Compress a stream of data into the zlib format.

This uses the default compression parameters. In particular it uses the default compression level which favours a higher compression ratio over compression speed, though it does not use the maximum compression level.

Use compressWith to adjust the compression level or other compression parameters.

Decompress a stream of data in the zlib format, throw DecompressError on failure.

Note that the decompression is performed lazily. Errors in the data stream may not be detected until the end of the stream is demanded (since it is only at the end that the final checksum can be checked). If this is important to you, you must make sure to consume the whole decompressed stream before doing any IO action that depends on it.

The possible error cases when decompressing a stream.

This can be shown to give a human readable error message.

Like compress but with the ability to specify various compression parameters. Typical usage:

compressWith defaultCompressParams { ... }

In particular you can set the compression level:

compressWith defaultCompressParams { compressLevel = BestCompression }

Like decompress but with the ability to specify various decompression parameters. Typical usage:

decompressWith defaultCompressParams { ... }

The full set of parameters for compression. The defaults are defaultCompressParams.

The compressBufferSize is the size of the first output buffer containing the compressed data. If you know an approximate upper bound on the size of the compressed data then setting this parameter can save memory. The default compression output buffer size is 16k. If your estimate is wrong it does not matter too much, the default buffer size will be used for the remaining chunks.

The default set of parameters for compression. This is typically used with compressWith or compressWith with specific parameters overridden.

The full set of parameters for decompression. The defaults are defaultDecompressParams.

The decompressBufferSize is the size of the first output buffer, containing the uncompressed data. If you know an exact or approximate upper bound on the size of the decompressed data then setting this parameter can save memory. The default decompression output buffer size is 32k. If your estimate is wrong it does not matter too much, the default buffer size will be used for the remaining chunks.

One particular use case for setting the decompressBufferSize is if you know the exact size of the decompressed data and want to produce a strict ByteString. The compression and decompression functions use lazy ByteStrings but if you set the decompressBufferSize correctly then you can generate a lazy ByteString with exactly one chunk, which can be converted to a strict ByteString in O(1) time using concat . toChunks.

The default set of parameters for decompression. This is typically used with decompressWith or decompressWith with specific parameters overridden.

The compression level parameter controls the amount of compression. This is a trade-off between the amount of compression and the time required to do the compression.

The default CompressionLevel.

No compression, just a block copy.

The fastest compression method (less compression).

The slowest compression method (best compression).

A specific compression level in the range 0..9. Throws an error for arguments outside of this range.

• 0 stands for noCompression,
• 1 stands for bestSpeed,
• 6 stands for defaultCompression,
• 9 stands for bestCompression.

The compression method

The only method supported in this version of zlib. Indeed it is likely to be the only method that ever will be supported.

This specifies the size of the compression window. Larger values of this parameter result in better compression at the expense of higher memory usage.

The compression window size is the value of the the window bits raised to the power 2. The window bits must be in the range 9..15 which corresponds to compression window sizes of 512b to 32Kb. The default is 15 which is also the maximum size.

The total amount of memory used depends on the window bits and the MemoryLevel. See the MemoryLevel for the details.

The default WindowBits. Equivalent to windowBits 15. which is also the maximum size.

A specific compression window size, specified in bits in the range 9..15. Throws an error for arguments outside of this range.

The MemoryLevel parameter specifies how much memory should be allocated for the internal compression state. It is a trade-off between memory usage, compression ratio and compression speed. Using more memory allows faster compression and a better compression ratio.

The total amount of memory used for compression depends on the WindowBits and the MemoryLevel. For decompression it depends only on the WindowBits. The totals are given by the functions:

compressTotal windowBits memLevel = 4 * 2^windowBits + 512 * 2^memLevel
decompressTotal windowBits = 2^windowBits

For example, for compression with the default windowBits = 15 and memLevel = 8 uses 256Kb. So for example a network server with 100 concurrent compressed streams would use 25Mb. The memory per stream can be halved (at the cost of somewhat degraded and slower compression) by reducing the windowBits and memLevel by one.

Decompression takes less memory, the default windowBits = 15 corresponds to just 32Kb.

The default MemoryLevel. Equivalent to memoryLevel 8.

Use minimum memory. This is slow and reduces the compression ratio. Equivalent to memoryLevel 1.

Use maximum memory for optimal compression speed. Equivalent to memoryLevel 9.

A specific memory level in the range 1..9. Throws an error for arguments outside of this range.

The strategy parameter is used to tune the compression algorithm.

The strategy parameter only affects the compression ratio but not the correctness of the compressed output even if it is not set appropriately.

Use this default compression strategy for normal data.

Use the filtered compression strategy for data produced by a filter (or predictor). Filtered data consists mostly of small values with a somewhat random distribution. In this case, the compression algorithm is tuned to compress them better. The effect of this strategy is to force more Huffman coding and less string matching; it is somewhat intermediate between defaultStrategy and huffmanOnlyStrategy.

Use the Huffman-only compression strategy to force Huffman encoding only (no string match).

Use rleStrategy to limit match distances to one (run-length encoding). rleStrategy is designed to be almost as fast as huffmanOnlyStrategy, but give better compression for PNG image data.

Since: 0.7.0.0

fixedStrategy prevents the use of dynamic Huffman codes, allowing for a simpler decoder for special applications.

Since: 0.7.0.0