Portability | portable (H98 + FFI) |
---|---|
Stability | provisional |
Maintainer | duncan.coutts@worc.ox.ac.uk |
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/
- compress :: ByteString -> ByteString
- compressWith :: CompressionLevel -> ByteString -> ByteString
- data CompressionLevel
- decompress :: ByteString -> ByteString
Documentation
This module provides pure functions for compressing and decompressing
streams of data 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)
Compression
compress :: ByteString -> ByteStringSource
Compress a stream of data into the gzip format.
This uses the default compression level which favours a higher compression
ratio over compression speed. Use compressWith
to adjust the compression
level.
compressWith :: CompressionLevel -> ByteString -> ByteStringSource
Like compress
but with an extra parameter to specify the compression
level.
There are a number of additional compression parameters which are rarely
necessary to change but if you need to you can do so using compressFull
.
data CompressionLevel Source
Control amount of compression. This is a trade-off between the amount of compression and the time and memory required to do the compression.
DefaultCompression | The default compression level is 6 (that is, biased towards high 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. |
Decompression
decompress :: ByteString -> ByteStringSource
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.