split off dependencies for optional installation (#546)

* add inheritance diagrams to all printers and exceptions
* split off printer implementations into separate files
* add wrapper that thros RuntimeError if not importable
* add dependency check for lp
* add dependency check for pyserial
* added check for usability
* import Win32Raw
* include WIn32Raw in documentation
* enable all extras on tox
* update github workflow

src/escpos/printer/network.py

@@ -0,0 +1,94 @@
+#!/usr/bin/python
+#  -*- coding: utf-8 -*-
+"""This module contains the implementation of the CupsPrinter printer driver.
+
+:author: python-escpos developers
+:organization: `python-escpos <https://github.com/python-escpos>`_
+:copyright: Copyright (c) 2012-2023 Bashlinux and python-escpos
+:license: MIT
+"""
+
+import socket
+
+from ..escpos import Escpos
+
+
+def is_usable() -> bool:
+    """Indicate whether this component can be used due to dependencies."""
+    return True
+
+
+class Network(Escpos):
+    """Network printer.
+
+    This class is used to attach to a networked printer. You can also use this in order to attach to a printer that
+    is forwarded with ``socat``.
+
+    If you have a local printer on parallel port ``/dev/usb/lp0`` then you could start ``socat`` with:
+
+    .. code-block:: none
+
+        socat -u TCP4-LISTEN:4242,reuseaddr,fork OPEN:/dev/usb/lp0
+
+    Then you should be able to attach to port ``4242`` with this class.
+    Otherwise the normal usecase would be to have a printer with ethernet interface. This type of printer should
+    work the same with this class. For the address of the printer check its manuals.
+
+    inheritance:
+
+    .. inheritance-diagram:: escpos.printer.Network
+        :parts: 1
+
+    """
+
+    @staticmethod
+    def is_usable() -> bool:
+        """Indicate whether this printer class is usable.
+
+        Will return True if dependencies are available.
+        Will return False if not.
+        """
+        return is_usable()
+
+    def __init__(self, host, port=9100, timeout=60, *args, **kwargs):
+        """Initialize network printer.
+
+        :param host:    Printer's hostname or IP address
+        :param port:    Port to write to
+        :param timeout: timeout in seconds for the socket-library
+        """
+        Escpos.__init__(self, *args, **kwargs)
+        self.host = host
+        self.port = port
+        self.timeout = timeout
+        self.open()
+
+    def open(self):
+        """Open TCP socket with ``socket``-library and set it as escpos device."""
+        self.device = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+        self.device.settimeout(self.timeout)
+        self.device.connect((self.host, self.port))
+
+        if self.device is None:
+            print("Could not open socket for {0}".format(self.host))
+
+    def _raw(self, msg):
+        """Print any command sent in raw format.
+
+        :param msg: arbitrary code to be printed
+        :type msg: bytes
+        """
+        self.device.sendall(msg)
+
+    def _read(self):
+        """Read data from the TCP socket."""
+        return self.device.recv(16)
+
+    def close(self):
+        """Close TCP connection."""
+        if self.device is not None:
+            try:
+                self.device.shutdown(socket.SHUT_RDWR)
+            except socket.error:
+                pass
+            self.device.close()