true) concatenated GZIP data streams, otherwise an exception is guaranteed.
>
> Archie Cobbs has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Revert all functional changes, leaving only tests & Javadoc.

src/java.base/share/classes/java/util/zip/GZIPInputStream.java line 43:

> 41:  * frame that marks the end of the compressed data. Therefore it's possible for the underlying
> 42:  * input to contain additional data beyond the end of the compressed GZIP data. In particular,
> 43:  * some GZIP compression tools function by partitioning the input, compressing each parttion

I think we need to simplify the above  keeping the focus on that GZIPInputStream supports the reading of concatenated  Gzip streams.  After reading  a streams trailer(though some docs refer to it as a footer, but I think we go with trailer),  if an additional gzip header is found, the stream will be decompressed... etc.. 

If there is additional data/byes after the trailer that does not represent another gzip, header, it will indicate you have reached the end of the input stream

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PR Review Comment: https://git.openjdk.org/jdk/pull/18385#discussion_r1735080776