Bug 307952 – DecompressionStream should output valid data before throwing for extra trailing bytes

• Status: RESOLVED
• Resolution: FIXED
• Component: WebKit Misc.

[Brandon]

Per the Compression Streams spec, when decompressing data with extra trailing bytes
after the end of the compressed stream, the decompressor must:
1. Enqueue the valid decompressed output first
2. Then throw a TypeError

Previously, WebKit threw immediately upon detecting extra bytes, discarding the
valid output. This change defers the error by:

- Adding a throwIfExtraBytes() method to DecompressionStreamDecoder that throws
  if extra bytes were detected during the previous decode() call
- Modifying the JS transform algorithm to call throwIfExtraBytes() after
  enqueuing the decoded output
- Separating "extra bytes" detection (Z_STREAM_END with remaining input) from
  "incomplete input" detection (Z_BUF_ERROR during flush) in the zlib path,
  since incomplete input should still throw immediately

[Radar WebKit Bug Importer]

<rdar://problem/170439927>

[Brandon]

Pull request: https://github.com/WebKit/WebKit/pull/58763

[Brandon]

See spec update here: https://github.com/whatwg/compression/pull/77

[EWS]

Committed 307650@main (61a06dede8c6): <https://commits.webkit.org/307650@main>

Reviewed commits have been landed. Closing PR #58763 and removing active labels.

[Brandon]

Re-opening for pull request https://github.com/apple/WebKit/pull/4621

[EWS]

Committed 305413.416@safari-7624-branch (8b3a915b1f5f): <https://commits.webkit.org/305413.416@safari-7624-branch>

Reviewed commits have been landed. Closing PR #4621 and removing active labels.