streaming-commons-0.1.18: Common lower-level functions needed by various streaming data libraries

Data.Streaming.Zlib

Contents

Description

This is a middle-level wrapper around the zlib C API. It allows you to work fully with bytestrings and not touch the FFI at all, but is still low-level enough to allow you to implement high-level abstractions such as enumerators. Significantly, it does not use lazy IO.

You'll probably need to reference the docs a bit to understand the WindowBits parameters below, but a basic rule of thumb is 15 is for zlib compression, and 31 for gzip compression.

A simple streaming compressor in pseudo-code would look like:

def <- initDeflate ...
popper <- feedDeflate def rawContent
pullPopper popper
...
finishDeflate def sendCompressedData

You can see a more complete example is available in the included file-test.hs.

Synopsis

# Inflate

data Inflate Source #

The state of an inflation (eg, decompression) process. All allocated memory is automatically reclaimed by the garbage collector. Also can contain the inflation dictionary that is used for decompression.

Initialize an inflation process with the given WindowBits. You will need to call feedInflate to feed compressed data to this and finishInflate to extract the final chunk of decompressed data.

Initialize an inflation process with the given WindowBits. Unlike initInflate a dictionary for inflation is set which must match the one set during compression.

Feed the given ByteString to the inflater. Return a Popper, an IO action that returns the decompressed data a chunk at a time. The Popper must be called to exhaustion before using the Inflate object again.

Note that this function automatically buffers the output to defaultChunkSize, and therefore you won't get any data from the popper until that much decompressed data is available. After you have fed all of the compressed data to this function, you can extract your final chunk of decompressed data using finishInflate.

As explained in feedInflate, inflation buffers your decompressed data. After you call feedInflate with your last chunk of compressed data, you will likely have some data still sitting in the buffer. This function will return it to you.

Flush the inflation buffer. Useful for interactive application.

This is actually a synonym for finishInflate. It is provided for its more semantic name.

Since 0.0.3

Retrieve any data remaining after inflating. For more information on motivation, see:

https://github.com/fpco/streaming-commons/issues/20

Since 0.1.11

Returns True if the inflater has reached end-of-stream, or False if it is still expecting more data.

Since 0.1.18

# Deflate

data Deflate Source #

The state of a deflation (eg, compression) process. All allocated memory is automatically reclaimed by the garbage collector.

Arguments

 :: Int Compression level -> WindowBits -> IO Deflate

Initialize a deflation process with the given compression level and WindowBits. You will need to call feedDeflate to feed uncompressed data to this and finishDeflate to extract the final chunks of compressed data.

Arguments

 :: Int Compression level -> ByteString Deflate dictionary -> WindowBits -> IO Deflate

Initialize an deflation process with the given compression level and WindowBits. Unlike initDeflate a dictionary for deflation is set.

Feed the given ByteString to the deflater. Return a Popper, an IO action that returns the compressed data a chunk at a time. The Popper must be called to exhaustion before using the Deflate object again.

Note that this function automatically buffers the output to defaultChunkSize, and therefore you won't get any data from the popper until that much compressed data is available. After you have fed all of the decompressed data to this function, you can extract your final chunks of compressed data using finishDeflate.

As explained in feedDeflate, deflation buffers your compressed data. After you call feedDeflate with your last chunk of uncompressed data, use this to flush the rest of the data and signal end of input.

Flush the deflation buffer. Useful for interactive application. Internally this passes Z_SYNC_FLUSH to the zlib library.

Unlike finishDeflate, flushDeflate does not signal end of input, meaning you can feed more uncompressed data afterward.

Since 0.0.3

Full flush the deflation buffer. Useful for interactive applications where previously streamed data may not be available. Using fullFlushDeflate too often can seriously degrade compression. Internally this passes Z_FULL_FLUSH to the zlib library.

Like flushDeflate, fullFlushDeflate does not signal end of input, meaning you can feed more uncompressed data afterward.

Since 0.1.5

# Data types

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

Instances

 Methods Methods MethodsshowList :: [WindowBits] -> ShowS # Associated Typestype Rep WindowBits :: * -> * # Methods type Rep WindowBits type Rep WindowBits = D1 (MetaData "WindowBits" "Codec.Compression.Zlib.Stream" "zlib-0.6.1.2-BfeUVhBVvrx1Nvtzv6OD9c" False) ((:+:) (C1 (MetaCons "WindowBits" PrefixI False) (S1 (MetaSel (Nothing Symbol) NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 Int))) (C1 (MetaCons "DefaultWindowBits" PrefixI False) U1))

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

Exception that can be thrown from the FFI code. The parameter is the numerical error code from the zlib library. Quoting the zlib.h file directly:

• #define Z_OK 0
• #define Z_STREAM_END 1
• #define Z_NEED_DICT 2
• #define Z_ERRNO (-1)
• #define Z_STREAM_ERROR (-2)
• #define Z_DATA_ERROR (-3)
• #define Z_MEM_ERROR (-4)
• #define Z_BUF_ERROR (-5)
• #define Z_VERSION_ERROR (-6)

Constructors

 ZlibException Int

Instances

 Source # MethodsshowList :: [ZlibException] -> ShowS # Source # Methods

An IO action that returns the next chunk of data, returning Nothing when there is no more data to be popped.

data PopperRes Source #

Constructors

 PRDone PRNext !ByteString PRError !ZlibException

Instances

 Source # MethodsshowList :: [PopperRes] -> ShowS #