NetworkTool/windows/NetworkTool.Client/Services/DiscoveryService.cs

using System.Net;
using System.Net.Sockets;
using System.Text;
using System.Text.Json;
using NetworkTool.Client.Models;

namespace NetworkTool.Client.Services;

public sealed class DiscoveryService
{
    private const int DiscoveryPort = 50000;

    public async Task<DiscoveredDevice?> DiscoverAsync(string localIPv4, CancellationToken cancellationToken = default)
    {
        if (string.IsNullOrWhiteSpace(localIPv4))
        {
            return null;
        }

        using var client = new UdpClient(AddressFamily.InterNetwork)
        {
            EnableBroadcast = true,
        };

        client.Client.Bind(new IPEndPoint(IPAddress.Parse(localIPv4), 0));
        var request = new
        {
            protocol_version = 1,
            message_type = "discover",
            request_id = Guid.NewGuid().ToString(),
            client_name = Environment.MachineName,
        };

        var payload = JsonSerializer.SerializeToUtf8Bytes(request);
        await client.SendAsync(payload, payload.Length, new IPEndPoint(IPAddress.Broadcast, DiscoveryPort));

        using var timeoutCts = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
        timeoutCts.CancelAfter(TimeSpan.FromSeconds(3));

        try
        {
            var result = await client.ReceiveAsync(timeoutCts.Token);
            var response = JsonSerializer.Deserialize<DiscoveryResponse>(result.Buffer);
            if (response is null || response.MessageType != "discover_response")
            {
                return null;
            }

            return new DiscoveredDevice
            {
                DeviceId = response.DeviceId ?? string.Empty,
                Hostname = response.Hostname ?? string.Empty,
                ServerVersion = response.ServerVersion ?? string.Empty,
                Lan2Ip = response.Lan2Ip ?? string.Empty,
                AuthRequired = response.AuthRequired,
            };
        }
        catch (OperationCanceledException)
        {
            return null;
        }
    }

    private sealed class DiscoveryResponse
    {
        public string? MessageType { get; set; }
        public string? DeviceId { get; set; }
        public string? Hostname { get; set; }
        public string? ServerVersion { get; set; }
        public string? Lan2Ip { get; set; }
        public bool AuthRequired { get; set; }
    }
}