| Copyright | (c) Don Stewart 2006-2008 (c) Duncan Coutts 2006-2011 |
|---|---|
| License | BSD-style |
| Maintainer | dons00@gmail.com, duncan@community.haskell.org |
| Stability | provisional |
| Portability | non-portable |
| Safe Haskell | Unsafe |
| Language | Haskell98 |
Data.ByteString.Unsafe
Contents
Description
A module containing unsafe ByteString operations.
While these functions have a stable API and you may use these functions in applications, do carefully consider the documented pre-conditions; incorrect use can break referential transparency or worse.
Synopsis
- unsafeHead :: ByteString -> Word8
- unsafeTail :: ByteString -> ByteString
- unsafeInit :: ByteString -> ByteString
- unsafeLast :: ByteString -> Word8
- unsafeIndex :: ByteString -> Int -> Word8
- unsafeTake :: Int -> ByteString -> ByteString
- unsafeDrop :: Int -> ByteString -> ByteString
- unsafeUseAsCString :: ByteString -> (CString -> IO a) -> IO a
- unsafeUseAsCStringLen :: ByteString -> (CStringLen -> IO a) -> IO a
- unsafePackCString :: CString -> IO ByteString
- unsafePackCStringLen :: CStringLen -> IO ByteString
- unsafePackMallocCString :: CString -> IO ByteString
- unsafePackMallocCStringLen :: CStringLen -> IO ByteString
- unsafePackAddress :: Addr# -> IO ByteString
- unsafePackAddressLen :: Int -> Addr# -> IO ByteString
- unsafePackCStringFinalizer :: Ptr Word8 -> Int -> IO () -> IO ByteString
- unsafeFinalize :: ByteString -> IO ()
Unchecked access
unsafeHead :: ByteString -> Word8 #
A variety of head for non-empty ByteStrings. unsafeHead omits the
check for the empty case, so there is an obligation on the programmer
to provide a proof that the ByteString is non-empty.
unsafeTail :: ByteString -> ByteString #
A variety of tail for non-empty ByteStrings. unsafeTail omits the
check for the empty case. As with unsafeHead, the programmer must
provide a separate proof that the ByteString is non-empty.
unsafeInit :: ByteString -> ByteString #
A variety of init for non-empty ByteStrings. unsafeInit omits the
check for the empty case. As with unsafeHead, the programmer must
provide a separate proof that the ByteString is non-empty.
unsafeLast :: ByteString -> Word8 #
A variety of last for non-empty ByteStrings. unsafeLast omits the
check for the empty case. As with unsafeHead, the programmer must
provide a separate proof that the ByteString is non-empty.
unsafeIndex :: ByteString -> Int -> Word8 #
Unsafe ByteString index (subscript) operator, starting from 0, returning a Word8
This omits the bounds check, which means there is an accompanying
obligation on the programmer to ensure the bounds are checked in some
other way.
unsafeTake :: Int -> ByteString -> ByteString #
unsafeDrop :: Int -> ByteString -> ByteString #
Low level interaction with CStrings
Using ByteStrings with functions for CStrings
unsafeUseAsCString :: ByteString -> (CString -> IO a) -> IO a #
O(1) construction Use a ByteString with a function requiring a
CString.
This function does zero copying, and merely unwraps a ByteString to
appear as a CString. It is unsafe in two ways:
- After calling this function the
CStringshares the underlying byte buffer with the originalByteString. Thus modifying theCString, either in C, or using poke, will cause the contents of theByteStringto change, breaking referential transparency. OtherByteStringscreated by sharing (such as those produced viatakeordrop) will also reflect these changes. Modifying theCStringwill break referential transparency. To avoid this, useuseAsCString, which makes a copy of the originalByteString. CStringsare often passed to functions that require them to be null-terminated. If the originalByteStringwasn't null terminated, neither will theCStringbe. It is the programmers responsibility to guarantee that theByteStringis indeed null terminated. If in doubt, useuseAsCString.- The memory may freed at any point after the subcomputation terminates, so the pointer to the storage must *not* be used after this.
unsafeUseAsCStringLen :: ByteString -> (CStringLen -> IO a) -> IO a #
O(1) construction Use a ByteString with a function requiring a
CStringLen.
This function does zero copying, and merely unwraps a ByteString to
appear as a CStringLen. It is unsafe:
- After calling this function the
CStringLenshares the underlying byte buffer with the originalByteString. Thus modifying theCStringLen, either in C, or using poke, will cause the contents of theByteStringto change, breaking referential transparency. OtherByteStringscreated by sharing (such as those produced viatakeordrop) will also reflect these changes. Modifying theCStringLenwill break referential transparency. To avoid this, useuseAsCStringLen, which makes a copy of the originalByteString.
Converting CStrings to ByteStrings
unsafePackCString :: CString -> IO ByteString #
O(n) Build a ByteString from a CString. This value will have no
finalizer associated to it, and will not be garbage collected by
Haskell. The ByteString length is calculated using strlen(3),
and thus the complexity is a O(n).
This function is unsafe. If the CString is later modified, this
change will be reflected in the resulting ByteString, breaking
referential transparency.
unsafePackCStringLen :: CStringLen -> IO ByteString #
O(1) Build a ByteString from a CStringLen. This value will
have no finalizer associated with it, and will not be garbage
collected by Haskell. This operation has O(1) complexity as we
already know the final size, so no strlen(3) is required.
This function is unsafe. If the original CStringLen is later
modified, this change will be reflected in the resulting ByteString,
breaking referential transparency.
unsafePackMallocCString :: CString -> IO ByteString #
O(n) Build a ByteString from a malloced CString. This value will
have a free(3) finalizer associated to it.
This function is unsafe. If the original CString is later
modified, this change will be reflected in the resulting ByteString,
breaking referential transparency.
This function is also unsafe if you call its finalizer twice,
which will result in a double free error, or if you pass it
a CString not allocated with malloc.
unsafePackMallocCStringLen :: CStringLen -> IO ByteString #
O(1) Build a ByteString from a malloced CStringLen. This
value will have a free(3) finalizer associated to it.
This function is unsafe. If the original CString is later
modified, this change will be reflected in the resulting ByteString,
breaking referential transparency.
This function is also unsafe if you call its finalizer twice,
which will result in a double free error, or if you pass it
a CString not allocated with malloc.
unsafePackAddress :: Addr# -> IO ByteString #
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.
unsafePackAddressLen :: Int -> Addr# -> IO ByteString #
O(1) unsafePackAddressLen provides constant-time construction of
ByteStrings, which is ideal for string literals. It packs a sequence
of bytes into a ByteString, given a raw Addr# to the string, and
the length of the string.
This function is unsafe in two ways:
- the length argument is assumed to be correct. If the length argument is incorrect, it is possible to overstep the end of the byte array.
- if the underying Addr# is later modified, this change will be
reflected in resulting
ByteString, breaking referential transparency.
If in doubt, don't use this function.
unsafePackCStringFinalizer :: Ptr Word8 -> Int -> IO () -> IO ByteString #
O(1) Construct a ByteString given a Ptr Word8 to a buffer, a
length, and an IO action representing a finalizer. This function is
not available on Hugs.
This function is unsafe, it is possible to break referential
transparency by modifying the underlying buffer pointed to by the
first argument. Any changes to the original buffer will be reflected
in the resulting ByteString.
unsafeFinalize :: ByteString -> IO () #
Explicitly run the finaliser associated with a ByteString.
References to this value after finalisation may generate invalid memory
references.
This function is unsafe, as there may be other
ByteStrings referring to the same underlying pages. If you use
this, you need to have a proof of some kind that all ByteStrings
ever generated from the underlying byte array are no longer live.