diff --git a/package.yaml b/package.yaml
index 68e68ac4c..a469396cb 100644
--- a/package.yaml
+++ b/package.yaml
@@ -13,10 +13,26 @@ extra-source-files:
 
 dependencies:
   - base >= 4.7 && < 5
+  - async
   - bytestring
+  - containers
   - network
+  - polysemy
+  - singletons
+  - stm
 
 executables:
   simplex-messaging:
     source-dirs: src
     main: Main.hs
+
+ghc-options:
+  - -haddock
+  - -O2
+  - -Wall
+  - -Wcompat
+  - -Werror=incomplete-patterns
+  - -Wredundant-constraints
+  - -Wincomplete-record-updates
+  - -Wincomplete-uni-patterns
+  - -Wunused-type-patterns
diff --git a/src/EnvStm.hs b/src/EnvStm.hs
new file mode 100644
index 000000000..5e5ef7012
--- /dev/null
+++ b/src/EnvStm.hs
@@ -0,0 +1,37 @@
+{-# LANGUAGE DuplicateRecordFields #-}
+{-# LANGUAGE NamedFieldPuns #-}
+
+module EnvStm where
+
+import Control.Concurrent.STM
+import qualified Data.Map as M
+import qualified Data.Set as S
+import Store
+import System.IO
+import Transmission
+
+data Env = Env
+  { port :: String,
+    server :: TVar Server,
+    connStore :: TVar ConnStoreData
+  }
+
+data Server = Server
+  { clients :: S.Set Client,
+    connections :: M.Map RecipientId Client
+  }
+
+data Client = Client
+  { handle :: Handle,
+    connections :: S.Set RecipientId,
+    channel :: TChan SomeSigned
+  }
+
+newServer :: STM (TVar Server)
+newServer = newTVar $ Server {clients = S.empty, connections = M.empty}
+
+newEnv :: String -> STM Env
+newEnv port = do
+  srv <- newServer
+  st <- newConnStore
+  return Env {port, server = srv, connStore = st}
diff --git a/src/Main.hs b/src/Main.hs
index ae9e7228c..232e3764f 100644
--- a/src/Main.hs
+++ b/src/Main.hs
@@ -1,45 +1,102 @@
+{-# LANGUAGE BlockArguments #-}
+{-# LANGUAGE DataKinds #-}
+{-# LANGUAGE DuplicateRecordFields #-}
+{-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE GADTs #-}
+{-# LANGUAGE NamedFieldPuns #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE TypeApplications #-}
+
 module Main where
 
 import Control.Concurrent
+import Control.Concurrent.Async
+import Control.Concurrent.STM
 import qualified Control.Exception as E
 import Control.Monad
+import Data.Function ((&))
+import Data.Map (Map)
+import qualified Data.Map as M
+import Data.Set (Set)
+import qualified Data.Set as S
+import EnvStm
 import Network.Socket
+import Polysemy
+import Polysemy.Embed
+import Polysemy.Resource
+import Store
 import System.IO
+import Transmission
+import Transport
 
+newClient :: Handle -> IO Client
+newClient h = do
+  c <- newTChanIO @SomeSigned
+  return Client {handle = h, connections = S.empty, channel = c}
+
+main :: IO ()
 main = do
-  putStrLn $ "Listening on port " ++ port
-  runTCPServer Nothing port talk
+  server <- atomically newServer
+  putStrLn $ "Listening on port " ++ port'
+  runTCPServer port' $ runClient server
 
-port :: String
-port = "5223"
+port' :: String
+port' = "5223"
 
-runTCPServer :: Maybe HostName -> ServiceName -> (Handle -> IO ()) -> IO ()
-runTCPServer mhost port server = withSocketsDo $ do
-  let hints = defaultHints {addrFlags = [AI_PASSIVE], addrSocketType = Stream}
-  addr : _ <- getAddrInfo (Just hints) mhost (Just port)
-  E.bracket (open addr) close loop
+runTCPServer :: ServiceName -> (Handle -> IO ()) -> IO ()
+runTCPServer port server =
+  E.bracket (startTCPServer port) close $ \sock -> forever $ do
+    h <- acceptTCPConn sock
+    hPutStrLn h "Welcome\r"
+    forkFinally (server h) (const $ hClose h)
+
+runClient :: TVar Server -> Handle -> IO ()
+runClient server h = do
+  c <- newClient h
+  void $ race (client server c) (receive c)
+
+receive :: Client -> IO ()
+receive Client {handle, channel} = forever $ do
+  signature <- hGetLine handle
+  connId <- hGetLine handle
+  command <- hGetLine handle
+  cmdOrError <- parseVerifyTransmission signature connId command
+  atomically $ writeTChan channel cmdOrError
+
+parseVerifyTransmission :: String -> String -> String -> IO SomeSigned
+parseVerifyTransmission _ connId command = do
+  return (Just connId, parseCommand command)
+
+parseCommand :: String -> SomeCom
+parseCommand command = case words command of
+  ["CREATE", recipientKey] -> rCmd $ CREATE recipientKey
+  ["SUB"] -> rCmd SUB
+  ["SECURE", senderKey] -> rCmd $ SECURE senderKey
+  ["DELMSG", msgId] -> rCmd $ DELMSG msgId
+  ["SUSPEND"] -> rCmd SUSPEND
+  ["DELETE"] -> rCmd DELETE
+  ["SEND", msgBody] -> SomeCom SSender $ SEND msgBody
+  "CREATE" : _ -> error SYNTAX
+  "SUB" : _ -> error SYNTAX
+  "SECURE" : _ -> error SYNTAX
+  "DELMSG" : _ -> error SYNTAX
+  "SUSPEND" : _ -> error SYNTAX
+  "DELETE" : _ -> error SYNTAX
+  "SEND" : _ -> error SYNTAX
+  _ -> error CMD
   where
-    open addr = do
-      sock <- socket (addrFamily addr) (addrSocketType addr) (addrProtocol addr)
-      setSocketOption sock ReuseAddr 1
-      withFdSocket sock $ setCloseOnExecIfNeeded
-      bind sock $ addrAddress addr
-      listen sock 1024
-      return sock
-    loop sock = forever $ do
-      (conn, peer) <- accept sock
-      putStrLn $ "Accepted connection from " ++ show peer
-      h <- socketToHandle conn ReadWriteMode
-      hSetBinaryMode h True
-      hSetBuffering h LineBuffering
-      hPutStrLn h "Welcome\r"
-      forkFinally (server h) (const $ hClose h)
+    rCmd = SomeCom SRecipient
+    error t = SomeCom SBroker $ ERROR t
 
-talk :: Handle -> IO ()
-talk h = do
-  line <- hGetLine h
-  if line == "end"
-    then hPutStrLn h "Bye\r"
-    else do
-      hPutStrLn h (show (2 * (read line :: Integer)) ++ "\r")
-      talk h
+client :: TVar Server -> Client -> IO ()
+client server Client {handle, channel} = loop
+  where
+    loop = do
+      (_, cmdOrErr) <- atomically $ readTChan channel
+      let response = case cmdOrErr of
+            SomeCom SRecipient _ -> "OK"
+            SomeCom SSender _ -> "OK"
+            SomeCom SBroker (ERROR t) -> "ERROR " ++ show t
+            _ -> "ERROR INTERNAL"
+      hPutStrLn handle response
+      loop
diff --git a/src/Store.hs b/src/Store.hs
new file mode 100644
index 000000000..52d6af751
--- /dev/null
+++ b/src/Store.hs
@@ -0,0 +1,85 @@
+{-# LANGUAGE AllowAmbiguousTypes #-}
+{-# LANGUAGE DataKinds #-}
+{-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE GADTs #-}
+{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE NamedFieldPuns #-}
+{-# LANGUAGE PolyKinds #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE TemplateHaskell #-}
+-- {-# LANGUAGE TypeApplications #-}
+{-# LANGUAGE TypeOperators #-}
+
+module Store where
+
+import Control.Concurrent.STM
+import Data.Map (Map)
+import qualified Data.Map as M
+import Polysemy
+import Polysemy.Input
+import Transmission
+
+type SMPResult a = Either SMPError a
+
+data SMPError = CmdError | SyntaxError | AuthError | InternalError
+
+data Connection = Connection
+  { recipientId :: ConnId,
+    recipientKey :: PublicKey,
+    senderId :: ConnId,
+    senderKey :: Maybe PublicKey,
+    active :: Bool
+  }
+
+data ConnStore m a where
+  CreateConn :: RecipientKey -> ConnStore m (SMPResult Connection)
+  GetConn :: Party -> ConnId -> ConnStore m (SMPResult Connection)
+
+-- SecureConn :: RecipientId -> SenderKey -> ConnStore m (SMPResult ())
+-- SuspendConn :: RecipientId -> ConnStore m (SMPResult ())
+-- DeleteConn :: RecipientId -> ConnStore m (SMPResult ())
+
+makeSem ''ConnStore
+
+data ConnStoreData = ConnStoreData
+  { connections :: Map RecipientId Connection,
+    senders :: Map SenderId RecipientId
+  }
+
+newConnStore :: STM (TVar ConnStoreData)
+newConnStore = newTVar ConnStoreData {connections = M.empty, senders = M.empty}
+
+newConnection :: RecipientKey -> Connection
+newConnection rKey =
+  Connection
+    { recipientId = "1",
+      recipientKey = rKey,
+      senderId = "2",
+      senderKey = Nothing,
+      active = True
+    }
+
+runConnStoreSTM :: Member (Embed STM) r => Sem (ConnStore ': r) a -> Sem (Input (TVar ConnStoreData) ': r) a
+runConnStoreSTM = reinterpret $ \case
+  CreateConn rKey -> do
+    store <- input
+    db <- embed $ readTVar store
+    let conn@Connection {senderId, recipientId} = newConnection rKey
+        db' =
+          ConnStoreData
+            { connections = M.insert recipientId conn (connections db),
+              senders = M.insert senderId recipientId (senders db)
+            }
+    embed $ writeTVar store db'
+    return $ Right conn
+  GetConn Recipient rId -> do
+    db <- input >>= embed . readTVar
+    return $ getConn db rId
+  GetConn Sender sId -> do
+    db <- input >>= embed . readTVar
+    return $ maybeError (getConn db) $ M.lookup sId $ senders db
+  GetConn Broker _ -> do
+    return $ Left InternalError
+  where
+    maybeError = maybe (Left AuthError)
+    getConn db rId = maybeError Right $ M.lookup rId $ connections db
diff --git a/src/Transmission.hs b/src/Transmission.hs
new file mode 100644
index 000000000..f3ae76f10
--- /dev/null
+++ b/src/Transmission.hs
@@ -0,0 +1,61 @@
+{-# LANGUAGE DataKinds #-}
+{-# LANGUAGE GADTs #-}
+{-# LANGUAGE TemplateHaskell #-}
+{-# LANGUAGE TypeFamilies #-}
+{-# OPTIONS_GHC -fno-warn-unticked-promoted-constructors #-}
+
+module Transmission where
+
+import Data.Singletons.TH
+
+$( singletons
+     [d|
+       data Party = Broker | Recipient | Sender
+       |]
+ )
+
+type Transmission (a :: Party) = (Signed a, Maybe Signature)
+
+type Signed (a :: Party) = (Maybe ConnId, Com a)
+
+data SomeCom where
+  SomeCom :: Sing a -> Com a -> SomeCom
+
+type SomeSigned = (Maybe ConnId, SomeCom)
+
+data Com (a :: Party) where
+  CREATE :: RecipientKey -> Com Recipient
+  SECURE :: SenderKey -> Com Recipient
+  DELMSG :: MsgId -> Com Recipient
+  SUB :: Com Recipient
+  SUSPEND :: Com Recipient
+  DELETE :: Com Recipient
+  SEND :: MsgBody -> Com Sender
+  MSG :: MsgId -> Timestamp -> MsgBody -> Com Broker
+  CONN :: SenderId -> RecipientId -> Com Broker
+  ERROR :: ErrorType -> Com Broker
+  OK :: Com Broker
+
+type Encoded = String
+
+type PublicKey = Encoded
+
+type Signature = Encoded
+
+type RecipientKey = PublicKey
+
+type SenderKey = PublicKey
+
+type RecipientId = ConnId
+
+type SenderId = ConnId
+
+type ConnId = Encoded
+
+type MsgId = Encoded
+
+type Timestamp = Encoded
+
+type MsgBody = Encoded
+
+data ErrorType = CMD | SYNTAX | AUTH | INTERNAL deriving (Show)
diff --git a/src/Transport.hs b/src/Transport.hs
index 9c0a0ca0d..eabd9ab8d 100644
--- a/src/Transport.hs
+++ b/src/Transport.hs
@@ -1,46 +1,51 @@
+{-# LANGUAGE AllowAmbiguousTypes #-}
 {-# LANGUAGE DataKinds #-}
+{-# LANGUAGE FlexibleContexts #-}
 {-# LANGUAGE GADTs #-}
-{-# LANGUAGE KindSignatures #-}
+{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE PolyKinds #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE TemplateHaskell #-}
+{-# LANGUAGE TypeOperators #-}
 
 module Transport where
 
-data Party = Broker | Recipient | Sender
+import Network.Socket
+import Polysemy
+import Polysemy.Reader
+import Polysemy.Resource
+import System.IO
 
-type Transmission (a :: Party) = (Signed a, Signature)
+data Transport h m a where
+  TReadLn :: h -> Transport h m String
+  TWriteLn :: h -> String -> Transport h m ()
 
-type Signed (a :: Party) = (ConnId, Com a)
+makeSem ''Transport
 
-data Com (a :: Party) where
-  CREATE :: RecipientKey -> Com Recipient
-  SECURE :: SenderKey -> Com Recipient
-  DELMSG :: MsgId -> Com Recipient
-  SUB :: Com Recipient
-  SUSPEND :: Com Recipient
-  DELETE :: Com Recipient
-  SEND :: MsgBody -> Com Sender
-  MSG :: MsgId -> Timestamp -> MsgBody -> Com Broker
-  CONN :: SenderId -> RecipientId -> Com Broker
-  ERROR :: ErrorType -> Com Broker
-  OK :: Com Broker
+type TCPTransport = Transport Handle
 
-type Encoded = String
+startTCPServer :: String -> IO Socket
+startTCPServer port = withSocketsDo $ do
+  let hints = defaultHints {addrFlags = [AI_PASSIVE], addrSocketType = Stream}
+  addr <- head <$> getAddrInfo (Just hints) Nothing (Just port)
+  sock <- socket (addrFamily addr) (addrSocketType addr) (addrProtocol addr)
+  setSocketOption sock ReuseAddr 1
+  withFdSocket sock setCloseOnExecIfNeeded
+  bind sock $ addrAddress addr
+  listen sock 1024
+  return sock
 
-type Signature = Encoded
+acceptTCPConn :: Socket -> IO Handle
+acceptTCPConn sock = do
+  (conn, peer) <- accept sock
+  putStrLn $ "Accepted connection from " ++ show peer
+  h <- socketToHandle conn ReadWriteMode
+  hSetBinaryMode h True
+  hSetNewlineMode h universalNewlineMode
+  hSetBuffering h LineBuffering
+  return h
 
-type RecipientKey = Encoded
-
-type SenderKey = Encoded
-
-type ConnId = Encoded
-
-type SenderId = Encoded
-
-type RecipientId = Encoded
-
-type MsgId = Encoded
-
-type Timestamp = Encoded
-
-type MsgBody = Encoded
-
-data ErrorType = CMD | SYNTAX | AUTH | INTERNAL
+runTCPTransportIO :: Member (Embed IO) r => Sem (TCPTransport ': r) a -> Sem r a
+runTCPTransportIO = interpret $ \case
+  TReadLn h -> embed $ hGetLine h
+  TWriteLn h str -> embed $ hPutStr h $ str ++ "\r\n"