Copyright	(c) 2016-present Facebook Inc. All rights reserved.
License	BSD3
Maintainer	bryano@fb.com
Stability	experimental
Portability	GHC
Safe Haskell	None
Language	Haskell2010

Codec.Compression.Zstd.Efficient

Contents

Basic entry points
- Cheaper operations using contexts
  - Compression
  - Decompression
Dictionary-based compression
- Basic pure API
- Pre-digested dictionaries

Description

These functions allow for pre-allocation and reuse of relatively expensive data structures, such as compression and decompression contexts and dictionaries.

If your application mostly deals with small payloads and is particularly sensitive to latency or throughput, using these pre-allocated structures may make a noticeable difference to performance.

Synopsis

data Decompress
- = Skip
- | Error String
- | Decompress ByteString
decompressedSize :: ByteString -> Maybe Int
maxCLevel :: Int
data CCtx
withCCtx :: (CCtx -> IO a) -> IO a
compressCCtx :: CCtx -> Int -> ByteString -> IO ByteString
data DCtx
withDCtx :: (DCtx -> IO a) -> IO a
decompressDCtx :: DCtx -> ByteString -> IO Decompress
data Dict
mkDict :: ByteString -> Dict
fromDict :: Dict -> ByteString
trainFromSamples :: Int -> [ByteString] -> Either String Dict
getDictID :: Dict -> Maybe Word
compressUsingDict :: Dict -> Int -> ByteString -> ByteString
decompressUsingDict :: Dict -> ByteString -> Decompress
data CDict
createCDict :: Int -> Dict -> CDict
compressUsingCDict :: CCtx -> CDict -> ByteString -> IO ByteString
data DDict
createDDict :: Dict -> DDict
decompressUsingDDict :: DCtx -> DDict -> ByteString -> IO Decompress

Basic entry points

data Decompress Source #

The result of a decompression operation.

Constructors

Skip	Either the compressed frame was empty, or it was compressed in streaming mode and so its size is not known.
Error String	An error occurred.
Decompress ByteString	The payload was successfully decompressed.

Instances

Eq Decompress Source #
Instance details Defined in Codec.Compression.Zstd.Types Methods (==) :: Decompress -> Decompress -> Bool # (/=) :: Decompress -> Decompress -> Bool #
Read Decompress Source #
Instance details Defined in Codec.Compression.Zstd.Types Methods readsPrec :: Int -> ReadS Decompress # readList :: ReadS [Decompress] # readPrec :: ReadPrec Decompress # readListPrec :: ReadPrec [Decompress] #
Show Decompress Source #
Instance details Defined in Codec.Compression.Zstd.Types Methods showsPrec :: Int -> Decompress -> ShowS # show :: Decompress -> String # showList :: [Decompress] -> ShowS #

decompressedSize :: ByteString -> Maybe Int Source #

Return the decompressed size of a compressed payload, as stored in the payload's header.

The returned value will be Nothing if it is either not known (probably because the payload was compressed using a streaming API), empty, or too large to fit in an Int.

Note: this value should not be trusted, as it can be controlled by an attacker.

maxCLevel :: Int Source #

The maximum compression level supported by the library.

Cheaper operations using contexts

Compression

data CCtx Source #

Compression context.

withCCtx :: (CCtx -> IO a) -> IO a Source #

Allocate a compression context, run an action that may reuse the context as many times as it needs, then free the context.

compressCCtx Source #

Arguments

:: CCtx	Compression context.
-> Int	Compression level. Must be >= 1 and <= `maxCLevel`.
-> ByteString	Payload to compress.
-> IO ByteString

Compress the given data as a single zstd compressed frame.

Decompression

data DCtx Source #

Decompression context.

withDCtx :: (DCtx -> IO a) -> IO a Source #

Allocate a decompression context, run an action that may reuse the context as many times as it needs, then free the context.

decompressDCtx Source #

Arguments

:: DCtx	Decompression context.
-> ByteString	Compressed payload.
-> IO Decompress

Decompress a single-frame payload of known size. Typically this will be a payload that was compressed with compress.

Note: This function is not capable of decompressing a payload generated by the streaming or lazy compression APIs.

Dictionary-based compression

data Dict Source #

Compression dictionary.

Instances

Eq Dict Source #
Instance details Defined in Codec.Compression.Zstd.Types Methods (==) :: Dict -> Dict -> Bool # (/=) :: Dict -> Dict -> Bool #
Ord Dict Source #
Instance details Defined in Codec.Compression.Zstd.Types Methods compare :: Dict -> Dict -> Ordering # (<) :: Dict -> Dict -> Bool # (<=) :: Dict -> Dict -> Bool # (>) :: Dict -> Dict -> Bool # (>=) :: Dict -> Dict -> Bool # max :: Dict -> Dict -> Dict # min :: Dict -> Dict -> Dict #
Read Dict Source #
Instance details Defined in Codec.Compression.Zstd.Types Methods readsPrec :: Int -> ReadS Dict # readList :: ReadS [Dict] # readPrec :: ReadPrec Dict # readListPrec :: ReadPrec [Dict] #
Show Dict Source #
Instance details Defined in Codec.Compression.Zstd.Types Methods showsPrec :: Int -> Dict -> ShowS # show :: Dict -> String # showList :: [Dict] -> ShowS #
NFData Dict Source #
Instance details Defined in Codec.Compression.Zstd.Types Methods rnf :: Dict -> () #

mkDict :: ByteString -> Dict Source #

Smart constructor.

fromDict :: Dict -> ByteString Source #

trainFromSamples Source #

Arguments

:: Int	Maximum size of the compression dictionary to create. The actual dictionary returned may be smaller.
-> [ByteString]	Samples to train with.
-> Either String Dict

Create and train a compression dictionary from a collection of samples.

To create a well-trained dictionary, here are some useful guidelines to keep in mind:

A reasonable dictionary size is in the region of 100 KB. (Trying to specify a dictionary size of less than a few hundred bytes will probably fail.)
To train the dictionary well, it is best to supply a few thousand training samples.
The combined size of all training samples should be 100 or more times larger than the size of the dictionary.

getDictID :: Dict -> Maybe Word Source #

Return the identifier for the given dictionary, or Nothing if not a valid dictionary.

Basic pure API

compressUsingDict Source #

Arguments

:: Dict	Compression dictionary.
-> Int	Compression level. Must be >= 1 and <= `maxCLevel`.
-> ByteString	Payload to compress.
-> ByteString

Compress the given data as a single zstd compressed frame, using a prebuilt dictionary.

decompressUsingDict Source #

Arguments

:: Dict	Dictionary.
-> ByteString	Payload to decompress.
-> Decompress

Decompress a single-frame payload of known size, using a prebuilt dictionary. Typically this will be a payload that was compressed with compressUsingDict.

Note: This function is not capable of decompressing a payload generated by the streaming or lazy compression APIs.

Pre-digested dictionaries

data CDict Source #

A pre-digested compression dictionary.

createCDict Source #

Arguments

:: Int	Compression level.
-> Dict	Dictionary.
-> CDict

Create a pre-digested compression dictionary.

compressUsingCDict Source #

Arguments

:: CCtx	Compression context.
-> CDict	Compression dictionary.
-> ByteString	Payload to compress.
-> IO ByteString

Compress the given data as a single zstd compressed frame, using a pre-built, pre-digested dictionary.

data DDict Source #

A pre-digested decompression dictionary.

createDDict Source #

Arguments

:: Dict	Dictionary.
-> DDict

Create a pre-digested compression dictionary.

decompressUsingDDict Source #

Arguments

:: DCtx	Decompression context.
-> DDict	Decompression dictionary.
-> ByteString	Payload to compress.
-> IO Decompress

Decompress a single-frame payload of known size, using a pre-built, pre-digested dictionary. Typically this will be a payload that was compressed with compressUsingCDict.

Note: This function is not capable of decompressing a payload generated by the streaming or lazy compression APIs.