diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,5 +1,12 @@
 # Revision history for haskell-lsp
 
+## 0.14.0.0 -- 2019-06-13
+
+* Add support for custom request and notification methods
+  (@cocreature)
+* Use attoparsec to parse message headers incrementally (@cocreature)
+* Only build lsp-hello when -fdemo flag is set (@bubba)
+
 ## 0.13.0.0 -- 2019-05-18
 
 * Fix relative posix URIs (@DavidM-D)
diff --git a/README.md b/README.md
--- a/README.md
+++ b/README.md
@@ -36,7 +36,7 @@
 
 ## Using the example server
 
-    stack install
+    stack install :lsp-hello --flag haskell-lsp:demo
 
 will generate a `lsp-hello` executable.
 
diff --git a/haskell-lsp.cabal b/haskell-lsp.cabal
--- a/haskell-lsp.cabal
+++ b/haskell-lsp.cabal
@@ -1,5 +1,5 @@
 name:                haskell-lsp
-version:             0.13.0.0
+version:             0.14.0.0
 synopsis:            Haskell library for the Microsoft Language Server Protocol
 
 description:         An implementation of the types, and basic message server to
@@ -38,6 +38,7 @@
   build-depends:       base >=4.9 && <4.13
                      , async
                      , aeson >=1.0.0.0
+                     , attoparsec
                      , bytestring
                      , containers
                      , directory
@@ -45,11 +46,10 @@
                      , filepath
                      , hslogger
                      , hashable
-                     , haskell-lsp-types == 0.13.*
+                     , haskell-lsp-types == 0.14.*
                      , lens >= 4.15.2
                      , mtl
                      , network-uri
-                     , parsec
                      , rope-utf16-splay >= 0.3.1.0
                      , sorted-list == 0.2.1.*
                      , stm
@@ -78,7 +78,6 @@
                      , lens >= 4.15.2
                      , mtl
                      , network-uri
-                     , parsec
                      , rope-utf16-splay >= 0.2
                      , stm
                      , text
@@ -88,6 +87,13 @@
                      , vector
                      -- the package library. Comment this out if you want repl changes to propagate
                      , haskell-lsp
+  if !flag(demo)
+    buildable:         False
+
+flag demo {
+  description: Build the lsp-hello demo executable
+  default:     False
+}
 
 test-suite haskell-lsp-test
   type:                exitcode-stdio-1.0
diff --git a/src/Language/Haskell/LSP/Control.hs b/src/Language/Haskell/LSP/Control.hs
--- a/src/Language/Haskell/LSP/Control.hs
+++ b/src/Language/Haskell/LSP/Control.hs
@@ -17,6 +17,10 @@
 import           Control.Monad
 import           Control.Monad.STM
 import qualified Data.Aeson as J
+import qualified Data.Attoparsec.ByteString as Attoparsec
+import Data.Attoparsec.ByteString.Char8
+import qualified Data.ByteString as BS
+import Data.ByteString.Builder.Extra (defaultChunkSize)
 import qualified Data.ByteString.Lazy as BSL
 import qualified Data.ByteString.Lazy.Char8 as B
 import           Data.Time.Clock
@@ -30,7 +34,6 @@
 import           Language.Haskell.LSP.Utility
 import           System.IO
 import           System.FilePath
-import           Text.Parsec
 
 -- ---------------------------------------------------------------------
 
@@ -94,40 +97,27 @@
                    -> Core.InitializeCallback c
                    -> TVar (Core.LanguageContextData c)
                    -> IO ()
-ioLoop hin dispatcherProc tvarDat = go BSL.empty
+ioLoop hin dispatcherProc tvarDat = do
+  go (parse parser "")
   where
-    go :: BSL.ByteString -> IO ()
-    go buf = do
-      c <- BSL.hGet hin 1
-
-      if c == BSL.empty
-        then do
-          logm $ B.pack "\nhaskell-lsp:Got EOF, exiting 1 ...\n"
-          return ()
-        else do
-          -- logs $ "ioLoop: got" ++ show c
-          let newBuf = BSL.append buf c
-          case readContentLength (lbs2str newBuf) of
-            Left _ -> go newBuf
-            Right len -> do
-              cnt <- BSL.hGet hin len
-
-              if cnt == BSL.empty
-                then do
-                  logm $ B.pack "\nhaskell-lsp:Got EOF, exiting 1 ...\n"
-                  return ()
-                else do
-                  logm $ B.pack "---> " <> cnt
-                  Core.handleMessage dispatcherProc tvarDat newBuf cnt
-                  ioLoop hin dispatcherProc tvarDat
-      where
-        readContentLength :: String -> Either ParseError Int
-        readContentLength = parse parser "readContentLength"
-
-        parser = do
-          _ <- string "Content-Length: "
-          len <- manyTill digit (string _TWO_CRLF)
-          return . read $ len
+    go :: Result BS.ByteString -> IO ()
+    go (Fail _ ctxs err) = logm $ B.pack
+      "\nhaskell-lsp: Failed to parse message header:\n" <> B.intercalate " > " (map str2lbs ctxs) <> ": " <>
+      str2lbs err <> "\n exiting 1 ...\n"
+    go (Partial c) = do
+      bs <- BS.hGetSome hin defaultChunkSize
+      if BS.null bs
+        then logm $ B.pack "\nhaskell-lsp:Got EOF, exiting 1 ...\n"
+        else go (c bs)
+    go (Done remainder msg) = do
+      logm $ B.pack "---> " <> BSL.fromStrict msg
+      Core.handleMessage dispatcherProc tvarDat (BSL.fromStrict msg)
+      go (parse parser remainder)
+    parser = do
+      _ <- string "Content-Length: "
+      len <- decimal
+      _ <- string _TWO_CRLF
+      Attoparsec.take len
 
 -- ---------------------------------------------------------------------
 
@@ -144,7 +134,7 @@
 
     let out = BSL.concat
                  [ str2lbs $ "Content-Length: " ++ show (BSL.length str)
-                 , str2lbs _TWO_CRLF
+                 , BSL.fromStrict _TWO_CRLF
                  , str ]
 
     BSL.hPut clientH out
@@ -156,7 +146,7 @@
 -- |
 --
 --
-_TWO_CRLF :: String
+_TWO_CRLF :: BS.ByteString
 _TWO_CRLF = "\r\n\r\n"
 
 
diff --git a/src/Language/Haskell/LSP/Core.hs b/src/Language/Haskell/LSP/Core.hs
--- a/src/Language/Haskell/LSP/Core.hs
+++ b/src/Language/Haskell/LSP/Core.hs
@@ -254,6 +254,10 @@
     , initializeRequestHandler                 :: !(Maybe (Handler J.InitializeRequest))
     -- Will default to terminating `exitMessage` if Nothing
     , exitNotificationHandler                  :: !(Maybe (Handler J.ExitNotification))
+
+    , customRequestHandler                     :: !(Maybe (Handler J.CustomClientRequest))
+    , customNotificationHandler                :: !(Maybe (Handler J.CustomClientNotification))
+
     }
 
 instance Default Handlers where
@@ -261,7 +265,7 @@
                  Nothing Nothing Nothing Nothing Nothing Nothing Nothing Nothing Nothing
                  Nothing Nothing Nothing Nothing Nothing Nothing Nothing Nothing Nothing
                  Nothing Nothing Nothing Nothing Nothing Nothing Nothing Nothing Nothing
-                 Nothing Nothing
+                 Nothing Nothing Nothing Nothing
 
 -- ---------------------------------------------------------------------
 nop :: a -> b -> IO a
@@ -337,17 +341,13 @@
 handlerMap _ h J.TextDocumentRename              = hh nop ReqRename $ renameHandler h
 handlerMap _ h J.TextDocumentFoldingRange        = hh nop ReqFoldingRange $ foldingRangeHandler h
 handlerMap _ _ J.WindowProgressCancel            = helper progressCancelHandler
-handlerMap _ _ (J.Misc x)   = helper f
-  where f ::  TVar (LanguageContextData c) -> J.Value -> IO ()
-        f tvarDat n = do
-          let msg = "haskell-lsp:Got " ++ T.unpack x ++ " ignoring"
-          logm (B.pack msg)
-
-          ctx <- readTVarIO tvarDat
-
-          captureFromClient (UnknownFromClientMessage n) (resCaptureFile ctx)
-
-          sendErrorLog tvarDat (T.pack msg)
+handlerMap _ h (J.CustomClientMethod _)          = \ctxData val ->
+    case val of
+        J.Object o | "id" `HM.member` o ->
+            -- Custom request
+            hh nop ReqCustomClient (customRequestHandler h) ctxData val
+        _ -> -- Custom notification
+            hh nop NotCustomClient (customNotificationHandler h) ctxData val
 
 -- ---------------------------------------------------------------------
 
@@ -497,8 +497,8 @@
 -- ---------------------------------------------------------------------
 
 handleMessage :: (Show c) => InitializeCallback c
-              -> TVar (LanguageContextData c) -> BSL.ByteString -> BSL.ByteString -> IO ()
-handleMessage dispatcherProc tvarDat contLenStr jsonStr = do
+              -> TVar (LanguageContextData c) -> BSL.ByteString -> IO ()
+handleMessage dispatcherProc tvarDat jsonStr = do
   {-
   Message Types we must handle are the following
 
@@ -510,7 +510,7 @@
 
   case J.eitherDecode jsonStr :: Either String J.Object of
     Left  err -> do
-      let msg =  T.pack $ unwords [ "haskell-lsp:incoming message parse error.", lbs2str contLenStr, lbs2str jsonStr, show err]
+      let msg =  T.pack $ unwords [ "haskell-lsp:incoming message parse error.", lbs2str jsonStr, show err]
               ++ L.intercalate "\n" ("" : "" : _ERR_MSG_URL)
               ++ "\n"
       sendErrorLog tvarDat msg
@@ -522,7 +522,7 @@
                                    J.Success m -> handle (J.Object o) m
                                    J.Error _ -> do
                                      let msg = T.pack $ unwords ["haskell-lsp:unknown message received:method='"
-                                                                 ++ T.unpack s ++ "',", lbs2str contLenStr, lbs2str jsonStr]
+                                                                 ++ T.unpack s ++ "',", lbs2str jsonStr]
                                      sendErrorLog tvarDat msg
         Just oops -> logs $ "haskell-lsp:got strange method param, ignoring:" ++ show oops
         Nothing -> do
diff --git a/src/Language/Haskell/LSP/Messages.hs b/src/Language/Haskell/LSP/Messages.hs
--- a/src/Language/Haskell/LSP/Messages.hs
+++ b/src/Language/Haskell/LSP/Messages.hs
@@ -61,8 +61,12 @@
                        | NotDidChangeWatchedFiles        DidChangeWatchedFilesNotification
                        | NotDidChangeWorkspaceFolders    DidChangeWorkspaceFoldersNotification
                        | NotProgressCancel               ProgressCancelNotification
-                       -- Unknown (The client sends something we don't understand)
-                       | UnknownFromClientMessage        Value
+
+                       -- It is common for language servers to add custom message types so these
+                       -- three constructors can be used to handle custom request, response or notification
+                       -- types.
+                       | ReqCustomClient                 CustomClientRequest
+                       | NotCustomClient                 CustomClientNotification
   deriving (Eq,Read,Show,Generic,ToJSON,FromJSON)
 
 -- | A wrapper around a message that originates from the server
@@ -110,4 +114,11 @@
                        | NotTelemetry                TelemetryNotification
                        -- A cancel request notification is duplex!
                        | NotCancelRequestFromServer  CancelNotificationServer
+
+                       -- It is common for language servers to add custom message types so these
+                       -- three constructors can be used to handle custom request, response or notification
+                       -- types.
+                       | ReqCustomServer             CustomServerRequest
+                       | RspCustomServer             CustomResponse
+                       | NotCustomServer             CustomServerNotification
   deriving (Eq,Read,Show,Generic,ToJSON,FromJSON)
diff --git a/test/URIFilePathSpec.hs b/test/URIFilePathSpec.hs
--- a/test/URIFilePathSpec.hs
+++ b/test/URIFilePathSpec.hs
@@ -1,12 +1,18 @@
+{-# LANGUAGE CPP #-}
 {-# LANGUAGE OverloadedStrings #-}
 module URIFilePathSpec where
 
+import Data.List
+import Data.Monoid ((<>))
 import Data.Text                              (pack)
 import Language.Haskell.LSP.Types
 
 import           Network.URI
+import qualified System.FilePath.Windows as FPW
 import Test.Hspec
+import Test.QuickCheck
 
+
 -- ---------------------------------------------------------------------
 
 main :: IO ()
@@ -27,7 +33,7 @@
 relativePosixFilePath = "myself/example.hs"
 
 testWindowsUri :: Uri
-testWindowsUri = Uri $ pack "file:///c%3A/Users/myself/example.hs"
+testWindowsUri = Uri $ pack "file:///c:/Users/myself/example.hs"
 
 testWindowsFilePath :: FilePath
 testWindowsFilePath = "c:\\Users\\myself\\example.hs"
@@ -61,8 +67,8 @@
     theFilePath `shouldBe` (Uri "file:///./Functional.hs")
 
   it "converts a Windows file path to a URI" $ do
-    let theFilePath = platformAwareFilePathToUri windowsOS "c:./Functional.hs"
-    theFilePath `shouldBe` (Uri "file:///c%3A/./Functional.hs")
+    let theFilePath = platformAwareFilePathToUri windowsOS "c:/Functional.hs"
+    theFilePath `shouldBe` (Uri "file:///c:/Functional.hs")
 
   it "converts a POSIX file path to a URI and back" $ do
     let theFilePath = platformAwareFilePathToUri "posix" "./Functional.hs"
@@ -76,9 +82,35 @@
       ,"")
     Just "./Functional.hs" `shouldBe` platformAwareUriToFilePath "posix" theFilePath
 
+  it "converts a Posix file path to a URI and back" $ property $ forAll genPosixFilePath $ \fp -> do
+      let uri = platformAwareFilePathToUri "posix" fp
+      platformAwareUriToFilePath "posix" uri `shouldBe` Just fp
 
+  it "converts a Windows file path to a URI and back" $ property $ forAll genWindowsFilePath $ \fp -> do
+      let uri = platformAwareFilePathToUri windowsOS fp
+      -- We normalise to account for changes in the path separator.
+      platformAwareUriToFilePath windowsOS uri `shouldBe` Just (FPW.normalise fp)
+
   it "converts a relative POSIX file path to a URI and back" $ do
     let uri = platformAwareFilePathToUri "posix" relativePosixFilePath
     uri `shouldBe` Uri "file://myself/example.hs"
     let back = platformAwareUriToFilePath "posix" uri
     back `shouldBe` Just relativePosixFilePath
+
+genWindowsFilePath :: Gen FilePath
+genWindowsFilePath = do
+    segments <- listOf pathSegment
+    pathSep <- elements ['/', '\\']
+    pure ("C:" <> [pathSep] <> intercalate [pathSep] segments)
+  where pathSegment = listOf1 (arbitraryASCIIChar `suchThat` (`notElem` ['/', '\\', '.', ':']))
+
+genPosixFilePath :: Gen FilePath
+genPosixFilePath = do
+    segments <- listOf pathSegment
+    pure ("/" <> intercalate "/" segments)
+  where pathSegment = listOf1 (arbitraryASCIIChar `suchThat` (`notElem` ['/', '.']))
+
+#if !MIN_VERSION_QuickCheck(2,10,0)
+arbitraryASCIIChar :: Gen Char
+arbitraryASCIIChar = arbitrary
+#endif
diff --git a/test/WorkspaceFoldersSpec.hs b/test/WorkspaceFoldersSpec.hs
--- a/test/WorkspaceFoldersSpec.hs
+++ b/test/WorkspaceFoldersSpec.hs
@@ -5,7 +5,6 @@
 import Control.Concurrent.MVar
 import Control.Concurrent.STM
 import Data.Aeson
-import qualified Data.ByteString.Lazy.Char8 as BSL
 import Data.Default
 import Language.Haskell.LSP.Core
 import Language.Haskell.LSP.Types
@@ -28,8 +27,7 @@
 
     let putMsg msg =
           let jsonStr = encode msg
-              clStr = BSL.pack $ "Content-Length: " ++ show (BSL.length jsonStr)
-            in handleMessage initCb tvarCtx clStr jsonStr
+            in handleMessage initCb tvarCtx jsonStr
 
     let starterWorkspaces = List [wf0]
         initParams = InitializeParams