Docu: add initial protocol docu

doc/protocol.md

@@ -0,0 +1,49 @@
+InstantChat WebSocket Protocol
+==============================
+
+Messages from client to server (commands)
+-----------------------------------------
+
+JSON objects. Key `action` determines type of message.
+
+### init
+Initialize the connection, set nickname and join/create a chat.
+
+**Parameters:**
+* `action` = `"init"`
+* `chat_id`: either an existing ID of a chat instance or *[TODO: ?]* empty string to
+  create a new chat
+* `nickname`: user's chosen nickname *[TODO: valid characters?]*
+
+**Example:**
+
+    {
+        "action": "init",
+        "chat_id": "42",
+        "nickname": "Alice"
+    }
+
+### send (?)
+Send a message...
+
+*[TODO]*
+
+
+Messages from server to client (responses/events)
+-------------------------------------------------
+
+JSON objects. Key `type` determines type of message.
+
+### init
+Response to `init` command. Confirms initialization and chat join.
+
+**Parameters:**
+* `type` = `"init"`
+* ***[TODO]***
+
+**Example:**
+
+    {
+        "type": "init",
+        TODO ???
+    }

server/chatserver.py

@@ -1,33 +1,59 @@
 #!/usr/bin/env python
 
-# Example code from:
-# https://websockets.readthedocs.io/en/stable/intro.html
-
 import asyncio
+import json
 import websockets
 
 
+def log_message_error(error, message_text):
+    print(f"[E] {error}")
+    print(f"  Message: {message_text}")
+
+
 async def parse_client_message(websocket, message_text):
     """Parse a message (JSON object) from a client."""
 
-    # TODO parse JSON
-    response = f"Hello {message_text}!"
+    try:
+        # Parse JSON
+        message = json.loads(message_text)
 
-    await websocket.send(response)
+        # Handle message types
+        if message['action'] == 'init':
+            await handle_client_init(websocket, message)
+        else:
+            log_message_error(f"Unknown action '{message['action']}'", message_text)
+    except json.decoder.JSONDecodeError as e:
+        log_message_error(f"JSON decode error: {e}", message_text)
+    except KeyError as e:
+        log_message_error(f"Missing key {e} in JSON message", message_text)
+
+
+async def handle_client_init(websocket, message):
+    """Handle client 'init' message."""
+
+    print(f"< init: chat_id='{message['chat_id']}', nickname='{message['nickname']}'")
+
+    # Send response to client
+    response = json.dumps({
+        'type': 'init'
+    })
     print(f"> {response}")
+    await websocket.send(response)
 
 
 async def client_handler(websocket, path):
     """Handle client connection."""
 
-    print(f"++ New client")
+    print(f"++ New client {websocket.remote_address}")
     try:
         # Read and parse messages until connection is closed
         async for message_text in websocket:
-            print(f"< {message_text}")
             await parse_client_message(websocket, message_text)
+    except websockets.exceptions.ConnectionClosed:
+        # Ignore ConnectionClosed exceptions because we handle this in finally
+        pass
     finally:
-        print(f"-- Client connection closed")
+        print(f"-- Client connection closed {websocket.remote_address}")
 
 # Create WebSocket listener
 start_server = websockets.serve(client_handler, '0.0.0.0', 32715)