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.

type StrictByteString = ByteString Source

Type synonym for the strict flavour of ByteString.

Since: bytestring-0.11.2.0

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

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.

unsafePackLenAddress :: Int -> Addr# -> IO ByteString Source

See unsafePackAddress. This function is similar, but takes an additional length argument rather then computing it with strlen. Therefore embedding '\0' characters is possible.

Since: bytestring-0.11.2.0

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.

Since: bytestring-0.11.1.0

unsafePackLenLiteral :: Int -> Addr# -> ByteString Source

See unsafePackLiteral. This function is similar, but takes an additional length argument rather then computing it with strlen. Therefore embedding '\0' characters is possible.

Since: bytestring-0.11.2.0

Low level imperative construction

empty :: ByteString Source

O(1) The empty ByteString

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-0.10.12.0

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 reallocated 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-0.10.12.0

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 should be using unsafePackCStringLen or unsafePackCStringFinalizer instead.

toForeignPtr Source

O(1) Deconstruct a ForeignPtr from a ByteString

fromForeignPtr0 Source

Since: bytestring-0.11.0.0

toForeignPtr0 Source

O(1) Deconstruct a ForeignPtr from a ByteString

Since: bytestring-0.11.0.0

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 -> CSize -> IO () Source

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

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

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

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

c_sort :: Ptr Word8 -> CSize -> IO () 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

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!

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-4.10.0.0

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.