{-# LANGUAGE Trustworthy #-}
{-# LANGUAGE NoImplicitPrelude #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE BangPatterns #-}

-----------------------------------------------------------------------------
-- |
-- Module      :  GHC.Foreign
-- Copyright   :  (c) The University of Glasgow, 2008-2011
-- License     :  see libraries/base/LICENSE
--
-- Maintainer  :  libraries@haskell.org
-- Stability   :  internal
-- Portability :  non-portable
--
-- Foreign marshalling support for CStrings with configurable encodings
--
-----------------------------------------------------------------------------

module GHC.Foreign (
    -- * C strings with a configurable encoding

    -- conversion of C strings into Haskell strings
    --
    peekCString,
    peekCStringLen,

    -- conversion of Haskell strings into C strings
    --
    newCString,
    newCStringLen,

    -- conversion of Haskell strings into C strings using temporary storage
    --
    withCString,
    withCStringLen,
    withCStringsLen,

    charIsRepresentable,
  ) where

import Foreign.Marshal.Array
import Foreign.C.Types
import Foreign.Ptr
import Foreign.Storable

import Data.Word

-- Imports for the locale-encoding version of marshallers

import Data.Tuple (fst)

import GHC.Show ( show )

import Foreign.Marshal.Alloc
import Foreign.ForeignPtr

import GHC.Debug
import GHC.List
import GHC.Num
import GHC.Base

import GHC.IO
import GHC.IO.Exception
import GHC.IO.Buffer
import GHC.IO.Encoding.Types


c_DEBUG_DUMP :: Bool
c_DEBUG_DUMP :: Bool
c_DEBUG_DUMP = Bool
False

putDebugMsg :: String -> IO ()
putDebugMsg :: String -> IO ()
putDebugMsg | Bool
c_DEBUG_DUMP = String -> IO ()
debugLn
            | Bool
otherwise    = forall a b. a -> b -> a
const (forall (m :: * -> *) a. Monad m => a -> m a
return ())


-- These definitions are identical to those in Foreign.C.String, but copied in here to avoid a cycle:
type CString    = Ptr CChar
type CStringLen = (Ptr CChar, Int)

-- exported functions
-- ------------------

-- | Marshal a NUL terminated C string into a Haskell string.
--
peekCString    :: TextEncoding -> CString -> IO String
peekCString :: TextEncoding -> CString -> IO String
peekCString TextEncoding
enc CString
cp = do
    Int
sz <- forall a. (Storable a, Eq a) => a -> Ptr a -> IO Int
lengthArray0 CChar
nUL CString
cp
    TextEncoding -> CStringLen -> IO String
peekEncodedCString TextEncoding
enc (CString
cp, Int
sz forall a. Num a => a -> a -> a
* Int
cCharSize)

-- | Marshal a C string with explicit length into a Haskell string.
--
peekCStringLen           :: TextEncoding -> CStringLen -> IO String
peekCStringLen :: TextEncoding -> CStringLen -> IO String
peekCStringLen = TextEncoding -> CStringLen -> IO String
peekEncodedCString

-- | Marshal a Haskell string into a NUL terminated C string.
--
-- * the Haskell string may /not/ contain any NUL characters
--
-- * new storage is allocated for the C string and must be
--   explicitly freed using 'Foreign.Marshal.Alloc.free' or
--   'Foreign.Marshal.Alloc.finalizerFree'.
--
newCString :: TextEncoding -> String -> IO CString
newCString :: TextEncoding -> String -> IO CString
newCString TextEncoding
enc = forall (m :: * -> *) a1 r. Monad m => (a1 -> r) -> m a1 -> m r
liftM forall a b. (a, b) -> a
fst forall b c a. (b -> c) -> (a -> b) -> a -> c
. TextEncoding -> Bool -> String -> IO CStringLen
newEncodedCString TextEncoding
enc Bool
True

-- | Marshal a Haskell string into a C string (ie, character array) with
-- explicit length information.
--
-- * new storage is allocated for the C string and must be
--   explicitly freed using 'Foreign.Marshal.Alloc.free' or
--   'Foreign.Marshal.Alloc.finalizerFree'.
--
newCStringLen     :: TextEncoding -> String -> IO CStringLen
newCStringLen :: TextEncoding -> String -> IO CStringLen
newCStringLen TextEncoding
enc = TextEncoding -> Bool -> String -> IO CStringLen
newEncodedCString TextEncoding
enc Bool
False

-- | Marshal a Haskell string into a NUL terminated C string using temporary
-- storage.
--
-- * the Haskell string may /not/ contain any NUL characters
--
-- * the memory is freed when the subcomputation terminates (either
--   normally or via an exception), so the pointer to the temporary
--   storage must /not/ be used after this.
--
withCString :: TextEncoding -> String -> (CString -> IO a) -> IO a
withCString :: forall a. TextEncoding -> String -> (CString -> IO a) -> IO a
withCString TextEncoding
enc String
s CString -> IO a
act = forall a.
TextEncoding -> Bool -> String -> (CStringLen -> IO a) -> IO a
withEncodedCString TextEncoding
enc Bool
True String
s forall a b. (a -> b) -> a -> b
$ \(CString
cp, Int
_sz) -> CString -> IO a
act CString
cp

-- | Marshal a Haskell string into a C string (ie, character array)
-- in temporary storage, with explicit length information.
--
-- * the memory is freed when the subcomputation terminates (either
--   normally or via an exception), so the pointer to the temporary
--   storage must /not/ be used after this.
--
withCStringLen         :: TextEncoding -> String -> (CStringLen -> IO a) -> IO a
withCStringLen :: forall a. TextEncoding -> String -> (CStringLen -> IO a) -> IO a
withCStringLen TextEncoding
enc = forall a.
TextEncoding -> Bool -> String -> (CStringLen -> IO a) -> IO a
withEncodedCString TextEncoding
enc Bool
False

-- | Marshal a list of Haskell strings into an array of NUL terminated C strings
-- using temporary storage.
--
-- * the Haskell strings may /not/ contain any NUL characters
--
-- * the memory is freed when the subcomputation terminates (either
--   normally or via an exception), so the pointer to the temporary
--   storage must /not/ be used after this.
--
withCStringsLen :: TextEncoding
                -> [String]
                -> (Int -> Ptr CString -> IO a)
                -> IO a
withCStringsLen :: forall a.
TextEncoding -> [String] -> (Int -> Ptr CString -> IO a) -> IO a
withCStringsLen TextEncoding
enc [String]
strs Int -> Ptr CString -> IO a
f = [CString] -> [String] -> IO a
go [] [String]
strs
  where
  go :: [CString] -> [String] -> IO a
go [CString]
cs (String
s:[String]
ss) = forall a. TextEncoding -> String -> (CString -> IO a) -> IO a
withCString TextEncoding
enc String
s forall a b. (a -> b) -> a -> b
$ \CString
c -> [CString] -> [String] -> IO a
go (CString
cforall a. a -> [a] -> [a]
:[CString]
cs) [String]
ss
  go [CString]
cs [] = forall a b. Storable a => [a] -> (Int -> Ptr a -> IO b) -> IO b
withArrayLen (forall a. [a] -> [a]
reverse [CString]
cs) Int -> Ptr CString -> IO a
f

-- | Determines whether a character can be accurately encoded in a
-- 'Foreign.C.String.CString'.
--
-- Pretty much anyone who uses this function is in a state of sin because
-- whether or not a character is encodable will, in general, depend on the
-- context in which it occurs.
charIsRepresentable :: TextEncoding -> Char -> IO Bool
-- We force enc explicitly because `catch` is lazy in its
-- first argument. We would probably like to force c as well,
-- but unfortunately worker/wrapper produces very bad code for
-- that.
--
-- TODO If this function is performance-critical, it would probably
-- pay to use a single-character specialization of withCString. That
-- would allow worker/wrapper to actually eliminate Char boxes, and
-- would also get rid of the completely unnecessary cons allocation.
charIsRepresentable :: TextEncoding -> Char -> IO Bool
charIsRepresentable !TextEncoding
enc Char
c =
  forall a. TextEncoding -> String -> (CString -> IO a) -> IO a
withCString TextEncoding
enc [Char
c]
              (\CString
cstr -> do String
str <- TextEncoding -> CString -> IO String
peekCString TextEncoding
enc CString
cstr
                           case String
str of
                             [Char
ch] | Char
ch forall a. Eq a => a -> a -> Bool
== Char
c -> forall (f :: * -> *) a. Applicative f => a -> f a
pure Bool
True
                             String
_ -> forall (f :: * -> *) a. Applicative f => a -> f a
pure Bool
False)
    forall e a. Exception e => IO a -> (e -> IO a) -> IO a
`catch`
       \(IOException
_ :: IOException) -> forall (f :: * -> *) a. Applicative f => a -> f a
pure Bool
False

-- auxiliary definitions
-- ----------------------

-- C's end of string character
nUL :: CChar
nUL :: CChar
nUL  = CChar
0

-- Size of a CChar in bytes
cCharSize :: Int
cCharSize :: Int
cCharSize = forall a. Storable a => a -> Int
sizeOf (forall a. HasCallStack => a
undefined :: CChar)


{-# INLINE peekEncodedCString #-}
peekEncodedCString :: TextEncoding -- ^ Encoding of CString
                   -> CStringLen
                   -> IO String    -- ^ String in Haskell terms
peekEncodedCString :: TextEncoding -> CStringLen -> IO String
peekEncodedCString (TextEncoding { mkTextDecoder :: ()
mkTextDecoder = IO (TextDecoder dstate)
mk_decoder }) (CString
p, Int
sz_bytes)
  = forall a b c. IO a -> (a -> IO b) -> (a -> IO c) -> IO c
bracket IO (TextDecoder dstate)
mk_decoder forall from to state. BufferCodec from to state -> IO ()
close forall a b. (a -> b) -> a -> b
$ \TextDecoder dstate
decoder -> do
      let chunk_size :: Int
chunk_size = Int
sz_bytes forall a. Ord a => a -> a -> a
`max` Int
1 -- Decode buffer chunk size in characters: one iteration only for ASCII
      Buffer Word8
from0 <- forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
fmap (\RawBuffer Word8
fp -> forall e. Int -> Buffer e -> Buffer e
bufferAdd Int
sz_bytes (forall e. RawBuffer e -> Int -> BufferState -> Buffer e
emptyBuffer RawBuffer Word8
fp Int
sz_bytes BufferState
ReadBuffer)) forall a b. (a -> b) -> a -> b
$ forall a. Ptr a -> IO (ForeignPtr a)
newForeignPtr_ (forall a b. Ptr a -> Ptr b
castPtr CString
p)
      CharBuffer
to <- Int -> BufferState -> IO CharBuffer
newCharBuffer Int
chunk_size BufferState
WriteBuffer

      let go :: t -> Buffer Word8 -> IO String
go !t
iteration Buffer Word8
from = do
            (CodingProgress
why, Buffer Word8
from', CharBuffer
to') <- forall from to state.
BufferCodec from to state -> CodeBuffer from to
encode TextDecoder dstate
decoder Buffer Word8
from CharBuffer
to
            if forall e. Buffer e -> Bool
isEmptyBuffer Buffer Word8
from'
             then
              -- No input remaining: @why@ will be InputUnderflow, but we don't care
              forall e a. Buffer e -> (Ptr e -> IO a) -> IO a
withBuffer CharBuffer
to' forall a b. (a -> b) -> a -> b
$ forall a. Storable a => Int -> Ptr a -> IO [a]
peekArray (forall e. Buffer e -> Int
bufferElems CharBuffer
to')
             else do
              -- Input remaining: what went wrong?
              String -> IO ()
putDebugMsg (String
"peekEncodedCString: " forall a. [a] -> [a] -> [a]
++ forall a. Show a => a -> String
show t
iteration forall a. [a] -> [a] -> [a]
++ String
" " forall a. [a] -> [a] -> [a]
++ forall a. Show a => a -> String
show CodingProgress
why)
              (Buffer Word8
from'', CharBuffer
to'') <- case CodingProgress
why of CodingProgress
InvalidSequence -> forall from to state.
BufferCodec from to state
-> Buffer from -> Buffer to -> IO (Buffer from, Buffer to)
recover TextDecoder dstate
decoder Buffer Word8
from' CharBuffer
to' -- These conditions are equally bad because
                                            CodingProgress
InputUnderflow  -> forall from to state.
BufferCodec from to state
-> Buffer from -> Buffer to -> IO (Buffer from, Buffer to)
recover TextDecoder dstate
decoder Buffer Word8
from' CharBuffer
to' -- they indicate malformed/truncated input
                                            CodingProgress
OutputUnderflow -> forall (m :: * -> *) a. Monad m => a -> m a
return (Buffer Word8
from', CharBuffer
to')       -- We will have more space next time round
              String -> IO ()
putDebugMsg (String
"peekEncodedCString: from " forall a. [a] -> [a] -> [a]
++ forall a. Buffer a -> String
summaryBuffer Buffer Word8
from forall a. [a] -> [a] -> [a]
++ String
" " forall a. [a] -> [a] -> [a]
++ forall a. Buffer a -> String
summaryBuffer Buffer Word8
from' forall a. [a] -> [a] -> [a]
++ String
" " forall a. [a] -> [a] -> [a]
++ forall a. Buffer a -> String
summaryBuffer Buffer Word8
from'')
              String -> IO ()
putDebugMsg (String
"peekEncodedCString: to " forall a. [a] -> [a] -> [a]
++ forall a. Buffer a -> String
summaryBuffer CharBuffer
to forall a. [a] -> [a] -> [a]
++ String
" " forall a. [a] -> [a] -> [a]
++ forall a. Buffer a -> String
summaryBuffer CharBuffer
to' forall a. [a] -> [a] -> [a]
++ String
" " forall a. [a] -> [a] -> [a]
++ forall a. Buffer a -> String
summaryBuffer CharBuffer
to'')
              String
to_chars <- forall e a. Buffer e -> (Ptr e -> IO a) -> IO a
withBuffer CharBuffer
to'' forall a b. (a -> b) -> a -> b
$ forall a. Storable a => Int -> Ptr a -> IO [a]
peekArray (forall e. Buffer e -> Int
bufferElems CharBuffer
to'')
              forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
fmap (String
to_charsforall a. [a] -> [a] -> [a]
++) forall a b. (a -> b) -> a -> b
$ t -> Buffer Word8 -> IO String
go (t
iteration forall a. Num a => a -> a -> a
+ t
1) Buffer Word8
from''

      forall {t}. (Show t, Num t) => t -> Buffer Word8 -> IO String
go (Int
0 :: Int) Buffer Word8
from0

{-# INLINE withEncodedCString #-}
withEncodedCString :: TextEncoding         -- ^ Encoding of CString to create
                   -> Bool                 -- ^ Null-terminate?
                   -> String               -- ^ String to encode
                   -> (CStringLen -> IO a) -- ^ Worker that can safely use the allocated memory
                   -> IO a
withEncodedCString :: forall a.
TextEncoding -> Bool -> String -> (CStringLen -> IO a) -> IO a
withEncodedCString (TextEncoding { mkTextEncoder :: ()
mkTextEncoder = IO (TextEncoder estate)
mk_encoder }) Bool
null_terminate String
s CStringLen -> IO a
act
  = forall a b c. IO a -> (a -> IO b) -> (a -> IO c) -> IO c
bracket IO (TextEncoder estate)
mk_encoder forall from to state. BufferCodec from to state -> IO ()
close forall a b. (a -> b) -> a -> b
$ \TextEncoder estate
encoder -> forall a b. Storable a => [a] -> (Int -> Ptr a -> IO b) -> IO b
withArrayLen String
s forall a b. (a -> b) -> a -> b
$ \Int
sz Ptr Char
p -> do
      CharBuffer
from <- forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
fmap (\RawBuffer Char
fp -> forall e. Int -> Buffer e -> Buffer e
bufferAdd Int
sz (forall e. RawBuffer e -> Int -> BufferState -> Buffer e
emptyBuffer RawBuffer Char
fp Int
sz BufferState
ReadBuffer)) forall a b. (a -> b) -> a -> b
$ forall a. Ptr a -> IO (ForeignPtr a)
newForeignPtr_ Ptr Char
p

      let go :: t -> Int -> IO a
go !t
iteration Int
to_sz_bytes = do
           String -> IO ()
putDebugMsg (String
"withEncodedCString: " forall a. [a] -> [a] -> [a]
++ forall a. Show a => a -> String
show t
iteration)
           forall a b. Int -> (Ptr a -> IO b) -> IO b
allocaBytes Int
to_sz_bytes forall a b. (a -> b) -> a -> b
$ \Ptr Word8
to_p -> do
            -- See Note [Check *before* fill in withEncodedCString] about why
            -- this is subtle.
            Maybe (Buffer Word8)
mb_res <- forall dstate.
TextEncoder dstate
-> Bool
-> CharBuffer
-> Ptr Word8
-> Int
-> IO (Maybe (Buffer Word8))
tryFillBuffer TextEncoder estate
encoder Bool
null_terminate CharBuffer
from Ptr Word8
to_p Int
to_sz_bytes
            case Maybe (Buffer Word8)
mb_res of
              Maybe (Buffer Word8)
Nothing  -> t -> Int -> IO a
go (t
iteration forall a. Num a => a -> a -> a
+ t
1) (Int
to_sz_bytes forall a. Num a => a -> a -> a
* Int
2)
              Just Buffer Word8
to_buf -> forall r. Buffer Word8 -> Bool -> (CStringLen -> IO r) -> IO r
withCStringBuffer Buffer Word8
to_buf Bool
null_terminate CStringLen -> IO a
act

      -- If the input string is ASCII, this value will ensure we only allocate once
      forall {t}. (Show t, Num t) => t -> Int -> IO a
go (Int
0 :: Int) (Int
cCharSize forall a. Num a => a -> a -> a
* (Int
sz forall a. Num a => a -> a -> a
+ Int
1))

withCStringBuffer :: Buffer Word8 -> Bool -> (CStringLen -> IO r) -> IO r
withCStringBuffer :: forall r. Buffer Word8 -> Bool -> (CStringLen -> IO r) -> IO r
withCStringBuffer Buffer Word8
to_buf Bool
null_terminate CStringLen -> IO r
act = do
  let bytes :: Int
bytes = forall e. Buffer e -> Int
bufferElems Buffer Word8
to_buf
  forall e a. Buffer e -> (Ptr e -> IO a) -> IO a
withBuffer Buffer Word8
to_buf forall a b. (a -> b) -> a -> b
$ \Ptr Word8
to_ptr -> do
    forall (f :: * -> *). Applicative f => Bool -> f () -> f ()
when Bool
null_terminate forall a b. (a -> b) -> a -> b
$ forall a. Storable a => Ptr a -> Int -> a -> IO ()
pokeElemOff Ptr Word8
to_ptr (forall e. Buffer e -> Int
bufR Buffer Word8
to_buf) Word8
0
    CStringLen -> IO r
act (forall a b. Ptr a -> Ptr b
castPtr Ptr Word8
to_ptr, Int
bytes) -- NB: the length information is specified as being in *bytes*

{-# INLINE newEncodedCString #-}
newEncodedCString :: TextEncoding  -- ^ Encoding of CString to create
                  -> Bool          -- ^ Null-terminate?
                  -> String        -- ^ String to encode
                  -> IO CStringLen
newEncodedCString :: TextEncoding -> Bool -> String -> IO CStringLen
newEncodedCString (TextEncoding { mkTextEncoder :: ()
mkTextEncoder = IO (TextEncoder estate)
mk_encoder }) Bool
null_terminate String
s
  = forall a b c. IO a -> (a -> IO b) -> (a -> IO c) -> IO c
bracket IO (TextEncoder estate)
mk_encoder forall from to state. BufferCodec from to state -> IO ()
close forall a b. (a -> b) -> a -> b
$ \TextEncoder estate
encoder -> forall a b. Storable a => [a] -> (Int -> Ptr a -> IO b) -> IO b
withArrayLen String
s forall a b. (a -> b) -> a -> b
$ \Int
sz Ptr Char
p -> do
      CharBuffer
from <- forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
fmap (\RawBuffer Char
fp -> forall e. Int -> Buffer e -> Buffer e
bufferAdd Int
sz (forall e. RawBuffer e -> Int -> BufferState -> Buffer e
emptyBuffer RawBuffer Char
fp Int
sz BufferState
ReadBuffer)) forall a b. (a -> b) -> a -> b
$ forall a. Ptr a -> IO (ForeignPtr a)
newForeignPtr_ Ptr Char
p

      let go :: t -> Ptr Word8 -> Int -> IO CStringLen
go !t
iteration Ptr Word8
to_p Int
to_sz_bytes = do
           String -> IO ()
putDebugMsg (String
"newEncodedCString: " forall a. [a] -> [a] -> [a]
++ forall a. Show a => a -> String
show t
iteration)
           Maybe (Buffer Word8)
mb_res <- forall dstate.
TextEncoder dstate
-> Bool
-> CharBuffer
-> Ptr Word8
-> Int
-> IO (Maybe (Buffer Word8))
tryFillBuffer TextEncoder estate
encoder Bool
null_terminate CharBuffer
from Ptr Word8
to_p Int
to_sz_bytes
           case Maybe (Buffer Word8)
mb_res of
             Maybe (Buffer Word8)
Nothing  -> do
                 let to_sz_bytes' :: Int
to_sz_bytes' = Int
to_sz_bytes forall a. Num a => a -> a -> a
* Int
2
                 Ptr Word8
to_p' <- forall a. Ptr a -> Int -> IO (Ptr a)
reallocBytes Ptr Word8
to_p Int
to_sz_bytes'
                 t -> Ptr Word8 -> Int -> IO CStringLen
go (t
iteration forall a. Num a => a -> a -> a
+ t
1) Ptr Word8
to_p' Int
to_sz_bytes'
             Just Buffer Word8
to_buf -> forall r. Buffer Word8 -> Bool -> (CStringLen -> IO r) -> IO r
withCStringBuffer Buffer Word8
to_buf Bool
null_terminate forall (m :: * -> *) a. Monad m => a -> m a
return

      -- If the input string is ASCII, this value will ensure we only allocate once
      let to_sz_bytes :: Int
to_sz_bytes = Int
cCharSize forall a. Num a => a -> a -> a
* (Int
sz forall a. Num a => a -> a -> a
+ Int
1)
      Ptr Word8
to_p <- forall a. Int -> IO (Ptr a)
mallocBytes Int
to_sz_bytes
      forall {t}.
(Show t, Num t) =>
t -> Ptr Word8 -> Int -> IO CStringLen
go (Int
0 :: Int) Ptr Word8
to_p Int
to_sz_bytes


tryFillBuffer :: TextEncoder dstate -> Bool -> Buffer Char -> Ptr Word8 -> Int
                    ->  IO (Maybe (Buffer Word8))
tryFillBuffer :: forall dstate.
TextEncoder dstate
-> Bool
-> CharBuffer
-> Ptr Word8
-> Int
-> IO (Maybe (Buffer Word8))
tryFillBuffer TextEncoder dstate
encoder Bool
null_terminate CharBuffer
from0 Ptr Word8
to_p Int
to_sz_bytes = do
    RawBuffer Word8
to_fp <- forall a. Ptr a -> IO (ForeignPtr a)
newForeignPtr_ Ptr Word8
to_p
    forall {t}.
(Show t, Num t) =>
t -> (CharBuffer, Buffer Word8) -> IO (Maybe (Buffer Word8))
go (Int
0 :: Int) (CharBuffer
from0, forall e. RawBuffer e -> Int -> BufferState -> Buffer e
emptyBuffer RawBuffer Word8
to_fp Int
to_sz_bytes BufferState
WriteBuffer)
  where
    go :: t -> (CharBuffer, Buffer Word8) -> IO (Maybe (Buffer Word8))
go !t
iteration (CharBuffer
from, Buffer Word8
to) = do
      (CodingProgress
why, CharBuffer
from', Buffer Word8
to') <- forall from to state.
BufferCodec from to state -> CodeBuffer from to
encode TextEncoder dstate
encoder CharBuffer
from Buffer Word8
to
      String -> IO ()
putDebugMsg (String
"tryFillBufferAndCall: " forall a. [a] -> [a] -> [a]
++ forall a. Show a => a -> String
show t
iteration forall a. [a] -> [a] -> [a]
++ String
" " forall a. [a] -> [a] -> [a]
++ forall a. Show a => a -> String
show CodingProgress
why forall a. [a] -> [a] -> [a]
++ String
" " forall a. [a] -> [a] -> [a]
++ forall a. Buffer a -> String
summaryBuffer CharBuffer
from forall a. [a] -> [a] -> [a]
++ String
" " forall a. [a] -> [a] -> [a]
++ forall a. Buffer a -> String
summaryBuffer CharBuffer
from')
      if forall e. Buffer e -> Bool
isEmptyBuffer CharBuffer
from'
       then if Bool
null_terminate Bool -> Bool -> Bool
&& forall e. Buffer e -> Int
bufferAvailable Buffer Word8
to' forall a. Eq a => a -> a -> Bool
== Int
0
             then forall (m :: * -> *) a. Monad m => a -> m a
return forall a. Maybe a
Nothing -- We had enough for the string but not the terminator: ask the caller for more buffer
             else forall (m :: * -> *) a. Monad m => a -> m a
return (forall a. a -> Maybe a
Just Buffer Word8
to')
       else case CodingProgress
why of -- We didn't consume all of the input
              CodingProgress
InputUnderflow  -> forall from to state.
BufferCodec from to state
-> Buffer from -> Buffer to -> IO (Buffer from, Buffer to)
recover TextEncoder dstate
encoder CharBuffer
from' Buffer Word8
to' forall (m :: * -> *) a b. Monad m => m a -> (a -> m b) -> m b
>>= t -> (CharBuffer, Buffer Word8) -> IO (Maybe (Buffer Word8))
go (t
iteration forall a. Num a => a -> a -> a
+ t
1) -- These conditions are equally bad
              CodingProgress
InvalidSequence -> forall from to state.
BufferCodec from to state
-> Buffer from -> Buffer to -> IO (Buffer from, Buffer to)
recover TextEncoder dstate
encoder CharBuffer
from' Buffer Word8
to' forall (m :: * -> *) a b. Monad m => m a -> (a -> m b) -> m b
>>= t -> (CharBuffer, Buffer Word8) -> IO (Maybe (Buffer Word8))
go (t
iteration forall a. Num a => a -> a -> a
+ t
1) -- since the input was truncated/invalid
              CodingProgress
OutputUnderflow -> forall (m :: * -> *) a. Monad m => a -> m a
return forall a. Maybe a
Nothing -- Oops, out of buffer during decoding: ask the caller for more
{-
Note [Check *before* fill in withEncodedCString]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

It's very important that the size check and readjustment peformed by tryFillBuffer
happens before the continuation is called. The size check is the part which can
fail, the call to the continuation never fails and so the caller should respond
first to the size check failing and *then* call the continuation. Making this evident
to the compiler avoids historic space leaks.

In a previous interation of this code we had a pattern that, somewhat simplified,
looked like this:

go :: State -> (State -> IO a) -> IO a
go state action =
    case tryFillBufferAndCall state action of
        Left state' -> go state' action
        Right result -> result

`tryFillBufferAndCall` performed some checks, and then we either called action,
or we modified the state and tried again.
This went wrong because `action` can be a function closure containing a reference to
a lazy data structure. If we call action directly, without retaining any references
to action, that is fine. The data structure is consumed as it is produced and we operate
in constant space.

However the failure branch `go state' action` *does* capture a reference to action.
This went wrong because the reference to action in the failure branch only becomes
unreachable *after* action returns. This means we keep alive the function closure
for `action` until `action` returns. Which in turn keeps alive the *whole* lazy list
via `action` until the action has fully run.
This went wrong in #20107, where the continuation kept an entire lazy bytestring alive
rather than allowing it to be incrementaly consumed and collected.
-}