fix timeoutmonitor loop (#463)

* fix timeoutmonitor loop

* Clarify that cancellation can happen while in timeoutMonitor

libp2p/stream/connection.nim

@@ -63,6 +63,7 @@ method closeImpl*(s: Connection): Future[void] =
   trace "Closing connection", s
   if not isNil(s.timerTaskFut) and not s.timerTaskFut.finished:
     s.timerTaskFut.cancel()
+    s.timerTaskFut = nil
 
   trace "Closed connection", s
 
@@ -71,6 +72,32 @@ method closeImpl*(s: Connection): Future[void] =
 func hash*(p: Connection): Hash =
   cast[pointer](p).hash
 
+proc pollActivity(s: Connection): Future[bool] {.async.} =
+  if s.closed and s.atEof:
+    return false # Done, no more monitoring
+
+  if s.activity:
+    s.activity = false
+    return true
+
+  # Inactivity timeout happened, call timeout monitor
+
+  trace "Connection timed out", s
+  if not(isNil(s.timeoutHandler)):
+    trace "Calling timeout handler", s
+
+    try:
+      await s.timeoutHandler()
+    except CancelledError:
+      # timeoutHandler is expected to be fast, but it's still possible that
+      # cancellation will happen here - no need to warn about it - we do want to
+      # stop the polling however
+      debug "Timeout handler cancelled", s
+    except CatchableError as exc: # Shouldn't happen
+      warn "exception in timeout handler", s, exc = exc.msg
+
+  return false
+
 proc timeoutMonitor(s: Connection) {.async, gcsafe.} =
   ## monitor the channel for inactivity
   ##
@@ -80,31 +107,14 @@ proc timeoutMonitor(s: Connection) {.async, gcsafe.} =
   ## be reset
   ##
 
-  try:
-    while true:
+  while true:
+    try: # Sleep at least once!
       await sleepAsync(s.timeout)
+    except CancelledError:
+      return
 
-      if s.closed and s.atEof:
-        return
-
-      if s.activity:
-        s.activity = false
-        continue
-
-      break
-
-    # reset channel on inactivity timeout
-    trace "Connection timed out", s
-    if not(isNil(s.timeoutHandler)):
-      trace "Calling timeout handler", s
-      await s.timeoutHandler()
-
-  except CancelledError as exc:
-    raise exc
-  except CatchableError as exc: # Shouldn't happen
-    warn "exception in timeout", s, exc = exc.msg
-  finally:
-    s.timerTaskFut = nil
+    if not await s.pollActivity():
+      return
 
 proc init*(C: type Connection,
            peerInfo: PeerInfo,