Implement -N, dry-run mode.

When -N is enabled, no sockets are bound and no events get persisted
to the datastore. We also pass the dry run flag to the serf, who
should not snapshot.

(For redundancy, we should probably also make king not send the save
snapshot commands, but I tested locally that the worker process
doesn't save.)

pkg/king/app/Main.hs

@@ -1,8 +1,4 @@
 {-
-    # Booting a Ship
-
-    - TODO Don't just boot, also run the ship (unless `-x` is set).
-
     # Event Pruning
 
     - `king discard-events NUM_EVENTS`: Delete the last `n` events from
@@ -12,10 +8,6 @@
       the event log, from last to first, pretty-print each event, and
       ask if it should be pruned.
 
-    # `-N` -- Dry Run
-
-    Disable all persistence and use no-op networking.
-
     # Implement subcommands to test event and effect parsing.
 
     - `king * --collect-fx`: All effects that come from the serf get
@@ -134,7 +126,9 @@ toSerfFlags CLI.Opts{..} = catMaybes m
 toPierConfig :: FilePath -> CLI.Opts -> PierConfig
 toPierConfig pierPath CLI.Opts{..} = PierConfig
   { pcPierPath = pierPath
-  , pcNetworking = if oLocalhost then NetworkLocalhost
+  , pcDryRun = oDryRun
+  , pcNetworking = if oDryRun then NetworkNone
+                   else if oLocalhost then NetworkLocalhost
                    else NetworkNormal
   , pcAmesPort = oAmesPort
   }

pkg/king/lib/PierConfig.hs

@@ -2,12 +2,13 @@ module PierConfig where
 
 import UrbitPrelude
 
-data NetworkingType = NetworkNormal | NetworkLocalhost
+data NetworkingType = NetworkNone | NetworkNormal | NetworkLocalhost
 
 -- All the configuration data revolving around a ship and the current execution
 -- options.
 data PierConfig = PierConfig
   { pcPierPath   :: FilePath
+  , pcDryRun     :: Bool
   -- Configurable networking options
   , pcNetworking :: NetworkingType
   , pcAmesPort   :: Maybe Word16
@@ -21,6 +22,11 @@ getPierPath = do
   PierConfig{..} <- view pierConfigL
   pure pcPierPath
 
+getIsDryRun :: (MonadReader env m, HasPierConfig env) => m Bool
+getIsDryRun = do
+  PierConfig{..} <- view pierConfigL
+  pure pcDryRun
+
 getNetworkingType :: (MonadReader env m, HasPierConfig env) => m NetworkingType
 getNetworkingType = do
   PierConfig{..} <- view pierConfigL

pkg/king/lib/Vere/Ames.hs

@@ -3,6 +3,7 @@ module Vere.Ames (ames) where
 import UrbitPrelude
 
 import Arvo                      hiding (Fake)
+import Control.Monad.Extra       hiding (mapM_)
 import Network.Socket            hiding (recvFrom, sendTo)
 import Network.Socket.ByteString
 import PierConfig
@@ -18,14 +19,14 @@ import qualified Urbit.Time      as Time
 data AmesDrv = AmesDrv
   { aTurfs         :: TVar (Maybe [Turf])
   , aGalaxies      :: IORef (M.Map Galaxy (Async (), TQueue ByteString))
-  , aSocket        :: Socket
+  , aSocket        :: Maybe Socket
   , aWakeTimer     :: Async ()
   , aListener      :: Async ()
   , aSendingQueue  :: TQueue (SockAddr, ByteString)
   , aSendingThread :: Async ()
   }
 
-data NetworkMode = Fake | Localhost | Real
+data NetworkMode = Fake | Localhost | Real | NoNetwork
   deriving (Eq, Ord, Show)
 
 -- Utils -----------------------------------------------------------------------
@@ -34,6 +35,7 @@ galaxyPort :: NetworkMode -> Galaxy -> PortNumber
 galaxyPort Fake (Galaxy g)      = fromIntegral g + 31337
 galaxyPort Localhost (Galaxy g) = fromIntegral g + 13337
 galaxyPort Real (Galaxy g)      = fromIntegral g + 13337
+galaxyPort NoNetwork _          = fromIntegral 0
 
 listenPort :: NetworkMode -> Ship -> PortNumber
 listenPort m s | s < 256 = galaxyPort m (fromIntegral s)
@@ -123,6 +125,7 @@ ames inst who isFake enqueueEv stderr =
       else getNetworkingType >>= \case
         NetworkNormal -> pure Real
         NetworkLocalhost -> pure Localhost
+        NetworkNone -> pure NoNetwork
 
     stop :: AmesDrv -> RIO e ()
     stop AmesDrv{..} = do
@@ -131,23 +134,26 @@ ames inst who isFake enqueueEv stderr =
         cancel aSendingThread
         cancel aWakeTimer
         cancel aListener
-        io $ close' aSocket
+        io $ maybeM (pure ()) (close') (pure aSocket)
+        -- io $ close' aSocket
 
     runTimer :: RIO e ()
     runTimer = forever $ do
         threadDelay (300 * 1000000) -- 300 seconds
         atomically (enqueueEv wakeEv)
 
-    bindSock :: RIO e Socket
+    bindSock :: RIO e (Maybe Socket)
     bindSock = getBindAddr >>= doBindSocket
         where
            getBindAddr = netMode >>= \case
-              Fake -> pure localhost
-              Localhost -> pure localhost
-              Real ->    pure inaddrAny
+              Fake      -> pure $ Just localhost
+              Localhost -> pure $ Just localhost
+              Real      -> pure $ Just inaddrAny
+              NoNetwork -> pure Nothing
 
-           doBindSocket :: HostAddress -> RIO e Socket
-           doBindSocket bindAddr = do
+           doBindSocket :: Maybe HostAddress -> RIO e (Maybe Socket)
+           doBindSocket Nothing = pure Nothing
+           doBindSocket (Just bindAddr) = do
              mode <- netMode
              mPort <- getAmesPort
              let ourPort = maybe (listenPort mode who) fromIntegral mPort
@@ -157,10 +163,11 @@ ames inst who isFake enqueueEv stderr =
              let addr = SockAddrInet ourPort bindAddr
              () <- io $ bind s addr
 
-             pure s
+             pure $ Just s
 
-    waitPacket :: Socket -> RIO e ()
-    waitPacket s = forever $ do
+    waitPacket :: Maybe Socket -> RIO e ()
+    waitPacket Nothing = pure ()
+    waitPacket (Just s) = forever $ do
         (bs, addr) <- io $ recvFrom s 4096
         logTrace $ displayShow ("(ames) Received packet from ", addr)
         wen        <- io $ Time.now
@@ -182,6 +189,8 @@ ames inst who isFake enqueueEv stderr =
 
     sendPacket :: AmesDrv -> NetworkMode -> AmesDest -> ByteString -> RIO e ()
 
+    sendPacket AmesDrv{..} NoNetwork dest bs = pure ()
+
     sendPacket AmesDrv{..} Fake dest bs = do
       when (okayFakeAddr dest) $ atomically $
         writeTQueue aSendingQueue ((localhostSockAddr Fake dest), bs)
@@ -209,8 +218,9 @@ ames inst who isFake enqueueEv stderr =
 
     -- An outbound queue of messages. We can only write to a socket from one
     -- thread, so coalesce those writes here.
-    sendingThread :: TQueue (SockAddr, ByteString) -> Socket -> RIO e ()
-    sendingThread queue socket = forever $
+    sendingThread :: TQueue (SockAddr, ByteString) -> Maybe Socket -> RIO e ()
+    sendingThread queue Nothing = pure ()
+    sendingThread queue (Just socket) = forever $
       do
         (dest, bs) <- atomically $ readTQueue queue
         logTrace $ displayShow ("(ames) Sending packet to ", socket, dest)

pkg/king/lib/Vere/Pier.hs

@@ -384,7 +384,7 @@ instance Exception PersistExn where
             , "\tExpected " <> show expected <> " but got " <> show got
             ]
 
-runPersist :: ∀e. HasLogFunc e
+runPersist :: ∀e. (HasPierConfig e, HasLogFunc e)
            => EventLog
            -> TQueue (Job, FX)
            -> (FX -> STM ())
@@ -393,11 +393,14 @@ runPersist log inpQ out =
     mkRAcquire runThread cancel
   where
     runThread :: RIO e (Async ())
-    runThread = asyncBound $ forever $ do
-        writs  <- atomically getBatchFromQueue
-        events <- validateJobsAndGetBytes (toNullable writs)
-        Log.appendEvents log events
-        atomically $ for_ writs $ \(_,fx) -> out fx
+    runThread = asyncBound $ do
+        dryRun <- getIsDryRun
+        forever $ do
+            writs  <- atomically getBatchFromQueue
+            unless dryRun $ do
+                events <- validateJobsAndGetBytes (toNullable writs)
+                Log.appendEvents log events
+            atomically $ for_ writs $ \(_,fx) -> out fx
 
     validateJobsAndGetBytes :: [(Job, FX)] -> RIO e (Vector ByteString)
     validateJobsAndGetBytes writs = do