使用 UDP 在 Wifi Direct 上广播

Question

我是 wifi direct 的新手，我希望能够广播消息，因为我有一个时间轴，当我单击 Post 按钮时，我希望所有连接的设备都显示该消息他们的时间表。我能够将数据发送到 peer.I 已经搜索过这个主题，我发现使用 UDP 是一个不错的选择，但我不知道如何在 wifi direct 中实现它。

我发现这段代码在 wifi 上使用 UDP 获取广播地址

InetAddress getBroadcastAddress() throws IOException {
WifiManager wifi = mContext.getSystemService(Context.WIFI_SERVICE);
DhcpInfo dhcp = wifi.getDhcpInfo();
// handle null somehow

int broadcast = (dhcp.ipAddress & dhcp.netmask) | ~dhcp.netmask;
byte[] quads = new byte[4];
for (int k = 0; k < 4; k++)
  quads[k] = (byte) ((broadcast >> k * 8) & 0xFF);
return InetAddress.getByAddress(quads);}

这用于发送和接收 UDP 广播数据包

DatagramSocket socket = new DatagramSocket(PORT);
socket.setBroadcast(true);
DatagramPacket packet = new DatagramPacket(data.getBytes(), data.length(),
getBroadcastAddress(), DISCOVERY_PORT);
socket.send(packet);

byte[] buf = new byte[1024];
DatagramPacket packet = new DatagramPacket(buf, buf.length);
socket.receive(packet);

你能帮我解释一下它是如何工作的吗提前致谢。

Answer 1

一种解决方案是将数据包多播到多播组。所有设备都加入一个多播 IP，发送方将数据包发送到该多播 IP。确保您分配的 IP 在多播 IP 范围内。在处理多播时，设备需要获取多播锁。请注意，由于多播基于 UDP，因此在传输中会出现一些错误。

AsyncTask Class 用于将接收数据包的设备：

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.InetAddress;
import java.net.MulticastSocket;
import java.net.UnknownHostException;

import android.content.Context;
import android.net.wifi.WifiManager;
import android.net.wifi.WifiManager.MulticastLock;
import android.os.AsyncTask;
import android.util.Log;
import android.view.View;
import android.widget.TextView;

public class ReceiverMulticastAsyncTask extends AsyncTask<Void, Integer ,String > {

    @Override
    protected String doInBackground(Void... params) {

        //Acquire the MulticastLock
        WifiManager wifi = (WifiManager)  getActivity().getSystemService(Context.WIFI_SERVICE);
        MulticastLock multicastLock = wifi.createMulticastLock("multicastLock");
        multicastLock.setReferenceCounted(true);
        multicastLock.acquire();

        //Join a Multicast Group
        InetAddress address=null;
        MulticastSocket clientSocket=null;
        try {
            clientSocket = new MulticastSocket(1212);
            address = InetAddress.getByName("224.0.0.1");
            clientSocket.joinGroup(address);
        } catch (UnknownHostException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();

        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();        
        }
        DatagramPacket packet=null;           
        byte[] buf = new byte[1024];
        packet = new DatagramPacket(buf, buf.length);
        //Receive packet and get the Data
        try {
            clientSocket.receive(packet);
            byte[] data = packet.getData();
            Log.d("DATA", data.toString()+"");

        } catch (Exception e) {
            e.printStackTrace();

        }
        multicastLock.release();

        try {
            clientSocket.leaveGroup(address);
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        clientSocket.close();
        return "";
    }

    @Override
    protected void onPostExecute(String result) {
        //do whatever...
    }
}

AsyncTask Class 用于将发送数据包的设备：

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.MulticastSocket;
import java.net.SocketException;
import java.net.UnknownHostException;

import android.content.Context;
import android.net.wifi.WifiManager;
import android.net.wifi.WifiManager.MulticastLock;
import android.os.AsyncTask;
import android.util.Log;
import android.view.View;
import android.widget.TextView;

public class SenderMulticastAsyncTask extends AsyncTask<Void, Integer, String> {

    @Override
    protected String doInBackground(Void... params) {

        int port =1212;
        DatagramSocket socket=null;
        try {
            socket = new DatagramSocket(port);
        } catch (SocketException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        InetAddress group = null;
        try {
            group = InetAddress.getByName("224.0.0.1");
        } catch (UnknownHostException e) {
            // TODO Auto-generated catch block
            socket.close();
            e.printStackTrace();
        }

        //Sending to Multicast Group
        String message_to_send ="Test";
        byte[] buf = message_to_send.getBytes();
        DatagramPacket packet = new DatagramPacket(buf, buf.length, group, port);
        try {
            socket.send(packet);
            Log.d("Send", "Sending Packet");
        } catch (IOException e) {
            // TODO Auto-generated catch block
            socket.close();
            e.printStackTrace();
        }

        socket.close();
        return "";
    }

    @Override
    protected void onPostExecute(String result) {
        //do whatever ...
    }
}

Answer 2

在Android的Wi-Fi P2P中有一个"group owner"的概念，就是作为接入点的设备。对于当前 API 组所有者的 IP 地址似乎设置为 192.168.49.1，我认为这是在某处进行了硬编码。快速猜测该组网络的广播地址为 192.168.49.255。到目前为止，我测试过的所有（少数）设备都是如此。

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