[GitHub] [commons-compress] quat1024 commented on pull request #360: pack200: Fix FileBands misusing InputStream#read(byte[])

["quat1024 (via GitHub)" <gi...@apache.org>]

quat1024 commented on PR #360:
URL: https://github.com/apache/commons-compress/pull/360#issuecomment-1429003923

   A little bit more code digging, just for fun:
   
   * If the provided `InputStream` does not support marking, [`unpack200.Segment` will wrap it in a `BufferedInputStream`](https://github.com/apache/commons-compress/blob/e6930d06cfebbdbee586b863481779b2c4b9b202/src/main/java/org/apache/commons/compress/harmony/unpack200/Segment.java#L499-L502), which does.
   * `BufferedInputStream`, "as a convenience", repeatedly calls `read` until it fills as many bytes of the user-provided input array as possible, using a driver loop not unlike the one in this PR. However, if the wrapped stream's `available` method returns `0` (signaling that further `read` calls will block), `BufferedInputStream` will stop early before filling the entire array (because it doesn't want to block).
   * `LZMACompressorInputStream` [delegates the `available` method](https://github.com/apache/commons-compress/blob/e6930d06cfebbdbee586b863481779b2c4b9b202/src/main/java/org/apache/commons/compress/compressors/lzma/LZMACompressorInputStream.java#L102-L106) through to `xz`'s `LZMAInputStream`.
   * [`LZMAInputStream` doesn't override `available`](https://git.tukaani.org/?p=xz-java.git;a=blob;f=src/org/tukaani/xz/LZMAInputStream.java;h=1432eb1037a513dcd997fb0a946cc978032565aa;hb=HEAD), so the default implementation is used.
   * The default implementation always returns 0,
   * -> causing `BufferedInputStream` to be okay with returning a half-filled buffer,
   * -> triggering the correctness error in the code that assumes `read(byte[])` fills the whole byte array,
   * -> breaking the file parse.
   
   A cheeky workaround is to wrap the stream provided to `Pack200CompressorInputStream` in one that returns `false` in `markSupported` and `Integer.MAX_VALUE` in `available`, this makes `BufferedInputStream` do your work for you.


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