add bluetooth backend

Author: gabrielgrant

README.md

@@ -37,6 +37,14 @@ font = ImageFont.truetype("FreeSans.ttf", SIZE)
 Text(font, pad_right=50)
 ```
 
+To use a Bluetooth connection:
+1. pair your device
+2. specify the serial device node when instantiating the printer:
+
+```
+printer = P700(BTSerialBackend.auto(devPath='/dev/ttyS8'))
+```
+
 The Following printers are currently supported:
 
  * Brother P-Touch PT-700 (aka P700)
@@ -50,6 +58,7 @@ but have not been tested (please tell us if they do!):
 The following backends are currently supported:
 
  * USB Printer Device Class via PyUSB
+ * Bluetooth Serial connection via PySerial
 
 The official source of this repository is at https://git.scc.kit.edu/scc-net/labelprinterkit.
 Pull requests and issues are also accepted on github at https://github.com/notafile/labelprinterkit.

labelprinterkit/backends/__init__.py

@@ -1,6 +1,7 @@
 import usb.core
 import usb.util
 import threading
+import serial
 
 def is_usb_printer(dev):
     if dev.bDeviceClass == 7:
@@ -27,3 +28,30 @@ def write(self, data: bytes):
 
     def read(self, count: int) -> bytes:
         return self.dev.read(0x81, count)
+
+class BTSerialBackend():
+    def __init__(self, dev):
+        self.dev = dev
+        self.lock = threading.Lock()
+
+    @classmethod
+    def auto(cls, devPath: str):
+        dev = serial.Serial(
+            devPath,
+            baudrate=9600,
+            stopbits=serial.STOPBITS_ONE,
+            parity=serial.PARITY_NONE,
+            bytesize=8,
+            dsrdtr=False,
+            timeout=1
+        )
+        if dev is None:
+            raise OSError('Device not found')
+        return cls(dev)
+
+    def write(self, data: bytes):
+        self.dev.write(data)
+
+    def read(self, count: int) -> bytes:
+        data = self.dev.read(count)
+        return data

setup.py

@@ -24,6 +24,7 @@
         'pillow',
         'pyusb',
         'packbits',
+        'pyserial'
     ],
     setup_requires=[
         'setuptools_scm'