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Pass binary parameter data without copying #31

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27 changes: 20 additions & 7 deletions src/Database/PostgreSQL/LibPQ.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -696,13 +696,26 @@ connectionUsedPassword connection =
newtype Result = Result (ForeignPtr PGresult) deriving (Eq, Show)
data PGresult

-- | Prepare the given parameter bytestring for passing on to libpq,
-- without copying for binary parameters.
--
-- This is safe to use to pass parameters to libpq considering:
-- * libpq treats the parameter data as read-only
-- * 'ByteString' uses pinned memory
-- * the reference to the 'CString' doesn't escape
unsafeUseParamAsCString :: (B.ByteString, Format) -> (CString -> IO a) -> IO a
unsafeUseParamAsCString (bs, format) =
case format of
Binary -> B.unsafeUseAsCString bs
Text -> B.useAsCString bs

-- | Convert a list of parameters to the format expected by libpq FFI calls.
withParams :: [Maybe (Oid, B.ByteString, Format)]
-> (CInt -> Ptr Oid -> Ptr CString -> Ptr CInt -> Ptr CInt -> IO a)
-> IO a
withParams params action =
unsafeWithArray n oids $ \ts ->
withMany (maybeWith B.useAsCString) values $ \c_values ->
withMany (maybeWith unsafeUseParamAsCString) values $ \c_values ->
unsafeWithArray n c_values $ \vs ->
unsafeWithArray n c_lengths $ \ls ->
unsafeWithArray n formats $ \fs ->
Expand All @@ -718,20 +731,20 @@ withParams params action =
accum (Just (t,v,f)) ~(AccumParams i xs ys zs ws) =
let !z = intToCInt (B.length v)
!w = toCInt f
in AccumParams (i + 1) (t : xs) (Just v : ys) (z : zs) (w : ws)
in AccumParams (i + 1) (t : xs) (Just (v, f) : ys) (z : zs) (w : ws)

intToCInt :: Int -> CInt
intToCInt = toEnum

data AccumParams = AccumParams !Int ![Oid] ![Maybe B.ByteString] ![CInt] ![CInt]
data AccumParams = AccumParams !Int ![Oid] ![Maybe (B.ByteString, Format)] ![CInt] ![CInt]

-- | Convert a list of parameters to the format expected by libpq FFI calls,
-- prepared statement variant.
withParamsPrepared :: [Maybe (B.ByteString, Format)]
-> (CInt -> Ptr CString -> Ptr CInt -> Ptr CInt -> IO a)
-> IO a
withParamsPrepared params action =
withMany (maybeWith B.useAsCString) values $ \c_values ->
withMany (maybeWith unsafeUseParamAsCString) values $ \c_values ->
unsafeWithArray n c_values $ \vs ->
unsafeWithArray n c_lengths $ \ls ->
unsafeWithArray n formats $ \fs ->
Expand All @@ -740,16 +753,16 @@ withParamsPrepared params action =
AccumPrepParams n values c_lengths formats =
foldr accum (AccumPrepParams 0 [] [] []) params

accum :: Maybe (B.ByteString ,Format) -> AccumPrepParams -> AccumPrepParams
accum :: Maybe (B.ByteString, Format) -> AccumPrepParams -> AccumPrepParams
accum Nothing ~(AccumPrepParams i a b c) =
AccumPrepParams (i + 1) (Nothing : a) (0 : b) (0 : c)

accum (Just (v, f)) ~(AccumPrepParams i xs ys zs) =
let !y = intToCInt (B.length v)
!z = toCInt f
in AccumPrepParams (i + 1) (Just v : xs) (y : ys) (z : zs)
in AccumPrepParams (i + 1) (Just (v, f) : xs) (y : ys) (z : zs)

data AccumPrepParams = AccumPrepParams !Int ![Maybe B.ByteString] ![CInt] ![CInt]
data AccumPrepParams = AccumPrepParams !Int ![Maybe (B.ByteString, Format)] ![CInt] ![CInt]

-- | Submits a command to the server and waits for the result.
--
Expand Down