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|
#!/usr/bin/env python
import asyncio
import json
import secrets
import websockets
from connect4 import PLAYER1, PLAYER2, Connect4
JOIN = {}
WATCH = {}
async def error(websocket, message):
"""
Send an error message.
"""
event = {
"type": "error",
"message": message,
}
await websocket.send(json.dumps(event))
async def replay(websocket, game):
"""
Send previous moves.
"""
# Make a copy to avoid an exception if game.moves changes while iteration
# is in progress. If a move is played while replay is running, moves will
# be sent out of order but each move will be sent once and eventually the
# UI will be consistent.
for player, column, row in game.moves.copy():
event = {
"type": "play",
"player": player,
"column": column,
"row": row,
}
await websocket.send(json.dumps(event))
async def play(websocket, game, player, connected):
"""
Receive and process moves from a player.
"""
async for message in websocket:
# Parse a "play" event from the UI.
event = json.loads(message)
assert event["type"] == "play"
column = event["column"]
try:
# Play the move.
row = game.play(player, column)
except RuntimeError as exc:
# Send an "error" event if the move was illegal.
await error(websocket, str(exc))
continue
# Send a "play" event to update the UI.
event = {
"type": "play",
"player": player,
"column": column,
"row": row,
}
websockets.broadcast(connected, json.dumps(event))
# If move is winning, send a "win" event.
if game.winner is not None:
event = {
"type": "win",
"player": game.winner,
}
websockets.broadcast(connected, json.dumps(event))
async def start(websocket):
"""
Handle a connection from the first player: start a new game.
"""
# Initialize a Connect Four game, the set of WebSocket connections
# receiving moves from this game, and secret access tokens.
game = Connect4()
connected = {websocket}
join_key = secrets.token_urlsafe(12)
JOIN[join_key] = game, connected
watch_key = secrets.token_urlsafe(12)
WATCH[watch_key] = game, connected
try:
# Send the secret access tokens to the browser of the first player,
# where they'll be used for building "join" and "watch" links.
event = {
"type": "init",
"join": join_key,
"watch": watch_key,
}
await websocket.send(json.dumps(event))
# Receive and process moves from the first player.
await play(websocket, game, PLAYER1, connected)
finally:
del JOIN[join_key]
del WATCH[watch_key]
async def join(websocket, join_key):
"""
Handle a connection from the second player: join an existing game.
"""
# Find the Connect Four game.
try:
game, connected = JOIN[join_key]
except KeyError:
await error(websocket, "Game not found.")
return
# Register to receive moves from this game.
connected.add(websocket)
try:
# Send the first move, in case the first player already played it.
await replay(websocket, game)
# Receive and process moves from the second player.
await play(websocket, game, PLAYER2, connected)
finally:
connected.remove(websocket)
async def watch(websocket, watch_key):
"""
Handle a connection from a spectator: watch an existing game.
"""
# Find the Connect Four game.
try:
game, connected = WATCH[watch_key]
except KeyError:
await error(websocket, "Game not found.")
return
# Register to receive moves from this game.
connected.add(websocket)
try:
# Send previous moves, in case the game already started.
await replay(websocket, game)
# Keep the connection open, but don't receive any messages.
await websocket.wait_closed()
finally:
connected.remove(websocket)
async def handler(websocket):
"""
Handle a connection and dispatch it according to who is connecting.
"""
# Receive and parse the "init" event from the UI.
message = await websocket.recv()
event = json.loads(message)
assert event["type"] == "init"
if "join" in event:
# Second player joins an existing game.
await join(websocket, event["join"])
elif "watch" in event:
# Spectator watches an existing game.
await watch(websocket, event["watch"])
else:
# First player starts a new game.
await start(websocket)
async def main():
async with websockets.serve(handler, "", 8001):
await asyncio.Future() # run forever
if __name__ == "__main__":
asyncio.run(main())
|
