HTTP Web Thing implementation
Project description
webthing
Implementation of an HTTP Web Thing. This library is compatible with Python 3.5+.
Installation
webthing can be installed via pip, as such:
$ pip install webthing
Example
In this example we will set up a dimmable light and a humidity sensor (both using fake data, of course). Both working examples can be found in here.
Dimmable Light
Imagine you have a dimmable Light that you want to expose via the web of things API. The Light can be turned on/off and the brightness can be set from 0% to 100%. Besides the name, description, and type, a dimmableLight is required to expose two properties:
on: the state of the light, whether it is turned on or off
Setting this property via a PUT {"on": true/false} call to the REST API toggles the light.
level: the brightness level of the light from 0-100%
Setting this property via a PUT call to the REST API sets the brightness level of this light.
First we create a new Thing:
light = Thing('My Lamp', 'dimmableLight', 'A web connected lamp')
Now we can add the required properties.
The on property reports and sets the on/off state of the light. For this, we need to have a Value Object which holds the actual state and also how to turn the light on/off. For our purposes, we just want to log the new state if the light is switched on/off.
light.add_property(
Property(
light,
'on',
Value(True, lambda v: print('On-State is now', v)),
metadata={
'type': 'boolean',
'description': 'Whether the lamp is turned on',
}))
The level property reports the brightness level of the light and sets the level. Like before, instead of actually setting the level of a light, we just log the level to std::out.
light.add_property(
Property(
light,
'level',
Value(0.0, lambda l: print('New light level is', l)),
metadata={
'type': 'number',
'description': 'The level of light from 0-100',
'minimum': 0,
'maximum': 100,
}))
Now we can add our newly created thing to the server and start it:
# If adding more than one thing, use MultipleThings() with a name.
# In the single thing case, the thing's name will be broadcast.
server = WebThingServer(SingleThing(light), port=8888)
try:
server.start()
except KeyboardInterrupt:
server.stop()
This will start the server, making the light available via the WoT REST API and announcing it as a discoverable resource on your local network via mDNS.
Sensor
Let’s now also connect a humidity sensor to the server we set up for our light.
A multiLevelSensor (a sensor that can also return a level instead of just true/false) has two required properties (besides the name, type, and optional description): on and level. We want to monitor those properties and get notified if the value changes.
First we create a new Thing:
sensor = Thing('My Humidity Sensor',
'multiLevelSensor',
'A web connected humidity sensor')
Then we create and add the appropriate properties:
on: tells us whether the sensor is on (i.e. high), or off (i.e. low)
sensor.add_property( Property( sensor, 'on', Value(True), metadata={ 'type': 'boolean', 'description': 'Whether the sensor is on', }))
level: tells us what the sensor is actually reading
Contrary to the light, the value cannot be set via an API call, as it wouldn’t make much sense, to SET what a sensor is reading. Therefore, we are utilizing a read-only Value by omitting the value_forwarder parameter.
level = Value(0.0); sensor.add_property( Property( sensor, 'level', level, metadata={ 'type': 'number', 'description': 'The current humidity in %', 'unit': '%', }))
Now we have a sensor that constantly reports 0%. To make it usable, we need a thread or some kind of input when the sensor has a new reading available. For this purpose we start a thread that queries the physical sensor every few seconds. For our purposes, it just calls a fake method.
self.sensor_update_task = \
get_event_loop().create_task(self.update_level())
async def update_level(self):
try:
while True:
await sleep(3)
new_level = self.read_from_gpio()
logging.debug('setting new humidity level: %s', new_level)
self.level.notify_of_external_update(new_level)
except CancelledError:
pass
This will update our Value object with the sensor readings via the self.level.notify_of_external_update(read_from_gpio()) call. The Value object now notifies the property and the thing that the value has changed, which in turn notifies all websocket listeners.
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