platypush/platypush/plugins/serial/__init__.py

import json
import serial

from platypush.message.response import Response

from .. import Plugin


class SerialPlugin(Plugin):
    """
    The serial plugin can read data from a serial device, as long as the serial
    device returns a JSON. You can use this plugin to interact for example with
    some sensors connected through an Arduino. Just make sure that the code on
    your serial device returns JSON values. If you're using an Arduino or any
    ATMega compatible device, take a look at
    https://github.com/bblanchon/ArduinoJson.
    """

    def __init__(self, device, baud_rate=9600, *args, **kwargs):
        super().__init__(*args, **kwargs)

        self.device = device
        self.baud_rate = baud_rate


    def _read_json(serial_port):
        n_brackets = 0
        is_escaped_ch = False
        parse_start = False
        output = bytearray()

        while True:
            ch = bytes([serial_port.read()])
            if not ch:
                break

            if ch.decode() == '{' and not is_escaped_ch:
                parse_start = True
                n_brackets += 1

            if not parse_start:
                continue

            output += ch

            if ch.decode() == '}' and not is_escaped_ch:
                n_brackets -= 1
                if n_brackets == 0:
                    break

            is_escaped_ch = ch.decode() == '\\'

        return output.decode().strip()

    def get_data(self):
        ser = serial.Serial(self.device, self.baud_rate)

        try:
            data = self._read_json(ser)
        finally:
            ser.close()

        try:
            data = json.loads(data)
        except:
            self.logger.warning('Invalid JSON message from {}: {}'.
                                format(self.device, data))

        return Response(output=data)


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