Connected World in android - Local data sharing and service discovery

Copyright ©2016 Talentica Software (I) Pvt Ltd. All rights reserved.
Connected world
in android
Local data sharing and
service discovery
Presented by:
Kaushal Dhruw
Naval Barthwal

Copyright © 2016 Talentica Software (I) Pvt Ltd. All rights reserved.Copyright ©2016 Talentica Software (I) Pvt Ltd. All rights reserved. 2
About PMD
• Started in August 2013
• “Increase awareness of fast growing mobile
technology among Developers”
• Currently has 3000+ members
• 21 meetups so far

Team
• Ashutosh
• Tarun
• Arvind
• Kaushal
• Suyash
• Vijendra
• Talentica Mobile Community

Agenda
 Network interfaces.
 Basic socket communication.
 Network service discovery.
 Wi-Fi direct.
 Wi-Fi direct service discovery.
 Bluetooth low energy (BLE).
 Demos (wherever needed)

Copyright ©2016 Talentica Software (I) Pvt Ltd. All rights reserved. 5
Introduction
Network interfaces

Network interface
 A Network interface is a point of interconnection between a device and a public or
private network.
 It can be a hardware (Network interface card).
 Or can be implemented in software.
 Some network interfaces:
 wlan: wireless networking interface.
 lo: loopback interface (localhost, usually 127.0.0.1).
 rmnet: usually associated with mobile data and USB tethering.
 p2p: a peer-to-peer interface.
 eth, en: Ethernet card interface.
 dummy: alternative for loopback interfaces.
NetworkInterface.getNetworkInterfaces() //gets list of all available network
interfaces

Network interface methods
 isUp(): Whether the network interface is up and running.
 isVirtual(): Whether the network interface is virtual or sub-
interface.
 getSubInterfaces(): gets all the sub interfaces bound to this
network interface (like eth0:1 for eth0)
 supportsMulticast(): checks multicast support.
 getInetAddresses(): get all the addresses bound to this network
interface.
 getHardwareAddress(): usually MAC.
 getByName():
 getByInetAddress():
 getByIndex():

Network interface selection
 When a socket is created it automatically determines which
network (that is currently up and running) to use.
 Most of the times you will not have to worry about the
network interface.
 When you want to use the address of a particular network
interface, use the get methods discussed in previous slide.
 To listen to all the network interfaces, bind your socket to
“0.0.0.0”
 Loopback and dummy interfaces are used for localhost
connection testing.
 use adb shell ifconfig to list all available network interfaces.

Agenda
 Wi-Fi direct.

Generic java not specific to android
Basic socket communication

Basic socket communication
 A socket is basically an end point for two-way communication link between two devices.
 In a typical client-server architecture.
 Server runs on a specific computer and has a socket that is bound to a specific port, the
server listens for a client to make connection request in that socket.
 Client knows the host name of server and port it is listening on. The client system usually
assigns a port to rendezvous with server’s machine and port.
 Client receives confirmation of connection acceptance and can use the socket for
communicating with server.
 Listening on a port for client requests is done via ServerSocket. A ServerSocket class
provides a system independent implementation of the server side of client/server socket
connection.
ServerSocket serverSocket = new ServerSocket(port);
Socket s = serverSocket.accept();

Basic socket communication contd…

Steps involved in socket
communication
 Create a ServerSocket. This socket waits for a connection from a client on a specified
port and blocks until it happens, so do this in a background thread.
 Create a client Socket. The client uses the IP address and port of the server socket to
connect to the server device.
 Send data from the client to the server. When the client socket successfully connects to
the server socket, you can send data from the client to the server with byte streams.
 The server socket waits for a client connection (with the accept() method). This call
blocks until a client connects, so call this in another thread. When a connection
happens, the server device can receive the data from the client.
 And carry out any actions with this data, such as saving it to a file or presenting it to the
user.

Client/server sockets
ServerSocket mServer = new
ServerSocket(mPort);
While(true){
Socket s = mServer.accept();
//process s and streams and
return response if required
}
socket = new Socket(host, port);
OutputStream outputStream =
socket.getOutputStream();
ObjectOutputStream oos = new
ObjectOutputStream(outputStream);
oos.writeObject(transferObject);
oos.close();
Server Client
mPort = (new ServerSocket(0)).getLocalPort()

Use case we are solving (Local chat)
Share files
&
Send chat
&
Receive chat and file from other
devices
Share files
&
Send chat
&
Receive chat and file from other
devices
Device 1 Device 2

Agenda
 Wi-Fi direct.

Discover services and devices in the same
network
Network service discovery
(NSD)

Network service discover (NSD)
 android.net.nsd.* package is used.
 It helps with many use cases like file sharing, multi-player games etc.
 Android network service discovery allows your app to identify other
devices in the same network that support the services your app
requests.
 NSD allows us to register our service(s) on the network, discover it, and
connect with it.
 Important classes:
 NsdManager
 NsdServiceInfo
 Although internet is not used, INTERNET permission is required for
socket communication.

Basic steps in NSD

NSD Service registration
Creating NsdServiceInfo Object

NSD Service registration Listener

NSD Service discovery

NSD Service discovery Listener

Resolving discovered NSD service
• NsdManager.ResolveListener
Note**: Do not forget to stop discovery and unregister service when app closes

NSD Demo
plus code walkthrough

Agenda
 Wi-Fi direct.

Connect with devices in vicinity (Wi-Fi p2p in
android)
Wi-Fi direct

Wi-Fi direct
 Wi-Fi direct is a Wi-Fi certified standard enabling devices to
connect with each other without requiring a wireless access point.
 Using this devices can communicate with each other at typical
Wi-Fi speeds, unlike ad-hoc wireless connections (which allows
two or more devices to connect and communicate, and has a
limit of 11Mbps).
 And Wi-Fi direct has much simpler setup that ad-hoc network.
 Wi-Fi direct assigns each member a limited access point (if it is
Wi-Fi direct enabled).
 Wi-Fi direct uses WPS and WPA2 to prevent unauthorized access
and keep communications private.

Wi-Fi direct contd…
 Wi-Fi direct allows devices to connect to each other and form groups. Not
only one-to-one, but also one-to-many.
 Compatible devices negotiate their roles in the connection:
 One of these assumes role of a traditional access point. Called Group Owner (GO).
 Other devices including non-Wi-Fi direct devices connect to the Group owner or
Access point as P2P clients.
 Any P2P device can assume the role of a Group owner and P2P client. The
purpose of role negotiation is to determine which of the peer devices will
exchange group characteristics (like operating channel, WPS configuration, is
the group persistent etc.).
 Devices can communicate their willingness to become group owner with the
GO intent attribute (0-15).
 After the role negotiation a confirmation is sent and devices move to their
specified roles. GO starts operating in Access point mode.

Wi-Fi direct and android
 Android’s Wi-Fi P2P framework complies with the Wi-Fi direct certification
program. It allows devices running android 4.0+ (API 14+) with appropriate
hardware to connect easily without an intermediate access point.
 Android Wi-Fi P2P API consists of:
 Methods that allows us to discover, request and connect to peers
(android.net.wifi.p2p.WifiP2pManager).
 Listeners that notifies us of success and failure of WifiP2pmanager’s method calls.
 Intents to notify specific events, such as new peer joined, connection dropped etc.
(like WIFI_P2P_PEERS_CHANGED_ACTION and
WIFI_P2P_CONNECTION_CHANGED_ACTION)
 A single call to WifiP2pManager’s discover peers is enough for Wi-Fi direct
peer discovery. Connection however with Wi-Fi direct group requires user’s
consent. This is unlike NSD.

Wi-Fi direct – Permissions

Wi-Fi direct – starting peer
discovery

Wi-Fi direct – getting peer list
This broadcast receiver needs to be registered dynamically. It notifies when peer list has
changed so peer list can be requested from WifiP2pManager

Wi-Fi direct – getting peer list
contd…
When WifiP2pManager.WIFI_P2P_PEERS_CHANGED_ACTION is received in the broadcast
receiver, peer list can be requested. With WifiP2pManager.requestPeers() method.

Wi-Fi direct – WifiP2pDevice
Important method in WifiP2pDeviceList is getDeviceList() which gives a collection of
WifiP2pDevice, it has the following important fields

Wi-Fi direct – Connecting to a
peer
Once a peer is discovered, connection request can be sent

Connecting to a peer –
WifiP2pInfo
Once connection is successful a connection info request can be issued via WifiP2pManager.
Which send callback to WifiP2pManager.ConnectionInfoListener. It has only one method
described below:
WifiP2pInfo 

WifiP2pManager - createGroup
 This method is to support older devices that do not support Wi-Fi direct. It creates
an Access point which non-Wi-Fi direct can connect to (like a regular Wi-Fi), and
continue communication.
 The device that calls this method must support Wi-Fi direct.
 The method creates a p2p group with the current device as its group owner.
 In addition to hosting an access point, it also allows other Wi-Fi direct enabled
devices to connect with it in regular fashion.
 Connecting with a Wi-Fi programmatically (if SSID and password are known):

Wi-Fi direct demo
Plus code walkthrough for our use case

Agenda
 Wi-Fi direct.

Discover devices and services in vicinity
(Irrespective of device connection status)
Wi-Fi direct service
discovery

Wi-Fi direct service discovery
 Similar function as NSD.
 Similar code like Wi-Fi direct.
 Kind of like a combination of both. And also more complex than BOTH.
 Same classes and listeners are used as in Wi-Fi direct.
 Here we find services in nearby devices. (Can work for devices in the
same network too).
 In this WifiP2pManager’s addLocalService() method is used.
 There is an additional option for adding key value pairs in a map (100-
200 bytes). This map can be received with service discovery.
 Any small additional data can be shared with service (like device’s port it
is listening to, name, device info etc.)

Wi-Fi direct adding local service
WifiP2pManager’s addLocalService():
WifiP2pServiceInfo is a class for storing service information that is advertised over a Wi-
Fi peer-to-peer setup. It has two direct subclasses. Both are bonjour service info:
 WifiP2pDnsSdServiceInfo – domain name system service discovery (service info)
 WifiP2pUpnpServiceInfo – Universal plug and play (service info)
For our use case we will be using the former in place of WifiP2pServiceInfo. With DNS-
SD service info we have an option to advertise additional data (relatively small 100-200
bytes). For this use case we will advertise port information.
Once the port and IP information is determined, rest of the work is similar (socket
programming).

Setting WifiP2pDnsSdServiceInfo

Wi-Fi direct service discovery
request
WifiP2pManager’s addServiceRequest():
Since we are searching for DNS-SD service the WifiP2pServiceRequest will be
of NDS-SD type.
Setting service discovery response listeners to WifiP2pManager

Wi-Fi direct service response
listeners
WifiP2pManager.DnsSdServiceResponseListener interface has only one
method:
WifiP2pManager.DnsSdTxtRecordListener interface:
Other callbacks and broadcasts are same as Wi-Fi direct

Wi-Fi direct… rest of it and more
 Rest of the flow in Wi-Fi Direct service discovery is same as Wi-Fi direct.
 A device will call connect.
 Other device will receive an invitation to connect.
 There will be role negotiation based on GO intent parameter.
 A group will be formed with one group owner and others as clients.
 After that information can be exchanged.
 If we look at our use case the only difference is instead of pre-fixing a
port, we are adding the port information when adding service request.
So no listeners on pre-fixed port.
 All the services should be unregistered and discovery request must be
stopped when exiting an application. We don’t want to drain the battery
for no reason.
 Use createGroup() method discussed in Wi-Fi direct section only when
supporting legacy devices.

Wi-Fi direct service
discovery demo
And a glance at some of the important
methods and classes in demo code

Agenda
 Wi-Fi direct.

In Android
Bluetooth Low Energy

In Android, BLE stack was introduced
in API 18 Jelly Bean 4.3, in July 2013.

Scene
Peripheral

Scene
Peripheral
Central

Generic Access Profile Roles
Broadcaster Observer

Generic Access Profile Roles
Peripheral
aka Slave
Central
aka Master
connect

GATT Server-Client
Server
(holding data)
Client
(asking data)
transact

Services
Characteristics
Class {
}
attributes;
get();
set();
• Read
• Write
Characteristics

BluetoothManager manager =
(BluetoothManager) context
.getSystemService(
Context.BLUETOOTH_SERVICE);
mBluetoothAdapter =
manager.getAdapter();
<uses-feature
android:name="android.hardware.bluetooth_le"
android:required="true"
/>

mBluetoothLeScanner
.startScan(callback);
mBluetoothLeScanner =
mBluetoothAdapter.getBluetoothLeScanner();
<uses-permission
android:name=
"android.permission.BLUETOOTH_ADMIN" />

ScanCallback{
public void onScanResult(int
callbackType, ScanResult result) {
}
public void onScanFailed(int
errorCode) {
}
}

mBluetoothGatt =
mBluetoothDevice.connectGatt(
context,
autoConnect,
gattCallback) ;
mBluetoothDevice =
bleScanResult.getBluetoothDevice();

BluetoothGattCallback {
public void
onConnectionStateChange(
BluetoothGatt gatt,
int status,
int newState) ;
}
if( newState ==
BluetoothProfile.STATE_CONNECTED)

bluetoothGatt.discoverServices();
public void onServicesDiscovered(
BluetoothGatt gatt, int status);
}
List<BluetoothGattService> serviceList =
gatt.getServices();

bluetoothGattCharacteristic.setValue(
intToByteArray(color));
List<BluetoothGattCharacteristic> list =
bluetoothGattService.getCharacteristics();
bluetoothGatt.writeCharacteristic(
bluetoothGattCharacteristic)

public void onCharacteristicWrite(
BluetoothGatt gatt,
BluetoothGattCharacteristic
characteristic,
int status) ;
}
if( status ==
BluetoothGatt.GATT_SUCCESS)

Demo code available at…
• https://github.com/drulabs/LocalDash
• https://github.com/navalkishoreb/IoT/tree/zone_dis
covery/Android

References
• https://docs.oracle.com/javase/tutorial/networking/nifs/index.html
• https://docs.oracle.com/javase/7/docs/api/java/net/NetworkInterface.html
• http://www.tldp.org/LDP/nag2/x-087-2-hwconfig.tour.html
• http://adbshell.com/commands/adb-shell-netstat
• https://www.freedesktop.org/wiki/Software/systemd/PredictableNetworkInterface
Names/
• https://docs.oracle.com/javase/tutorial/networking/sockets/definition.html
• https://developer.android.com/guide/topics/connectivity/wifip2p.html

BLE has 40 channels of 2Mhz bandwidth
Out of which 37 are Data channels
Only 3 are for Advertising data

GND
+5Volt
+3.3 Volt
_Tx_
_Rx_
PIN 6

Connected World in android - Local data sharing and service discovery

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