Adding Simple external control server example (#22)

* Adding Simple external control server example

Adding a python3 server script that can be used to
serve the URCap.

Co-authored-by: mahp <[email protected]>

Author: urrsk

examples/simple_external_control_server/Readme.md

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+# Simple External Control Server example
+
+This simple server, serves the External Control with URScript provided by a file
+
+Example of use:
+
+```bash
+python3 simple_external_control_server.py hello_world.script
+```
+
+To install and use the URCap external control, follow the instructions from the ROS Driver for [e-Series](https://github.com/UniversalRobots/Universal_Robots_ROS_Driver/blob/master/ur_robot_driver/doc/install_urcap_e_series.md)
+or for [cb3-Series](https://github.com/UniversalRobots/Universal_Robots_ROS_Driver/blob/master/ur_robot_driver/doc/install_urcap_cb3.md).
+
+Once you play the program on a robot, a popup with the message "Hello World" should appear.

examples/simple_external_control_server/hello_world.script

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+popup("Hello world")

examples/simple_external_control_server/simple_external_control_server.py

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+#!/usr/bin/env python3
+
+# // -- BEGIN LICENSE BLOCK ----------------------------------------------
+# // Copyright 2021 Universal Robots A/S
+# //
+# // Licensed under the Apache License, Version 2.0 (the "License");
+# // you may not use this file except in compliance with the License.
+# // You may obtain a copy of the License at
+# //
+# //     http://www.apache.org/licenses/LICENSE-2.0
+# //
+# // Unless required by applicable law or agreed to in writing, software
+# // distributed under the License is distributed on an "AS IS" BASIS,
+# // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# // See the License for the specific language governing permissions and
+# // limitations under the License.
+# // -- END LICENSE BLOCK ------------------------------------------------
+
+# A simple python 3 server to test the External Control URCap
+# The server answer request from the URCap with the context of the given file
+
+import socket
+import socketserver
+import threading
+import argparse
+
+parser = argparse.ArgumentParser(description='Simple External Control server')
+parser.add_argument(
+    "file", type=str, help="Path to the UR script file, which will be sent to the robot")
+parser.add_argument("-p", "--port", type=int,
+                    default=50002, help="Port number to use")
+
+args = parser.parse_args()
+
+
+class ThreadedTCPServer(socketserver.ThreadingMixIn, socketserver.TCPServer):
+    daemon_threads = True
+    allow_reuse_address = True
+
+
+class FileHandler(socketserver.StreamRequestHandler):
+    def handle(self):
+        client = f'{self.client_address} on {threading.currentThread().getName()}'
+        print(f'Connected: {client}')
+        file = open(args.file, "r")
+        while True:
+            data = file.read()
+
+            print(data)
+            if not data:
+                break
+            self.wfile.write(data.encode('utf-8'))
+        print(f'Closed: {client}')
+
+
+with ThreadedTCPServer(('', args.port), FileHandler) as server:
+    print(f'The Simple External Control server is running on port', args.port)
+    try:
+        server.serve_forever()
+    except KeyboardInterrupt:
+        pass
+
+    server.server_close()