I'm just playing around with mosquitto ans mqtt protocol
following the very good video
https://www.youtube.com/watch?feature=player_embedded&v=WE7GVIFRV7Q
trying to test it on my localhost
in a terminal window I run :
mosquitto_sub -t "nodeconf/eu" -v
but when I run this snippet:
var mqtt = require('mqtt');
var client = mqtt.connect();
client.on('connect', function () {
client.subscribe('nodeconf/eu');
client.publish('nodeconf/eu','Hello');
});
client.on('message', function (topic, message) {
// message is Buffer
console.log(message.toString());
client.end();
});
I don't see (in my terminal window) any Hello.
What's wrong, please ?
BTW
I'm also looking for good tutorial and guide on the topic thanks.
You have to add a console.log to your second (the javascript) client to see why it doesn't publishes the Hello properly.
But you can do a typical test with the mosquitto clients:
1) Subscribing to a topic:
mosquitto_sub -d -h localhost -p 1883 -t "myfirst/test"
2) Other client publishes a message content to that topic:
mosquitto_pub -d -h localhost -p 1883 -t "myfirst/test" -m "Hello"
3) All the subscribed clients to this topic will automatically get the message.
Related
I have installed a mosquitto server on a raspberry server.
This server works fine: I have test with mosquitto_sub and mosquitto_pub commands.
I have write this python script:
import paho.mqtt.client as mqtt
import time
client = mqtt.Client('module_test_4')
client.connect('127.0.0.1', 1883, 10)
client.loop_start()
for i in range(10):
client.publish('topic_2', "valeur %d" % i, qos=0)
time.sleep(1)
client.loop_stop()
client.disconnect()
I have launched this script twice on 2 consoles:
mosquitto_sub -h 127.0.0.1 -i module_test_2 -t topic_2
It works fine: I see messages on each console.
Now, i have tried to change qos parameter to 0,1 and 2.
I have tried to run my python script without lauching any occurence of mosquitto_sub.
I was thinking mosquitto will buffer messages and send it again when mosquitto_sub will be launched but this does not work.
So i am wondering how qos works...
Thanks
QOS only applies to one leg of the connection at a time.
This means the QOS can be different between the publisher/broker and broker/subscriber.
So in the example you have posted you set QOS to 2 between the publisher and the broker, but it is still the default 0 between the subscriber and the broker. This means that as far as the broker is concerned the subscribing client only wants QOS 0.
If you want to test with mosquitto_sub you need to include a higher QOS on the command line as well. You need to have established a subscription at QOS 2 before disconnecting like so:
mosquitto_sub -h 127.0.0.1 -i module_test_2 -t topic_2 -q 2
You also need to tell mosquitto_sub not to ask for a clean session when it reconnects:
mosquitto_sub -h 127.0.0.1 -i module_test_2 -t topic_2 -q 2 -c
I am new to Mosquitto. I have installed Mosquitto and Mosquitto Client in Ubuntu. I am trying to subscribe with client-id also publish with client-id, please look the command that I have run in console, but unfortunately, the subscriber is not receiving the message.
Subscription
mosquitto_sub -h localhost -t temp/city1 -c -q 2 --id client-one
Publish
mosquitto_pub -h localhost -t temp/city1 -m "32 Celsius" -q 2 --id client-one
but if I Publish message without client id the subscriber is receiving message, so please help me where I did the mistake?
As mentioned in the comment, clientIds are just that, they are a unique identifier for each client connected to the broker.
ClientIds need to be totally unique, if a second client tries to connect with a clientid that is already connected the broker must disconnect the first client to allow the second to connect (this is dictated by the specification). In the example you have given the subscriber will be disconnected before it receives the message published by the second.
Messages are published to topics and clients can subscribe to these topics (or patterns of topics with wildcards)
So using the mosquitto command line tools you can do the following:
mosquitto_sub -v -t 'foo/bar'
This will subscribe to the topic foo/bar and will print out the topic and then message when ever a message is published to that topic. To publish a message containing the string testing you would use:
mosquitto_pub -t 'foo/bar' -m 'testing'
The mosquitto command line tools will generate random clientids if none are provided on the command line.
The following command shows all the messages published to topics that match the regex but not the exact topic itself.
mosquitto_sub -h localhost -u user -P pass -t 'devices/#'
{"value":"50"}
{"value":"45"}
For example the above json messages were published to topic devices/1234/transducer/46364/ but I could not figure any way to print the topic as well using mosquitto_sub.
Use the -v option
mosquitto_sub -h localhost -u user -P pass -v -t 'devices/#'
From the man page:
-v, --verbose
Print received messages verbosely. With this argument, messages
will be printed as "topic payload". When this argument is not
given, the messages are printed as "payload".
I have successfully connected a device and an application to the Watson IoT platform over MQTT protocal, the application subscribe the event published by device. example:http://iotf.readthedocs.io/en/latest/getting_started/quickstart/index.html
then I tried to let the device subscrbe a command published by the application.
device:
mosquitto_sub -h 184.172.124.189 -p 1883 -i "d:quickstart:devicetype:deviceid" -t iot-2/cmd/cid/fmt/json
application:
mosquitto_pub -h 184.172.124.189 -p 1883 -i "a:quickstart:applicationid" -t iot-2/type/devicetype/id/deviceid/cmd/cid/fmt/json -m " {\"d\" : {\"temp\" : 36 }}"
the device can't receive the message published by application.
what does the command include and how doed it work ?
Quickstart (which is completely unauthenticated, was intended to do what it says on the tin) doesn't include the ability to send commands to devices. You will have to create a device type and register a device, then something like this could work.
When you do this, in the strings you use to authenticate e.g. quickstart will be replaced by your organization id, devicetype and deviceid by the names you use for the device type and the device name.
I am unable to receive messages on first time connection. for in more detail,user A is connected and publishing messages,but user B is not connected to that topic.So when user B will connect,he will not get any message from user A because there is first time connection b/w user a and user b.
How we can resolve this issue ?
Thanks
A principle of pub/sub is that the publisher and subscriber are decoupled, so you shouldn't really be thinking in terms of user a being connected to user b.
If you want a client to receive messages when they are not connected (leaving retained messages to one side), the only way to do this is:
Connect beforehand with cleansession=false
Subscribe with QoS>0 (or on mosquitto use the queue_qos0_messages option)
Ensure that messages are published with QoS>0
When the client reconnects, use cleansession=false
To test this, try:
mosquitto_sub -i prajbot-singh -h test.mosquitto.org -t prajbot-singh -c -q 1
Then quit from mosquitto_sub and run:
mosquitto_pub -h test.mosquitto.org -t prajbot-singh -m hello -q 1
And run mosquitto_sub again:
mosquitto_sub -i prajbot-singh -h test.mosquitto.org -t prajbot-singh -c -q 1