前后端分离项目使用WebSocket,报错 The remote party closed the WebSocket connection without completing the close handshake. 怎么解决，或者给一个完整的.net core案例

同样的错误在 .NET Core 中的解决方法也是类似的。下面是一个基于 .NET Core 的 WebSocket 示例代码，可能对你有帮助：

前端代码（使用 JavaScript）：

var socket = new WebSocket('ws://localhost:5000/ws');

socket.onopen = function() {
  console.log('WebSocket connected');
}

socket.onmessage = function(event) {
  console.log('Received message: ' + event.data);
}

socket.onclose = function(event) {
  console.log('WebSocket closed with code: ' + event.code + ', reason: ' + event.reason);
}

socket.onerror = function(error) {
  console.error('WebSocket error: ' + error);
}

后端代码（使用 .NET Core）：

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.DependencyInjection;
using System.Net.WebSockets;
using System.Threading;
using System.Threading.Tasks;

namespace WebSocketExample
{
    public class Startup
    {
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddWebSocketManager();
        }

        public void Configure(IApplicationBuilder app)
        {
            app.UseWebSockets();
            app.Map("/ws", ws =>
            {
                ws.UseMiddleware<WebSocketManagerMiddleware>();
            });

            app.Run(async context =>
            {
                await context.Response.WriteAsync("Hello World!");
            });
        }
    }

    public class WebSocketManagerMiddleware
    {
        private readonly RequestDelegate _next;
        private readonly WebSocketHandler _webSocketHandler;

        public WebSocketManagerMiddleware(RequestDelegate next, WebSocketHandler webSocketHandler)
        {
            _next = next;
            _webSocketHandler = webSocketHandler;
        }

        public async Task InvokeAsync(HttpContext context)
        {
            if (!context.WebSockets.IsWebSocketRequest)
            {
                await _next(context);
                return;
            }

            var webSocket = await context.WebSockets.AcceptWebSocketAsync();
            await _webSocketHandler.OnConnected(webSocket);

            await Receive(webSocket, async (result, buffer) =>
            {
                if (result.MessageType == WebSocketMessageType.Text)
                {
                    await _webSocketHandler.ReceiveAsync(webSocket, result, buffer);
                    return;
                }

                await webSocket.CloseAsync(result.CloseStatus.Value, result.CloseStatusDescription, CancellationToken.None);
                await _webSocketHandler.OnDisconnected(webSocket);
            });
        }

        private async Task Receive(WebSocket webSocket, WebSocketReceiveAsyncCallback callback)
        {
            var buffer = new byte[1024 * 4];

            while (webSocket.State == WebSocketState.Open)
            {
                var result = await webSocket.ReceiveAsync(new ArraySegment<byte>(buffer), CancellationToken.None);
                await callback(result, buffer);
            }
        }
    }

    public class WebSocketHandler
    {
        public virtual Task OnConnected(WebSocket webSocket)
        {
            return Task.CompletedTask;
        }

        public virtual Task OnDisconnected(WebSocket webSocket)
        {
            return Task.CompletedTask;
        }

        public virtual async Task ReceiveAsync(WebSocket webSocket, WebSocketReceiveResult result, byte[] buffer)
        {
            var message = System.Text.Encoding.UTF8.GetString(buffer, 0, result.Count);
            await SendMessageAsync(webSocket, $"Hello, {message}!");
        }

        public async Task SendMessageAsync(WebSocket webSocket, string message)
        {
            var buffer = System.Text.Encoding.UTF8.GetBytes(message);
            await webSocket.SendAsync(new ArraySegment<byte>(buffer, 0, buffer.Length), WebSocketMessageType.Text, true, CancellationToken.None);
        }
    }

    public class WebSocketManager : WebSocketHandler
    {
        private readonly WebSocketConnectionManager _connectionManager;

        public WebSocketManager(WebSocketConnectionManager connectionManager)
        {
            _connectionManager = connectionManager;
        }

        public override Task OnConnected(WebSocket webSocket)
        {
            return _connectionManager.AddWebSocketAsync(webSocket);
        }

        public override Task OnDisconnected(WebSocket webSocket)
        {
            return _connectionManager.RemoveWebSocketAsync(_connectionManager.GetId(webSocket));
        }
    }

    public static class WebSocketExtensions
    {
        public static IServiceCollection AddWebSocketManager(this IServiceCollection services)
        {
            services.AddSingleton<WebSocketConnectionManager>();
            services.AddSingleton<WebSocketManager>();

            return services;
        }
    }

    public class WebSocketConnectionManager
    {
        private readonly ConcurrentDictionary<string, WebSocket> _webSockets = new ConcurrentDictionary<string, WebSocket>();

        public WebSocket GetWebSocketById(string id)
        {
            _webSockets.TryGetValue(id, out WebSocket webSocket);
            return webSocket;
        }

        public ConcurrentDictionary<string, WebSocket> GetAll()
        {
            return _webSockets;
        }

        public string GetId(WebSocket webSocket)
        {
            return _webSockets.FirstOrDefault(x => x.Value == webSocket).Key;
        }

        public async Task AddWebSocketAsync(WebSocket webSocket)
        {
            _webSockets.TryAdd(Guid.NewGuid().ToString(), webSocket);
        }

        public async Task RemoveWebSocketAsync(string id)
        {
            _webSockets.TryRemove(id, out WebSocket webSocket);
            await webSocket.CloseAsync(WebSocketCloseStatus.NormalClosure, "WebSocket closed", CancellationToken.None);
        }
    }
}

这个示例代码同样实现了一个简单的 WebSocket 服务，前端代码连接到 ws://localhost:5000/ws，后端代码使用 .NET Core 实现了一个 WebSocketManagerMiddleware 中间件来处理 WebSocket 连接。如果连接关闭时未完成关闭握手，会输出类似如下的错误信息：

System.Net.WebSockets.WebSocketException (0x80004005): The remote party closed the WebSocket connection without completing the close handshake.
   at System.Net.WebSockets.ManagedWebSocket.ThrowIfEOFUnexpected(Boolean throwOnPrematureClosure)
   at System.Net.WebSockets.ManagedWebSocket.<SendAsyncPrivate>d__60.MoveNext()

希望对你有帮助！