Develop Reference

How to get IP addresses of computers using BroadcastAddress in Android

In my application I'd like to get all the IP addresses that are taken by computers in the LAN using the broadcast address. I used the following code to determine the broadcast address.
InetAddress getBroadcastAddress()
{
try
{
WifiManager wifi = (WifiManager) 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);
}
catch (Exception e)
{
e.printStackTrace();
}
return null;
}
Now that I have it, as far as I know, when one uses the broadcast address, every computer answers it, so if I simply send a "ping" message to that address, the computers of the LAN will answer it. How should I ping them in Android? What command would send me the taken addresses?
The following code simply returns the packet from the sending phone but I need the computers' addresses:
int PORT = 8080;
int DISCOVERY_PORT = 8080;
try
{
DatagramSocket socket = new DatagramSocket(PORT);
socket.setBroadcast(true);
String data="TEST";
DatagramPacket packet = new DatagramPacket(data.getBytes(), data.length(),
getBroadcastAddress(), DISCOVERY_PORT);
socket.send(packet);
byte[] buf = new byte[1024];
DatagramPacket packet2 = new DatagramPacket(buf, buf.length);
Log.w(Tags.DEBUG,"Receive start");
socket.receive(packet2);
Log.w(Tags.DEBUG,packet2.getAddress().toString());
}
catch (Exception e)
{
e.printStackTrace();
}
Is it even possible?
EDIT:
If I'm honest it works as it is written: my phone sends an UDP packet and my phone receives the incoming packages. As the only package is coming from my phone, it is obvious that the address is my phone's address. However, if the broadcast address is valid, each network interface should send the signal back. Am I correct?

You are partially correct.
When you send a UDP packet to a broadcast address, all the computers on the network will receive the packet, unless a router on the network restricts UDP packets being sent to the broadcast address. This is mostly the case on a corporate network.
But not all computers will reply to that packet, they need to know what to do with it.
Either you write a server application that understands your UDP packet and is configured to reply to that packet and deploy that server application to all of the computers on the network.
Or you implement an existing discovery protocol such as Bonjour (Mac) or SSDP (Windows)
I suggest you take a look at ZeroConf Service Discovery if you want to use existing protocols rather then deploying your own application.
http://en.wikipedia.org/wiki/Zero-configuration_networking#Service_discovery
I hope this explanation helps you with your problem.

Android send mpegts streams over udp

I want to receive mpegts over udp in my android application. I am using gstreamer for that. Right now, I am trying to send the mpegts stream from vlc player from the same computer over udp.
In my android application, I am giving the uri udp://10.0.2.2:1234 but the application gives error Could not get/set settings from/on resource. I have tried to get solutions from internet, but no luck so far.

1) UDP address range is from 224.0.0.0 to 239.255.255.255, so you cannot use 10.x.x.x
2) After you deal with adresses, refer to this link to deal with programmatic part:
Getting the Broadcast Address You need to access the wifi manager to get the DHCP info and construct a broadcast address from that:
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);
}
Sending and Receiving UDP Broadcast Packets Having constructed the broadcast address, things work as normal. The following code would
send the string data over broadcast and then wait for a response:
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);

Device discovery in local network

I'm currently developing an android app using SDK >= 16 which should be able to discover different android devices (later also iOS devices) in a local area network using the WiFi radio.
My first guess was to use multicast which turned out to be non functional on my Samsung Galaxy S2: packets are only received when sent from the same device.
My second guess is to actively scan the network using a limited IP address range and wait for a proper response. Unfortunately, this implies that the network uses DHCP to address the IP addresses.
None of the above solutions seem to be the perfect solution.
My current solution for my first guess:
public class MulticastReceiver extends AsyncTask<Activity, Integer, String> {
private static final String host = "224.1.1.1";
private static final int port = 5007;
private static final String TAG = "MulticastReceiver";
protected String doInBackground(Activity... activities) {
WifiManager wm = (WifiManager)activities[0].getSystemService(Context.WIFI_SERVICE);
WifiManager.MulticastLock multicastLock = wm.createMulticastLock("mydebuginfo");
multicastLock.acquire();
String message = "Nothing";
if (multicastLock.isHeld()) {
Log.i(TAG, "held multicast lock");
}
try {
InetAddress addr = InetAddress.getByName(host);
MulticastSocket socket = new MulticastSocket(port);
socket.setTimeToLive(4);
socket.setReuseAddress(true);
socket.joinGroup(addr);
byte[] buf = new byte[5];
DatagramPacket recv = new DatagramPacket(buf, buf.length, addr, port);
socket.receive(recv);
message = new String(recv.getData());
socket.leaveGroup(addr);
socket.close();
} catch (Exception e) {
message = "ERROR " + e.toString();
}
multicastLock.release();
return message;
}
}
This code results in blocking on line socket.receive(recv); If I specify a timeout, I get a timeout exception.

Check my answer in very similar question Android Network Discovery Service (ish) before API 14
I do not belive that multicast is not working on Galaxy S2, some time ago when I was coding some network application, I made several test on many devices, some older like G1 but also on S2, S3 and Galaxy Tab 10.
But to be able to use multicast you must enable it programatically.
Have you used this piece of code?
WifiManager wifi = (WifiManager)getSystemService( Context.WIFI_SERVICE );
if(wifi != null){
WifiManager.MulticastLock lock = wifi.createMulticastLock("Log_Tag");
lock.acquire();
}

Check out http://developer.android.com/training/connect-devices-wirelessly/index.html It mentions two ways of finding local services- NSD and wifi direct.

wifi search for the devices connected to the same network i.e other than acces point(for android)

i want to make a modification to my project and right now the project status is.....
it is searches the available WiFi networks and shows the list with info of the network this works properly.Now i want to search and see the details of the devices connected to the network.
Is there any way to find these devices ?
Your comment will be useful for me, Thanks.

You can loop over the IP ranges, and "ping" them.
It is not the best / fastest method (UDP is better) but, it works in many cases.
The sample code below returns the list of the IP addresses connected to the current network.
private int LoopCurrentIP = 0;
public ArrayList<InetAddress> getConnectedDevices(String YourPhoneIPAddress) {
ArrayList<InetAddress> ret = new ArrayList<InetAddress>();
LoopCurrentIP = 0;
String IPAddress = "";
String[] myIPArray = YourPhoneIPAddress.split("\\.");
InetAddress currentPingAddr;
for (int i = 0; i <= 255; i++) {
try {
// build the next IP address
currentPingAddr = InetAddress.getByName(myIPArray[0] + "." +
myIPArray[1] + "." +
myIPArray[2] + "." +
Integer.toString(LoopCurrentIP));
// 50ms Timeout for the "ping"
if (currentPingAddr.isReachable(50)) {
ret.add(currentPingAddr);
}
} catch (UnknownHostException ex) {
} catch (IOException ex) {
}
LoopCurrentIP++;
}
return ret;
}

Would you like to discover a specific device ? Or you need the list of all connected devices? The second I don't think is possible.
EDIT
Discovering specific devices:
Using UDP Broadcast. Some reference can be found here!
There are some protocols that are supported by some devices( routers, HDD, etc...), like UPNP!
If you develop a software on the device which you would like to discover you could create a UDP server listening on a specific port.
Your client will just send a broadcast message on that port and your Server will send a response with the information you need.
Here it is a simple example.

How to achieve service discovery like "Printer Discover" on android?

I would like to know about the 'service discovery' mechanisms supported by android - particularly, Printer Discovery.
Does android provide such a discovery option? example : support for snmp broadcast?
I tried out an application "PrinterShare" link : http://www.printeranywhere.com/mobile.sdf where Printer Discovery is achieved through ipp.
Any help is appreciated.

Roy, I came across the same problem as you, and was even getting the same behavior when running that code snippet on an actual device (while running the code standalone, not in android, worked fine). I found this page and got it working, although only on the device, by using the following to figure out the Broadcast IP (instead of 239.255.255.250):
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);
}
Hope that helps:)

Does android provide such a discovery option?
Not that I am aware of, sorry.

This code snippet works fine on J2SE. However, on the Android emulator, I get a 'Time Out Exception' with response = 'null'
`DatagramSocket clientSocket = new DatagramSocket(8888);
clientSocket.setSoTimeout(20000);
/**
* SSDP is a text-based protocol based on the Hypertext Transfer Protocol (RFC 2616).
* However, it uses the User Datagram Protocol (UDP) as underlying transport protocol.
* Services are announced by the hosting system with multicast addressing to a
* specifically designated IP multicast address at port number 1900. In IPv4,
* the multicast address is 239.255.255.250.
*/
//getByName(host) //host the hostName to be resolved to an address or null.
InetAddress group = InetAddress.getByName("239.255.255.250");
//host can be null which means that an address of the loopback interface is returned.
if(group == null){
Log.d("Discovery","getByName(): returns address of loopback interface.");
}
byte[] sendData;
byte[] receiveData = new byte[128];
String sentence = "M-SEARCH * HTTP/1.1\r\n"
+ "HOST: 239.255.255.250:1900\r\n"
+ "MAN: \"ssdp:discover\"\r\n"
+ "MX: 10\r\n"
+ "ST: ssdp:all\r\n"
+ "\r\n";
sendData = sentence.getBytes();
//public DatagramPacket (byte[] data, int length, InetAddress host, int port)
DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, group, 1900);
try {
clientSocket.send(sendPacket);
} catch (Exception e) {
e.getMessage();
e.printStackTrace();
}
Log.d("Discovery","sent packet...");
while( true)
{
DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);
try
{
boolean isc = clientSocket.isConnected();
clientSocket.receive(receivePacket);
}
catch ( Exception Ex)
{
Log.d("Discovery","Time out Exception");
}
if (receivePacket.getAddress() == null)
{
Log.d("Discovery","receivePacket.getAddress() == null");
break;
}
Log.d("Discovery","Senders Address : " + receivePacket.getAddress().getHostAddress());
String controllerResponse = new String(receivePacket.getData());
} //end of while()
clientSocket.close(); `

For evaluation of SSDP in .NET this library may be useful
https://yortw.github.io/RSSDP/