jsonchangewatch

watch.js

var http = require('http');
var child_process = require('child_process');

function poll(url, cb) {
    http.get(url, function(res) {
	var body = "";
	res.setEncoding('utf8');
	res.on('data', function(data) {
	    body += data;
	});
	res.on('end', function() {
	    var json;
	    try {
		json = JSON.parse(body);
	    } catch (e) {
		console.error(e);
		return cb(error);
	    }
	    return cb(null, json);
	});
	res.on('error', cb);
    });
}


var mailTo = process.argv[2];
var url = process.argv[3];
var interval = parseInt(process.argv[4], 10);
var keys = process.argv.slice(5).map(function(s) {
    var m;
    if ((m = s.match(/^(.+):(\d+)$/))) {
	return { path: m[1].split('.'),
		 ttl: parseInt(m[2], 10) * 1000,
		 updated: new Date().getTime()
	       };
    } else
	return { path: s.split('.'),
		 ttl: 3600000,
		 updated: new Date().getTime()
	       };
});

function sendMail(subject, mailTo, body) {
    var mail = child_process.spawn("mail", ["-s", subject, mailTo]);
    mail.stdin.write(body);
    mail.stdin.end();
    mail.on('exit', function(code) {
	if (code !== 0)
	    console.error("mail exited with " + code);
    });
}

if (keys.length < 1) {
    console.log("Usage: " + process.argv.slice(0, 2).join(" ") + " <mail-to> <json-url> <interval> <key1:maxage1> [key2:maxage2] [.. keyN:maxageN]");
    process.exit(1);
}

setInterval(function() {
    poll(url, function(error, json) {
	if (error) {
	    sendMail("Watch error for " + url, mailTo, error.message || error.toString());
	    return;
	}

	// console.log(json);
	var now = new Date().getTime();
	keys.forEach(function(key) {
	    var a = json, p = key.path;
	    while(a && p.length > 0) {
		a = a[p[0]];
		p = p.slice(1);
	    }
	    if (key.state !== a) {
		key.state = a;
		key.updated = now;
	    }
	});
	var report = [];
	keys.forEach(function(key) {
	    var age = now - key.updated;
	    if (age >= key.ttl) {
		report.push(key.path.join('.') +
			    " has been " +
			    (key.state ? ("at " + key.state) : "unknown") +
			    " for " +
			    Math.floor(age / 1000) +
			    " seconds.");
	    }
	});
	if (report.length > 0) {
	    console.log(report);
	    sendMail("Watch alert for " + url, mailTo, report.join("\n"));
	}
    });
}, interval * 1000);