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#140 in HTTP server

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Used in somfy

MPL-2.0 license



Build Status Crates.io license

Implementation of an HTTP Web Thing.


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

webthing = "0.15"

TLS Support

If you need TLS support for the server, you'll need to compile with the ssl feature set.


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);

let on_description = json!({
    "@type": "OnProperty",
    "title": "On/Off",
    "type": "boolean",
    "description": "Whether the lamp is turned on"
let on_description = on_description.as_object().unwrap().clone();

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);

let brightness_description = json!({
    "@type": "BrightnessProperty",
    "title": "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();

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

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

// 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 mut server = WebThingServer::new(
    ThingsType::Multiple(things, "LightAndTempDevice".to_owned()),
let server_addr = server.create();

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.


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("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",
        "title": "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();

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 {
        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());

            .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.

Adding to Gateway

To add your web thing to the WebThings Gateway, install the "Web Thing" add-on and follow the instructions here.


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