zlib-0.6.2.2: Compression and decompression in the gzip and zlib formats

Copyright | (c) 2006-2014 Duncan Coutts
License | BSD-style
Maintainer | duncan@community.haskell.org
Safe Haskell | Safe
Language | Haskell2010

Codec.Compression.GZip

Contents

- Simple compression and decompression
- Extended api with control over compression parameters
  - The compression parameter types

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

- compress :: ByteString -> ByteString
- decompress :: ByteString -> ByteString
- compressWith :: CompressParams -> ByteString -> ByteString
- decompressWith :: DecompressParams -> ByteString -> ByteString
- data CompressParams = CompressParams {
  - compressLevel :: !CompressionLevel
  - compressMethod :: !Method
  - compressWindowBits :: !WindowBits
  - compressMemoryLevel :: !MemoryLevel
  - compressStrategy :: !CompressionStrategy
  - compressBufferSize :: !Int
  - compressDictionary :: Maybe ByteString
  }
- defaultCompressParams :: CompressParams
- data DecompressParams = DecompressParams {
  - decompressWindowBits :: !WindowBits
  - decompressBufferSize :: !Int
  - decompressDictionary :: Maybe ByteString
  - decompressAllMembers :: Bool
  }
- defaultDecompressParams :: DecompressParams
- data CompressionLevel
  - = DefaultCompression
  - | NoCompression
  - | BestSpeed
  - | BestCompression
  - | CompressionLevel Int
- defaultCompression :: CompressionLevel
- noCompression :: CompressionLevel
- bestSpeed :: CompressionLevel
- bestCompression :: CompressionLevel
- compressionLevel :: Int -> CompressionLevel
- data Method = Deflated
- deflateMethod :: Method
- data WindowBits
  - = WindowBits Int
  - | DefaultWindowBits
- defaultWindowBits :: WindowBits
- windowBits :: Int -> WindowBits
- data MemoryLevel
  - = DefaultMemoryLevel
  - | MinMemoryLevel
  - | MaxMemoryLevel
  - | MemoryLevel Int
- defaultMemoryLevel :: MemoryLevel
- minMemoryLevel :: MemoryLevel
- maxMemoryLevel :: MemoryLevel
- memoryLevel :: Int -> MemoryLevel
- data CompressionStrategy
  - = DefaultStrategy
  - | Filtered
  - | HuffmanOnly
- defaultStrategy :: CompressionStrategy
- filteredStrategy :: CompressionStrategy
- huffmanOnlyStrategy :: CompressionStrategy

# Documentation

This module provides pure functions for compressing and decompressing streams of data in the gzip format and represented by lazy `ByteString`s. 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 partiular 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.

There are a number of errors that can occur. In each case an exception will be thrown. The possible error conditions are:

- if the stream does not start with a valid gzip header
- if the compressed stream is corrupted
- if the compressed stream ends permaturely

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.

# 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 extimate is wrong it does not matter too much, the default buffer size will be used for the remaining chunks.

Constructors

CompressParams |

Fields

- compressLevel :: !CompressionLevel
- compressMethod :: !Method
- compressWindowBits :: !WindowBits
- compressMemoryLevel :: !MemoryLevel
- compressStrategy :: !CompressionStrategy
- compressBufferSize :: !Int
- compressDictionary :: Maybe ByteString

#### Instances

Instances details

Show CompressParams Source # |
Instance details Defined in Codec.Compression.Zlib.Internal Methods showsPrec :: Int -> CompressParams -> ShowS show :: CompressParams -> String showList :: [CompressParams] -> ShowS

defaultCompressParams :: CompressParams Source #

The default set of parameters for compression. This is typically used with the `compressWith` function 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 extimate 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 deccompression functions use lazy `ByteString`s 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``.

Constructors

DecompressParams |

Fields

- decompressWindowBits :: !WindowBits
- decompressBufferSize :: !Int
- decompressDictionary :: Maybe ByteString
- decompressAllMembers :: Bool

#### Instances

Instances details

Show DecompressParams Source # |
Instance details Defined in Codec.Compression.Zlib.Internal Methods showsPrec :: Int -> DecompressParams -> ShowS show :: DecompressParams -> String showList :: [DecompressParams] -> ShowS

defaultDecompressParams :: DecompressParams Source #

The default set of parameters for decompression. This is typically used with the `compressWith` function with specific parameters overridden.

## The compression parameter types

data 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.

Constructors

DefaultCompression | Deprecated: Use defaultCompression. CompressionLevel constructors will be hidden in version 0.7
NoCompression | Deprecated: Use noCompression. CompressionLevel constructors will be hidden in version 0.7
BestSpeed | Deprecated: Use bestSpeed. CompressionLevel constructors will be hidden in version 0.7
BestCompression | Deprecated: Use bestCompression. CompressionLevel constructors will be hidden in version 0.7
CompressionLevel Int |

#### Instances

Instances details

Eq CompressionLevel Source # |
Instance details Defined in Codec.Compression.Zlib.Stream Methods (==) :: CompressionLevel -> CompressionLevel -> Bool (/=) :: CompressionLevel -> CompressionLevel -> Bool
Show CompressionLevel Source # |
Instance details Defined in Codec.Compression.Zlib.Stream Methods showsPrec :: Int -> CompressionLevel -> ShowS show :: CompressionLevel -> String showList :: [CompressionLevel] -> ShowS
Generic CompressionLevel Source # |
Instance details Defined in Codec.Compression.Zlib.Stream Associated Types type Rep CompressionLevel :: Type -> Type Methods from :: CompressionLevel -> Rep CompressionLevel x to :: Rep CompressionLevel x -> CompressionLevel
type Rep CompressionLevel Source # |

Instance details

Defined in Codec.Compression.Zlib.Stream

type Rep CompressionLevel = D1 ('MetaData "CompressionLevel" "Codec.Compression.Zlib.Stream" "zlib-0.6.2.2-5b26HP1zXA26xBLybZk8Ph" 'False) ((C1 ('MetaCons "DefaultCompression" 'PrefixI 'False) (U1 :: Type -> Type) :+: C1 ('MetaCons "NoCompression" 'PrefixI 'False) (U1 :: Type -> Type)) :+: (C1 ('MetaCons "BestSpeed" 'PrefixI 'False) (U1 :: Type -> Type) :+: (C1 ('MetaCons "BestCompression" 'PrefixI 'False) (U1 :: Type -> Type) :+: C1 ('MetaCons "CompressionLevel" 'PrefixI 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 Int)))))

defaultCompression :: CompressionLevel Source #

The default compression level is 6 (that is, biased towards higher compression at expense of speed).

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 between 0 and 9.

data Method Source #

The compression method

Constructors

Deflated | Deprecated: Use deflateMethod. Method constructors will be hidden in version 0.7

#### Instances

Instances details

Bounded Method Source # |
Instance details Defined in Codec.Compression.Zlib.Stream Methods minBound :: Method maxBound :: Method
Enum Method Source # |
Instance details Defined in Codec.Compression.Zlib.Stream Methods succ :: Method -> Method pred :: Method -> Method toEnum :: Int -> Method fromEnum :: Method -> Int enumFrom :: Method -> [Method] enumFromThen :: Method -> Method -> [Method] enumFromTo :: Method -> Method -> [Method] enumFromThenTo :: Method -> Method -> Method -> [Method]
Eq Method Source # |
Instance details Defined in Codec.Compression.Zlib.Stream Methods (==) :: Method -> Method -> Bool (/=) :: Method -> Method -> Bool
Ord Method Source # |
Instance details Defined in Codec.Compression.Zlib.Stream Methods compare :: Method -> Method -> Ordering (<) :: Method -> Method -> Bool (<=) :: Method -> Method -> Bool (>) :: Method -> Method -> Bool (>=) :: Method -> Method -> Bool max :: Method -> Method -> Method min :: Method -> Method -> Method
Show Method Source # |
Instance details Defined in Codec.Compression.Zlib.Stream Methods showsPrec :: Int -> Method -> ShowS show :: Method -> String showList :: [Method] -> ShowS
Generic Method Source # |
Instance details Defined in Codec.Compression.Zlib.Stream Associated Types type Rep Method :: Type -> Type Methods from :: Method -> Rep Method x to :: Rep Method x -> Method
type Rep Method Source # |
Instance details Defined in Codec.Compression.Zlib.Stream type Rep Method = D1 ('MetaData "Method" "Codec.Compression.Zlib.Stream" "zlib-0.6.2.2-5b26HP1zXA26xBLybZk8Ph" 'False) (C1 ('MetaCons "Deflated" 'PrefixI 'False) (U1 :: Type -> Type))

deflateMethod :: Method Source #

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

data 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 |
DefaultWindowBits | Deprecated: Use defaultWindowBits. WindowBits constructors will be hidden in version 0.7

#### Instances

Instances details

Eq WindowBits Source # |
Instance details Defined in Codec.Compression.Zlib.Stream Methods (==) :: WindowBits -> WindowBits -> Bool (/=) :: WindowBits -> WindowBits -> Bool
Ord WindowBits Source # |
Instance details Defined in Codec.Compression.Zlib.Stream Methods compare :: WindowBits -> WindowBits -> Ordering (<) :: WindowBits -> WindowBits -> Bool (<=) :: WindowBits -> WindowBits -> Bool (>) :: WindowBits -> WindowBits -> Bool (>=) :: WindowBits -> WindowBits -> Bool max :: WindowBits -> WindowBits -> WindowBits min :: WindowBits -> WindowBits -> WindowBits
Show WindowBits Source # |
Instance details Defined in Codec.Compression.Zlib.Stream Methods showsPrec :: Int -> WindowBits -> ShowS show :: WindowBits -> String showList :: [WindowBits] -> ShowS
Generic WindowBits Source # |
Instance details Defined in Codec.Compression.Zlib.Stream Associated Types type Rep WindowBits :: Type -> Type Methods from :: WindowBits -> Rep WindowBits x to :: Rep WindowBits x -> WindowBits
type Rep WindowBits Source # |

Instance details

Defined in Codec.Compression.Zlib.Stream

type Rep WindowBits = D1 ('MetaData "WindowBits" "Codec.Compression.Zlib.Stream" "zlib-0.6.2.2-5b26HP1zXA26xBLybZk8Ph" 'False) (C1 ('MetaCons "WindowBits" 'PrefixI 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 Int)) :+: C1 ('MetaCons "DefaultWindowBits" 'PrefixI 'False) (U1 :: Type -> Type))

defaultWindowBits :: WindowBits Source #

The default `WindowBits` is 15 which is also the maximum size.

windowBits :: Int -> WindowBits Source #

A specific compression window size, specified in bits in the range `9..15`

data MemoryLevel Source #

The `MemoryLevel` parameter specifies how much memory should be allocated for the internal compression state. It is a tradoff 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 compressionby) by reducing the `windowBits` and `memLevel` by one.

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

Constructors

DefaultMemoryLevel | Deprecated: Use defaultMemoryLevel. MemoryLevel constructors will be hidden in version 0.7
MinMemoryLevel | Deprecated: Use minMemoryLevel. MemoryLevel constructors will be hidden in version 0.7
MaxMemoryLevel | Deprecated: Use maxMemoryLevel. MemoryLevel constructors will be hidden in version 0.7
MemoryLevel Int |

#### Instances

Instances details

Eq MemoryLevel Source # |
Instance details Defined in Codec.Compression.Zlib.Stream Methods (==) :: MemoryLevel -> MemoryLevel -> Bool (/=) :: MemoryLevel -> MemoryLevel -> Bool
Show MemoryLevel Source # |
Instance details Defined in Codec.Compression.Zlib.Stream Methods showsPrec :: Int -> MemoryLevel -> ShowS show :: MemoryLevel -> String showList :: [MemoryLevel] -> ShowS
Generic MemoryLevel Source # |
Instance details Defined in Codec.Compression.Zlib.Stream Associated Types type Rep MemoryLevel :: Type -> Type Methods from :: MemoryLevel -> Rep MemoryLevel x to :: Rep MemoryLevel x -> MemoryLevel
type Rep MemoryLevel Source # |

Instance details

Defined in Codec.Compression.Zlib.Stream

type Rep MemoryLevel = D1 ('MetaData "MemoryLevel" "Codec.Compression.Zlib.Stream" "zlib-0.6.2.2-5b26HP1zXA26xBLybZk8Ph" 'False) ((C1 ('MetaCons "DefaultMemoryLevel" 'PrefixI 'False) (U1 :: Type -> Type) :+: C1 ('MetaCons "MinMemoryLevel" 'PrefixI 'False) (U1 :: Type -> Type)) :+: (C1 ('MetaCons "MaxMemoryLevel" 'PrefixI 'False) (U1 :: Type -> Type) :+: C1 ('MetaCons "MemoryLevel" 'PrefixI 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 Int))))

defaultMemoryLevel :: MemoryLevel Source #

The default memory level. (Equivalent to ``memoryLevel` 8`)

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 level in the range `1..9`

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.

Constructors

DefaultStrategy | Deprecated: Use defaultStrategy. CompressionStrategy constructors will be hidden in version 0.7
Filtered | Deprecated: Use filteredStrategy. CompressionStrategy constructors will be hidden in version 0.7
HuffmanOnly | Deprecated: Use huffmanOnlyStrategy. CompressionStrategy constructors will be hidden in version 0.7

#### Instances

Instances details

Bounded CompressionStrategy Source # |
Instance details Defined in Codec.Compression.Zlib.Stream Methods minBound :: CompressionStrategy maxBound :: CompressionStrategy
Enum CompressionStrategy Source # |

Instance details

Defined in Codec.Compression.Zlib.Stream

Methods

succ :: CompressionStrategy -> CompressionStrategy

pred :: CompressionStrategy -> CompressionStrategy

toEnum :: Int -> CompressionStrategy

fromEnum :: CompressionStrategy -> Int

enumFrom :: CompressionStrategy -> [CompressionStrategy]

enumFromThen :: CompressionStrategy -> CompressionStrategy -> [CompressionStrategy]

enumFromTo :: CompressionStrategy -> CompressionStrategy -> [CompressionStrategy]

enumFromThenTo :: CompressionStrategy -> CompressionStrategy -> CompressionStrategy -> [CompressionStrategy]

Eq CompressionStrategy Source # |
Instance details Defined in Codec.Compression.Zlib.Stream Methods (==) :: CompressionStrategy -> CompressionStrategy -> Bool (/=) :: CompressionStrategy -> CompressionStrategy -> Bool
Ord CompressionStrategy Source # |

Instance details

Defined in Codec.Compression.Zlib.Stream

Methods

compare :: CompressionStrategy -> CompressionStrategy -> Ordering

(<) :: CompressionStrategy -> CompressionStrategy -> Bool

(<=) :: CompressionStrategy -> CompressionStrategy -> Bool

(>) :: CompressionStrategy -> CompressionStrategy -> Bool

(>=) :: CompressionStrategy -> CompressionStrategy -> Bool

max :: CompressionStrategy -> CompressionStrategy -> CompressionStrategy

min :: CompressionStrategy -> CompressionStrategy -> CompressionStrategy

Show CompressionStrategy Source # |
Instance details Defined in Codec.Compression.Zlib.Stream Methods showsPrec :: Int -> CompressionStrategy -> ShowS show :: CompressionStrategy -> String showList :: [CompressionStrategy] -> ShowS
Generic CompressionStrategy Source # |
Instance details Defined in Codec.Compression.Zlib.Stream Associated Types type Rep CompressionStrategy :: Type -> Type Methods from :: CompressionStrategy -> Rep CompressionStrategy x to :: Rep CompressionStrategy x -> CompressionStrategy
type Rep CompressionStrategy Source # |

Instance details

Defined in Codec.Compression.Zlib.Stream

type Rep CompressionStrategy = D1 ('MetaData "CompressionStrategy" "Codec.Compression.Zlib.Stream" "zlib-0.6.2.2-5b26HP1zXA26xBLybZk8Ph" '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)))

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 `defaultCompressionStrategy` and `huffmanOnlyCompressionStrategy`.

huffmanOnlyStrategy :: CompressionStrategy Source #

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