Length-prefix message framing in Python

client.py

import asyncio
import struct

def send_message(writer, message):
    data = message.encode()
    size = struct.pack('>L', len(data))
    writer.write(size + data)

async def receive_message(reader):
    data = await reader.readexactly(4)
    size = struct.unpack('>L', data)[0]
    data = await reader.readexactly(size)
    return data.decode()

async def tcp_echo_client():
    reader, writer = await asyncio.open_connection(
        '127.0.0.1', 8888)

    print('Sending first message')
    send_message(writer, 'Hello...')
    print('Sending second message')
    send_message(writer, 'World!')

    print(f'Awaiting response...')
    message = await receive_message(reader)
    print(f'Received: {message!r}')
    message = await receive_message(reader)
    print(f'Received: {message!r}')

    print('Close the connection')
    writer.close()

asyncio.run(tcp_echo_client())

server.py

import asyncio
import struct

def send_message(writer, message):
    data = message.encode()
    size = struct.pack('>L', len(data))
    writer.write(size + data)

async def receive_message(reader):
    data = await reader.readexactly(4)
    size = struct.unpack('>L', data)[0]
    data = await reader.readexactly(size)
    return data.decode()

async def handle_echo(reader, writer):
    try:
        while True:
            message = await receive_message(reader)

            addr = writer.get_extra_info('peername')
            print(f"Received {message!r} from {addr!r}")

            print(f"Send: {message!r}")
            send_message(writer, message)
    except:
        await writer.drain()
        print("Close the connection")
        writer.close()

async def main():
    server = await asyncio.start_server(
        handle_echo, '127.0.0.1', 8888)

    addr = server.sockets[0].getsockname()
    print(f'Serving on {addr}')

    async with server:
        await server.serve_forever()

asyncio.run(main())