Start working on download map example

examples/download_map/README.md

@@ -0,0 +1,12 @@
+# download_map.py
+
+```
+pip install twnet_parser
+```
+
+And then you can run the example like this:
+
+```
+$ ./download_map.py serverip port
+```
+

examples/download_map/download_map.py

@@ -0,0 +1,59 @@
+#!/usr/bin/env python
+
+import socket
+
+from twnet_parser.packet import TwPacket, parse7
+from twnet_parser.messages7.control.token import CtrlToken
+from twnet_parser.messages7.control.connect import CtrlConnect
+from twnet_parser.messages7.system.info import MsgInfo
+
+# TODO: import twnet_parser.constants.NET_MAX_PACKETSIZE
+NET_MAX_PACKETSIZE = 1400
+
+host = 'localhost'
+port = 8303
+dest_srv = (host, port)
+
+sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
+sock.bind(('', 0))
+
+my_token = b'\xff\xaa\xbb\xee'
+srv_token = b'\xff\xff\xff\xff'
+
+def send_msg(messages):
+    global srv_token
+    if not isinstance(messages, list):
+        messages = [messages]
+    packet = TwPacket()
+    packet.header.token = srv_token
+    for msg in messages:
+        packet.messages.append(msg)
+    print(f"sending {packet.pack()}")
+    sock.sendto(packet.pack(), dest_srv)
+
+# TODO: we should be able to set this
+# ctrl_token = CtrlToken(we_are_a_client = True)
+ctrl_token = CtrlToken()
+ctrl_token.response_token = my_token
+send_msg(ctrl_token)
+
+while True:
+    data, addr = sock.recvfrom(NET_MAX_PACKETSIZE)
+    packet = parse7(data)
+    print(packet)
+
+    for msg in packet.messages:
+        if msg.message_name == 'token':
+            srv_token = msg.response_token
+            print(f"got server token {srv_token}")
+
+            ctrl_connect = CtrlConnect()
+            ctrl_connect.response_token = my_token
+            send_msg(ctrl_connect)
+        if msg.message_name == 'accept':
+            # TODO: make these default values
+            send_msg(MsgInfo(
+                    version = "0.7 802f1be60a05665f",
+                    client_version = 1797
+            ))
+            print("got accept")