Raspberry Pi i2C LCD Server

lcd_server.py

#!/usr/bin/env python3

from RPLCD.i2c import CharLCD
from argparse import ArgumentParser
from http.server import ThreadingHTTPServer, BaseHTTPRequestHandler
from json import dumps as json_dumps
from sys import stderr
from threading import Lock
from board import I2C

I2C_ADDR_DEFAULT = "0x27"
I2C_TYPE_DEFAULT = "PCF8574"
I2C_ROWS = 2
I2C_COLS = 16


class Handler(BaseHTTPRequestHandler):
    CODE_BAD_REQUEST = 400
    CODE_NO_CONTENT = 204
    CODE_INTERNAL_SERVER_ERROR = 500

    protocol_version = "HTTP/1.1"
    error_content_type = "application/json;charset=utf-8"
    error_message_format = json_dumps({"message": "%(explain)s"})

    @property
    def content_length(self):
        if self.headers["Content-Length"] is None:
            return None
        return int(self.headers["Content-Length"])

    def do_POST(self):
        try:
            if not self.content_length:
                self.send_error(Handler.CODE_BAD_REQUEST, explain="Content-Length is not set")

            elif not "Content-Type" in self.headers.keys() or not self.headers["Content-Type"].startswith("text/plain"):
                self.send_error(Handler.CODE_BAD_REQUEST, explain="Plaintext should be sent")

            else:
                with self.server.lcd_lock:
                    #self.server.lcd.clear()
                    self.server.lcd.cursor_pos = (0, 0)
                    self.server.lcd.write_string(self.rfile.read(self.content_length).decode("utf-8"))
                self.send_response(Handler.CODE_NO_CONTENT)

        except Exception as e:
            self.log_error(str(e))
            self.send_response(Handler.CODE_INTERNAL_SERVER_ERROR)

        self.end_headers()


class Server(ThreadingHTTPServer):
    allow_reuse_address = True

    def __init__(self, address, handler, lcd_i2c, lcd_address, lcd_rows, lcd_cols):
        super().__init__(address, handler)
        self.lcd = CharLCD(lcd_i2c, lcd_address, rows=lcd_rows, cols=lcd_cols)
        self.lcd_lock = Lock()
        self.lcd.clear()


if __name__ == "__main__":
    parser = ArgumentParser(description="LCD Server")
    parser.add_argument("port", type=int, help="The port to the the server on")
    parser.add_argument("--lcd-address", type=str, help="The i2c address of the LCD", default=I2C_ADDR_DEFAULT)
    parser.add_argument("--lcd-i2c", choices=("PCF8574", "MCP23008", "MCP23017"), help="The i2c backpack type for the LCD", default=I2C_TYPE_DEFAULT)
    parser.add_argument("--lcd-rows", type=int, help="The number of rows on the LCD", default=I2C_ROWS)
    parser.add_argument("--lcd-cols", type=int, help="The number of columns on the LCD", default=I2C_COLS)

    args = parser.parse_args()

    try:
        lcd_address = int(args.lcd_address, 16)
    except:
        print("Invalid LCD address, this should be a hexidecimal number (e.g. '0x27')", file=stderr)
        exit(1)

    with Server(("0.0.0.0", args.port), Handler, args.lcd_i2c, lcd_address, args.lcd_rows, args.lcd_cols) as httpd:
        print("Server running on port {}...".format(args.port))
        try:
            httpd.serve_forever()
        except KeyboardInterrupt:
            httpd.shutdown()