| Portability | portable (H98 + FFI) |
|---|---|
| Stability | provisional |
| Maintainer | duncan@haskell.org |
Codec.Compression.Zlib.Raw
Contents
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/
- compress :: ByteString -> ByteString
- decompress :: ByteString -> ByteString
- compressWith :: CompressParams -> ByteString -> ByteString
- decompressWith :: DecompressParams -> ByteString -> ByteString
- data CompressParams = CompressParams {}
- defaultCompressParams :: CompressParams
- data DecompressParams = DecompressParams {}
- defaultDecompressParams :: DecompressParams
- data CompressionLevel
- data Method = Deflated
- data WindowBits
- data MemoryLevel
- data CompressionStrategy
Simple compression and decompression
Extended api with control over compression parameters
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 | |
defaultCompressParams :: CompressParamsSource
The default set of parameters for compression. This is typically used with
the compressWith function with specific paramaters 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
Data.ByteString.ByteString. The compression and deccompression functions
use lazy Data.ByteString.Lazy.ByteStrings but if you set the
decompressBufferSize correctly then you can generate a lazy
Data.ByteString.Lazy.ByteString with exactly one chunk, which can be
converted to a strict Data.ByteString.ByteString in O(1) time using
Data.ByteString.concat . Data.ByteString.Lazy.toChunks
Constructors
| DecompressParams | |
Fields | |
defaultDecompressParams :: DecompressParamsSource
The default set of parameters for decompression. This is typically used with
the compressWith function with specific paramaters 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 | The default compression level is 6 (that is, biased towards higher compression at expense of speed). |
| NoCompression | No compression, just a block copy. |
| BestSpeed | The fastest compression method (less compression) |
| BestCompression | The slowest compression method (best compression). |
| CompressionLevel Int | A specific compression level between 1 and 9. |
The compression method
Constructors
| Deflated | '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.
Constructors
| DefaultWindowBits | |
| WindowBits Int |
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 | The default. (Equivalent to |
| MinMemoryLevel | Use minimum memory. This is slow and reduces the
compression ratio. (Equivalent to |
| MaxMemoryLevel | Use maximum memory for optimal compression speed.
(Equivalent to |
| MemoryLevel Int | Use a specific level in the 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.
Constructors
| DefaultStrategy | Use the |
| Filtered | Use |
| HuffmanOnly | Use |