Android/MAUI Blazor项目中MqttNet服务器无法被PC客户端连接

我创建了一个Android Blazor MAUI服务器项目，将其作为前台服务绑定并启动，但无法通过PC客户端连接到该服务器。测试其他Android MQTT Broker应用可正常连接，说明我的平板设备对外可访问。已尝试使用本地IP和设备IP进行连接，但均未成功。核心代码如下：

public async Task StartServer()
{
    IPHostEntry ipHostInfo = Dns.GetHostEntry(Dns.GetHostName());
    IPAddress ipAddress = ipHostInfo.AddressList[0];

    var result = new List<IPAddress>();
    try
    {
        var upAndNotLoopbackNetworkInterfaces = NetworkInterface.GetAllNetworkInterfaces()
            .Where(n => n.NetworkInterfaceType != NetworkInterfaceType.Loopback 
                && n.OperationalStatus == OperationalStatus.Up);

        foreach (var networkInterface in upAndNotLoopbackNetworkInterfaces)
        {
            var iPInterfaceProperties = networkInterface.GetIPProperties();

            var unicastIpAddressInformation = iPInterfaceProperties.UnicastAddresses
                .FirstOrDefault(u => u.Address.AddressFamily == AddressFamily.InterNetwork);

            if (unicastIpAddressInformation == null)
                continue;

            result.Add(unicastIpAddressInformation.Address);
        }
    }
    catch (Exception ex)
    {
        Console.WriteLine($"Unable to find IP: {ex.Message}");
    }

    // if (result.Count() > 0)
    // {
    //     ipAddress = result.FirstOrDefault();
    // }

    Console.Write("IP ADRESS: ");
    Console.WriteLine(ipAddress);

    var options = new MqttServerOptionsBuilder()
        .WithDefaultEndpointPort(1883)
        .WithDefaultEndpointBoundIPAddress(ipAddress)
        .WithDefaultEndpointBoundIPV6Address(IPAddress.None)
        .WithPersistentSessions()
        .WithDefaultEndpointPort(1883)
        .WithKeepAlive()
        .WithoutEncryptedEndpoint()
        .Build();

    var server = new MqttFactory().CreateMqttServer(options);
    try
    {
        await server.StartAsync();
        Console.WriteLine("MQTT SERVER STARTED..............");

        await Task.CompletedTask;
        // await server.StopAsync();
        // Console.WriteLine("MQTT SERVER STOPPED..............");
    }
    catch (Exception ex)
    {
        Console.WriteLine(ex.Message);
    }
}

问题排查 #

• IP绑定错误：代码中已实现局域网IP排查逻辑，但被注释，当前使用的Dns.GetHostEntry(Dns.GetHostName()).AddressList[0]大概率是回环地址（127.0.0.1）或无法被局域网PC访问的IP
• 冗余配置：重复调用WithDefaultEndpointPort(1883)，属于无效冗余代码
• 权限缺失：Android应用可能缺少必要网络权限，导致服务器无法监听外部连接

解决方案 #

1. 启用有效IP绑定：取消注释IP替换逻辑，使用排查到的局域网IP绑定服务器
2. 添加必要权限：在Android项目的AndroidManifest.xml中添加网络及前台服务权限
3. 验证网络环境：确保PC与Android设备处于同一局域网，使用Android设备的局域网IP（如192.168.x.x）连接
4. 检查端口拦截：确认Android设备防火墙未拦截1883端口

修改后的核心代码 #

public async Task StartServer()
{
    IPHostEntry ipHostInfo = Dns.GetHostEntry(Dns.GetHostName());
    IPAddress ipAddress = ipHostInfo.AddressList[0];

    var result = new List<IPAddress>();
    try
    {
        var upAndNotLoopbackNetworkInterfaces = NetworkInterface.GetAllNetworkInterfaces()
            .Where(n => n.NetworkInterfaceType != NetworkInterfaceType.Loopback 
                && n.OperationalStatus == OperationalStatus.Up);

        foreach (var networkInterface in upAndNotLoopbackNetworkInterfaces)
        {
            var iPInterfaceProperties = networkInterface.GetIPProperties();

            var unicastIpAddressInformation = iPInterfaceProperties.UnicastAddresses
                .FirstOrDefault(u => u.Address.AddressFamily == AddressFamily.InterNetwork);

            if (unicastIpAddressInformation == null)
                continue;

            result.Add(unicastIpAddressInformation.Address);
        }
    }
    catch (Exception ex)
    {
        Console.WriteLine($"Unable to find IP: {ex.Message}");
    }

    // 启用局域网IP绑定逻辑
    if (result.Count > 0)
    {
        ipAddress = result.FirstOrDefault();
    }

    Console.Write("IP ADRESS: ");
    Console.WriteLine(ipAddress);

    var options = new MqttServerOptionsBuilder()
        .WithDefaultEndpointPort(1883)
        .WithDefaultEndpointBoundIPAddress(ipAddress)
        .WithDefaultEndpointBoundIPV6Address(IPAddress.None)
        .WithPersistentSessions()
        .WithKeepAlive()
        .WithoutEncryptedEndpoint()
        .Build();

    var server = new MqttFactory().CreateMqttServer(options);
    try
    {
        await server.StartAsync();
        Console.WriteLine("MQTT SERVER STARTED..............");
    }
    catch (Exception ex)
    {
        Console.WriteLine(ex.Message);
    }
}

必要权限配置 #

在AndroidManifest.xml中添加以下权限：

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.FOREGROUND_SERVICE" />

内容的提问来源于stack exchange，提问作者N. OZER SENOL