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Avoid copies when passing binary parameters #1

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Sep 5, 2022
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Avoid copies when passing binary parameters #1

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361e088
exec, query: factor out common parameter handling helpers
robx Jun 29, 2022
bc69f4b
withParams*: drop redundant map
robx Jun 29, 2022
325087f
withParams*: drop redundant call to 'length' by using 'withArrayLen'
robx Jun 29, 2022
ed00f57
don't copy binary parameter data
robx Jun 29, 2022
e7b0be3
add a CHANGELOG entry
robx Sep 5, 2022
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2 changes: 2 additions & 0 deletions CHANGELOG.md
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Original file line number Diff line number Diff line change
@@ -1,3 +1,5 @@
- Avoid copies when passing binary parameters

0.9.4.3
-------

Expand Down
176 changes: 87 additions & 89 deletions src/Database/PostgreSQL/LibPQ.hsc
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Original file line number Diff line number Diff line change
Expand Up @@ -746,6 +746,70 @@ newtype Oid = Oid CUInt deriving (Eq, Ord, Read, Show, Storable, Typeable)
invalidOid :: Oid
invalidOid = Oid (#const InvalidOid)


-- | Prepare the given parameter bytestring for passing on to libpq,
-- without copying for binary parameters.
--
-- This 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 =
withArray oids $ \ts ->
withMany (maybeWith unsafeUseParamAsCString) values $ \c_values ->
withArray c_values $ \vs ->
withArray c_lengths $ \ls ->
withArrayLen formats $ \n fs ->
action (toEnum n) ts vs ls fs
where
(oids, values, c_lengths, formats) =
foldl' accum ([],[],[],[]) $ reverse params

accum (!a,!b,!c,!d) Nothing = ( invalidOid:a
, Nothing:b
, 0:c
, 0:d
)
accum (!a,!b,!c,!d) (Just (t,v,f)) = ( t:a
, (Just (v,f)):b
, (toEnum $ B.length v):c
, (toEnum $ fromEnum f):d
)

-- | 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 unsafeUseParamAsCString) values $ \c_values ->
withArray c_values $ \vs ->
withArray c_lengths $ \ls ->
withArrayLen formats $ \n fs ->
action (toEnum n) vs ls fs
where
(values, c_lengths, formats) = foldl' accum ([],[],[]) $ reverse params

accum (!a,!b,!c) Nothing = ( Nothing:a
, 0:b
, 0:c
)
accum (!a,!b,!c) (Just (v, f)) = ( (Just (v,f)):a
, (toEnum $ B.length v):b
, (toEnum $ fromEnum f):c
)


-- | Submits a command to the server and waits for the result.
--
-- Returns a 'Result' or possibly 'Nothing'. A 'Result' will generally
Expand Down Expand Up @@ -812,31 +876,12 @@ execParams :: Connection -- ^ connection
-> Format -- ^ result format
-> IO (Maybe Result) -- ^ result
execParams connection statement params rFmt =
do let (oids, values, lengths, formats) =
foldl' accum ([],[],[],[]) $ reverse params
!c_lengths = map toEnum lengths :: [CInt]
!n = toEnum $ length params
!f = toEnum $ fromEnum rFmt
resultFromConn connection $ \c ->
B.useAsCString statement $ \s ->
withArray oids $ \ts ->
withMany (maybeWith B.useAsCString) values $ \c_values ->
withArray c_values $ \vs ->
withArray c_lengths $ \ls ->
withArray formats $ \fs ->
c_PQexecParams c s n ts vs ls fs f

where
accum (!a,!b,!c,!d) Nothing = ( invalidOid:a
, Nothing:b
, 0:c
, 0:d
)
accum (!a,!b,!c,!d) (Just (t,v,f)) = ( t:a
, (Just v):b
, (B.length v):c
, (toEnum $ fromEnum f):d
)
resultFromConn connection $ \c ->
B.useAsCString statement $ \s ->
withParams params $ \n ts vs ls fs ->
c_PQexecParams c s n ts vs ls fs f
where
!f = toEnum $ fromEnum rFmt


-- | Submits a request to create a prepared statement with the given
Expand Down Expand Up @@ -911,28 +956,13 @@ execPrepared :: Connection -- ^ connection
-> [Maybe (B.ByteString, Format)] -- ^ parameters
-> Format -- ^ result format
-> IO (Maybe Result) -- ^ result
execPrepared connection stmtName mPairs rFmt =
do let (values, lengths, formats) = foldl' accum ([],[],[]) $ reverse mPairs
!c_lengths = map toEnum lengths :: [CInt]
!n = toEnum $ length mPairs
!f = toEnum $ fromEnum rFmt
resultFromConn connection $ \c ->
B.useAsCString stmtName $ \s ->
withMany (maybeWith B.useAsCString) values $ \c_values ->
withArray c_values $ \vs ->
withArray c_lengths $ \ls ->
withArray formats $ \fs ->
c_PQexecPrepared c s n vs ls fs f

execPrepared connection stmtName params rFmt =
resultFromConn connection $ \c ->
B.useAsCString stmtName $ \s ->
withParamsPrepared params $ \n vs ls fs ->
c_PQexecPrepared c s n vs ls fs f
where
accum (!a,!b,!c) Nothing = ( Nothing:a
, 0:b
, 0:c
)
accum (!a,!b,!c) (Just (v, f)) = ( (Just v):a
, (B.length v):b
, (toEnum $ fromEnum f):c
)
!f = toEnum $ fromEnum rFmt


-- | Submits a request to obtain information about the specified
Expand Down Expand Up @@ -1676,31 +1706,13 @@ sendQueryParams :: Connection
-> Format
-> IO Bool
sendQueryParams connection statement params rFmt =
do let (oids, values, lengths, formats) =
foldl' accum ([],[],[],[]) $ reverse params
!c_lengths = map toEnum lengths :: [CInt]
!n = toEnum $ length params
!f = toEnum $ fromEnum rFmt
enumFromConn connection $ \c ->
B.useAsCString statement $ \s ->
withArray oids $ \ts ->
withMany (maybeWith B.useAsCString) values $ \c_values ->
withArray c_values $ \vs ->
withArray c_lengths $ \ls ->
withArray formats $ \fs ->
c_PQsendQueryParams c s n ts vs ls fs f
enumFromConn connection $ \c ->
B.useAsCString statement $ \s ->
withParams params $ \n ts vs ls fs ->
c_PQsendQueryParams c s n ts vs ls fs f

where
accum (!a,!b,!c,!d) Nothing = ( invalidOid:a
, Nothing:b
, 0:c
, 0:d
)
accum (!a,!b,!c,!d) (Just (t,v,f)) = ( t:a
, (Just v):b
, (B.length v):c
, (toEnum $ fromEnum f):d
)
!f = toEnum $ fromEnum rFmt


-- | Sends a request to create a prepared statement with the given
Expand All @@ -1726,28 +1738,14 @@ sendQueryPrepared :: Connection
-> [Maybe (B.ByteString, Format)]
-> Format
-> IO Bool
sendQueryPrepared connection stmtName mPairs rFmt =
do let (values, lengths, formats) = foldl' accum ([],[],[]) $ reverse mPairs
!c_lengths = map toEnum lengths :: [CInt]
!n = toEnum $ length mPairs
!f = toEnum $ fromEnum rFmt
enumFromConn connection $ \c ->
B.useAsCString stmtName $ \s ->
withMany (maybeWith B.useAsCString) values $ \c_values ->
withArray c_values $ \vs ->
withArray c_lengths $ \ls ->
withArray formats $ \fs ->
c_PQsendQueryPrepared c s n vs ls fs f
sendQueryPrepared connection stmtName params rFmt =
enumFromConn connection $ \c ->
B.useAsCString stmtName $ \s ->
withParamsPrepared params $ \n vs ls fs ->
c_PQsendQueryPrepared c s n vs ls fs f

where
accum (!a,!b,!c) Nothing = ( Nothing:a
, 0:b
, 0:c
)
accum (!a,!b,!c) (Just (v, f)) = ( (Just v):a
, (B.length v):b
, (toEnum $ fromEnum f):c
)
!f = toEnum $ fromEnum rFmt


-- | Submits a request to obtain information about the specified
Expand Down