Support websocket based pushing.

src/Aiursoft.ChessServer/Controllers/GamesController.cs

@@ -1,14 +1,24 @@
 using Aiursoft.ChessServer.Data;
+using Aiursoft.ChessServer.Models;
+using Aiursoft.ChessServer.Services;
+using Aiursoft.CSTools.Services;
 using Microsoft.AspNetCore.Mvc;
 
 namespace Aiursoft.ChessServer.Controllers;
 
 public class GamesController : Controller
 {
+    private readonly Counter _counter;
+    private readonly WebSocketPusher _pusher;
     private readonly InMemoryDatabase _database;
 
-    public GamesController(InMemoryDatabase database)
+    public GamesController(
+        Counter counter,
+        WebSocketPusher pusher,
+        InMemoryDatabase database)
     {
+        _counter = counter;
+        _pusher = pusher;
         _database = database;
     }
 
@@ -38,10 +48,44 @@ public class GamesController : Controller
                 { "fen", $"games/{id}/fen"},
                 { "pgn", $"games/{id}/pgn"},
                 { "html", $"games/{id}/html"},
+                {"websocket", $"games/{id}/websocket"},
                 { "move-post", $"games/{id}/move/{{player}}/{{move_algebraic_notation}}"}
             }
         });
     }
+    
+    [Route("games/{id}/ws")]
+    public async Task<IActionResult> GetWebSocket([FromRoute] int id)
+    {
+        var lastReadId = _counter.GetCurrent;
+        var (channel, blocker) = _database.ListenChannel(id);
+        
+        await _pusher.Accept(HttpContext);
+        try
+        {
+            await Task.Factory.StartNew(_pusher.PendingClose);
+            while (_pusher.Connected)
+            {
+                await blocker.WaitAsync();
+                var nextMessages = channel
+                    .GetMessagesFrom(lastReadId)
+                    .ToList();
+                var messageToPush = nextMessages.MinBy(t => t.Id);
+                await _pusher.SendMessage(messageToPush!.Content);
+                lastReadId = messageToPush.Id;
+            }
+        }
+        finally
+        {
+            await _pusher.Close();
+            if (!channel.UnRegister(out blocker))
+            { 
+                throw new InvalidOperationException("Failed to unregister blocker!");
+            }
+        }
+
+        return NoContent();
+    }
 
     [Route("games/{id}/ascii")]
     public IActionResult GetAscii([FromRoute] int id)
@@ -80,7 +124,15 @@ public class GamesController : Controller
             if (game.IsValidMove(move) && !game.IsEndGame && game.Turn.AsChar.ToString() == player)
             {
                 game.Move(move);
-                return Ok(game.ToFen());
+                var fen = game.ToFen();
+                if (_database.Channels.TryGetValue(id, out var channel))
+                {
+                    channel.Push(new Message(fen)
+                    {
+                        Id = _counter.GetUniqueNo(),
+                    });
+                }
+                return Ok(fen);
             }
             return BadRequest();
         }

src/Aiursoft.ChessServer/Data/InMemoryDatabase.cs

@@ -1,6 +1,7 @@
 using Aiursoft.Scanner.Abstractions;
 using Chess;
 using System.Collections.Concurrent;
+using Aiursoft.ChessServer.Models;
 
 namespace Aiursoft.ChessServer.Data;
 
@@ -12,7 +13,8 @@ public class Game
 
 public class InMemoryDatabase : ISingletonDependency
 {
-    public ConcurrentDictionary<int, ChessBoard> Boards { get; private set; } = new ConcurrentDictionary<int, ChessBoard>();
+    public ConcurrentDictionary<int, ChessBoard> Boards { get; } = new();
+    public ConcurrentDictionary<int, Channel> Channels { get; } = new();
 
     public Game[] GetActiveGames()
     { 
@@ -27,4 +29,12 @@ public class InMemoryDatabase : ISingletonDependency
     {
         return Boards.GetOrAdd(id, _ => new ChessBoard());
     }
+    
+    public (Channel, SemaphoreSlim) ListenChannel(int id)
+    {
+        var channel = Channels.GetOrAdd(id, _ => new Channel());
+        var blocker = new SemaphoreSlim(0);
+        channel.HasNewMessageBlocker.Add(blocker);
+        return (channel, blocker);
+    }
 }

src/Aiursoft.ChessServer/Models/Channel.cs

@@ -0,0 +1,40 @@
+using System.Collections.Concurrent;
+
+namespace Aiursoft.ChessServer.Models;
+
+public class Message
+{
+    public Message(string content)
+    {
+        Content = content;
+    }
+
+    public int Id { get; init; }
+    public string Content { get; set; }
+}
+
+public class Channel
+{
+    private ConcurrentBag<Message> Messages { get; } = new();
+
+    public ConcurrentBag<SemaphoreSlim> HasNewMessageBlocker { get; } = new();
+
+    public IEnumerable<Message> GetMessagesFrom(int lastReadId)
+    {
+        return Messages.Where(t => t.Id > lastReadId);
+    }
+
+    public void Push(Message message)
+    {
+        Messages.Add(message);
+        foreach (var blocker in HasNewMessageBlocker)
+        {
+            blocker.Release();
+        }
+    }
+    
+    public bool UnRegister(out SemaphoreSlim blocker)
+    {
+        return HasNewMessageBlocker.TryTake(out blocker!);
+    }
+}

src/Aiursoft.ChessServer/Program.cs

@@ -19,6 +19,7 @@ public class Startup : IWebStartup
     public void ConfigureServices(IConfiguration configuration, IWebHostEnvironment environment, IServiceCollection services)
     {
         services.AddLibraryDependencies();
+        
         services
             .AddControllersWithViews()
             .AddApplicationPart(Assembly.GetExecutingAssembly());
@@ -30,5 +31,6 @@ public class Startup : IWebStartup
         app.UseStaticFiles();
         app.UseRouting();
         app.MapDefaultControllerRoute();
+        app.UseWebSockets();
     }
 }

src/Aiursoft.ChessServer/Services/WebSocketPusher.cs

@@ -0,0 +1,57 @@
+using System.Net.WebSockets;
+using Aiursoft.CSTools.Tools;
+using Aiursoft.Scanner.Abstractions;
+
+namespace Aiursoft.ChessServer.Services;
+
+public class WebSocketPusher : IScopedDependency
+{
+    private bool _dropped;
+    private WebSocket? _ws;
+
+    public bool Connected => !_dropped && _ws?.State == WebSocketState.Open;
+
+    public async Task Accept(HttpContext context)
+    {
+        _ws = await context.WebSockets.AcceptWebSocketAsync();
+    }
+
+    public async Task SendMessage(string message)
+    {
+        await (_ws?.SendMessage(message) ?? throw new InvalidOperationException("WebSocket is not connected!"));
+    }
+
+    public async Task PendingClose()
+    {
+        try
+        {
+            var buffer = new ArraySegment<byte>(new byte[4096 * 20]);
+            while (true)
+            {
+                await (_ws?.ReceiveAsync(buffer, CancellationToken.None) ?? throw new InvalidOperationException("WebSocket is not connected!"));
+                if (_ws.State == WebSocketState.Open)
+                {
+                    continue;
+                }
+
+                _dropped = true;
+                return;
+            }
+        }
+        catch (Exception e) when (!e.Message.StartsWith("The remote party closed the WebSocket connection"))
+        {
+            _dropped = true;
+        }
+    }
+
+    public Task Close()
+    {
+        if (_ws?.State == WebSocketState.Open)
+        {
+            return _ws.CloseOutputAsync(WebSocketCloseStatus.NormalClosure, "Close because of error.",
+                CancellationToken.None);
+        }
+        
+        return Task.CompletedTask;
+    }
+}

src/Aiursoft.ChessServer/Views/Games/GetHtml.cshtml

@@ -11,10 +11,8 @@
 </head>
 <body>
 <div id="board" style="width: 400px"></div>
-<button id="refresh" style="margin-top: 5px">Refresh</button>
 <p id="status"></p>
 <p id="fen"></p>
-<p id="pgn"></p>
 <script type="module" src="~/chess.js/dist/esm/chess.js"></script>
 <script src="~/jquery/dist/jquery.min.js"></script>
 <script src="~/chessboardjs/js/chessboard-1.0.0.min.js"></script>

src/Aiursoft.ChessServer/wwwroot/site.js

@@ -1,19 +1,12 @@
 import {Chess} from "/chess.js/dist/esm/chess.js";
 
+const statusControl = $('#status');
+const fenControl = $('#fen');
+
 const initGameBoard = function (player, gameId) {
     $.get("/games/" + gameId + "/fen", function (fen) {
-        let board = null
-        let game = new Chess(fen);
-        const refreshButton = $('#refresh');
-        const statusControl = $('#status');
-        const fenControl = $('#fen');
-        const pgnControl = $('#pgn');
-
-        function refresh(newFen) {
-            game = new Chess(newFen);
-            board.position(newFen);
-            updateStatus();
-        }
+        let board = null;
+        let game = null;
 
         // Happens when a player picks up a piece.
         function onDragStart(source, piece, position, _) {
@@ -32,27 +25,20 @@ const initGameBoard = function (player, gameId) {
             }
         }
 
-        // Happens when a player drops a piece.
         function onDrop(source, target) {
             try {
-                // see if the move is legal
                 const move = game.move({
                     from: source,
                     to: target,
-                    promotion: 'q' // NOTE: always promote to a queen for example simplicity
+                    promotion: 'q' 
                 })
-
                 if (move === null) {
                     return 'snapback'
                 }
-
-                // Get the last move and send it to server.
                 const lastMove = game.history({verbose: true}).pop().san;
-                $.post("/games/" + gameId + "/move/" + player + "/" + lastMove, function (fen) {
-                    refresh(fen);
-                });
+                $.post("/games/" + gameId + "/move/" + player + "/" + lastMove);
             } catch (e) {
-                return 'snapback'
+                return 'snapback';
             }
         }
 
@@ -61,36 +47,23 @@ const initGameBoard = function (player, gameId) {
             board.position(game.fen())
         }
 
-        function updateStatus() {
+        function updateStatusText() {
             let status;
             let moveColor = 'White';
             if (game.turn() === 'b') {
-                moveColor = 'Black'
-            }
-
-            // checkmate?
-            if (game.isCheckmate()) {
-                status = 'Game over, ' + moveColor + ' is in checkmate.'
-            }
-
-            // draw?
-            else if (game.isDraw()) {
-                status = 'Game over, drawn position'
-            }
-
-            // game still on
-            else {
-                status = moveColor + ' to move'
-
-                // check?
+                moveColor = 'Black';
+            } if (game.isCheckmate()) {
+                status = 'Game over, ' + moveColor + ' is in checkmate, and winner is ' + (game.turn() === 'w' ? 'Black' : 'White');
+            } else if (game.isDraw()) {
+                status = 'Game over, drawn position';
+            } else {
+                status = moveColor + ' to move';
                 if (game.isCheck()) {
-                    status += ', ' + moveColor + ' is in check'
+                    status += ', ' + moveColor + ' is in check';
                 }
             }
-
-            statusControl.html(status)
-            fenControl.html(game.fen())
-            pgnControl.html(game.pgn())
+            statusControl.html(status);
+            fenControl.html(game.fen());
         }
 
         const config = {
@@ -104,14 +77,26 @@ const initGameBoard = function (player, gameId) {
         };
         board = ChessBoard('board', config);
 
-        // Bind Refresh button.
-        refreshButton.click(function () {
-            $.get("/games/" + gameId + "/fen", function (fen) {
-                refresh(fen);
-            });
-        });
+        function refresh(newFen) {
+            game = new Chess(newFen);
+            board.position(newFen);
+            updateStatusText();
+        }
 
-        updateStatus();
+        refresh(fen);
+        
+        const wsScheme = window.location.protocol === "https:" ? "wss://" : "ws://";
+        const socket = new WebSocket(wsScheme + window.location.host + "/games/" + gameId + "/ws");
+        socket.onmessage = function (event) {
+            refresh(event.data);
+        };
+        
+        // Auto reconnect.
+        socket.onclose = function (event) {
+            setTimeout(function () {
+                initGameBoard(player, gameId);
+            }, 1000);
+        };
     });
 
 };