compress

This package provides various compression algorithms.

• zstandard compression and decompression in pure Go.
• S2 is a high performance replacement for Snappy.
• Optimized deflate packages which can be used as a dropin replacement for gzip, zip and zlib.
• snappy is a drop-in replacement for github.com/golang/snappy offering better compression and concurrent streams.
• huff0 and FSE implementations for raw entropy encoding.
• gzhttp Provides client and server wrappers for handling gzipped/zstd HTTP requests efficiently.
• pgzip is a separate package that provides a very fast parallel gzip implementation.

package usage

Use go get github.com/klauspost/compress@latest to add it to your project.

This package will support the current Go version and 2 versions back.

• Use the nounsafe tag to disable all use of the "unsafe" package.
• Use the noasm tag to disable all assembly across packages.

Use the links above for more information on each.

changelog

• Feb 9th, 2026 1.18.4

  • gzhttp: Add zstandard to server handler wrapper https://github.com/klauspost/compress/pull/1121
  • zstd: Add ResetWithOptions to encoder/decoder https://github.com/klauspost/compress/pull/1122
  • gzhttp: preserve qvalue when extra parameters follow in Accept-Encoding by @analytically in https://github.com/klauspost/compress/pull/1116

• Jan 16th, 2026 1.18.3

  • Downstream CVE-2025-61728. See golang/go#77102.

• Dec 1st, 2025 - 1.18.2

  • flate: Fix invalid encoding on level 9 with single value input in https://github.com/klauspost/compress/pull/1115
  • flate: reduce stateless allocations by @RXamzin in https://github.com/klauspost/compress/pull/1106

• Oct 20, 2025 - 1.18.1 - RETRACTED

• zstd: Add simple zstd EncodeTo/DecodeTo functions https://github.com/klauspost/compress/pull/1079
• zstd: Fix incorrect buffer size in dictionary encodes https://github.com/klauspost/compress/pull/1059
• s2: check for cap, not len of buffer in EncodeBetter/Best by @vdarulis in https://github.com/klauspost/compress/pull/1080
• zlib: Avoiding extra allocation in zlib.reader.Reset by @travelpolicy in https://github.com/klauspost/compress/pull/1086
• gzhttp: remove redundant err check in zstdReader by @ryanfowler in https://github.com/klauspost/compress/pull/1090
• flate: Faster load+store https://github.com/klauspost/compress/pull/1104
• flate: Simplify matchlen https://github.com/klauspost/compress/pull/1101

• flate: Use exact sizes for huffman tables https://github.com/klauspost/compress/pull/1103

• Feb 19th, 2025 - 1.18.0

• Add unsafe little endian loaders https://github.com/klauspost/compress/pull/1036
• fix: check r.err != nil but return a nil value error err by @alingse in https://github.com/klauspost/compress/pull/1028
• flate: Simplify L4-6 loading https://github.com/klauspost/compress/pull/1043
• flate: Simplify matchlen (remove asm) https://github.com/klauspost/compress/pull/1045
• s2: Improve small block compression speed w/o asm https://github.com/klauspost/compress/pull/1048
• flate: Fix matchlen L5+L6 https://github.com/klauspost/compress/pull/1049
• flate: Cleanup & reduce casts https://github.com/klauspost/compress/pull/1050

See changes to v1.17.x

• Oct 11th, 2024 - 1.17.11
• zstd: Fix extra CRC written with multiple Close calls https://github.com/klauspost/compress/pull/1017
• s2: Don't use stack for index tables https://github.com/klauspost/compress/pull/1014
• gzhttp: No content-type on no body response code by @juliens in https://github.com/klauspost/compress/pull/1011

• gzhttp: Do not set the content-type when response has no body by @kevinpollet in https://github.com/klauspost/compress/pull/1013

• Sep 23rd, 2024 - 1.17.10

  • gzhttp: Add TransportAlwaysDecompress option. https://github.com/klauspost/compress/pull/978
  • gzhttp: Add supported decompress request body by @mirecl in https://github.com/klauspost/compress/pull/1002
  • s2: Add EncodeBuffer buffer recycling callback https://github.com/klauspost/compress/pull/982
  • zstd: Improve memory usage on small streaming encodes https://github.com/klauspost/compress/pull/1007
  • flate: read data written with partial flush by @vajexal in https://github.com/klauspost/compress/pull/996

• Jun 12th, 2024 - 1.17.9

  • s2: Reduce ReadFrom temporary allocations https://github.com/klauspost/compress/pull/949
  • flate, zstd: Shave some bytes off amd64 matchLen by @greatroar in https://github.com/klauspost/compress/pull/963
  • Upgrade zip/zlib to 1.22.4 upstream https://github.com/klauspost/compress/pull/970 https://github.com/klauspost/compress/pull/971
  • zstd: BuildDict fails with RLE table https://github.com/klauspost/compress/pull/951

• Apr 9th, 2024 - 1.17.8

  • zstd: Reject blocks where reserved values are not 0 https://github.com/klauspost/compress/pull/885
  • zstd: Add RLE detection+encoding https://github.com/klauspost/compress/pull/938

• Feb 21st, 2024 - 1.17.7

  • s2: Add AsyncFlush method: Complete the block without flushing by @Jille in https://github.com/klauspost/compress/pull/927
  • s2: Fix literal+repeat exceeds dst crash https://github.com/klauspost/compress/pull/930

• Feb 5th, 2024 - 1.17.6

  • zstd: Fix incorrect repeat coding in best mode https://github.com/klauspost/compress/pull/923
  • s2: Fix DecodeConcurrent deadlock on errors https://github.com/klauspost/compress/pull/925

• Jan 26th, 2024 - v1.17.5

  • flate: Fix reset with dictionary on custom window encodes https://github.com/klauspost/compress/pull/912
  • zstd: Add Frame header encoding and stripping https://github.com/klauspost/compress/pull/908
  • zstd: Limit better/best default window to 8MB https://github.com/klauspost/compress/pull/913
  • zstd: Speed improvements by @greatroar in https://github.com/klauspost/compress/pull/896 https://github.com/klauspost/compress/pull/910
  • s2: Fix callbacks for skippable blocks and disallow 0xfe (Padding) by @Jille in https://github.com/klauspost/compress/pull/916 https://github.com/klauspost/compress/pull/917 https://github.com/klauspost/compress/pull/919 https://github.com/klauspost/compress/pull/918

• Dec 1st, 2023 - v1.17.4

  • huff0: Speed up symbol counting by @greatroar in https://github.com/klauspost/compress/pull/887
  • huff0: Remove byteReader by @greatroar in https://github.com/klauspost/compress/pull/886
  • gzhttp: Allow overriding decompression on transport https://github.com/klauspost/compress/pull/892
  • gzhttp: Clamp compression level https://github.com/klauspost/compress/pull/890
  • gzip: Error out if reserved bits are set https://github.com/klauspost/compress/pull/891

• Nov 15th, 2023 - v1.17.3

  • fse: Fix max header size https://github.com/klauspost/compress/pull/881
  • zstd: Improve better/best compression https://github.com/klauspost/compress/pull/877
  • gzhttp: Fix missing content type on Close https://github.com/klauspost/compress/pull/883

• Oct 22nd, 2023 - v1.17.2

  • zstd: Fix rare CORRUPTION output in "best" mode. See https://github.com/klauspost/compress/pull/876

• Oct 14th, 2023 - v1.17.1

  • s2: Fix S2 "best" dictionary wrong encoding https://github.com/klauspost/compress/pull/871
  • flate: Reduce allocations in decompressor and minor code improvements by @fakefloordiv in https://github.com/klauspost/compress/pull/869
  • s2: Fix EstimateBlockSize on 6&7 length input https://github.com/klauspost/compress/pull/867

• Sept 19th, 2023 - v1.17.0

  • Add experimental dictionary builder https://github.com/klauspost/compress/pull/853
  • Add xerial snappy read/writer https://github.com/klauspost/compress/pull/838
  • flate: Add limited window compression https://github.com/klauspost/compress/pull/843
  • s2: Do 2 overlapping match checks https://github.com/klauspost/compress/pull/839
  • flate: Add amd64 assembly matchlen https://github.com/klauspost/compress/pull/837
  • gzip: Copy bufio.Reader on Reset by @thatguystone in https://github.com/klauspost/compress/pull/860

See changes to v1.16.x

• July 1st, 2023 - v1.16.7

  • zstd: Fix default level first dictionary encode https://github.com/klauspost/compress/pull/829
  • s2: add GetBufferCapacity() method by @GiedriusS in https://github.com/klauspost/compress/pull/832

• June 13, 2023 - v1.16.6

  • zstd: correctly ignore WithEncoderPadding(1) by @ianlancetaylor in https://github.com/klauspost/compress/pull/806
  • zstd: Add amd64 match length assembly https://github.com/klauspost/compress/pull/824
  • gzhttp: Handle informational headers by @rtribotte in https://github.com/klauspost/compress/pull/815
  • s2: Improve Better compression slightly https://github.com/klauspost/compress/pull/663

• Apr 16, 2023 - v1.16.5

  • zstd: readByte needs to use io.ReadFull by @jnoxon in https://github.com/klauspost/compress/pull/802
  • gzip: Fix WriterTo after initial read https://github.com/klauspost/compress/pull/804

• Apr 5, 2023 - v1.16.4

  • zstd: Improve zstd best efficiency by @greatroar and @klauspost in https://github.com/klauspost/compress/pull/784
  • zstd: Respect WithAllLitEntropyCompression https://github.com/klauspost/compress/pull/792
  • zstd: Fix amd64 not always detecting corrupt data https://github.com/klauspost/compress/pull/785
  • zstd: Various minor improvements by @greatroar in https://github.com/klauspost/compress/pull/788 https://github.com/klauspost/compress/pull/794 https://github.com/klauspost/compress/pull/795
  • s2: Fix huge block overflow https://github.com/klauspost/compress/pull/779
  • s2: Allow CustomEncoder fallback https://github.com/klauspost/compress/pull/780
  • gzhttp: Support ResponseWriter Unwrap() in gzhttp handler by @jgimenez in https://github.com/klauspost/compress/pull/799

• Mar 13, 2023 - v1.16.1

  • zstd: Speed up + improve best encoder by @greatroar in https://github.com/klauspost/compress/pull/776
  • gzhttp: Add optional BREACH mitigation. https://github.com/klauspost/compress/pull/762 https://github.com/klauspost/compress/pull/768 https://github.com/klauspost/compress/pull/769 https://github.com/klauspost/compress/pull/770 https://github.com/klauspost/compress/pull/767
  • s2: Add Intel LZ4s converter https://github.com/klauspost/compress/pull/766
  • zstd: Minor bug fixes https://github.com/klauspost/compress/pull/771 https://github.com/klauspost/compress/pull/772 https://github.com/klauspost/compress/pull/773
  • huff0: Speed up compress1xDo by @greatroar in https://github.com/klauspost/compress/pull/774

• Feb 26, 2023 - v1.16.0

  • s2: Add Dictionary support. https://github.com/klauspost/compress/pull/685
  • s2: Add Compression Size Estimate. https://github.com/klauspost/compress/pull/752
  • s2: Add support for custom stream encoder. https://github.com/klauspost/compress/pull/755
  • s2: Add LZ4 block converter. https://github.com/klauspost/compress/pull/748
  • s2: Support io.ReaderAt in ReadSeeker. https://github.com/klauspost/compress/pull/747
  • s2c/s2sx: Use concurrent decoding. https://github.com/klauspost/compress/pull/746

See changes to v1.15.x

• Jan 21st, 2023 (v1.15.15)
  • deflate: Improve level 7-9 https://github.com/klauspost/compress/pull/739
  • zstd: Add delta encoding support by @greatroar in https://github.com/klauspost/compress/pull/728
  • zstd: Various speed