Adding basic suport for MQTT client

[refaktor]

We got proposal on the email to add support for mqtt protocol. This was already in longterm plan so basic MQTT client should be added to Rye.

It's always much more motivating to work with real examples, so this is a first target example from the request. Using Rye to do the timing will also be interesting.

#!/usr/local/bin/lua54

function measureRespTime()
       local sum = 0.0
        for i=1,3,1 do
        local handle = io.popen("curl -so /dev/null -w '%{time_total}\n' https://url/")
        local result = handle:read("*a")
	local res = result
        local resp = res:gsub("[\n\r]", " ")
	sum = sum + resp
									                   
	handle:close()
	end
	local avg = sum/3
--print(avg)
       publishMessage(avg)
end

function publishMessage(measurement)
      local resptime = measurement
      --local response = resptime:gsub("[-h]", " ")
      local str1 = "nanomq_cli pub -t \"website/monitoring\" -q 2 -u ohab_client --password **** -m "
      local str2 = " -h HOSTNAME -p PORT"
      local str3 = str1 .. tostring(resptime) 
    
      local rtime = str3 .. str2
    
      local handle = io.popen(rtime)
      local result = handle:read("*a")
      handle:close()
end

measureRespTime()

Thanks to mr. Serge for request and example.

[refaktor]

This minimal example works now, not yet committed.

#!/usr/bin/env rye

client: Open mqtt://test.mosquitto.org:1883/rye-client-id
|^check "couldn't connect to MQTT"

^ensure client .Is-connected "MQTT not really connected"

client .Publish\simple "rye/test" "Hello from Rye!"
|^check "failed to sent a message"
        
client .Disconnect
|^check "failed to disconnect"
	
print "Very basic MQTT functionality works"

I want to add support for subscribing to topics so I can test it then.

[refaktor]

Added Subscribe:

#!/usr/bin/env rye

client: Open mqtt://test.mosquitto.org:1883/rye-test
|^check "couldn't connect to MQTT"

^ensure is-positive client .Is-connected "Not really connected"

handler: fn { txt msg } {
    print "\n-NEW-MESSAGE----" ,
	print txt 
	print ""
    print "Topic: " ++ "topic" <- msg
    print "QoS:" ++ "qos" <- msg
    print "Retained:" ++ "retained" <- msg
}

topic: "rye/test"

client .Subscribe topic 1 ?handler

print "listening ..."

select { }

[refaktor]

Something similar to your Lua code could then be:

monitor-resp-time: does { 
    map range 1 3 { time-it { Get https://google.com } } 
   |avg |publish-time 
}

publish-time: fn { time } { 
    Open mqtt://test.mosquitto.org:1883/rye-test-p 
    |Publish-simple "website/monitoring" to-string time 
}

I will look into adding additional options like user / password for publishing like in your example. I will probably be able to commit mqtt bindings to github, I could make a new (binary) release also soon. What OS are you using BTW?

[lacey10]

The mqtt client code looks very promising. Most MQTT brokers require authentication (username + password) but also the quality of service (QoS) level to use for the subscription (value 0 or 1 or 2)

QoS 0: "At most once". This is a fire-and-forget approach, where the message is sent but no confirmation is expected.
QoS 1: "At least once". The sender guarantees delivery but acknowledges that duplicate messages might occur.
QoS 2: "Exactly once". This is the highest level of reliability, ensuring no messages are lost or duplicated.

https://www.emqx.com/en/blog/introduction-to-mqtt-qos
Go MQTT client lib
https://github.com/eclipse-paho/paho.mqtt.golang
Building the rye executable with the go build command is straightforward (no worries about the OS)

[refaktor]

mqtt will support providing username and password as a part of Uri,

mqtt://username:password@test.mosquitto.org:1883/rye-test

this could be ok for simple quick repl code and consistent with how Uris work in generl

In most cases it's better (safer) to provide password separately, which I plan to do general for all kinds of Uri-s. Something like uri .add-password "pwd" and mqtt will also as Go client does support "mqtt-options" value where you can set various details, also username and password.

QoS can also be set per message using .Publish method that also takes QoS (versus Publish\simple which does not).

I am working on changes and will post today or tomorrow.

Thank you for your feedback!

[refaktor]

I will be closing the issue once I upload the MQTT Cookbook pages.

[refaktor]

I somewhat lost the red-line on MQTT ... many other things took my focus from this. But I will try to make multiple examples work this week, add at least basic page on Cookbook about it and then close this issue.