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.
• lzw is a drop-in replacement for compress/lzw with 1.4-4x faster decompression and 1.1-2.7x faster compression, depending on the data.
• huff0 and FSE implementations for raw entropy encoding.
• Xpress decompression of the Microsoft XPRESS (MS-XCA) plain LZ77 and LZ77+Huffman formats (the LZ77+Huffman variant is the one used in WIM images and Windows Compact OS / WOF data).
• 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

• Sep 25th, 2026 1.20.1

  • zstd: Apply reset options to reused frame decoders by @pellared in https://github.com/klauspost/compress/pull/1226
  • flate: Report unexpected EOF for truncated Huffman extra bits by @rupayon123 in https://github.com/klauspost/compress/pull/1229
  • flate: Avoid FMA in EstimatedBits for portable rounding by @malt3 in https://github.com/klauspost/compress/pull/1224
  • gzhttp: Preserve caller request headers in Transport by @jakezwang in https://github.com/klauspost/compress/pull/1225
  • gzhttp: Only decompress a request when gzip is the outermost coding by @youdie006 in https://github.com/klauspost/compress/pull/1223
  • zstd/huff0: Optimizations by @lizthegrey in https://github.com/klauspost/compress/pull/1203 https://github.com/klauspost/compress/pull/1205 https://github.com/klauspost/compress/pull/1207 https://github.com/klauspost/compress/pull/1204 https://github.com/klauspost/compress/pull/1208 https://github.com/klauspost/compress/pull/1211 https://github.com/klauspost/compress/pull/1209 https://github.com/klauspost/compress/pull/1210
  • flate: Speed improvements by @alex in https://github.com/klauspost/compress/pull/1220 https://github.com/klauspost/compress/pull/1218 https://github.com/klauspost/compress/pull/1216 https://github.com/klauspost/compress/pull/1215 https://github.com/klauspost/compress/pull/1214 https://github.com/klauspost/compress/pull/1217

• Sep 2nd, 2026 1.20.0

  • lzw: Add lzw reader/writer in https://github.com/klauspost/compress/pull/1189
  • xpress: Add Microsoft XPRESS (MS-XCA) decompression by @MP-GOWTHAM in https://github.com/klauspost/compress/pull/1195
  • s2: arm64 assembly encoders by @lizthegrey in https://github.com/klauspost/compress/pull/1187
  • zstd, huff0: Improved arm64 assembly by @lizthegrey in https://github.com/klauspost/compress/pull/1175 https://github.com/klauspost/compress/pull/1199 https://github.com/klauspost/compress/pull/1197
  • flate: Writer L7-9 with dictionary can emit the dictionary to stream in https://github.com/klauspost/compress/pull/1201
  • gzhttp: Limit jitter hash to jitterBuffer bytes by @VedantMadane in https://github.com/klauspost/compress/pull/1192
  • s2: Clamp the Go EncodeBetter skip to match the assembly by @lizthegrey in https://github.com/klauspost/compress/pull/1190
  • xxhash: Bound input of non-preemptive assembly by @AskAlexSharov in https://github.com/klauspost/compress/pull/1196

• Aug 6th, 2026 1.19.2

  • huff0: Add arm64 assembly for Decompress4X/1X by @lizthegrey in https://github.com/klauspost/compress/pull/1172
  • zstd: Re-enable unsafe decodeSync memory copies by @lizthegrey in https://github.com/klauspost/compress/pull/1171
  • zstd: Fix arm64 asm frame offsets placing locals on the saved LR slot by @lizthegrey in https://github.com/klauspost/compress/pull/1176
  • zstd: Avoid racing MaxDecodedSize write on shared dict litEnc by @zanarellidev in https://github.com/klauspost/compress/pull/1182
  • zstd: Keep BuildDict recent-offsets positive and loadable by @zanarellidev in https://github.com/klauspost/compress/pull/1184
  • zstd: Handle zero-literal BuildDict corpus by @cyphercodes in https://github.com/klauspost/compress/pull/1178
  • zstd: Don't clear the registered dictionary when decoding past the window by @sueun-dev in https://github.com/klauspost/compress/pull/1177

• Jul 20th, 2026 1.19.1

  • zstd: Validate SnappyConverter literal copies in https://github.com/klauspost/compress/pull/1170
  • flate: Use Peek instead of ReadByte for the bufio.Reader decode path by @joechenrh in https://github.com/klauspost/compress/pull/1169
  • zstd: Bump avo pin, regenerate arm64 asm by @lizthegrey in https://github.com/klauspost/compress/pull/1167

• Jul 1st, 2026 1.19.0

  • zstd: Add true concurrent stream encoding in https://github.com/klauspost/compress/pull/1136
  • zstd: arm64 decoder asm by @lizthegrey in https://github.com/klauspost/compress/pull/1160
  • flate: Add inflate checkpoints in https://github.com/klauspost/compress/pull/1154
  • zstd: avoid unused BuildDict encoder allocation by @snissn in https://github.com/klauspost/compress/pull/1147
  • snappy/s2: Limit length of varint in decodedLen by @eustas in https://github.com/klauspost/compress/pull/1148
  • gzhttp: match qvalue parameter case-insensitively (RFC 7231) by @z9z in https://github.com/klauspost/compress/pull/1149
  • zip: add NameDecoder callback for legacy encoding rewrite by @SAY-5 in https://github.com/klauspost/compress/pull/1150
  • huff0: Allow building tables from histogram in https://github.com/klauspost/compress/pull/1155
  • huff0: Allow building table from oversized histogram in https://github.com/klauspost/compress/pull/1156
  • s2sx: Clean symlink targets in https://github.com/klauspost/compress/pull/1163