{- P2P protocol, IO implementation
 -
 - Copyright 2016-2018 Joey Hess <id@joeyh.name>
 -
 - Licensed under the GNU AGPL version 3 or higher.
 -}

{-# LANGUAGE RankNTypes, FlexibleContexts, CPP #-}

module P2P.IO
	( RunProto
	, RunState(..)
	, mkRunState
	, P2PConnection(..)
	, ConnIdent(..)
	, ClosableConnection(..)
	, stdioP2PConnection
	, connectPeer
	, closeConnection
	, serveUnixSocket
	, setupHandle
	, ProtoFailure(..)
	, describeProtoFailure
	, runNetProto
	, runNet
	) where

import Common
import P2P.Protocol
import P2P.Address
import Git
import Git.Command
import Utility.AuthToken
import Utility.SimpleProtocol
import Utility.Metered
import Utility.Tor
import Utility.FileMode
import Types.UUID
import Annex.ChangedRefs
import qualified Utility.RawFilePath as R

import Control.Monad.Free
import Control.Monad.IO.Class
import System.IO.Error
import Network.Socket
import Control.Concurrent
import Control.Concurrent.Async
import Control.Concurrent.STM
import qualified Data.ByteString as B
import qualified Data.ByteString.Lazy as L
import System.Log.Logger (debugM)
import qualified Network.Socket as S

-- Type of interpreters of the Proto free monad.
type RunProto m = forall a. Proto a -> m (Either ProtoFailure a)

data ProtoFailure
	= ProtoFailureMessage String
	| ProtoFailureException SomeException
	| ProtoFailureIOError IOError

describeProtoFailure :: ProtoFailure -> String
describeProtoFailure (ProtoFailureMessage s) = s
describeProtoFailure (ProtoFailureException e) = show e
describeProtoFailure (ProtoFailureIOError e) = show e

data RunState
	= Serving UUID (Maybe ChangedRefsHandle) (TVar ProtocolVersion)
	| Client (TVar ProtocolVersion)

mkRunState :: (TVar ProtocolVersion -> RunState) -> IO RunState
mkRunState mk = do
	tvar <- newTVarIO defaultProtocolVersion
	return (mk tvar)

data P2PConnection = P2PConnection
	{ connRepo :: Repo
	, connCheckAuth :: (AuthToken -> Bool)
	, connIhdl :: Handle
	, connOhdl :: Handle
	, connIdent :: ConnIdent
	}

-- Identifier for a connection, only used for debugging.
newtype ConnIdent = ConnIdent (Maybe String)

data ClosableConnection conn
	= OpenConnection conn
	| ClosedConnection

-- P2PConnection using stdio.
stdioP2PConnection :: Git.Repo -> P2PConnection
stdioP2PConnection g = P2PConnection
	{ connRepo = g
	, connCheckAuth = const False
	, connIhdl = stdin
	, connOhdl = stdout
	, connIdent = ConnIdent Nothing
	}

-- Opens a connection to a peer. Does not authenticate with it.
connectPeer :: Git.Repo -> P2PAddress -> IO P2PConnection
connectPeer g (TorAnnex onionaddress onionport) = do
	h <- setupHandle =<< connectHiddenService onionaddress onionport
	return $ P2PConnection
		{ connRepo = g
		, connCheckAuth = const False
		, connIhdl = h
		, connOhdl = h
		, connIdent = ConnIdent Nothing
		}

closeConnection :: P2PConnection -> IO ()
closeConnection conn = do
	hClose (connIhdl conn)
	hClose (connOhdl conn)

-- Serves the protocol on a unix socket.
--
-- The callback is run to serve a connection, and is responsible for
-- closing the Handle when done.
--
-- Note that while the callback is running, other connections won't be
-- processed, so longterm work should be run in a separate thread by
-- the callback.
serveUnixSocket :: FilePath -> (Handle -> IO ()) -> IO ()
serveUnixSocket unixsocket serveconn = do
	removeWhenExistsWith R.removeLink (toRawFilePath unixsocket)
	soc <- S.socket S.AF_UNIX S.Stream S.defaultProtocol
	S.bind soc (S.SockAddrUnix unixsocket)
	-- Allow everyone to read and write to the socket,
	-- so a daemon like tor, that is probably running as a different
	-- de sock $ addModes
	-- user, can access it.
	-- 
        -- Connections have to authenticate to do anything,
        -- so it's fine that other local users can connect to the
        -- socket.
	modifyFileMode (toRawFilePath unixsocket) $ addModes
		[groupReadMode, groupWriteMode, otherReadMode, otherWriteMode]
	S.listen soc 2
	forever $ do
		(conn, _) <- S.accept soc
		setupHandle conn >>= serveconn

setupHandle :: Socket -> IO Handle
setupHandle s = do
	h <- socketToHandle s ReadWriteMode
	hSetBuffering h LineBuffering
	hSetBinaryMode h False
	return h

-- Purposefully incomplete interpreter of Proto.
--
-- This only runs Net actions. No Local actions will be run
-- (those need the Annex monad) -- if the interpreter reaches any,
-- it returns Nothing.
runNetProto :: RunState -> P2PConnection -> Proto a -> IO (Either ProtoFailure a)
runNetProto runst conn = go
  where
	go :: RunProto IO
	go (Pure v) = return (Right v)
	go (Free (Net n)) = runNet runst conn go n
	go (Free (Local _)) = return $ Left $
		ProtoFailureMessage "unexpected annex operation attempted"

-- Interpreter of the Net part of Proto.
--
-- An interpreter of Proto has to be provided, to handle the rest of Proto
-- actions.
runNet :: (MonadIO m, MonadMask m) => RunState -> P2PConnection -> RunProto m -> NetF (Proto a) -> m (Either ProtoFailure a)
runNet runst conn runner f = case f of
	SendMessage m next -> do
		v <- liftIO $ tryNonAsync $ do
			let l = unwords (formatMessage m)
			debugMessage conn "P2P >" m
			hPutStrLn (connOhdl conn) l
			hFlush (connOhdl conn)
		case v of
			Left e -> return $ Left $ ProtoFailureException e
			Right () -> runner next
	ReceiveMessage next -> do
		v <- liftIO $ tryIOError $ getProtocolLine (connIhdl conn)
		case v of
			Left e -> return $ Left $ ProtoFailureIOError e
			Right Nothing -> return $ Left $
				ProtoFailureMessage "protocol error"
			Right (Just l) -> case parseMessage l of
				Just m -> do
					liftIO $ debugMessage conn "P2P <" m
					runner (next (Just m))
				Nothing -> runner (next Nothing)
	SendBytes len b p next -> do
		v <- liftIO $ tryNonAsync $ do
			ok <- sendExactly len b (connOhdl conn) p
			hFlush (connOhdl conn)
			return ok
		case v of
			Right True -> runner next
			Right False -> return $ Left $
				ProtoFailureMessage "short data write"
			Left e -> return $ Left $ ProtoFailureException e
	ReceiveBytes len p next -> do
		v <- liftIO $ tryNonAsync $ receiveExactly len (connIhdl conn) p
		case v of
			Left e -> return $ Left $ ProtoFailureException e
			Right b -> runner (next b)
	CheckAuthToken _u t next -> do
		let authed = connCheckAuth conn t
		runner (next authed)
	Relay hin hout next -> do
		v <- liftIO $ runRelay runnerio hin hout
		case v of
			Left e -> return $ Left e
			Right exitcode -> runner (next exitcode)
	RelayService service next -> do
		v <- liftIO $ runRelayService conn runnerio service
		case v of
			Left e -> return $ Left e
			Right () -> runner next
	SetProtocolVersion v next -> do
		liftIO $ atomically $ writeTVar versiontvar v
		runner next
	GetProtocolVersion next ->
		liftIO (readTVarIO versiontvar) >>= runner . next
  where
	-- This is only used for running Net actions when relaying,
	-- so it's ok to use runNetProto, despite it not supporting
	-- all Proto actions.
	runnerio = runNetProto runst conn
	versiontvar = case runst of
		Serving _ _ tv -> tv
		Client tv -> tv

debugMessage :: P2PConnection -> String -> Message -> IO ()
debugMessage conn prefix m = do
	tid <- myThreadId	
	debugM "p2p" $ concat $ catMaybes $
		[ (\ident -> "[" ++ ident ++ "] ") <$> mident
		, Just $ "[" ++ show tid ++ "] "
		, Just $ prefix ++ " " ++ unwords (formatMessage safem)
		]
  where
	safem = case m of
		AUTH u _ -> AUTH u nullAuthToken
		_ -> m
	ConnIdent mident = connIdent conn

-- Send exactly the specified number of bytes or returns False.
--
-- The ByteString can be larger or smaller than the specified length.
-- For example, it can be lazily streaming from a file that gets
-- appended to, or truncated.
--
-- Must avoid sending too many bytes as it would confuse the other end.
-- This is easily dealt with by truncating it.
--
-- If too few bytes are sent, the only option is to give up on this
-- connection. False is returned to indicate this problem.
sendExactly :: Len -> L.ByteString -> Handle -> MeterUpdate -> IO Bool
sendExactly (Len n) b h p = do
	sent <- meteredWrite' p h (L.take (fromIntegral n) b)
	return (fromBytesProcessed sent == n)

receiveExactly :: Len -> Handle -> MeterUpdate -> IO L.ByteString
receiveExactly (Len n) h p = hGetMetered h (Just n) p

runRelay :: RunProto IO -> RelayHandle -> RelayHandle -> IO (Either ProtoFailure ExitCode)
runRelay runner (RelayHandle hout) (RelayHandle hin) = 
	bracket setup cleanup go
		`catchNonAsync` (return . Left . ProtoFailureException)
  where
	setup = do
		v <- newEmptyMVar
		t1 <- async $ relayFeeder runner v hin
		t2 <- async $ relayReader v hout
		return (v, t1, t2)
	
	cleanup (_, t1, t2) = do
		hClose hin
		hClose hout
		cancel t1
		cancel t2
	
	go (v, _, _) = relayHelper runner v

runRelayService :: P2PConnection -> RunProto IO -> Service -> IO (Either ProtoFailure ())
runRelayService conn runner service =
	withCreateProcess serviceproc' go
		`catchNonAsync` (return . Left . ProtoFailureException)
  where
	cmd = case service of
		UploadPack -> "upload-pack"
		ReceivePack -> "receive-pack"
	
	serviceproc = gitCreateProcess
		[ Param cmd
		, File (fromRawFilePath (repoPath (connRepo conn)))
		] (connRepo conn)
	serviceproc' = serviceproc 
		{ std_out = CreatePipe
		, std_in = CreatePipe
		}

	go (Just hin) (Just hout) _ pid = do
		v <- newEmptyMVar
		r <- withAsync (relayFeeder runner v hin) $ \_ ->
			withAsync (relayReader v hout) $ \_ ->
				withAsync (waitexit v pid) $ \_ -> do
					r <- runrelay v
					hClose hin
					hClose hout
					return r
		void $ waitForProcess pid
		return r
	go _ _ _ _ = error "internal"
	
	runrelay v = relayHelper runner v >>= \case
		Left e -> return $ Left e
		Right exitcode -> runner $
			net $ relayToPeer (RelayDone exitcode)

	waitexit v pid = putMVar v . RelayDone =<< waitForProcess pid

-- Processes RelayData as it is put into the MVar.
relayHelper :: RunProto IO -> MVar RelayData -> IO (Either ProtoFailure ExitCode)
relayHelper runner v = loop
  where
	loop = do
		d <- takeMVar v
		case d of
			RelayToPeer b -> do
				r <- runner $ net $ relayToPeer (RelayToPeer b)
				case r of
					Left e -> return (Left e)
					Right () -> loop
			RelayDone exitcode -> do
				_ <- runner $ net $ relayToPeer (RelayDone exitcode)
				return (Right exitcode)
			RelayFromPeer _ -> loop -- not handled here

-- Takes input from the peer, and sends it to the relay process's stdin.
-- Repeats until the peer tells it it's done or hangs up.
relayFeeder :: RunProto IO -> MVar RelayData -> Handle -> IO ()
relayFeeder runner v hin = loop
  where
	loop = do
		mrd <- runner $ net relayFromPeer
		case mrd of
			Left _e ->
				putMVar v (RelayDone (ExitFailure 1))
			Right (RelayDone exitcode) ->
				putMVar v (RelayDone exitcode)
			Right (RelayFromPeer b) -> do
				L.hPut hin b
				hFlush hin
				loop
			Right (RelayToPeer _) -> loop -- not handled here

-- Reads input from the Handle and puts it into the MVar for relaying to
-- the peer. Continues until EOF on the Handle.
relayReader :: MVar RelayData -> Handle -> IO ()
relayReader v hout = loop
  where
	loop = do
		bs <- getsome []
		case bs of
			[] -> return ()
			_ -> do
				putMVar v $ RelayToPeer (L.fromChunks bs)
				loop
	
	-- Wait for the first available chunk. Then, without blocking,
	-- try to get more chunks, in case a stream of chunks is being
	-- written in close succession. 
	--
	-- On Windows, hGetNonBlocking is broken, so avoid using it there.
	getsome [] = do
		b <- B.hGetSome hout chunk
		if B.null b
			then return []
#ifndef mingw32_HOST_OS
			else getsome [b]
#else
			else return [b]
#endif
	getsome bs = do
		b <- B.hGetNonBlocking hout chunk
		if B.null b
			then return (reverse bs)
			else getsome (b:bs)
	
	chunk = 65536