nats example

-----pub/sub------------------
import asyncio
from nats.aio.client import Client as NATS

async def main():
    nc = NATS()

    # Connect to a NATS server
    await nc.connect("nats://localhost:4222")

    # 1. Subscriber: Listening for messages on "updates.news"
    async def message_handler(msg):
        subject = msg.subject
        data = msg.data.decode()
        print(f"Received a message on '{subject}': {data}")

    await nc.subscribe("updates.news", cb=message_handler)

    # 2. Publisher: Sending a message
    await nc.publish("updates.news", b"Hello Python!")

    # Wait a moment to ensure the message is processed
    await asyncio.sleep(1)
    await nc.close()

if __name__ == '__main__':
    asyncio.run(main())
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async def request_reply_example():
    nc = NATS()
    await nc.connect("nats://localhost:4222")

    # The Responder (Service)
    async def help_request(msg):
        print(f"Received help request: {msg.data.decode()}")
        await nc.publish(msg.reply, b"I can help with that!")

    await nc.subscribe("help.system", cb=help_request)

    # The Requester (Client)
    try:
        # Sends request and waits up to 2 seconds for a response
        response = await nc.request("help.system", b"I need assistance", timeout=2)
        print(f"Response received: {response.data.decode()}")
    except asyncio.TimeoutError:
        print("Request timed out!")

    await nc.close()
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async def jetstream_example():
    nc = NATS()
    await nc.connect("nats://localhost:4222")

    # Create JetStream context
    js = nc.jetstream()

    # Create a stream to store messages (if it doesn't exist)
    await js.add_stream(name="ORDERS", subjects=["orders.>"])

    # Publish to JetStream
    # This is "Acked" - NATS confirms it saved the message to disk
    ack = await js.publish("orders.new", b"Order #1234")
    print(f"Published to JetStream. Sequence: {ack.seq}")

    # Pull Subscriber (fetch messages when ready)
    sub = await js.pull_subscribe("orders.new", "psub")
    msgs = await sub.fetch(1)
    for msg in msgs:
        print(f"Retrieved from storage: {msg.data.decode()}")
        await msg.ack() # Tell NATS we successfully processed it

    await nc.close()