import aiohttp
import asyncio

import sys
url = sys.argv[1]

async def main():
    async with aiohttp.ClientSession() as client:
        async with client.ws_connect(url) as ws:
            async for msg in ws:
                if 'Echo:' not in msg.data:
                    await ws.send_str(f"Echo: {msg.data}")

asyncio.run(main())