grid: Simpler reconnect logic (#18889)

Do not rely on `connChange` to do reconnects.

Instead, you can block while the connection is running and reconnect 
when handleMessages returns.

Add fully async monitoring instead of monitoring on the main goroutine 
and keep this to avoid full network lockup.

internal/grid/connection.go

@@ -707,26 +707,15 @@ func (c *Connection) connect() {
 		if debugPrint {
 			fmt.Println(c.Local, "Connected Waiting for Messages")
 		}
-		c.updateState(StateConnected)
-		go c.handleMessages(c.ctx, conn)
-		// Monitor state changes and reconnect if needed.
-		c.connChange.L.Lock()
-		for {
-			newState := c.State()
-			if newState != StateConnected {
-				c.connChange.L.Unlock()
-				if newState == StateShutdown {
-					conn.Close()
-					return
-				}
-				if debugPrint {
-					fmt.Println(c.Local, "Disconnected")
-				}
-				// Reconnect
-				break
-			}
-			// Unlock and wait for state change.
-			c.connChange.Wait()
+		// Handle messages...
+		c.handleMessages(c.ctx, conn)
+		// Reconnect unless we are shutting down (debug only).
+		if c.State() == StateShutdown {
+			conn.Close()
+			return
+		}
+		if debugPrint {
+			fmt.Println(c.Local, "Disconnected. Attempting to reconnect.")
 		}
 	}
 }
@@ -818,7 +807,7 @@ func (c *Connection) handleIncoming(ctx context.Context, conn net.Conn, req conn
 	rid := uuid.UUID(req.ID)
 	c.remoteID = &rid
 
-	c.updateState(StateConnected)
+	// Handle incoming messages until disconnect.
 	c.handleMessages(ctx, conn)
 	return nil
 }
@@ -867,12 +856,36 @@ func (c *Connection) updateState(s State) {
 	c.connChange.Broadcast()
 }
 
+// monitorState will monitor the state of the connection and close the net.Conn if it changes.
+func (c *Connection) monitorState(conn net.Conn, cancel context.CancelCauseFunc) {
+	c.connChange.L.Lock()
+	defer c.connChange.L.Unlock()
+	for {
+		newState := c.State()
+		if newState != StateConnected {
+			conn.Close()
+			cancel(ErrDisconnected)
+			return
+		}
+		// Unlock and wait for state change.
+		c.connChange.Wait()
+	}
+}
+
 // handleMessages will handle incoming messages on conn.
 // caller *must* hold reconnectMu.
 func (c *Connection) handleMessages(ctx context.Context, conn net.Conn) {
+	c.updateState(StateConnected)
+	ctx, cancel := context.WithCancelCause(ctx)
+	defer cancel(ErrDisconnected)
+
+	// This will ensure that is something asks to disconnect and we are blocked on reads/writes
+	// the connection will be closed and readers/writers will unblock.
+	go c.monitorState(conn, cancel)
+
 	c.handleMsgWg.Add(2)
 	c.reconnectMu.Unlock()
-	ctx, cancel := context.WithCancelCause(ctx)
+
 	// Read goroutine
 	go func() {
 		defer func() {
@@ -1034,7 +1047,6 @@ func (c *Connection) handleMessages(ctx context.Context, conn net.Conn) {
 				lastPongTime := time.Unix(lastPong, 0)
 				if d := time.Since(lastPongTime); d > connPingInterval*2 {
 					logger.LogIf(ctx, fmt.Errorf("host %s last pong too old (%v); disconnecting", c.Remote, d.Round(time.Millisecond)))
-					cancel(ErrDisconnected)
 					return
 				}
 			}
@@ -1084,14 +1096,12 @@ func (c *Connection) handleMessages(ctx context.Context, conn net.Conn) {
 			err := wsw.writeMessage(&buf, c.side, ws.OpBinary, toSend)
 			if err != nil {
 				logger.LogIf(ctx, fmt.Errorf("ws writeMessage: %w", err))
-				cancel(ErrDisconnected)
 				return
 			}
 			PutByteBuffer(toSend)
 			_, err = buf.WriteTo(conn)
 			if err != nil {
 				logger.LogIf(ctx, fmt.Errorf("ws write: %w", err))
-				cancel(ErrDisconnected)
 				return
 			}
 			continue
@@ -1109,7 +1119,6 @@ func (c *Connection) handleMessages(ctx context.Context, conn net.Conn) {
 		toSend, err = m.MarshalMsg(toSend)
 		if err != nil {
 			logger.LogIf(ctx, fmt.Errorf("msg.MarshalMsg: %w", err))
-			cancel(ErrDisconnected)
 			return
 		}
 		// Append as byte slices.
@@ -1126,14 +1135,12 @@ func (c *Connection) handleMessages(ctx context.Context, conn net.Conn) {
 		err = wsw.writeMessage(&buf, c.side, ws.OpBinary, toSend)
 		if err != nil {
 			logger.LogIf(ctx, fmt.Errorf("ws writeMessage: %w", err))
-			cancel(ErrDisconnected)
 			return
 		}
-		// Tosend is our local buffer, so we can reuse it.
+		// buf is our local buffer, so we can reuse it.
 		_, err = buf.WriteTo(conn)
 		if err != nil {
 			logger.LogIf(ctx, fmt.Errorf("ws write: %w", err))
-			cancel(ErrDisconnected)
 			return
 		}