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technical:mqtt [2022/06/19 20:07]
admin [Introduction] 		technical:mqtt [2022/06/19 21:48] (current)
admin
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   * It is ideal for hardware that is used in a IOT environment where you need immediate execution of commands.    * It is ideal for hardware that is used in a IOT environment where you need immediate execution of commands. 
 ===== Architecture ===== ===== Architecture =====
 +  * Consider the following diagram and then the subsequent discussion of each of the components. 
 {{:technical:mqtt-implementation.png|}} {{:technical:mqtt-implementation.png|}}
 +
 +==== ExtJS GUI ====
 +  * The ExtJS GUI can be used to send commands to the mesh nodes and access points managed by MESHdesk and APdesk respectively.
 +  * The communication between ExtJS and the CakePHP application consists of REST-like API calls using HTTP or HTTPS.
 +  * This means essentially that these actions can easily be automated or done with another GUI should the need arise.
 +
 +==== CakePHP ====
 +  * If MQTT support is enabled on the system and someone initiate a command execution action from the GUI, the controller code handling this request will send the request to the API Gateway.
 +  * This communication between the CakePHP controller and the API Gateway also consist of REST-like API calls using HTTP or HTTPS.
 +
 +==== API Gateway ====
 +  * The API Gateway is a Node.js based web service that acts as a middle man.
 +  * The MQTT implementation uses a command and response principle. 
 +  *  The API Gateway
 +        * Receive instructions from CakePHP and translate them to MQTT **publish** actions (Command) which are published to the Mosquitto MQTT Broker. 
 +        * Subscribe to MQTT topics (Response) on the Mosquitto MQTT Broker which will get input from the mesh nodes and access points and translate them to HTTP/HTTPS based API calls to CakePHP. 
 +
 +==== Mesh nodes and access points ====
 +  * The mesh nodes and access points communicate with the CakePHP back-end using HTTP/HTTPS to fetch its configuration and do reporting.
 +  * If the system has MQTT support enabled the mesh node or access point will configure itself to publish and subscribe to certain topics on the Mosquitto MQTT Broker.
 +  * The system works on a **command** and **response** principle.
 +        * The mesh node or access point **subscribe** to a topic where it will expect **commands** from the API Gateway.
 +        * The mesh node or access point will **publish** to a topic where the API Gateway expect **responses**.
 +        * The API Gateway will **publish** to a topic where the mesh node or access point expect **commands**.
 +        * The API Gateway will **subscribe** to a topic where the mesh node or access points **publish** their **responses**.
 +
 + 
 +
 +===== Enable MQTT =====
 +  * There are two components of the MQTT setup that needs to be configured
 +        * Configuration settings for mesh nodes and access points (MESHdesk and APdesk)
 +        * Configuration settings for the MQTT API Gateway.
 +
 ===== Looking at the code ===== ===== Looking at the code =====
 +==== Command -> CakePHP Controller ====
 +  * Lets look at the **/var/www/html/cake3/rd_cake/src/Controller/NodeActionsController.php** file.
 +  * When an action is added to a node and MQTT is enabled on the system this code is executed:
 +<code php>
 +if ($cfg['api_mqtt_enabled'] == "1"){
 +    //Talk to MQTT Broker
 +     $data = $this->_get_node_mac_mesh_id($formData['node_id']);
 +     $payload = [
 +         'mode'     => 'mesh',
 +         'node_id'  => $formData['node_id'],
 +         'mac'      => strtoupper($data['mac']),
 +         'mesh_id'  => strtoupper($data['ssid']),
 +         'cmd_id'   => $entity->id,
 +         'cmd'      => $formData['command'],
 +         'action'   => $formData['action'],
 +     ];
 +
 +     if($this->_check_server($client, $cfg['api_gateway_url'], 5)){
 +         try {
 +             $client->request('POST', $cfg['api_gateway_url'] . '/rd/mesh/command', ['json' => ['message' => $payload]]);
 +         } catch (\Exception $e) {
 +             // Do Nothing
 +         }
 +     }
 +}
 +</code>
 +==== Command -> API Gateway ====
 +  * The API call to the API Gateway will execute this piece of code in the **/opt/Rdcore-API-Gateway/routes/rdmesh.js** file
 +<code javascript>
 +router.post('/mesh/command', function(req, res){
 +    //var data = JSON.parse(req.body.message);
 +    var data = req.body.message;
 +    var message = JSON.stringify(data);
 + console.log(message);
 +    client.publish('/RD/MESH/' + data.node_id + '/COMMAND', message);
 +    console.log("Published command to Mesh node: " + data.mac + " MODE "+data.mode);
 +    res.json(message);
 +});
 +</code>
 +==== Command -> mqtt.lua ====
 +  * Here is a snippet in **/etc/MESHdesk/mqtt.lua** which shows what it will do when a message is published from the API Gateway.
 +  * This is the command which it will then respond to.
 +<code lua>
 +client.ON_MESSAGE = function(mid, topic, payload)
 +    -- Parse/Decode JSON Payload
 +    local jsonStr           = luci_json.parse(payload)
 +    -- Check if message belongs to us (MAC Address)
 +</code>
 +==== Response -> mqtt.lua ====
 +  * Depending on the type of command the code in Lua will determine the correct response.
 +  * Here is a snippet in **/etc/MESHdesk/mqtt.lua** which respond to the **execute** action.
 +  * This is part of the code which are processing the command that the mesh node or access point received (inside the **ON_MESSAGE** event)
 +<code lua>
 +--Here depending on the value of jsonStr['action'] we will either just execute the command or execute and report the output
 +if(jsonStr['action'] == 'execute')then
 +    print("MODE IS "..mode);
 +    if(mode == 'mesh')then
 +        message = luci_json.stringify({mode=mode,node_id=nodeId,mesh_id=meshId,mac=macAddr,cmd_id=cmdId,status='os_command'});
 +    end
 +    if(mode == 'ap')then
 +        message = luci_json.stringify({mode=mode,ap_id=apId,mac=macAddr,cmd_id=cmdId,status='os_command'});
 +    end
 +    
 +    local cl_execute = mqtt.new();
 +    cl_execute:login_set(MQTT_USER, MQTT_PASS)
 +    cl_execute:connect(MQTT_HOST)
 +    --Connected now publish
 +    cl_execute.ON_CONNECT = function()
 +        cl_execute:publish(cmdTopic, message, qos, retain);
 +    end
 +    --Done publishing - now execute command 
 +    cl_execute.ON_PUBLISH = function()
 +        cl_execute:disconnect();
 +        os.execute(jsonStr['cmd']);
 +    end
 +    cl_execute:loop_forever();                
 +end
 +
 +</code>
 +==== Response -> API Gateway ====
 +  * The API Gateway subscribe to the topic which the mesh node or access point publishes to.
 +  * Here is a snippet from the **/opt/Rdcore-API-Gateway/routes/rdmesh.js** file that execute some code when a message is received on that topic
 +<code javascript>
 +default:
 +    request.put({
 +            url: mesh_controller + '/cake3/rd_cake/node-actions/node-command.json',
 +            form: data
 +        },
 +        function (err, res, body) {
 +            if (err) {
 +                console.error('Error Occurred: ' + err);
 +            }
 +
 +            console.log(body);
 +        }
 +    );
 +    break;
 +</code>
 +==== Response -> CakePHP Controller ====
 +  * Finally we can look at the CakePHP code that process the response so our system know and can indicate the mesh node or access point did receive the instruction.
 +  * Lets look at the **/var/www/html/cake3/rd_cake/src/Controller/NodeActionsController.php** file.
 +<code php>
 +//--This comes from the NodeJS API Gateway Application in response to 'execute' type node_actions
 +//--This comes from the NodeJS API Gateway Application in FIRST response to 'execute_and_reply' type node_actions
 +public function nodeCommand(){
 +
 +    if($this->request->is('put')){
 +        $data = $this->request->data;
 +        if((!empty($data['node_id']))||(!empty($data['ap_id']))){
 +            // update command status to fetched
 +            $model = 'NodeActions';
 +            if($data['mode'] == 'ap'){
 +                $model = 'ApActions';
 +            }
 +            
 +            $entity  = $this->{$model}->find()->where(['id' => $data['cmd_id']])->first();
 +            if($entity){
 +                $entity->status = 'fetched';
 +                $this->{$model}->save($entity);
 +            }
 +
 +            $this->set(array(
 +                'data'          => $data,
 +                'success'       => true,
 +                '_serialize'    => array('data','success')
 +            ));
 +        } else {
 +            $this->set(array(
 +                'message'     => 'Node ID not found',
 +                'success'       => false,
 +                '_serialize'    => array('message','success')
 +            ));
 +        }
 +
 +    } else {
 +        $this->set(array(
 +            'message'         => 'Send only PUT request',
 +            'success'       => false,
 +            '_serialize'    => array('message','success')
 +        ));
 +    }
 +}
 +</code>
 +
 +
  
  
  
  
Last modified: 2022/06/19 20:07