安卓系统:SSDP卡在MulticastSocket.rereceive()上

Question

TL；DR:SSDP库未接收到数据报。Wireshark显示预期流量。

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我正在使用安卓dlna库来支持安卓应用程序中的SSDP。目标是发现一个自定义的SSDP-enabled设备，获取其IP地址，然后对其进行RESTful API调用。这在iOS上运行良好，但我在Android上接收数据报时遇到了一些问题。

使用Wireshark，我可以确定SSDP搜索结束，设备返回状态为OK，但此循环从未通过receive()方法：

SSDPSearchMsg search = new SSDPSearchMsg(SSDP.ST_ContentDirectory);
Log.e("SSDP", search.toString());
SSDPSocket sock = null;
try {
    sock = new SSDPSocket();
    sock.send(search.toString());
    while (true) {
        Log.e("SSDP", "Receive...");//only called once (stuck here)
        DatagramPacket dp = sock.receive();
        Log.e("SSDP", "Datagram Received with data " + new String(dp.getData()));
    }
} catch (IOException e) {
    e.printStackTrace();
}
finally {
    Log.e("SSDP", "Closing Socket");
    if (sock != null)
        sock.close();
}

这一切都是在AsyncTask中完成的。我看到以下内容打印到logcat：

SSDP    M-SEARCH * HTTP/1.1
SSDP    Host:239.255.255.250:1900
SSDP    Man:"ssdp:discover"
SSDP    ST:urn:schemas-upnp-org:service:ContentDirectory:1
SSDP    MX:3
SSDP    
SSDP    Receive...

Wireshark报告以下相关数据报：

    Source      Destination    Protocol    Length    Info
---------------------------------------------------------------------------
 192.168.1.7  239.255.255.250    SSDP       175       M-SEARCH * HTTP/1.1
 192.168.1.1    192.168.1.7      SSDP       356       HTTP/1.1 200 OK

最后，我有以下清单权限：

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.INTERNET"/>
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
<uses-permission android:name="android.permission.ACCESS_WIFI_STATE"/>
<uses-permission android:name="android.permission.CHANGE_NETWORK_STATE"/>
<uses-permission android:name="android.permission.CHANGE_WIFI_STATE"/>
<uses-permission android:name="android.permission.CHANGE_WIFI_MULTICAST_STATE" />

我在俯瞰什么？为什么我没有收到响应数据报？

Answer 1

我知道这是一个老问题，但它也让我绊倒了，所以也许这会帮助其他在这个问题上绊倒的人。如果你没有获得MulticastLock，Android会过滤掉多播数据包，所以更新代码以获得MulticastLock，并在完成后释放它。

final WifiManager wifi = (WifiManager) context.getSystemService(Context.WIFI_SERVICE);
WifiManager.MulticastLock lock = wifi.createMulticastLock("ssdp");
try {
    lock.acquire();
    sock = new SSDPSocket();
    sock.send(search.toString());
    while (true) {
        Log.e("SSDP", "Receive...");//only called once (stuck here)
        DatagramPacket dp = sock.receive();
        Log.e("SSDP", "Datagram Received with data " + new String(dp.getData()));
    }
} catch (IOException e) {
    e.printStackTrace();
} finally {
    Log.e("SSDP", "Closing Socket");
    if (sock != null)
        sock.close();
    if(lock.isHeld()) {
        lock.release();
    }
}

需要以下权限（已经在OP的清单文件中）--

<uses-permission android:name="android.permission.ACCESS_WIFI_STATE"/>
<uses-permission android:name="android.permission.CHANGE_WIFI_MULTICAST_STATE"/>