Ping-Pong: Basic Event Loop

The simplest event-based example. Alice sends a sequence of messages to Bob, who replies to each one. No state machine — just a simple if/else to choose the reply. Found in examples/event-based/pingPong/.

This is purely classical (no quantum operations). It demonstrates the basic async event loop pattern before adding state machines and quantum in later examples.

Alice (client)

Alice sends a list of messages and prints Bob’s replies:

async def run_alice(reader: StreamReader, writer: StreamWriter):
    messages = ["ping", "ping", "hello", "ping"]

    for msg in messages:
        print(f"Alice: sending  '{msg}'")
        writer.write(msg.encode("utf-8"))
        await writer.drain()

        reply_data = await reader.read(255)
        reply = reply_data.decode("utf-8")
        print(f"Alice: received '{reply}'")

Bob (server)

Bob replies “pong” to “ping” and “no way!” to anything else:

async def run_bob(reader: StreamReader, writer: StreamWriter):
    while True:
        data = await reader.read(255)
        if not data:
            break  # Alice disconnected

        message = data.decode("utf-8")
        if message == "ping":
            reply = "pong"
        else:
            reply = "no way!"

        writer.write(reply.encode("utf-8"))
        await writer.drain()

Key concepts

• reader/writer: The async streams for classical TCP communication. writer.write() sends bytes, await reader.read(N) receives up to N bytes.

• await writer.drain(): Ensures the write buffer is flushed to the network.

• Connection lifecycle: Bob’s loop exits when reader.read() returns empty bytes, meaning Alice has disconnected.

Running

cd examples/event-based/pingPong
bash run.sh

Expected output:

Alice: sending  'ping'
Bob: received 'ping'
Bob: sending  'pong'
Alice: received 'pong'
Alice: sending  'ping'
...
Alice: sending  'hello'
Bob: received 'hello'
Bob: sending  'no way!'
Alice: received 'no way!'