RFR: 8322256: Define and document GZIPInputStream concatenated stream semantics [v10]

[Eirik Bjørsnøs]

On Wed, 28 Aug 2024 21:56:50 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:
> 
>   Shorten the description of concatenation behavior per review comments.

The parameter source methods in both tests could benefit from using the `Arguments` class in JUnit, see comments for details.

test/jdk/java/util/zip/GZIP/GZIPInputStreamConcat.java line 44:

> 42:     private int bufsize;
> 43: 
> 44:     public static Stream<Object[]> testScenarios() throws IOException {

I think the best practice for JUnit 5 when providing more than one argument is to return a `Stream<Arguments>`. (IntelliJ IDEA also suggests this in a code inspection)

So, something like:


    public static Stream<Arguments> testScenarios() throws IOException {
        // Test concat vs. non-concat, garbage vs. no-garbage, and various buffer sizes on random data
        Random random = new Random();
        List<Arguments> scenarios = new ArrayList<>();
        for (int bufsize = 1; bufsize < 1024; bufsize += random.nextInt(32) + 1) {
            scenarios.add(Arguments.of(randomData(0, 100), bufsize));
        }
        return scenarios.stream();
    }

test/jdk/java/util/zip/GZIP/GZIPInputStreamGzipCommand.java line 44:

> 42: 
> 43:     public static Stream<String[]> gzipScenarios() throws IOException {
> 44:         final ArrayList<String[]> scenarios = new ArrayList();

Similar to the comment for the other test, this could be:


return Stream.of(Arguments.of(expected, hex),  Arguments.of(expected, hex), ...);

test/jdk/java/util/zip/GZIP/GZIPInputStreamGzipCommand.java line 122:

> 120: 
> 121:         // Get expected result
> 122:         final byte[] expected = input.getBytes(StandardCharsets.UTF_8);

IMHO the use of `final` for local variables in this method adds visual clutter without providing much value.

-------------

PR Review: https://git.openjdk.org/jdk/pull/18385#pullrequestreview-2269041615
PR Review Comment: https://git.openjdk.org/jdk/pull/18385#discussion_r1736385638
PR Review Comment: https://git.openjdk.org/jdk/pull/18385#discussion_r1736394966
PR Review Comment: https://git.openjdk.org/jdk/pull/18385#discussion_r1736428169