Codec.Compression.Zlib.Raw

zlib-0.5.4.2: Compression and decompression in the gzip and zlib formats

Copyright | (c) 2006-2008 Duncan Coutts
License | BSD-style
Maintainer | duncan@haskell.org
Stability | provisional
Portability | portable (H98 + FFI)
Safe Haskell | None
Language | Haskell98

Codec.Compression.Zlib.Raw

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 raw deflate format.

The format is described in detail in RFC #1951: http://www.ietf.org/rfc/rfc1951.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
  }
- 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

# Simple compression and decompression

compress :: ByteString -> ByteString

decompress :: ByteString -> ByteString

# Extended api with control over compression parameters

compressWith :: CompressParams -> ByteString -> ByteString

decompressWith :: DecompressParams -> ByteString -> ByteString

data CompressParams

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

defaultCompressParams :: CompressParams

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

data DecompressParams

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

defaultDecompressParams :: DecompressParams

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

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 |

defaultCompression :: CompressionLevel

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

noCompression :: CompressionLevel

No compression, just a block copy.

bestSpeed :: CompressionLevel

The fastest compression method (less compression)

bestCompression :: CompressionLevel

The slowest compression method (best compression).

compressionLevel :: Int -> CompressionLevel

A specific compression level between 0 and 9.

data Method

The compression method

Constructors

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

deflateMethod :: Method

'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

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 `8..15` which corresponds to compression window sizes of 256b 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

defaultWindowBits :: WindowBits

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

windowBits :: Int -> WindowBits

A specific compression window size, specified in bits in the range `8..15`

data MemoryLevel

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 |

defaultMemoryLevel :: MemoryLevel

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

minMemoryLevel :: MemoryLevel

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

maxMemoryLevel :: MemoryLevel

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

memoryLevel :: Int -> MemoryLevel

A specific level in the range `1..9`

data CompressionStrategy

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

defaultStrategy :: CompressionStrategy

Use this default compression strategy for normal data.

filteredStrategy :: CompressionStrategy

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

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