perf: Process chunks of bracketed pastes only once.

The current code is `O(n^2)` because it processes the entire input each
time a new chunk arrives. This gets very expensive for large inputs.

This commit changes the code to process each chunk exactly twice: once
to see if it contains the end of the bracketed paste, and another time
to parse the whole paste and return it as an event.

The code can now process more than 1MB/sec. At this point, my tests are
probably more network bound, so these timings might be off, and instead
be testing my network throughput. Good enough for me anyway :).

Timing:
* 1MB: 1s
* 4MB: 3s
* 7MB: 6s
* 10MB: 7s
* 13MB: 10s
* 15MB: 12s
* 20MB: 16s

src/Graphics/Vty/Input/Classify.hs

@@ -5,6 +5,7 @@
 module Graphics.Vty.Input.Classify
   ( classify
   , KClass(..)
+  , ClassifierState(..)
   )
 where
 
@@ -27,6 +28,17 @@ import qualified Data.ByteString as BS
 import qualified Data.ByteString.Char8 as BS8
 import Data.ByteString.Char8 (ByteString)
 
+-- | Whether the classifier is currently processing a chunked format.
+-- Currently, only bracketed pastes use this.
+data ClassifierState
+    = ClassifierStart
+    -- ^ Not processing a chunked format.
+    | ClassifierInChunk ByteString [ByteString]
+    -- ^ Currently processing a chunked format. The initial chunk is in the
+    -- first argument and a reversed remainder of the chunks is collected in
+    -- the second argument. At the end of the processing, the chunks are
+    -- reversed and concatenated with the final chunk.
+
 compile :: ClassifyMap -> ByteString -> KClass
 compile table = cl' where
     -- take all prefixes and create a set of these
@@ -54,18 +66,27 @@ compile table = cl' where
                         -- neither a prefix or a full event.
                         [] -> Invalid
 
-classify :: ClassifyMap -> ByteString -> KClass
-classify table =
-    let standardClassifier = compile table
-    in \s -> case BS.uncons s of
-        _ | bracketedPasteStarted s ->
+classify :: ClassifyMap -> ClassifierState -> ByteString -> KClass
+classify table = process
+    where
+        standardClassifier = compile table
+
+        process ClassifierStart s =
+            case BS.uncons s of
+                _ | bracketedPasteStarted s ->
+                    if bracketedPasteFinished s
+                    then parseBracketedPaste s
+                    else Chunk
+                _ | isMouseEvent s      -> classifyMouseEvent s
+                _ | isFocusEvent s      -> classifyFocusEvent s
+                Just (c,cs) | c >= 0xC2 -> classifyUtf8 c cs
+                _                       -> standardClassifier s
+
+        process (ClassifierInChunk p ps) s | bracketedPasteStarted p =
             if bracketedPasteFinished s
-            then parseBracketedPaste s
-            else Prefix
-        _ | isMouseEvent s      -> classifyMouseEvent s
-        _ | isFocusEvent s      -> classifyFocusEvent s
-        Just (c,cs) | c >= 0xC2 -> classifyUtf8 c cs
-        _                       -> standardClassifier s
+            then parseBracketedPaste $ BS.concat $ p:reverse (s:ps)
+            else Chunk
+        process ClassifierInChunk{} _ = Invalid
 
 classifyUtf8 :: Word8 -> ByteString -> KClass
 classifyUtf8 c cs =

src/Graphics/Vty/Input/Classify/Types.hs

@@ -19,4 +19,7 @@ data KClass
     | Prefix
     -- ^ The input characters form the prefix of a valid event character
     -- sequence.
+    | Chunk
+    -- ^ The input characters are either start of a bracketed paste chunk
+    -- or in the middle of a bracketed paste chunk.
     deriving(Show, Eq)

src/Graphics/Vty/Input/Loop.hs

@@ -80,9 +80,10 @@ makeLenses ''InputBuffer
 
 data InputState = InputState
     { _unprocessedBytes :: ByteString
+    , _classifierState :: ClassifierState
     , _appliedConfig :: Config
     , _inputBuffer :: InputBuffer
-    , _classifier :: ByteString -> KClass
+    , _classifier :: ClassifierState -> ByteString -> KClass
     }
 
 makeLenses ''InputState
@@ -154,28 +155,40 @@ applyConfig _ _ = fail "(vty) applyConfig was not provided a complete configurat
 parseEvent :: InputM Event
 parseEvent = do
     c <- use classifier
+    s <- use classifierState
     b <- use unprocessedBytes
-    case c b of
+    case c s b of
         Valid e remaining -> do
             logMsg $ "valid parse: " ++ show e
             logMsg $ "remaining: " ++ show remaining
+            classifierState .= ClassifierStart
             unprocessedBytes .= remaining
             return e
-        _                   -> mzero
+        _ -> mzero
 
 dropInvalid :: InputM ()
 dropInvalid = do
     c <- use classifier
+    s <- use classifierState
     b <- use unprocessedBytes
-    when (c b == Invalid) $ do
-        logMsg "dropping input bytes"
-        unprocessedBytes .= BS8.empty
+    case c s b of
+        Chunk -> do
+            classifierState .=
+                case s of
+                  ClassifierStart -> ClassifierInChunk b []
+                  ClassifierInChunk p bs -> ClassifierInChunk p (b:bs)
+            unprocessedBytes .= BS8.empty
+        Invalid -> do
+            logMsg "dropping input bytes"
+            classifierState .= ClassifierStart
+            unprocessedBytes .= BS8.empty
+        _ -> return ()
 
 runInputProcessorLoop :: ClassifyMap -> Input -> IO ()
 runInputProcessorLoop classifyTable input = do
     let bufferSize = 1024
     allocaArray bufferSize $ \(bufferPtr :: Ptr Word8) -> do
-        s0 <- InputState BS8.empty
+        s0 <- InputState BS8.empty ClassifierStart
                 <$> readIORef (_configRef input)
                 <*> pure (InputBuffer bufferPtr bufferSize)
                 <*> pure (classify classifyTable)