Bind a Bluetooth device to a rfcomm via Python

I was able to search and pair a Raspberry Pi 4 to a Bluetooth 4.0 thermal printer using the BlueZ API.

In order to use the python-escpos library, I need to create a serial port /dev/rfcomm, which I can do with sudo rfcomm bind /dev/rfcomm0 XX:XX:XX:XX:XX:XX 1.

How can I do it programatically in Python (without having to use python-subprocess)?

rfcomm was one of the tools deprecated by the BlueZ project in 2017. I would suggest that you avoid using functionality related to that.

The python-escpos library takes the location of a serial port device so I would suggest using the Python pty library which creates two pseudo-devices, the pts, emulates a hardware serial port device.

How exactly you want to architect this will depend on your project but I did a simple test where I had a script creating a pseudo serial port that it listened on and sent to the BLE device if data was received:

import os
import pty
from time import sleep

import pydbus

dev_addr = 'xx:xx:xx:xx:xx:xx'

ptmx_fd, pts_fd = pty.openpty()
pts_name = os.ttyname(pts_fd)
print(f"Printer port: {pts_name}")

bus = pydbus.SystemBus()

mngr = bus.get('org.bluez', '/')


def get_characteristic_path(dev_path, uuid):
    mng_objs = mngr.GetManagedObjects()
    for path in mng_objs:
        chr_uuid = mng_objs[path].get('org.bluez.GattCharacteristic1', {}).get('UUID')
        if path.startswith(dev_path) and chr_uuid == uuid.casefold():
            return path


class MyRemoteDevice:
    # CHAR_UUID = '0000ff02-0000-1000-8000-00805f9b34fb'  # Real printer
    CHAR_UUID = '6E400003-B5A3-F393-E0A9-E50E24DCCA9E'  # my test device

    def __init__(self, mac_addr):
        device_path = f"/org/bluez/hci0/dev_{mac_addr.replace(':', '_')}"
        self.device = bus.get('org.bluez', device_path)

        # Placeholder for characteristic details
        self.characteristic = None

    def _get_gatt_details(self):
        char_path = get_characteristic_path(self.device._path,
                                            MyRemoteDevice.CHAR_UUID)
        self.characteristic = bus.get('org.bluez', char_path)

    def connect(self):
        self.device.Connect()
        # Check GATT services have been resolved before continuing
        while not self.device.ServicesResolved:
            sleep(0.25)
        self._get_gatt_details()

    def disconnect(self):
        self.device.Disconnect()

    def read(self):
        return self.characteristic.ReadValue({})

    def write(self, new_value):
        self.characteristic.WriteValue(new_value, {})


my_first_dev = MyRemoteDevice(dev_addr)

my_first_dev.connect()
try:
    while True:
        data = os.read(ptmx_fd, 1000)
        if data:
            print("data received:", data)
            my_first_dev.write(data)
except:
    pass
finally:
    my_first_dev.disconnect()

In a Python prompt I then sent values to the serial port using the escpos library:

from escpos.printer import Serial
# 9600 Baud, 8N1, Flow Control Enabled
p = Serial(devfile='/dev/pts/3',
           baudrate=9600,
           bytesize=8,
           parity='N',
           stopbits=1,
           timeout=1.00,

p.text("Hello Printer#")