在Asp.net Core中使用中间件来管理websocket

介绍

ASP.NET Core SignalR是一个有用的库，能够简化Web应用程序中实时通讯的管理。可是，我宁愿使用WebSockets，由于我想要更灵活，而且与任何WebSocket客户端兼容。

在Microsoft的文档中，我找到了一个很好的WebSockets工做示例。它仍然是管理链接，以便可以从一个链接向其余链接广播消息，这是SignalR开箱即用的功能。指望这个逻辑很是复杂，我想从Startup类中删除它。

背景

要阅读ASP.NET Core中的WebSockets支持，能够在此处查看。若是您想了解中间件以及如何在ASP.NET Core中编写它，请阅读此连接。

代码使用

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

如今，您能够建立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);
    }
}

在这种状况下，WebSockets请求在URL中始终包含“/ ws”。查询字符串包含用于将WebSocket与登陆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; }
}

我也建立了自定义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是您可能拥有的不一样类型消息的枚举。

在Startup类中，您必须注册如下服务：

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

CustomWebSocketFactory负责收集链接的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（即在链接时须要发送任何消息以及如何对传入消息做出反应）

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类中添加如下内容：

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

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

经过这种方式，Starup类保持干净，管理WebSockets的逻辑能够扩展，使您能够根据本身的喜爱灵活地组织它。喜欢这篇文章就转载吧。在Asp.net Core中使用中间件来管理websocket