CODEWITHSUNDEEP
androidudpwifibroadcastandroid-networking
user2224350
user2224350

Reputation: 2304

Android sending UDP broadcast on a hotspot enabling device

In my app I want to broadcast some UDP packets. I'm currently using this methode to get the required broadcast address:

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);
}

-> https://code.google.com/p/boxeeremote/wiki/AndroidUDP

That works fine, but if the devices has activated a hotspot and tries to broadcast a packet following SocketException is thrown: SocketException: sendto failed: ENETUNREACH (Network is unreachable)
How can I get the right broadcast-address on a device which is "providing" a hotspot? All unicast addresses I tried yet worked fine...

thx & regards

PS: minimum SDK is API 8 !

Upvotes: 2

Views: 4462

Answers (1)

user2224350
user2224350

Reputation: 2304

I managed the problem using this code:

private InetAddress getBroadcastAddress(WifiManager wm, int ipAddress) throws IOException {
    DhcpInfo dhcp = wm.getDhcpInfo();
    if(dhcp == null)
        return InetAddress.getByName("255.255.255.255");
    int broadcast = (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);
}

Important is that you call getBroadcastAddress with the "real" ip-address (some methods I've seen can't provide that on a hotspot):

public static int getCodecIpAddress(WifiManager wm, NetworkInfo wifi){
    WifiInfo wi = wm.getConnectionInfo();
    if(wifi.isConnected())
        return wi.getIpAddress(); //normal wifi
    Method method = null;
    try {
        method = wm.getClass().getDeclaredMethod("getWifiApState");
    } catch (NoSuchMethodException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    if(method != null)
        method.setAccessible(true);
    int actualState = -1;
    try {
        if(method!=null)
            actualState = (Integer) method.invoke(wm, (Object[]) null);
    } catch (IllegalArgumentException e) {
        e.printStackTrace();
    } catch (IllegalAccessException e) {
        e.printStackTrace();
    } catch (InvocationTargetException e) {
        e.printStackTrace();
    }
    if(actualState==13){  //if wifiAP is enabled
        return "192.168.43.1" //hardcoded WifiAP ip
    }
        return 0;
}
public static int convertIP2Int(byte[] ipAddress){
    return (int) (Math.pow(256, 3)*Integer.valueOf(ipAddress[3] & 0xFF)+Math.pow(256, 2)*Integer.valueOf(ipAddress[2] & 0xFF)+256*Integer.valueOf(ipAddress[1] & 0xFF)+Integer.valueOf(ipAddress[0] & 0xFF));
}

Upvotes: 5

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