jetstream.py

import asyncio
import nats
from nats.errors import TimeoutError


async def main():
    nc = await nats.connect("localhost")

    # Create JetStream context.
    js = nc.jetstream()

    # Persist messages on 'foo's subject.
    await js.add_stream(name="sample-stream", subjects=["foo"])

    for i in range(0, 10):
        ack = await js.publish("foo", f"hello world: {i}".encode())
        print(ack)

    # Create pull based consumer on 'foo'.
    psub = await js.pull_subscribe("foo", "psub")

    # Fetch and ack messagess from consumer.
    for i in range(0, 10):
        msgs = await psub.fetch(1)
        for msg in msgs:
            print(msg)

    # Create single ephemeral push based subscriber.
    sub = await js.subscribe("foo")
    msg = await sub.next_msg()
    await msg.ack()

    # Create single push based subscriber that is durable across restarts.
    sub = await js.subscribe("foo", durable="myapp")
    msg = await sub.next_msg()
    await msg.ack()

    # Create deliver group that will be have load balanced messages.
    async def qsub_a(msg):
        print("QSUB A:", msg)
        await msg.ack()

    async def qsub_b(msg):
        print("QSUB B:", msg)
        await msg.ack()
    await js.subscribe("foo", "workers", cb=qsub_a)
    await js.subscribe("foo", "workers", cb=qsub_b)

    for i in range(0, 10):
        ack = await js.publish("foo", f"hello world: {i}".encode())
        print("\t", ack)

    # Create ordered consumer with flow control and heartbeats
    # that auto resumes on failures.
    osub = await js.subscribe("foo", ordered_consumer=True)
    data = bytearray()

    while True:
        try:
            msg = await osub.next_msg()
            data.extend(msg.data)
        except TimeoutError:
            break
    print("All data in stream:", len(data))

    await nc.close()

if __name__ == '__main__':
    asyncio.run(main())