bytestring- Fast, compact, strict and lazy byte strings with a list interface
Copyright(c) Don Stewart 2006-2008
(c) Duncan Coutts 2006-2012
Safe HaskellUnsafe



A module containing semi-public ByteString internals. This exposes the ByteString representation and low level construction functions. As such all the functions in this module are unsafe. The API is also not stable.

Where possible application should instead use the functions from the normal public interface modules, such as Data.ByteString.Unsafe. Packages that extend the ByteString system at a low level will need to use this module.


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.


BS !(ForeignPtr Word8) !Int 

Bundled Patterns

pattern PS :: ForeignPtr Word8 -> Int -> Int -> ByteString

PS foreignPtr offset length represents a ByteString with data backed by a given foreignPtr, starting at a given offset in bytes and of a specified length.

This pattern is used to emulate the legacy ByteString data constructor, so that pre-existing code generally doesn't need to change to benefit from the simplified BS constructor and can continue to function unchanged.

Note: Matching with this constructor will always be given a 0 offset, as the base will be manipulated by plusForeignPtr instead.


Instances details
Data ByteString # 
Instance details

Defined in Data.ByteString.Internal


gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> ByteString -> c ByteString Source #

gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c ByteString Source #

toConstr :: ByteString -> Constr Source #

dataTypeOf :: ByteString -> DataType Source #

dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c ByteString) Source #

dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c ByteString) Source #

gmapT :: (forall b. Data b => b -> b) -> ByteString -> ByteString Source #

gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> ByteString -> r Source #

gmapQr :: forall r r'. (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> ByteString -> r Source #

gmapQ :: (forall d. Data d => d -> u) -> ByteString -> [u] Source #

gmapQi :: Int -> (forall d. Data d => d -> u) -> ByteString -> u Source #

gmapM :: Monad m => (forall d. Data d => d -> m d) -> ByteString -> m ByteString Source #

gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> ByteString -> m ByteString Source #

gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> ByteString -> m ByteString Source #

IsString ByteString #

Beware: fromString truncates multi-byte characters to octets. e.g. "枯朶に烏のとまりけり秋の暮" becomes �6k�nh~�Q��n�

Instance details

Defined in Data.ByteString.Internal

Monoid ByteString # 
Instance details

Defined in Data.ByteString.Internal

Semigroup ByteString # 
Instance details

Defined in Data.ByteString.Internal

IsList ByteString #

Since: bytestring-

Instance details

Defined in Data.ByteString.Internal

Associated Types

type Item ByteString Source #

Read ByteString # 
Instance details

Defined in Data.ByteString.Internal

Show ByteString # 
Instance details

Defined in Data.ByteString.Internal

NFData ByteString # 
Instance details

Defined in Data.ByteString.Internal


rnf :: ByteString -> () Source #

Eq ByteString # 
Instance details

Defined in Data.ByteString.Internal

Ord ByteString # 
Instance details

Defined in Data.ByteString.Internal

type Item ByteString # 
Instance details

Defined in Data.ByteString.Internal

Internal indexing

findIndexOrLength :: (Word8 -> Bool) -> ByteString -> Int Source #

findIndexOrLength is a variant of findIndex, that returns the length of the string if no element is found, rather than Nothing.

Conversion with lists: packing and unpacking

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.

unsafePackLiteral :: Addr# -> ByteString Source #

See unsafePackAddress. This function has similar behavior. Prefer this function when the address in known to be an Addr# literal. In that context, there is no need for the sequencing guarantees that IO provides. On GHC 9.0 and up, this function uses the FinalPtr data constructor for ForeignPtrContents.

Low level imperative construction

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

Create ByteString of size l and use action f to fill its contents.

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

Given a maximum size l and an action f that fills the ByteString starting at the given Ptr and returns the actual utilized length, createUpToN` l f returns the filled ByteString.

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

Like createUpToN, but also returns an additional value created by the action.

Since: bytestring-

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.

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

Since: bytestring-

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

Wrapper of mallocForeignPtrBytes with faster implementation for GHC

Conversion to and from ForeignPtrs

fromForeignPtr Source #


:: ForeignPtr Word8 
-> Int


-> Int


-> ByteString 

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 #


:: ByteString 
-> (ForeignPtr Word8, Int, Int)

(ptr, offset, length)

O(1) Deconstruct a ForeignPtr from a ByteString

toForeignPtr0 Source #


:: ByteString 
-> (ForeignPtr Word8, Int)

(ptr, length)

O(1) Deconstruct a ForeignPtr from a ByteString


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

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

cbits functions


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

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:

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!

Exported compatibility shim

plusForeignPtr :: ForeignPtr a -> Int -> ForeignPtr b Source #

Advances the given address by the given offset in bytes.

The new ForeignPtr shares the finalizer of the original, equivalent from a finalization standpoint to just creating another reference to the original. That is, the finalizer will not be called before the new ForeignPtr is unreachable, nor will it be called an additional time due to this call, and the finalizer will be called with the same address that it would have had this call not happened, *not* the new address.

Since: base-

unsafeWithForeignPtr :: ForeignPtr a -> (Ptr a -> IO b) -> IO b Source #

This is similar to withForeignPtr but comes with an important caveat: the user must guarantee that the continuation does not diverge (e.g. loop or throw an exception). In exchange for this loss of generality, this function offers the ability of GHC to optimise more aggressively.

Specifically, applications of the form: unsafeWithForeignPtr fptr (forever something)

See GHC issue #17760 for more information about the unsoundness behavior that this function can result in.