A Python async client for the NATS messaging system.
Should be compatible with Python 2.7 using Tornado 4.2+ (less than 6.0).
For Python 3, check nats.py
pip install nats-clientimport tornado.ioloop
import tornado.gen
import time
from nats.io.client import Client as NATS
@tornado.gen.coroutine
def main():
nc = NATS()
# Establish connection to the server.
yield nc.connect("nats://demo.nats.io:4222")
@tornado.gen.coroutine
def message_handler(msg):
subject = msg.subject
data = msg.data
print("[Received on '{}'] : {}".format(subject, data.decode()))
# Simple async subscriber
sid = yield nc.subscribe("foo", cb=message_handler)
# Stop receiving after 2 messages.
yield nc.auto_unsubscribe(sid, 2)
yield nc.publish("foo", b'Hello')
yield nc.publish("foo", b'World')
yield nc.publish("foo", b'!!!!!')
# Request/Response
@tornado.gen.coroutine
def help_request_handler(msg):
print("[Received on '{}']: {}".format(msg.subject, msg.data))
yield nc.publish(msg.reply, "OK, I can help!")
# Susbcription using distributed queue named 'workers'
sid = yield nc.subscribe("help", "workers", help_request_handler)
try:
# Send a request and expect a single response
# and trigger timeout if not faster than 200 ms.
msg = yield nc.request("help", b"Hi, need help!", timeout=0.2)
print("[Response]: %s" % msg.data)
except tornado.gen.TimeoutError:
print("Timeout!")
# Remove interest in subscription.
yield nc.unsubscribe(sid)
# Terminate connection to NATS.
yield nc.close()
if __name__ == '__main__':
tornado.ioloop.IOLoop.current().run_sync(main)import tornado.ioloop
import tornado.gen
from datetime import timedelta
from nats.io import Client as NATS
from nats.io.errors import ErrConnectionClosed
@tornado.gen.coroutine
def main():
nc = NATS()
# Set pool servers in the cluster and give a name to the client
# each with its own auth credentials.
options = {
"servers": [
"nats://secret1:[email protected]:4222",
"nats://secret2:[email protected]:4223",
"nats://secret3:[email protected]:4224"
]
}
# Error callback takes the error type as param.
def error_cb(e):
print("Error! ", e)
def close_cb():
print("Connection was closed!")
def disconnected_cb():
print("Disconnected!")
def reconnected_cb():
print("Reconnected!")
# Set callback to be dispatched whenever we get
# protocol error message from the server.
options["error_cb"] = error_cb
# Called when we are not connected anymore to the NATS cluster.
options["closed_cb"] = close_cb
# Called whenever we become disconnected from a NATS server.
options["disconnected_cb"] = disconnected_cb
# Called when we connect to a node in the NATS cluster again.
options["reconnected_cb"] = reconnected_cb
yield nc.connect(**options)
@tornado.gen.coroutine
def subscriber(msg):
yield nc.publish("pong", "pong:{0}".format(msg.data))
yield nc.subscribe("ping", "", subscriber)
for i in range(0, 100):
yield nc.publish("ping", "ping:{0}".format(i))
yield tornado.gen.sleep(0.1)
yield nc.close()
try:
yield nc.publish("ping", "ping")
except ErrConnectionClosed:
print("No longer connected to NATS cluster.")
if __name__ == '__main__':
tornado.ioloop.IOLoop.current().run_sync(main)import tornado.ioloop
import tornado.gen
import time
from nats.io import Client as NATS
@tornado.gen.coroutine
def main():
nc = NATS()
yield nc.connect("demo.nats.io")
@tornado.gen.coroutine
def subscriber(msg):
print("Msg received on [{0}]: {1}".format(msg.subject, msg.data))
yield nc.subscribe("foo.*.baz", "", subscriber)
yield nc.subscribe("foo.bar.*", "", subscriber)
yield nc.subscribe("foo.>", "", subscriber)
yield nc.subscribe(">", "", subscriber)
# Matches all of above
yield nc.publish("foo.bar.baz", b"Hello World")
yield tornado.gen.sleep(1)
if __name__ == '__main__':
tornado.ioloop.IOLoop.current().run_sync(main)import tornado.ioloop
import tornado.gen
from nats.io import Client as NATS
from nats.io.errors import ErrNoServers
@tornado.gen.coroutine
def main():
nc = NATS()
try:
# Setting explicit list of servers in a cluster and
# max reconnect retries.
servers = [
"nats://127.0.0.1:4222",
"nats://127.0.0.1:4223",
"nats://127.0.0.1:4224"
]
yield nc.connect(max_reconnect_attempts=2, servers=servers)
except ErrNoServers:
print("No servers available!")
return
@tornado.gen.coroutine
def message_handler(msg):
subject = msg.subject
reply = msg.reply
data = msg.data.decode()
for i in range(0, 20):
yield nc.publish(reply, "i={i}".format(i=i).encode())
yield nc.subscribe("help.>", cb=message_handler)
@tornado.gen.coroutine
def request_handler(msg):
subject = msg.subject
reply = msg.reply
data = msg.data.decode()
print("Received a message on '{subject} {reply}': {data}".format(
subject=subject, reply=reply, data=data))
# Signal the server to stop sending messages after we got 10 already.
yield nc.request(
"help.please", b'help', expected=10, cb=request_handler)
# Flush connection to server, returns when all messages have been processed.
# It raises a timeout if roundtrip takes longer than 1 second.
yield nc.flush()
# Drain gracefully closes the connection, allowing all subscribers to
# handle any pending messages inflight that the server may have sent.
yield nc.drain()
# Drain works async in the background.
yield tornado.gen.sleep(1)
if __name__ == '__main__':
tornado.ioloop.IOLoop.instance().run_sync(main)Advanced customizations options for setting up a secure connection can be done by including them on connect:
# Establish secure connection to the server, tls options parameterize
# the wrap_socket available from ssl python package.
options = {
"servers": ["nats://127.0.0.1:4444"],
"tls": {
"cert_reqs": ssl.CERT_REQUIRED,
"ca_certs": "./configs/certs/ca.pem",
"keyfile": "./configs/certs/client-key.pem",
"certfile": "./configs/certs/client-cert.pem"
}
}
yield nc.connect(**options)The client will also automatically create a TLS context with defaults in case it detects that it should connect securely against the server:
yield nc.connect("tls://demo.nats.io:4443")In this repo there are also included a couple of simple utilities for subscribing and publishing messages to NATS:
# Make a subscription to 'hello'
$ python examples/nats-sub hello
Subscribed to 'hello'
[Received: hello] world
# Send a message to hello
$ python examples/nats-pub hello -d "world"Unless otherwise noted, the NATS source files are distributed under the Apache Version 2.0 license found in the LICENSE file.
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