Evok WebSocket API

The WebSocket API allows for two-way communication between the client and the server over an open connection. Evok sends changes to every connected client. A list of reflected devices can be defined. It is suitable for cases, where you need to immediately react to events in your application.

Examples

For python examples you need installed websocket-client package. You can install it with this command: pip3 install websocket-client.

Listening on WebSocket without filter

Python

import websocket


def on_message(ws, message):
    print(f"Received message: {message}")


def on_close(ws, status, message):
    print(f"WebSocket connection closed")


def on_open(ws):
    print("WebSocket connection opened")


if __name__ == "__main__":
    url = 'ws://127.0.0.1/ws'
    ws = websocket.WebSocketApp(url, on_message=on_message, on_close=on_close, on_open=on_open)
    ws.run_forever()

Output

WebSocket connection opened
Received message: [{"dev": "ai", "circuit": "2_01", "value": 132798232.0, "unit": "Ohm", "glob_dev_id": 3, "mode": "Resistance2W", "modes": {"Disabled": {"value": 0}, "Voltage10": {"value": 1, "unit": "V", "range": [0, 10]}, "Voltage2V5": {"value": 2, "unit": "V", "range": [0, 2.5]}, "Current20m": {"value": 3, "unit": "mA", "range": [0, 20]}, "Resistance3W": {"value": 4, "unit": "Ohm", "range": [0, 1960]}, "Resistance2W": {"value": 5, "unit": "Ohm", "range": [0, 100000]}}, "range": [0, 100000]}]
Received message: [{"dev": "ai", "circuit": "3_01", "value": -0.004, "unit": "V", "glob_dev_id": 4, "mode": "Voltage10", "modes": {"Disabled": {"value": 0}, "Voltage10": {"value": 1, "unit": "V", "range": [0, 10]}, "Voltage2V5": {"value": 2, "unit": "V", "range": [0, 2.5]}, "Current20m": {"value": 3, "unit": "mA", "range": [0, 20]}, "Resistance3W": {"value": 4, "unit": "Ohm", "range": [0, 1960]}, "Resistance2W": {"value": 5, "unit": "Ohm", "range": [0, 100000]}}, "range": [0, 10]}]
Received message: [{"dev": "ai", "circuit": "1_01", "value": 8.703, "unit": "V", "glob_dev_id": 2, "mode": "Voltage", "modes": {"Voltage": {"value": 0, "unit": "V", "range": [0, 10]}, "Current": {"value": 1, "unit": "mA", "range": [0, 20]}}, "range": [0, 10]}]
Received message: [{"dev": "ai", "circuit": "2_04", "value": -0.004, "unit": "V", "glob_dev_id": 3, "mode": "Voltage10", "modes": {"Disabled": {"value": 0}, "Voltage10": {"value": 1, "unit": "V", "range": [0, 10]}, "Voltage2V5": {"value": 2, "unit": "V", "range": [0, 2.5]}, "Current20m": {"value": 3, "unit": "mA", "range": [0, 20]}, "Resistance3W": {"value": 4, "unit": "Ohm", "range": [0, 1960]}, "Resistance2W": {"value": 5, "unit": "Ohm", "range": [0, 100000]}}, "range": [0, 10]}, {"dev": "ai", "circuit": "2_03", "value": -0.003, "unit": "V", "glob_dev_id": 3, "mode": "Voltage10", "modes": {"Disabled": {"value": 0}, "Voltage10": {"value": 1, "unit": "V", "range": [0, 10]}, "Voltage2V5": {"value": 2, "unit": "V", "range": [0, 2.5]}, "Current20m": {"value": 3, "unit": "mA", "range": [0, 20]}, "Resistance3W": {"value": 4, "unit": "Ohm", "range": [0, 1960]}, "Resistance2W": {"value": 5, "unit": "Ohm", "range": [0, 100000]}}, "range": [0, 10]}]
Received message: [{"dev": "ai", "circuit": "3_01", "value": -0.0, "unit": "V", "glob_dev_id": 4, "mode": "Voltage10", "modes": {"Disabled": {"value": 0}, "Voltage10": {"value": 1, "unit": "V", "range": [0, 10]}, "Voltage2V5": {"value": 2, "unit": "V", "range": [0, 2.5]}, "Current20m": {"value": 3, "unit": "mA", "range": [0, 20]}, "Resistance3W": {"value": 4, "unit": "Ohm", "range": [0, 1960]}, "Resistance2W": {"value": 5, "unit": "Ohm", "range": [0, 100000]}}, "range": [0, 10]}]
Received message: [{"dev": "ai", "circuit": "1_01", "value": 8.7, "unit": "V", "glob_dev_id": 2, "mode": "Voltage", "modes": {"Voltage": {"value": 0, "unit": "V", "range": [0, 10]}, "Current": {"value": 1, "unit": "mA", "range": [0, 20]}}, "range": [0, 10]}]
Received message: [{"dev": "ai", "circuit": "2_04", "value": -0.003, "unit": "V", "glob_dev_id": 3, "mode": "Voltage10", "modes": {"Disabled": {"value": 0}, "Voltage10": {"value": 1, "unit": "V", "range": [0, 10]}, "Voltage2V5": {"value": 2, "unit": "V", "range": [0, 2.5]}, "Current20m": {"value": 3, "unit": "mA", "range": [0, 20]}, "Resistance3W": {"value": 4, "unit": "Ohm", "range": [0, 1960]}, "Resistance2W": {"value": 5, "unit": "Ohm", "range": [0, 100000]}}, "range": [0, 10]}, {"dev": "ai", "circuit": "2_03", "value": -0.001, "unit": "V", "glob_dev_id": 3, "mode": "Voltage10", "modes": {"Disabled": {"value": 0}, "Voltage10": {"value": 1, "unit": "V", "range": [0, 10]}, "Voltage2V5": {"value": 2, "unit": "V", "range": [0, 2.5]}, "Current20m": {"value": 3, "unit": "mA", "range": [0, 20]}, "Resistance3W": {"value": 4, "unit": "Ohm", "range": [0, 1960]}, "Resistance2W": {"value": 5, "unit": "Ohm", "range": [0, 100000]}}, "range": [0, 10]}]
...

Listening on WebSocket with filter on 'do' and 'ao'

Python

import websocket, json


def on_message(ws, message):
    print(f"Received message: {message}")


def on_close(ws, status, message):
    print(f"WebSocket connection closed")


def on_open(ws):
    print("WebSocket connection opened")
    msg = {"cmd": "filter", "devices": ["do", "ao"]}
    ws.send(json.dumps(msg))


if __name__ == "__main__":
    url = 'ws://127.0.0.1/ws'
    ws = websocket.WebSocketApp(url, on_message=on_message, on_close=on_close, on_open=on_open)
    ws.run_forever()

Output

WebSocket connection opened
Received message: [{"dev": "do", "circuit": "1_01", "value": 1, "pending": false, "mode": "Simple", "modes": ["Simple", "PWM"], "glob_dev_id": 2, "pwm_freq": 4800.0, "pwm_duty": 0}]
Received message: [{"dev": "do", "circuit": "1_04", "value": 1, "pending": false, "mode": "Simple", "modes": ["Simple", "PWM"], "glob_dev_id": 2, "pwm_freq": 4800.0, "pwm_duty": 0}]
Received message: [{"dev": "ao", "circuit": "2_03", "mode": "Voltage", "modes": {"Voltage": {"unit": "V", "range": [0, 10]}}, "glob_dev_id": 3, "value": 5.9, "unit": "V", "range": [0, 10]}]
Received message: [{"dev": "ao", "circuit": "2_04", "mode": "Voltage", "modes": {"Voltage": {"unit": "V", "range": [0, 10]}}, "glob_dev_id": 3, "value": 1.3, "unit": "V", "range": [0, 10]}]
Received message: [{"dev": "do", "circuit": "1_01", "value": 0, "pending": false, "mode": "Simple", "modes": ["Simple", "PWM"], "glob_dev_id": 2, "pwm_freq": 4800.0, "pwm_duty": 0}]
Received message: [{"dev": "do", "circuit": "1_04", "value": 0, "pending": false, "mode": "Simple", "modes": ["Simple", "PWM"], "glob_dev_id": 2, "pwm_freq": 4800.0, "pwm_duty": 0}]
...

Setting DO

DO 1.01 will be set to HIGH.

Python

import websocket, json


def on_message(ws, message):
    print(f"Received message: {message}")


def on_close(ws, status, message):
    print(f"WebSocket connection closed")


def on_open(ws):
    print("WebSocket connection opened")
    msg = {"cmd": "set", "dev": "do", "circuit": "1_01", "value": 1}
    ws.send(json.dumps(msg))
    print("WebSocket send DO 1.01 to HIGH")
    ws.close()


if __name__ == "__main__":
    url = 'ws://127.0.0.1/ws'
    ws = websocket.WebSocketApp(url, on_message=on_message, on_close=on_close, on_open=on_open)
    ws.run_forever()

Output

WebSocket connection opened
WebSocket send DO 1.01 to HIGH
WebSocket connection closed

Tip

You can learn more about the circuit parameter here