duplicati/Duplicati/WebserverCore/Middlewares/WebsocketExtensions.cs

// Copyright (C) 2025, The Duplicati Team
// https://duplicati.com, hello@duplicati.com
// 
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// copy of this software and associated documentation files (the "Software"), 
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// and/or sell copies of the Software, and to permit persons to whom the 
// Software is furnished to do so, subject to the following conditions:
// 
// The above copyright notice and this permission notice shall be included in 
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// 
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// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE 
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using System.Net.WebSockets;
using System.Text;
using Duplicati.WebserverCore.Abstractions.Notifications;

namespace Duplicati.WebserverCore.Middlewares;

public static class WebsocketExtensions
{
    public static IApplicationBuilder UseNotifications(this IApplicationBuilder app, string notificationPath)
    {
        var opts = new WebSocketOptions();

        app.UseWebSockets(opts);
        return app.Use(async (context, next) =>
        {
            if (context.Request.Path != notificationPath)
            {
                // TODO: Exceptions have a stack trace pointing to here,
                // if the exception is thrown in the next middleware.
                await next(context);
            }
            else
            {
                if (context.User.Identity?.IsAuthenticated == false)
                {
                    using var webSocket = await context.WebSockets.AcceptWebSocketAsync();
                    await webSocket.CloseAsync((WebSocketCloseStatus)4401, "User is not authenticated!",
                        CancellationToken.None);
                    return;
                }

                var websocketAccessor = context.RequestServices.GetRequiredService<IWebsocketAccessor>();
                if (context.WebSockets.IsWebSocketRequest)
                {
                    using var webSocket = await context.WebSockets.AcceptWebSocketAsync();
                    await websocketAccessor.AddConnection(webSocket);
                    await HandleClientData(webSocket, websocketAccessor);
                }
                else
                {
                    context.Response.StatusCode = StatusCodes.Status400BadRequest;
                }
            }
        });
    }

    private static async Task HandleClientData(WebSocket webSocket, IWebsocketAccessor websocketAccessor,
        CancellationToken cancellationToken = default)
    {
        var buffer = new byte[1024 * 4];

        var result = await ReceiveAsync();

        while (!result?.CloseStatus.HasValue == true)
        {
            result = await ReceiveAsync();
        }

        if (result?.CloseStatus is not null)
        {
            await webSocket.CloseAsync(result.CloseStatus.Value, result.CloseStatusDescription, CancellationToken.None);
        }

        return;

        async Task<WebSocketReceiveResult?> ReceiveAsync()
        {
            WebSocketReceiveResult? receiveResult;
            try
            {
                receiveResult = await webSocket.ReceiveAsync(new ArraySegment<byte>(buffer), cancellationToken);
            }
            catch (WebSocketException e)
                when (e is { WebSocketErrorCode: WebSocketError.ConnectionClosedPrematurely })
            {
                Console.WriteLine("[WebSocket] Client closed connection prematurely.");
                receiveResult = null;
            }

            if (receiveResult?.CloseStatus is not null)
            {
                var message = Encoding.Default.GetString(buffer[..receiveResult.Count]);
                await websocketAccessor.HandleClientMessage(message);
            }

            return receiveResult;
        }
    }
}