On Sun, 11 Aug 2024 18:58:05 GMT, Archie Cobbs <aco...@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 ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/18385#discussion_r1735080776
