zlib-0.5.3.3: Compression and decompression in the gzip and zlib formats

Portabilityportable (H98 + FFI)
Stabilityprovisional
Maintainerduncan@haskell.org
Safe HaskellSafe-Infered

Codec.Compression.Zlib.Stream

Contents

Description

Zlib wrapper layer

Synopsis

The Zlib state monad

data Stream a Source

Instances

run :: Stream a -> aSource

finalise :: Stream ()Source

This never needs to be used as the stream's resources will be released automatically when no longer needed, however this can be used to release them early. Only use this when you can guarantee that the stream will no longer be needed, for example if an error occurs or if the stream ends.

Initialisation

Initialisation parameters

data Format Source

The format used for compression or decompression. There are three variations.

Constructors

GZip 
Zlib 
Raw 
GZipOrZlib 

Instances

gzipFormat :: FormatSource

The gzip format uses a header with a checksum and some optional meta-data about the compressed file. It is intended primarily for compressing individual files but is also sometimes used for network protocols such as HTTP. The format is described in detail in RFC #1952 http://www.ietf.org/rfc/rfc1952.txt

zlibFormat :: FormatSource

The zlib format uses a minimal header with a checksum but no other meta-data. It is especially designed for use in network protocols. The format is described in detail in RFC #1950 http://www.ietf.org/rfc/rfc1950.txt

rawFormat :: FormatSource

The 'raw' format is just the compressed data stream without any additional header, meta-data or data-integrity checksum. The format is described in detail in RFC #1951 http://www.ietf.org/rfc/rfc1951.txt

gzipOrZlibFormat :: FormatSource

This is not a format as such. It enabled zlib or gzip decoding with automatic header detection. This only makes sense for decompression.

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.

defaultCompression :: CompressionLevelSource

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

noCompression :: CompressionLevelSource

No compression, just a block copy.

bestSpeed :: CompressionLevelSource

The fastest compression method (less compression)

bestCompression :: CompressionLevelSource

The slowest compression method (best compression).

compressionLevel :: Int -> CompressionLevelSource

A specific compression level between 0 and 9.

data Method Source

The compression method

Constructors

Deflated 

deflateMethod :: MethodSource

'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 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.

defaultWindowBits :: WindowBitsSource

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

windowBits :: Int -> WindowBitsSource

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

defaultMemoryLevel :: MemoryLevelSource

The default memory level. (Equivalent to memoryLevel 8)

minMemoryLevel :: MemoryLevelSource

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

maxMemoryLevel :: MemoryLevelSource

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

memoryLevel :: Int -> MemoryLevelSource

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.

defaultStrategy :: CompressionStrategySource

Use this default compression strategy for normal data.

filteredStrategy :: CompressionStrategySource

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 :: CompressionStrategySource

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

The buisness

data ErrorCode Source

Constructors

NeedDict 
FileError 
StreamError 
DataError 
MemoryError 
BufferError

No progress was possible or there was not enough room in the output buffer when Finish is used. Note that BuferError is not fatal, and inflate can be called again with more input and more output space to continue.

VersionError 
Unexpected 

Buffer management

Input buffer

Output buffer