Upgrade zlib to upstream (#971)

Mostly cosmetic changes.

Update README.md

tests: Rename fuzz helpers back. (#931)

s2: Fix DecodeConcurrent deadlock on errors (#925)

When DecodeConcurrent encounters an error it can lock up in some cases.

Fix and add fuzz test for stream decoding.

Fixes #920

s2: Document and test how to peek the stream for skippable blocks (#918)

Co-authored-by: Klaus Post <[email protected]>

gzhttp: Allow overriding decompression on transport (#892)

This allows getting compressed data even if `Content-Encoding` is set.

Also allows decompression even if "Accept-Encoding" was not set by this client.

gzhttp: Fix missing content type on Close (#883)

If compression had not yet been triggered in Write, be sure to detect content type on Close.

Fixes #882

zstd: Fix corrupted output in "best" (#876)

* zstd: Fix corrupted output in "best"

Regression from #784 and followup #793

Fixes #875

A 0 offset backreference was possible when "improve" was successful twice in a row in the "skipBeginning" part, only finding 2 (previously unmatches) length 4 matches, but where start offset decreased by 2 in both cases.

This would result in output where the end offset would equal to the next 's', thereby doing a self-reference.

Add a general check in "improve" and just reject these. Will also guard against similar issues in the future.

This also hints at some potentially suboptimal hash indexing - but I will take that improvement separately.

Fuzz test set updated.

s2: Fix S2 best dictionary wrong encoding (#871)

A dictionary match one byte out of dictionary range was possible.

Recovery is possible. Send me a request if you find any content with this error in the [discussion](https://github.com/klauspost/compress/discussions/categories/general).

gzip: Copy bufio.Reader on Reset (#860)

The code already checks to see if the buffer can be reused, but since
it's not copied in the overwrite, a new buffer is allocated each time.