webthing

Implementation of an HTTP Web Thing.

Using

If you're using Cargo, just add webthing to your Cargo.toml:

[dependencies]
webthing = "0.5"

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 Light 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.
• brightness: 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:

let mut light = BaseThing::new(
    "My Lamp".to_owned(),
    Some(vec!["OnOffSwitch".to_owned(), "Light".to_owned()]),
    Some("A web connected lamp".to_owned()),
);

Now we can add the required properties.

The on property reports and sets the on/off state of the light. For our purposes, we just want to log the new state if the light is switched on/off.

struct OnValueForwarder;

impl ValueForwarder for OnValueForwarder {
    fn set_value(&mut self, value: serde_json::Value) -> Result<serde_json::Value, &'static str> {
        println!("On-State is now {}", value);
        Ok(value)
    }
}

let on_description = json!({
    "@type": "OnProperty",
    "label": "On/Off",
    "type": "boolean",
    "description": "Whether the lamp is turned on"
});
let on_description = on_description.as_object().unwrap().clone();
thing.add_property(Box::new(BaseProperty::new(
    "on".to_owned(),
    json!(true),
    Some(Box::new(OnValueForwarder)),
    Some(on_description),
)));

The brightness 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.

struct BrightnessValueForwarder;

impl ValueForwarder for BrightnessValueForwarder {
    fn set_value(&mut self, value: serde_json::Value) -> Result<serde_json::Value, &'static str> {
        println!("Brightness is now {}", value);
        Ok(value)
    }
}

let brightness_description = json!({
    "@type": "BrightnessProperty",
    "label": "Brightness",
    "type": "number",
    "description": "The level of light from 0-100",
    "minimum": 0,
    "maximum": 100,
    "unit": "percent"
});
let brightness_description = brightness_description.as_object().unwrap().clone();
thing.add_property(Box::new(BaseProperty::new(
    "brightness".to_owned(),
    json!(50),
    Some(Box::new(BrightnessValueForwarder)),
    Some(brightness_description),
)));

Now we can add our newly created thing to the server and start it:

let mut things: Vec<Arc<RwLock<Box<Thing + 'static>>>> = Vec::new();
things.push(Arc::new(RwLock::new(Box::new(light)));

// If adding more than one thing, use ThingsType::Multiple() with a name.
// In the single thing case, the thing's name will be broadcast.
let server = WebThingServer::new(
    ThingsType::Multiple(things, "LightAndTempDevice".to_owned()),
    Some(8888),
    None,
    Box::new(Generator),
);
server.start();

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 returns a level instead of just on/off) has one required property (besides the name, type, and optional description): level. We want to monitor this property and get notified if the value changes.

First we create a new Thing:

let mut thing = BaseThing::new(
    "My Humidity Sensor".to_owned(),
    Some(vec!["MultiLevelSensor".to_owned()]),
    Some("A web connected humidity sensor".to_owned()),
);

Then we create and add the appropriate property:

• 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 creating a readOnly property.

  let level_description = json!({
      "@type": "LevelProperty",
      "label": "Humidity",
      "type": "number",
      "description": "The current humidity in %",
      "minimum": 0,
      "maximum": 100,
      "unit": "percent",
      "readOnly": true
  });
  let level_description = level_description.as_object().unwrap().clone();
  thing.add_property(Box::new(BaseProperty::new(
      "level".to_owned(),
      json!(0),
      None,
      Some(level_description),
  )));
  

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.

let sensor = Arc::new(RwLock::new(Box::new(sensor))));
let cloned = sensor.clone();
thread::spawn(move || {
    let mut rng = rand::thread_rng();

    // Mimic an actual sensor updating its reading every couple seconds.
    loop {
        thread::sleep(time::Duration::from_millis(3000));
        let t = cloned.clone();
        let new_value = json!(
            70.0 * rng.gen_range::<f32>(0.0, 1.0) * (-0.5 + rng.gen_range::<f32>(0.0, 1.0))
        );

        {
            let mut t = t.write().unwrap();
            let prop = t.find_property("level".to_owned()).unwrap();
            let _ = prop.set_value(new_value.clone());
        }

        t.write()
            .unwrap()
            .property_notify("level".to_owned(), new_value);
    }
});

This will update our property with random sensor readings. The new property value is then sent to all websocket listeners.