Data.ByteString.Internal

Copyright	(c) Don Stewart 2006-2008 (c) Duncan Coutts 2006-2012
License	BSD-style
Maintainer	[email protected], [email protected]
Stability	unstable
Portability	non-portable
Safe Haskell	Unsafe
Language	Haskell98

The ByteString type and representation

data ByteString Source

A space-efficient representation of a Word8 vector, supporting many efficient operations.

A ByteString contains 8-bit bytes, or by using the operations from Data.ByteString.Char8 it can be interpreted as containing 8-bit characters.

Conversion with lists: packing and unpacking

packBytes :: [Word8] -> ByteString Source

packUptoLenBytes :: Int -> [Word8] -> (ByteString, [Word8]) Source

unsafePackLenBytes :: Int -> [Word8] -> ByteString Source

packChars :: [Char] -> ByteString Source

packUptoLenChars :: Int -> [Char] -> (ByteString, [Char]) Source

unsafePackLenChars :: Int -> [Char] -> ByteString Source

unpackBytes :: ByteString -> [Word8] Source

unpackAppendBytesLazy :: ByteString -> [Word8] -> [Word8] Source

unpackAppendBytesStrict :: ByteString -> [Word8] -> [Word8] Source

unpackChars :: ByteString -> [Char] Source

unpackAppendCharsLazy :: ByteString -> [Char] -> [Char] Source

unpackAppendCharsStrict :: ByteString -> [Char] -> [Char] Source

unsafePackAddress :: Addr# -> IO ByteString Source

O(n) Pack a null-terminated sequence of bytes, pointed to by an Addr# (an arbitrary machine address assumed to point outside the garbage-collected heap) into a ByteString. A much faster way to create an Addr# is with an unboxed string literal, than to pack a boxed string. A unboxed string literal is compiled to a static char [] by GHC. Establishing the length of the string requires a call to strlen(3), so the Addr# must point to a null-terminated buffer (as is the case with "string"# literals in GHC). Use unsafePackAddressLen if you know the length of the string statically.

An example:

literalFS = unsafePackAddress "literal"#

This function is unsafe. If you modify the buffer pointed to by the original Addr# this modification will be reflected in the resulting ByteString, breaking referential transparency.

Note this also won't work if your Addr# has embedded '\0' characters in the string, as strlen will return too short a length.

Low level imperative construction

create :: Int -> (Ptr Word8 -> IO ()) -> IO ByteString Source

Create ByteString of size l and use action f to fill it's contents.

createUptoN :: Int -> (Ptr Word8 -> IO Int) -> IO ByteString Source

Create ByteString of up to size size l and use action f to fill it's contents which returns its true size.

createAndTrim :: Int -> (Ptr Word8 -> IO Int) -> IO ByteString Source

Given the maximum size needed and a function to make the contents of a ByteString, createAndTrim makes the ByteString. The generating function is required to return the actual final size (<= the maximum size), and the resulting byte array is realloced to this size.

createAndTrim is the main mechanism for creating custom, efficient ByteString functions, using Haskell or C functions to fill the space.

createAndTrim' :: Int -> (Ptr Word8 -> IO (Int, Int, a)) -> IO (ByteString, a) Source

unsafeCreate :: Int -> (Ptr Word8 -> IO ()) -> ByteString Source

A way of creating ByteStrings outside the IO monad. The Int argument gives the final size of the ByteString.

unsafeCreateUptoN :: Int -> (Ptr Word8 -> IO Int) -> ByteString Source

Like unsafeCreate but instead of giving the final size of the ByteString, it is just an upper bound. The inner action returns the actual size. Unlike createAndTrim the ByteString is not reallocated if the final size is less than the estimated size.

mallocByteString :: Int -> IO (ForeignPtr a) Source

Wrapper of mallocForeignPtrBytes with faster implementation for GHC

Conversion to and from ForeignPtrs

fromForeignPtr Source

O(1) Build a ByteString from a ForeignPtr.

If you do not need the offset parameter then you do should be using unsafePackCStringLen or unsafePackCStringFinalizer instead.

toForeignPtr Source

O(1) Deconstruct a ForeignPtr from a ByteString

Utilities

nullForeignPtr :: ForeignPtr Word8 Source

The 0 pointer. Used to indicate the empty Bytestring.

checkedAdd :: String -> Int -> Int -> Int Source

Add two non-negative numbers. Errors out on overflow.

Standard C Functions

c_strlen :: CString -> IO CSize Source

c_free_finalizer :: FunPtr (Ptr Word8 -> IO ()) Source

memchr :: Ptr Word8 -> Word8 -> CSize -> IO (Ptr Word8) Source

memcmp :: Ptr Word8 -> Ptr Word8 -> Int -> IO CInt Source

memcpy :: Ptr Word8 -> Ptr Word8 -> Int -> IO () Source

memset :: Ptr Word8 -> Word8 -> CSize -> IO (Ptr Word8) Source

cbits functions

c_reverse :: Ptr Word8 -> Ptr Word8 -> CULong -> IO () Source

c_intersperse :: Ptr Word8 -> Ptr Word8 -> CULong -> Word8 -> IO () Source

c_maximum :: Ptr Word8 -> CULong -> IO Word8 Source

c_minimum :: Ptr Word8 -> CULong -> IO Word8 Source

c_count :: Ptr Word8 -> CULong -> Word8 -> IO CULong Source

Chars

w2c :: Word8 -> Char Source

Conversion between Word8 and Char. Should compile to a no-op.

c2w :: Char -> Word8 Source

Unsafe conversion between Char and Word8. This is a no-op and silently truncates to 8 bits Chars > '255'. It is provided as convenience for ByteString construction.

isSpaceWord8 :: Word8 -> Bool Source

Selects words corresponding to white-space characters in the Latin-1 range ordered by frequency.

isSpaceChar8 :: Char -> Bool Source

Selects white-space characters in the Latin-1 range

Deprecated and unmentionable

accursedUnutterablePerformIO :: IO a -> a Source

This "function" has a superficial similarity to unsafePerformIO but it is in fact a malevolent agent of chaos. It unpicks the seams of reality (and the IO monad) so that the normal rules no longer apply. It lulls you into thinking it is reasonable, but when you are not looking it stabs you in the back and aliases all of your mutable buffers. The carcass of many a seasoned Haskell programmer lie strewn at its feet.

Witness the trail of destruction:

• https://github.com/haskell/bytestring/commit/71c4b438c675aa360c79d79acc9a491e7bbc26e7
• https://github.com/haskell/bytestring/commit/210c656390ae617d9ee3b8bcff5c88dd17cef8da
• https://ghc.haskell.org/trac/ghc/ticket/3486
• https://ghc.haskell.org/trac/ghc/ticket/3487
• https://ghc.haskell.org/trac/ghc/ticket/7270

Do not talk about "safe"! You do not know what is safe!

Yield not to its blasphemous call! Flee traveller! Flee or you will be corrupted and devoured!

inlinePerformIO :: IO a -> a Source