zlib-0.7.1.0: Compression and decompression in the gzip and zlib formats
Copyright(c) 2006-2014 Duncan Coutts
LicenseBSD-style
Maintainerduncan@community.haskell.org
Safe HaskellSafe-Inferred
LanguageHaskell2010

Codec.Compression.GZip

Description

Compression and decompression of data streams in the gzip format.

The format is described in detail in RFC #1952: http://www.ietf.org/rfc/rfc1952.txt

See also the zlib home page: http://zlib.net/

Synopsis

Documentation

This module provides pure functions for compressing and decompressing streams of data in the gzip format and represented by lazy ByteStrings. This makes it easy to use either in memory or with disk or network IO.

For example a simple gzip compression program is just:

import qualified Data.ByteString.Lazy as ByteString
import qualified Codec.Compression.GZip as GZip

main = ByteString.interact GZip.compress

Or you could lazily read in and decompress a .gz file using:

content <- fmap GZip.decompress (readFile file)

Simple compression and decompression

compress :: ByteString -> ByteString Source #

Compress a stream of data into the gzip 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 :: ByteString -> ByteString Source #

Decompress a stream of data in the gzip 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.

data DecompressError Source #

The possible error cases when decompressing a stream.

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

Constructors

TruncatedInput

The compressed data stream ended prematurely. This may happen if the input data stream was truncated.

DictionaryRequired

It is possible to do zlib compression with a custom dictionary. This allows slightly higher compression ratios for short files. However such compressed streams require the same dictionary when decompressing. This error is for when we encounter a compressed stream that needs a dictionary, and it's not provided.

DictionaryMismatch

If the stream requires a dictionary and you provide one with the wrong DictionaryHash then you will get this error.

DataFormatError String

If the compressed data stream is corrupted in any way then you will get this error, for example if the input data just isn't a compressed zlib data stream. In particular if the data checksum turns out to be wrong then you will get all the decompressed data but this error at the end, instead of the normal successful StreamEnd.

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Exception DecompressError Source # 
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Generic DecompressError Source # 
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type Rep DecompressError :: Type -> Type #

Show DecompressError Source # 
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Eq DecompressError Source # 
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type Rep DecompressError Source #

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Defined in Codec.Compression.Zlib.Internal

type Rep DecompressError = D1 ('MetaData "DecompressError" "Codec.Compression.Zlib.Internal" "zlib-0.7.1.0-CGuErZzQdopDLQfJcnDfAG" 'False) ((C1 ('MetaCons "TruncatedInput" 'PrefixI 'False) (U1 :: Type -> Type) :+: C1 ('MetaCons "DictionaryRequired" 'PrefixI 'False) (U1 :: Type -> Type)) :+: (C1 ('MetaCons "DictionaryMismatch" 'PrefixI 'False) (U1 :: Type -> Type) :+: C1 ('MetaCons "DataFormatError" 'PrefixI 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 String))))

Extended API with control over compression parameters

compressWith :: CompressParams -> ByteString -> ByteString Source #

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 }

decompressWith :: DecompressParams -> ByteString -> ByteString Source #

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

decompressWith defaultCompressParams { ... }

data CompressParams Source #

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.

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Generic CompressParams Source # 
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Defined in Codec.Compression.Zlib.Internal

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type Rep CompressParams :: Type -> Type #

Show CompressParams Source # 
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type Rep CompressParams Source #

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type Rep CompressParams = D1 ('MetaData "CompressParams" "Codec.Compression.Zlib.Internal" "zlib-0.7.1.0-CGuErZzQdopDLQfJcnDfAG" 'False) (C1 ('MetaCons "CompressParams" 'PrefixI 'True) ((S1 ('MetaSel ('Just "compressLevel") 'NoSourceUnpackedness 'SourceStrict 'DecidedStrict) (Rec0 CompressionLevel) :*: (S1 ('MetaSel ('Just "compressMethod") 'NoSourceUnpackedness 'SourceStrict 'DecidedStrict) (Rec0 Method) :*: S1 ('MetaSel ('Just "compressWindowBits") 'NoSourceUnpackedness 'SourceStrict 'DecidedStrict) (Rec0 WindowBits))) :*: ((S1 ('MetaSel ('Just "compressMemoryLevel") 'NoSourceUnpackedness 'SourceStrict 'DecidedStrict) (Rec0 MemoryLevel) :*: S1 ('MetaSel ('Just "compressStrategy") 'NoSourceUnpackedness 'SourceStrict 'DecidedStrict) (Rec0 CompressionStrategy)) :*: (S1 ('MetaSel ('Just "compressBufferSize") 'NoSourceUnpackedness 'SourceStrict 'DecidedStrict) (Rec0 Int) :*: S1 ('MetaSel ('Just "compressDictionary") 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 (Maybe ByteString))))))

defaultCompressParams :: CompressParams Source #

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

data DecompressParams Source #

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.

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Generic DecompressParams Source # 
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type Rep DecompressParams :: Type -> Type #

Show DecompressParams Source # 
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type Rep DecompressParams Source #

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Defined in Codec.Compression.Zlib.Internal

type Rep DecompressParams = D1 ('MetaData "DecompressParams" "Codec.Compression.Zlib.Internal" "zlib-0.7.1.0-CGuErZzQdopDLQfJcnDfAG" 'False) (C1 ('MetaCons "DecompressParams" 'PrefixI 'True) ((S1 ('MetaSel ('Just "decompressWindowBits") 'NoSourceUnpackedness 'SourceStrict 'DecidedStrict) (Rec0 WindowBits) :*: S1 ('MetaSel ('Just "decompressBufferSize") 'NoSourceUnpackedness 'SourceStrict 'DecidedStrict) (Rec0 Int)) :*: (S1 ('MetaSel ('Just "decompressDictionary") 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 (Maybe ByteString)) :*: S1 ('MetaSel ('Just "decompressAllMembers") 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 Bool))))

defaultDecompressParams :: DecompressParams Source #

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

The compression parameter types

newtype CompressionLevel Source #

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.

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CompressionLevel Int 

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Generic CompressionLevel Source # 
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type Rep CompressionLevel :: Type -> Type #

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type Rep CompressionLevel Source # 
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type Rep CompressionLevel = D1 ('MetaData "CompressionLevel" "Codec.Compression.Zlib.Stream" "zlib-0.7.1.0-CGuErZzQdopDLQfJcnDfAG" 'True) (C1 ('MetaCons "CompressionLevel" 'PrefixI 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 Int)))

noCompression :: CompressionLevel Source #

No compression, just a block copy.

bestSpeed :: CompressionLevel Source #

The fastest compression method (less compression).

bestCompression :: CompressionLevel Source #

The slowest compression method (best compression).

compressionLevel :: Int -> CompressionLevel Source #

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

data Method Source #

The compression method

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Bounded Method Source # 
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Enum Method Source # 
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Generic Method Source # 
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type Rep Method :: Type -> Type #

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(==) :: Method -> Method -> Bool #

(/=) :: Method -> Method -> Bool #

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type Rep Method Source # 
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type Rep Method = D1 ('MetaData "Method" "Codec.Compression.Zlib.Stream" "zlib-0.7.1.0-CGuErZzQdopDLQfJcnDfAG" 'False) (C1 ('MetaCons "Deflated" 'PrefixI 'False) (U1 :: Type -> Type))

deflateMethod :: Method Source #

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

newtype WindowBits Source #

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.

Constructors

WindowBits Int 

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Generic WindowBits Source # 
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type Rep WindowBits :: Type -> Type #

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type Rep WindowBits Source # 
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type Rep WindowBits = D1 ('MetaData "WindowBits" "Codec.Compression.Zlib.Stream" "zlib-0.7.1.0-CGuErZzQdopDLQfJcnDfAG" 'True) (C1 ('MetaCons "WindowBits" 'PrefixI 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 Int)))

defaultWindowBits :: WindowBits Source #

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

windowBits :: Int -> WindowBits Source #

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

newtype MemoryLevel Source #

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.

Constructors

MemoryLevel Int 

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Generic MemoryLevel Source # 
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type Rep MemoryLevel :: Type -> Type #

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type Rep MemoryLevel Source # 
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type Rep MemoryLevel = D1 ('MetaData "MemoryLevel" "Codec.Compression.Zlib.Stream" "zlib-0.7.1.0-CGuErZzQdopDLQfJcnDfAG" 'True) (C1 ('MetaCons "MemoryLevel" 'PrefixI 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 Int)))

minMemoryLevel :: MemoryLevel Source #

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

maxMemoryLevel :: MemoryLevel Source #

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

memoryLevel :: Int -> MemoryLevel Source #

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

data CompressionStrategy Source #

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.

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Bounded CompressionStrategy Source # 
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Enum CompressionStrategy Source # 
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Generic CompressionStrategy Source # 
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type Rep CompressionStrategy :: Type -> Type #

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type Rep CompressionStrategy Source # 
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type Rep CompressionStrategy = D1 ('MetaData "CompressionStrategy" "Codec.Compression.Zlib.Stream" "zlib-0.7.1.0-CGuErZzQdopDLQfJcnDfAG" 'False) ((C1 ('MetaCons "DefaultStrategy" 'PrefixI 'False) (U1 :: Type -> Type) :+: C1 ('MetaCons "Filtered" 'PrefixI 'False) (U1 :: Type -> Type)) :+: (C1 ('MetaCons "HuffmanOnly" 'PrefixI 'False) (U1 :: Type -> Type) :+: (C1 ('MetaCons "RLE" 'PrefixI 'False) (U1 :: Type -> Type) :+: C1 ('MetaCons "Fixed" 'PrefixI 'False) (U1 :: Type -> Type))))

defaultStrategy :: CompressionStrategy Source #

Use this default compression strategy for normal data.

filteredStrategy :: CompressionStrategy Source #

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.

huffmanOnlyStrategy :: CompressionStrategy Source #

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

rleStrategy :: CompressionStrategy Source #

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 :: CompressionStrategy Source #

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

Since: 0.7.0.0