[WIP] Add span-based Deflate, ZLib and GZip encoder/decoder APIs #123145

iremyux · 2026-01-13T18:46:21Z

This PR introduces new span-based, streamless compression and decompression APIs for Deflate, ZLib, and GZip formats, matching the existing BrotliEncoder/BrotliDecoder pattern.

New APIs

DeflateEncoder / DeflateDecoder
ZLibEncoder / ZLibDecoder
GZipEncoder / GZipDecoder

These classes provide:

Instance-based API for streaming/chunked compression with Compress(), Decompress(), and Flush()
Static one-shot API via TryCompress() and TryDecompress() for simple scenarios
GetMaxCompressedLength() to calculate buffer sizes

Closes #62113
Closes #39327

src/libraries/System.IO.Compression/src/System/IO/Compression/ZlibEncoderOptions.cs

src/libraries/System.IO.Compression/src/System/IO/Compression/ZlibEncoder.cs

src/libraries/System.IO.Compression/ref/System.IO.Compression.cs

src/libraries/System.IO.Compression/src/System/IO/Compression/ZlibDecoder.cs

src/libraries/System.IO.Compression/src/System/IO/Compression/ZlibEncoder.cs

rzikm · 2026-01-16T10:40:13Z

src/libraries/System.IO.Compression/src/System/IO/Compression/ZlibEncoder.cs

+        /// <returns>One of the enumeration values that describes the status with which the operation finished.</returns>
+        public OperationStatus Flush(Span<byte> destination, out int bytesWritten)
+        {
+            return Compress(ReadOnlySpan<byte>.Empty, destination, out _, out bytesWritten, isFinalBlock: false);


does this force writing output (if available), I think this should lead to FlushCode.SyncFlush to the native API

rzikm · 2026-01-16T10:44:14Z

src/libraries/System.IO.Compression/src/System/IO/Compression/ZlibEncoder.cs

+        /// <param name="source">A read-only span of bytes containing the source data to compress.</param>
+        /// <param name="destination">When this method returns, a span of bytes where the compressed data is stored.</param>
+        /// <param name="bytesWritten">When this method returns, the total number of bytes that were written to <paramref name="destination"/>.</param>
+        /// <param name="compressionLevel">A number representing compression level. -1 is default, 0 is no compression, 1 is best speed, 9 is best compression.</param>


We should be more clear which default we mean.

Suggested change

/// <param name="compressionLevel">A number representing compression level. -1 is default, 0 is no compression, 1 is best speed, 9 is best compression.</param>

/// <param name="compressionLevel">A number representing compression level. -1 means implementation default, 0 is no compression, 1 is best speed, 9 is best compression.</param>

…mpressedLength

AraHaan · 2026-01-22T23:44:38Z

src/libraries/System.IO.Compression/src/System/IO/Compression/ZlibEncoder.cs

+                CompressionLevel.Fastest => ZLibNative.CompressionLevel.BestSpeed,
+                CompressionLevel.NoCompression => ZLibNative.CompressionLevel.NoCompression,
+                CompressionLevel.SmallestSize => ZLibNative.CompressionLevel.BestCompression,
+                _ => throw new ArgumentOutOfRangeException(nameof(compressionLevel)),


This would fail on valid native compression levels not covered by the CompressionLevel enum. Instead I think it should check if the value is is < -1 or > 9 to throw out of range instead.

iremyux and others added 3 commits January 12, 2026 20:46

Add Zlib Encoder and Decoder classes

e402958

Add tests

95ac930

Merge branch 'dotnet:main' into 62113-zlib-encoder-decoder

88acc57

iremyux self-assigned this Jan 13, 2026

iremyux added the area-System.IO.Compression label Jan 13, 2026