a Twisted implementation of Device-Hive client protocol v8

• devicehive.DeviceDelegate class was replaced with devicehive.interfaces.IProtoHandler interface.
• long polling transport related classes were moved into separate module (devicehive.poll).
• web-socket transport support has been added (devicehive.ws module).
• devicehive.auto.AutoFactory was added - factory which select devicehive transport depends on info-call result.
• under devicehive.gateway a few classes have been added which support creation of a custom gateway.
• gateway's binary protocol has been added
• an IProtoHandler instance can implement logic for a few devices at once.

Before reading this tutorial you should know a bit of Python. If you wish to work example in this tutorial you also have to install some software on your computer or target device:

• Python 2.7 http://python.org
• Twisted http://twistedmatrix.com
• devicehive python library http://devicehive.com

Certainly, you may skip this section and bundle entire devicehive library with your application. In some situations it may be a case. But more common way to work with devicehive library is to install it first. The simplest way to do this is to run command:

	python setup.py install

In case if setuptools is installed on your computer the command above will automatically install devicehive library itself and all necessary dependencies (actually there is only one dependency - twisted). Otherwise you should to download and install dependencies manually or use one of methods described in Python Package Index tutorial http://wiki.python.org/moin/CheeseShopTutorial.

Creating a simple application using new version of library is not much harder then is was before. The only difference is that now you need to implement devicehive.interfaces.IProtoHandler interface instead of overriding devicehive.DeviceDelegate class methods.

This way now your application class has to implement all methods which IProtoHandler interface defines. This means that you class most likly will look like this:

    class YourApplicationClass(object):
        zope.interface.implements(devicehive.interfaces.IProtoHandler)
        def on_apimeta(self, websocket_server, server_time):
            pass
        def on_connected(self):
            pass
        def on_connection_failed(self, reason) :
            pass
        def on_closing_connection(self): 
            pass
        def on_failure(self, device_id, reason):
            pass
        def on_command(self, device_id, command, finished):
            pass

For instance, if your application does not requires to handle transport failures then you may leave on_failure method empty.

Here I need to mention that during protocol-factory initialization it will set a reference to itself in YourApplication.factory attribute. And every devicehive protocol-factory implements devicehive.interfaces.IProtoFactory interface. And using factory methods an application of yours can interact upon underlying devicehive protocol. For example, it can send a notification message using self.factory.notify(...) call. Or it can register one or more devices using self.factory.device_save method. For a simple application the most appropriate place to register device would be on_connected method.

    def on_connected(self):
        self.factory.device_save(iDeviceInfoInstance)

A class which you pass into device_save method has to conform to devicehive.interfaces.IDeviceInfo interface. We suggested that implementation of IDeviceInfo interface will not differ to much from application to application, that is why we included it's typical implementation into devicehive.DeviceInfo class. Also under devicehive.* namespace you will find a few other classes which will be helpfull during constuction of IDeviceInfo object. These are:

• devicehive.Network is a typical implementation of devicehive.interfaces.INetwork interface.
• devicehive.DeviceClass - implements devicehive.interfaces.IDeviceClass.
• and devicehive.Equipment which implements devicehive.interfaces.IEquipment interface. Please see complete description of IProtoFactory methods in devicehive.interfaces module's documentation.

I would also like to note that protocol factories do not do any additional verifications and will allow you, lets say, to call notify() method even before devicehive connection had been established. Application of yours has to implement all neccessary logic to avoid such situations.

In order to handle device-hive command your application has to allow it for specific device by calling factory.subscribe method. Command handling should be done in on_command method. The procedure of command handling in the new version of the library did not changed much. Except that in the new version on_command method expects device_info variable and command parameter now implements devicehive.interfaces.ICommand interface. The device_info variable specifies for which device a command was sent.

Device-Hive gateway is built on the same principles as the client API. devicehive.gateway.IGateway defines the interface to which every custom gateway has to be conformed to. Although in most cases it would be appropriate to use devicehive.BaseGateway class as a starting point of your custom implementation. In file basic_gateway_example.py you can see such an implementation. This example creates Gateway class instance. A constructor of this class expects devicehive URL as it's first parameter and a class of protocol-factory as it's second parameter. This protocol-factory will be used to form transport layer between gateway and device-hive server. A end point and it's protocol factory define a channel and a protocol which will be used to transfer commands between gateway and end device. Thus to customize Gateway's behaviuor you need to override BaseGateway's class methods. An if you want to change device-to-gateway transport you will need to provide a protocol-factory implementation of that transport into gateway 'run' method.

In this tutorial we have implemented the simplest Device-Hive application. For more examples please see examples subdirectory under devicehive python library distribution. And of cause you may use python build-in help system to take a closer look at library's API. For further reading please see examples under examples folder.