Managing Incoming Device Connections
Iotellect Server normally establishes outgoing TCP/UDP connections to networked devices, authenticating itself with credentials contained inside the device account. However, certain devices connect to server themselves. These are mostly M2M devices connected to IP network via GPRS/3G modems. Such devices do not have static IP addresses and host names and, thus, cannot be accessed by a server.
Device drivers servicing incoming device connections require special design approach:
1. The globalInit() method of a device driver should call createGlobalConfigContext(Context rootContext, VariableDefinition... properties) method. Its parameters should include definition of variable that contains global connection settings of the driver, i.e. at least port number to listen for incoming device connections.
2. globalStart() method of the driver should open a listening socket and start a separate thread that accepts and services incoming device connections. This method can access global configuration properties of the driver by getting global properties context via getGlobalConfigContext() and retrieving value of global configuration variable from this context. It's possible (hence not necessary) to create a class inherited from SocketServerThread (for normal sockets) or SslSocketServerThread (for SSL-secured sockets) and use this class as a listening socket thread.
3. The aforementioned server socket thread should be interrupted from globalStop() method of the driver.
4. The server socket thread should accept incoming connections and create a new thread (connection controller thread) to service each connection. For example, a non-abstract implementation of SocketServerThread or SslSocketServerThread should include createConnectionThread() method that creates an incoming connection controller thread each time a new device connects to the server.
5. Each device account should in most cases define some unique device ID (such as mobile device's IMEI code) and device password used to authenticate and authorize incoming device connections. A variable containing this information should be added to device account by implementation of setupDeviceContext() method.
6. The connection controller thread should first authenticate and authorize the device by using device's native protocol to retrieve the unique device ID, finding a device account that matches this ID, and checking that device password matches password specified in the device account settings.
7. Once the device is authenticated and matching server-side device account (context) is identified, the device controller thread should:
- 1. Get per-device instance of driver/plugin class by calling
deviceContext.getDriver(). - 2. Register current device controller inside the driver instance to establish temporary relationship between the device account/driver and current incoming connection operated by controller.
- 3. Call
deviceContext.requestSynchronization()to order a normal synchronization sequence.
8. All "classic" methods of the driver should perform device I/O through the instance of device controller registered by the incoming connection controller thread. However, incoming connections add several peculiarities to this process:
- 1.
shouldSynchronize()method of the driver should return true if an incoming connection controller is currently registered within the driver instance and false otherwise. - 2.
connect()method of the driver should send some test commands to the device to make sure that the incoming connection is still alive. If the TCP/UDP connection is dead or device didn't reply, the connect method should throw an exception to prevent further synchronization. - 3.
disconnect()method of the driver should shutdown incoming connection controller and close its incoming connection if it's alive.
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