Unfinished decoder for Numeric

Author: VyacheslavHashov

postgres-wire.cabal

@@ -35,6 +35,7 @@ library
                      , Database.PostgreSQL.Protocol.Codecs.Decoders
                      , Database.PostgreSQL.Protocol.Codecs.PgTypes
                      , Database.PostgreSQL.Protocol.Codecs.Time
+                     , Database.PostgreSQL.Protocol.Codecs.Numeric
   other-modules:       Database.PostgreSQL.Protocol.Utils
   build-depends:       base >= 4.7 && < 5
                      , bytestring

src/Database/PostgreSQL/Protocol/Codecs/Decoders.hs

@@ -2,6 +2,8 @@ module Database.PostgreSQL.Protocol.Codecs.Decoders where
 
 import Data.Word
 import Data.Int
+import Data.Maybe
+import Data.Fixed
 import Data.Char
 import Data.UUID (UUID, fromWords)
 import Data.Time (Day, UTCTime, LocalTime, DiffTime)
@@ -14,6 +16,7 @@ import Prelude hiding (bool)
 import Database.PostgreSQL.Protocol.Store.Decode
 import Database.PostgreSQL.Protocol.Types
 import Database.PostgreSQL.Protocol.Codecs.Time
+import Database.PostgreSQL.Protocol.Codecs.Numeric
 
 -- | Decodes DataRow header.
 -- 1 byte - Message Header
@@ -62,15 +65,15 @@ arrayHeader = skipBytes 12
 arrayDimensions :: Int -> Decode (V.Vector Int)
 arrayDimensions dims = V.reverse <$> V.replicateM dims arrayDimSize 
   where
-    -- 4 bytes - count of elements in dimension
+    -- 4 bytes - count of elements in the dimension
     -- 4 bytes - lower bound
     arrayDimSize = (fromIntegral <$> getWord32BE) <* getWord32BE
 
 {-# INLINE arrayFieldDecoder #-}
 arrayFieldDecoder :: Int -> (V.Vector Int -> Decode a) -> FieldDecoder a
 arrayFieldDecoder dims f _ = arrayHeader *> arrayDimensions dims >>= f
 
--- | Decodes only content of a field.
+-- | Decodes only a content of the field.
 type FieldDecoder a = Int -> Decode a 
 
 --
@@ -103,15 +106,15 @@ float8 _ = getFloat64BE
 
 {-# INLINE int2 #-}
 int2 :: FieldDecoder Int16
-int2 _ =  getInt16BE
+int2 _ = getInt16BE
 
 {-# INLINE int4 #-}
 int4 :: FieldDecoder Int32
-int4 _ =  getInt32BE 
+int4 _ = getInt32BE 
 
 {-# INLINE int8 #-}
 int8 :: FieldDecoder Int64
-int8 _ =  getInt64BE 
+int8 _ = getInt64BE 
 
 {-# INLINE interval #-}
 interval :: FieldDecoder DiffTime
@@ -127,8 +130,15 @@ bsJsonText = getByteString
 bsJsonBytes :: FieldDecoder B.ByteString
 bsJsonBytes len = getWord8 *> getByteString (len - 1)
 
--- numeric :: FieldDecoder Scientific
--- numeric = undefined
+numeric :: HasResolution a => FieldDecoder (Fixed a)
+numeric _ = do
+   ndigits <- getWord16BE
+   weight <- getInt16BE
+   msign <- numericSign <$> getWord16BE
+   sign <- maybe (fail "unknown numeric") pure msign
+   dscale <- getWord16BE
+   digits <- replicateM (fromIntegral ndigits) getWord16BE
+   pure $ undefined
 
 -- | Decodes text without applying encoding.
 {-# INLINE bsText #-}

src/Database/PostgreSQL/Protocol/Codecs/Numeric.hs

@@ -0,0 +1,21 @@
+module Database.PostgreSQL.Protocol.Codecs.Numeric where
+
+-- TODO test it
+import Data.Word
+import Data.Int
+import Data.Foldable
+import Data.Fixed
+
+numericDigit :: [Word16] -> Integer
+numericDigit = foldl' (\acc n -> acc * nBase + fromIntegral n) 0
+
+numericSign :: Num a => Word16 -> Maybe a
+numericSign 0x0000 = Just 1
+numericSign 0x4000 = Just $ -1
+numericSign _      = Nothing  -- NaN code is 0xC000, it is not supported.
+
+fixedFromNumeric :: HasResolution a => Int16 -> [Word16] -> Fixed a
+fixedFromNumeric weight digits = undefined
+
+nBase :: Num a => a
+nBase = 10000