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mqttLogCatcher.js
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mqttLogCatcher.js
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/********************************************************************
* Program: mqttLogCatcher
* Module: mqttLogCatcher.js
* Description: Captures the content of a MQTT topic(s) and writes them
* to a file(s)
* Inputs: MQTT Broker, Topic(s), ClientID, File Location
* Outputs: File
*
* Revisions:
* Date Who Description
* ---------- ---- ----------------------------------------
* 2019-10-02 prw Created
* 2019-10-04 prw Few more minor tweaks, commenting
*
********************************************************************/
// minimist captures command line parameters in an easy to use way.
const args = require('minimist')(process.argv.slice(2));
// Check for required arguments (one of each -b, -t, -c, -f), display an error and exit if not present.
if ( args.h || (!args.b || !args.t || !args.f || !args.c)) {
console.log('');
console.log(' ERROR: Insufficient number of arguments!');
console.log(' Example: node MQTTCapture.js -b BROKER -t TOPIC1 [-t TOPIC2] -c CLIENT -f FILEDIR [-d] [-h]');
console.log(' Where:');
console.log(' -b is the broker URL ex: "mqtt://localhost:1883".');
console.log(' -t [one or more] is a topic ex: "dev/6881/app/log".');
console.log(' -c is this client ID ex : "mqttLogCatcher".');
console.log(' -f base log directory.');
console.log(' -d [optional] is for debug mode that enables console output.');
console.log(' -h [optional] this help message.');
console.log('');
if (args.d) {
if (args.b) { console.log('BROKER = '+args.b); }
if (args.t) { console.log('TOPIC = '+args.t); }
if (args.c) { console.log('CLIENTs = '+args.c); }
if (args.f) { console.log('FILEDIR = '+args.f); }
if (args.d) { console.log('Debug = True'); } else { console.log('Debug = False'); }
if (args.h) { console.log('Help = True'); } else { console.log('Help = False'); }
}
console.log('');
process.exit(1);
}
// Display command line argument if debug is enabled
if (args.d) {
if (args.b) { console.log('DEUBG: BROKER = '+args.b); }
if (args.t) { console.log('DEUBG: TOPIC = '+args.t); }
if (args.c) { console.log('DEUBG: CLIENT = '+args.c); }
if (args.f) { console.log('DEUBG: LOGGILE = '+args.f); }
if (args.d) { console.log('DEUBG: Debug = True'); }
if (args.h) { console.log('DEUBG: Help = True'); }
if (args.d) { console.log(''); }
}
// Real program starts here
var MQTT = require("mqtt");
var fs = require("fs");
// Create a connection to the MQTT Broker
var client = MQTT.connect(args.b, {clientId: args.c});
client.on("connect", onConnected);
client.on("message", onMessageReceived);
// Once connected subscribe to the or all of the topic provided
function onConnected() {
if (Array.isArray(args.t)) {
for (var i = 0; i < args.t.length; i++) {
client.subscribe(args.t[i]);
}
} else {
client.subscribe(args.t);
}
}
// Process any message recieved
function onMessageReceived(topic, message) {
// Gather the source information from the topic
// My topic string looks like: dev/1234/myApp/log
var src = topic.split("/");
// Create a "source" json object for the log entry
var source = {
"env":src[0],
"inst":src[1],
"app":src[2],
"reason":src[3]
};
// The intent of this application os to capture json formatted log entries.
// if you would like process other specific format or only log parts of the
// json message you will need to make edits to this section and / or the
// sections below that write to the log files.
// For now this basically checks to see that the incoming message is a json
// structure, otherwise it puts in an error structure.
var theMsg = {};
theMsg.source = source;
try {
if (args.d) { console.log("DEBUG: typeof message = " + typeof message); }
theMsg.message = JSON.parse(message);
if (args.d) { console.log("DEBUG: typeof theMsg.message = " + typeof theMsg.message); }
if ( typeof theMsg.message === "number") { throw err; }
} catch {
theMsg.message = { "ERROR":"non-json data found" };
}
// Write to a log file based on the reason for logging.
// Check to see if the message is a "log" message
if(source.reason === "log") {
var fn = args.f + source.environment +"-"+ source.instance +"-"+ source.application +"-"+ source.reason + ".json";
if (args.d) { console.log("DEBUG: TO log: " + JSON.stringify(theMsg) +"\n"); }
fs.appendFile(fn, JSON.stringify(theMsg)+"\n", (err) => { if (err) throw err; });
// If you want to add other specific log files you would add a elseif here to handle each one.
// I can see a source.reason === "err" and a source.reason === "txn" for instance.
// All undefined logs will go into a txt file log
// expeting ascii data - json, xml, html ... what ever as long as it's ascii text.
} else {
var fn = args.f + source.environment +"-"+ source.instance +"-"+ source.application +"-"+ source.reason + ".txt";
if (args.d) { console.log("DEBUG: TO test: " + message +"\n"); }
fs.appendFile(fn, message + "\n", (err) => { if (err) throw err; });
}
}