Asp.net Core中如何使用中间件来管理websocket

介绍

我喜欢.NET CORE 这个东西，其实不仅仅源于它性能很高，可以跨平台，还因为它的设计模式确实令人着迷。以前没.NET CORE 的时候，.NET用websocket必须跑在windows server 2012上，但我一般不会这么干，都把websocket架在nodejs的服务器上。这么分出来，麻烦肯定是麻烦的，而且js这东西，写复杂和几年后再看都是头疼的问题。那么，如果.NET CORE是以kestrel运行的，那么就不再需要考虑服务器的版本运行，任何一个地方都可以用websocket

ASP.NET Core SignalR是一个有用的库，可以简化Web应用程序中实时通信的管理。但是，我宁愿使用WebSockets，因为我想要更灵活，并且与任何WebSocket客户端兼容。

在Microsoft的文档中，我找到了一个很好的WebSockets工作示例。它仍然是管理连接，以便能够从一个连接向其他连接广播消息，这是SignalR开箱即用的功能。期望这个逻辑非常复杂，我想从Startup类中删除它。

背景

要阅读ASP.NET Core中的WebSockets支持，可以在此处查看。如果您想了解中间件以及如何在ASP.NET Core中编写它，请阅读此链接。

代码使用

首先，你必须添加 Microsoft.AspNetCore.WebSockets 包到你的项目。

现在，您可以创建一个扩展方法和类来管理WebSockets：

public static class WebSocketExtensions
{
 public static IApplicationBuilder UseCustomWebSocketManager(this IApplicationBuilder app)
 {
  return app.UseMiddleware<CustomWebSocketManager>();
 }
}

public class CustomWebSocketManager
{
 private readonly RequestDelegate _next;

 public CustomWebSocketManager(RequestDelegate next)
 {
  _next = next;
 }

 public async Task Invoke(HttpContext context, ICustomWebSocketFactory wsFactory, ICustomWebSocketMessageHandler wsmHandler)
 {
  if (context.Request.Path == "/ws")
  {
   if (context.WebSockets.IsWebSocketRequest)
   {
    string username = context.Request.Query["u"];
    if (!string.IsNullOrEmpty(username))
    {
     WebSocket webSocket = await context.WebSockets.AcceptWebSocketAsync();
     CustomWebSocket userWebSocket = new CustomWebSocket()
     {
      WebSocket = webSocket,
      Username = username
     };
     wsFactory.Add(userWebSocket);
     await wsmHandler.SendInitialMessages(userWebSocket);
     await Listen(context, userWebSocket, wsFactory, wsmHandler);
    }
   }
   else
   {
     context.Response.StatusCode = 400;
   }
  }
  await _next(context);
 }

 private async Task Listen(HttpContext context, CustomWebSocket userWebSocket, ICustomWebSocketFactory wsFactory, ICustomWebSocketMessageHandler wsmHandler)
 {
  WebSocket webSocket = userWebSocket.WebSocket;
  var buffer = new byte[1024 * 4];
  WebSocketReceiveResult result = await webSocket.ReceiveAsync(new ArraySegment<byte>(buffer), CancellationToken.None);
  while (!result.CloseStatus.HasValue)
  {
    await wsmHandler.HandleMessage(result, buffer, userWebSocket, wsFactory);
    buffer = new byte[1024 * 4];
    result = await webSocket.ReceiveAsync(new ArraySegment<byte>(buffer), CancellationToken.None);
  } 
  wsFactory.Remove(userWebSocket.Username);
  await webSocket.CloseAsync(result.CloseStatus.Value, result.CloseStatusDescription, CancellationToken.None);
 }
}

在这种情况下，WebSockets请求在URL中始终包含“/ ws”。查询字符串包含用于将WebSocket与登录用户相关联的用户名的参数u。

CustomWebSocket是一个包含WebSocket和用户名的类：

public class CustomWebSocket
{
 public WebSocket WebSocket { get; set; }
 public string Username { get; set; }
}

我也创建了自定义WebSocket消息:

class CustomWebSocketMessage
{
 public string Text { get; set; }
 public DateTime MessagDateTime { get; set; }
 public string Username { get; set; }
 public WSMessageType Type { get; set; }
}

其中Type是您可能拥有的不同类型消息的枚举。

在Startup类中，您必须注册以下服务：

services.AddSingleton<ICustomWebSocketFactory, CustomWebSocketFactory>();
services.AddSingleton<ICustomWebSocketMessageHandler, CustomWebSocketMessageHandler>();

CustomWebSocketFactory负责收集连接的WebSockets列表：

public interface ICustomWebSocketFactory
{
 void Add(CustomWebSocket uws);
 void Remove(string username);
 List<CustomWebSocket> All();
 List<CustomWebSocket> Others(CustomWebSocket client);
 CustomWebSocket Client(string username);
}

public class CustomWebSocketFactory : ICustomWebSocketFactory
{
 List<CustomWebSocket> List;

 public CustomWebSocketFactory()
 {
  List = new List<CustomWebSocket>();
 }

 public void Add(CustomWebSocket uws)
 {
  List.Add(uws);
 }

 //when disconnect
 public void Remove(string username) 
 {
  List.Remove(Client(username));
 }

 public List<CustomWebSocket> All()
 {
  return List;
 }
 
 public List<CustomWebSocket> Others(CustomWebSocket client)
 {
  return List.Where(c => c.Username != client.Username).ToList();
 }
 
 public CustomWebSocket Client(string username)
 {
  return List.First(c=>c.Username == username);
 }
}

CustomWebSocketMessageHandler包含有关消息的逻辑（即在连接时需要发送任何消息以及如何对传入消息作出反应）

public interface ICustomWebSocketMessageHandler
{
 Task SendInitialMessages(CustomWebSocket userWebSocket);
 Task HandleMessage(WebSocketReceiveResult result, byte[] buffer, CustomWebSocket userWebSocket, ICustomWebSocketFactory wsFactory);
 Task BroadcastOthers(byte[] buffer, CustomWebSocket userWebSocket, ICustomWebSocketFactory wsFactory);
 Task BroadcastAll(byte[] buffer, CustomWebSocket userWebSocket, ICustomWebSocketFactory wsFactory);
}

public class CustomWebSocketMessageHandler : ICustomWebSocketMessageHandler
{
 public async Task SendInitialMessages(CustomWebSocket userWebSocket)
 {
  WebSocket webSocket = userWebSocket.WebSocket;
  var msg = new CustomWebSocketMessage
  {
   MessagDateTime = DateTime.Now,
   Type = WSMessageType.anyType,
   Text = anyText,
   Username = "system"
  };

  string serialisedMessage = JsonConvert.SerializeObject(msg);
  byte[] bytes = Encoding.ASCII.GetBytes(serialisedMessage);
  await webSocket.SendAsync(new ArraySegment<byte>(bytes, 0, bytes.Length), WebSocketMessageType.Text, true, CancellationToken.None);
 }

 public async Task HandleMessage(WebSocketReceiveResult result, byte[] buffer, CustomWebSocket userWebSocket, ICustomWebSocketFactory wsFactory)
 {
  string msg = Encoding.ASCII.GetString(buffer);
  try
  {
   var message = JsonConvert.DeserializeObject<CustomWebSocketMessage>(msg);
   if (message.Type == WSMessageType.anyType)
   {
   await BroadcastOthers(buffer, userWebSocket, wsFactory);
   }
  }
  catch (Exception e)
  {
   await userWebSocket.WebSocket.SendAsync(new ArraySegment<byte>(buffer, 0, result.Count), result.MessageType, result.EndOfMessage, CancellationToken.None);
  }
 }

 public async Task BroadcastOthers(byte[] buffer, CustomWebSocket userWebSocket, ICustomWebSocketFactory wsFactory)
 {
  var others = wsFactory.Others(userWebSocket);
  foreach (var uws in others)
  {
   await uws.WebSocket.SendAsync(new ArraySegment<byte>(buffer, 0, buffer.Length), WebSocketMessageType.Text, true, CancellationToken.None);
  }
 }

 public async Task BroadcastAll(byte[] buffer, CustomWebSocket userWebSocket, ICustomWebSocketFactory wsFactory)
 {
  var all = wsFactory.All();
  foreach (var uws in all)
  {
   await uws.WebSocket.SendAsync(new ArraySegment<byte>(buffer, 0, buffer.Length), WebSocketMessageType.Text, true, CancellationToken.None);
  }
 }
}

最后，在Configure方法的Startup类中添加以下内容：

var webSocketOptions = new WebSocketOptions()
{
 KeepAliveInterval = TimeSpan.FromSeconds(120),
 ReceiveBufferSize = 4 * 1024
};

app.UseWebSockets(webSocketOptions);
app.UseCustomWebSocketManager();

通过这种方式，Starup类保持干净，管理WebSockets的逻辑可以扩展，使您可以根据自己的喜好灵活地组织它。

总结

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