SKITSANOS.ETC

Code bits, ideas, tips and other programming related thoughts mainly about sensor networks, Industrial Internet of Things and micro computing in logistics, cold chain management, HVAC and few other industries of our interest.

[skitsanoscom]

Open source design system for your next travel project

Orbit is an open-source design system created for specific needs of Kiwi.com and together with that – for needs of travel projects.

From Kiwi.com perspective, Orbit aims to bring order and consistency to Kiwi.com products and processes behind building them.

[skitsanoscom]

A Quick Guide to Open Source Licenses

When you create software that you want to share, or you use a product that you want to adapt, questions about what is and is not legal pop up. Even programs that have an open source license aren’t free-for-alls. If you don’t know the specifics of what the license allows, you could get into legal hot...

[skitsanoscom]

count(doc) is faster than count(doc._key)

One more hint on queries performance tuning. Although document keys (_key) are indexed, counting docs is faster by the entire doc, not by a key of the doc.

So the following query will be faster

let ds = (for doc in random_data return doc) return count(ds)

Compare to this one, that in my case went for entire 12ms slower on 100K records

let ds = (for doc in random_data return doc) return count(ds._key)

[skitsanoscom]

AQL performance and indexes

A little experiment with 100,000 randomly generated docs queried in two ways produce the same result, but time takes on execution is like 80 times different.

The following query took like 1.6s to execute

for doc in random_data limit 1,100 return merge(doc, { client: ( for client in random_data_details filter client.source==doc.value return unset(client, "_id","_rev") ) })

While this one, took just 0.02s

for doc in random_data limit 1,100 sort doc._key DESC collect project = doc, found_client = ( for client in random_data_details filter client.source==doc.value return unset(client, "_id","_rev") )[0] || {} return merge(project, { client: found_client })

Worth mentioning here that those benchmarks are valid only for the case when you have indexes enabled on datasets you querying.

Without indexes enabled the first query took 17s and second one executed with 8.5s.

Indexes allow fast access to documents, provided the indexed attribute(s) are used in a query. While ArangoDB automatically indexes some system attributes, users are free to create extra indexes on non-system attributes of documents.

[skitsanoscom]

JavaScript: check if date is next week or next month

moment.js has couple of nice functions that allows us to check if the given date is next week or next month:

const today = '2019-09-06'; const nextWeek = '2019-09-11'; const nextMonth = '2019-10-11'; console.log(moment(today).isSame(today, 'day')); console.log(moment(nextWeek).isAfter(today, 'week')); console.log(moment(nextMonth).isAfter(today, 'month'));

[skitsanoscom]

Writing simple Webix component

Unfortunately Webix is rather poorly documented when you trying to do something more than app with basic functionality. Coming from Extjs, YUI, Flex, working with React, today Webix is still my number one choice when it comes to building enterprise apps.

Today's code snippet demonstrates you how to create your own basic component. In my particular case, I'm creating header component that can uses title and icon as its view properties. So if icon property is set, it renders FontAwesome icon and title, otherwise just a title.

webix.protoUI({ name: 'header', defaults: { height: 40, icon: undefined, title: 'Untitled' }, $init: function (cfg) { this.$ready.push(() => { if (this.config.icon === undefined) { this.$view.innerHTML = this.title; } else { this.$view.innerHTML = `<i class="fas fa-${this.config.icon}"></i> ${this.config.title}`; } }); this.$view.className += ' webix_header'; this.$view.innerHTML = ''; this.$view.style.paddingLeft = '0.5rem'; }, $getSize: function (x, y) { // own logic // ... // parent logic return webix.ui.view.prototype.$getSize.call(this, x, y); }, $setSize: function (x, y) { //if parent has changed its size if (webix.ui.view.prototype.$setSize.call(this, x, y)) { //custom logic } }, title_setter: function (value) { return value; }, icon_setter: function (value) { return value; } }, webix.ui.view);

Now you can use your new component within application you create:

const ui = { rows: [ { id: 'appheader', view: 'header', title: 'SKITSANOS', icon: 'dizzy' }, {}, { height: 40, template: 'Copyright ® Skitsanos' } ] }; webix.ui(ui)

Please make sure you added FontAwesome into your html header, like this:

<link rel="stylesheet" href="https://use.fontawesome.com/releases/v5.10.2/css/all.css">

To change config properties, like title for example, you need redefine them this way, (assuming your header component id is 'appheader'):

$$('appheader').define('title', 'My app');

[skitsanoscom]

Remove IIS Server version HTTP Response Header - Sysadmins of the North

Remove HTTP response headers in IIS 7, 7.5, 8.0, 8.5, 10 and ASP.NET Windows Server IIS loves to tell the world that a website runs on IIS. It does so with the Server header in the HTTP response, as shown below. In this post I’ll show you how to remove response server headers in IIS. You don’t want to give hackers too much information about …

[skitsanoscom]

Why we prefer CSS Custom Properties to SASS variables | CodyHouse

Some practical examples of how CSS variables can power-up your workflow

[skitsanoscom]

Writing schemas with hapi/joi is quite different to Ajv, you might find its syntax is somewhat readable, just keep in mind it is not a JSON-Schema stard actually.

const Joi = require('@hapi/joi'); const SchemaBase = require('~framework/schemas/joi'); class User extends SchemaBase { constructor() { super(); this.schema = Joi.object().keys({ email: Joi.string().required().email({minDomainSegments: 2}), password: Joi.string().alphanum().min(3).max(30), access_token: [Joi.string(), Joi.number()], role: Joi.string().alphanum().min(3).max(128) }).or('password', 'access_token').without('password', 'role'); } } module.exports = User;

SchemaBase class defined like that:

const Joi = require('@hapi/joi'); class JoiSchema { constructor() { this.schema = {}; } validate(data) { return Joi.validate(data, this.schema); } describe() { return Joi.describe(this.schema); } } module.exports = JoiSchema;

[skitsanoscom]

AJV sample schema

Example on how to write JSON Schema with AJV:

const SchemaBase = require('~framework/schemas/ajv'); class User extends SchemaBase { constructor() { super(); this.schema = { type: 'object', properties: { email: { type: 'string', minLength: 5, maxLength: 254, format: 'email' }, password: { type: 'string', minLength: 6, maxLength: 30 }, role: { type: 'string', enum: ['admin', 'user'], default: 'user' } }, required: ['email', 'password'] }; } } module.exports = User;

and AJV Schema Base class:

const Ajv = require('ajv'); const ajv = new Ajv({allErrors: true}); class AjvSchema { constructor() { this.schema = {}; } validate(data) { return ajv.validate(this.schema, data); } } module.exports = AjvSchema;

[skitsanoscom]

Lorem Ipsum... but for photos

Just add your desired image size (width & height) after our URL, and you'll get a random image.

[skitsanoscom]

Oh, the Many Ways to Make Triangular Breadcrumb Ribbons! | CSS-Tricks

Oh, the Many Ways to Make Triangular Breadcrumb Ribbons Let’s have a look at how we can create a row of links that sorta run into each other with a

[skitsanoscom]

Getting To Know The MutationObserver API — Smashing Magazine

Monitoring for changes to the DOM is sometimes needed in complex web apps and frameworks. By means of explanations along with interactive demos, this article will show you how you can use the MutationObserver API to make observing for DOM changes relatively easy.

[skitsanoscom]

On npm install: Unhandled rejection Error: EACCES: permission denied

A simple way to resolve EACCES rejection error when trying to perform npm install:

sudo chown -R $USER:$GROUP ~/.npm sudo chown -R $USER:$GROUP ~/.config

[skitsanoscom]

Fixing that ‘Brownout detector was triggered’ error

Although some suggest to switch pff entirely that brownout detector with this line:

WRITE_PERI_REG(RTC_CNTL_BROWN_OUT_REG, 0);

Reality is, - it might be just your USB cable... Get a better cable and you might have your problem fixed. Worked for me.

[skitsanoscom]

JavaScript Array unions, intersection and difference

Below are handy utilties to obtain union, intersection and difference on two arrays.

const app = { utils: { array: { union: (arr_a, arr_b) => { const set_a = new Set(arr_a); const set_b = new Set(arr_b); return new Set([...set_a, ...set_b]); }, intersection: (arr_a, arr_b) => { const set_a = new Set(arr_a); const set_b = new Set(arr_b); return new Set([...set_a].filter(x => set_b.has(x))); }, difference: (arr_a, arr_b) => { const set_a = new Set(arr_a); const set_b = new Set(arr_b); return new Set([...set_a].filter(x => !set_b.has(x))); } } } }; const arr1 = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]; const arr2 = [1, 22, 3, 74, 5, 26, 7, 8, 9, 10]; const set_union = app.utils.array.union(arr1, arr2); const set_intersection = app.utils.array.intersection(arr1, arr2); const set_difference = app.utils.array.difference(arr1, arr2); console.log(set_union); console.log(set_intersection); console.log(set_difference); console.log(Array.from(set_intersection)); //converts set to array

[skitsanoscom]

Reading MHZ-19 sensor data in Node.js

Below is an example on how to read CO2 level readings from MHZ-19 NDIR sensor via serial port in Node.js

/** * MHZ-19 UART Monitor * @author skitsanos */ const winston = require('winston'); const Transport = require('winston-transport'); const fs = require('fs'); const SerialPort = require('serialport'); const port = new SerialPort('/dev/tty.usbserial', {baudRate: 9600, autoOpen: false}); class FileTransport extends Transport { constructor(opts) { super(opts); } log(info, callback) { fs.appendFile(process.cwd() + '/app.log', `${info.level} ${info.message}\n`, (err) => { if (err) { console.log(err.message); } }); callback(); } } const loggingFormat = winston.format.combine( winston.format.colorize(), winston.format.splat(), winston.format.printf(info => { return ` ${(new Date()).getTime()} ${info.level}: ${info.message}`; })); const log = winston.createLogger({ exitOnError: false, //level: 'debug', transports: [ new FileTransport( { format: loggingFormat, timestamp: true } ), new winston.transports.Console({ format: loggingFormat }) ] }); let app = { meta: require('./package'), commands: { READ_VALUE: Buffer.from([0xff, 0x01, 0x86, 0x00, 0x00, 0x00, 0x00, 0x00, 0x79]) }, utils: { ord: (str) => { console.log(str); return str.charCodeAt(0); }, sleep: (ms) => new Promise(resolve => setTimeout(resolve, ms)) }, serial: { list: () => { SerialPort.list().then((arr_portInfo) => { arr_portInfo.map(el => { console.log(el); log.info('Found: ' + el.comName); }); }); }, open: () => { if (port !== undefined) { return new Promise((resolve, reject) => { port.open(err => { if (err) { return reject(err); } return resolve(); }); }); } else { log.error('Failed to open port. Not found?'); } }, close: () => { if (port !== undefined) { log.debug('Closing serial port'); port.close(); } else { log.error('Failed to open port. Not found?'); } }, write: (data) => { return new Promise((resolve, reject) => { if (port !== undefined) { log.debug('Writing to serial port...'); port.write(data, (err) => { if (err) { return reject(err); } return resolve(); }); } else { return reject({message: 'Failed to write. Not found?'}); } }); } } }; log.info(`${app.meta.name} ver. ${app.meta.version}`); app.serial.open().then(() => { log.debug('Port open'); port.on('readable', async () => { const buf = port.read(9); if (buf !== null && Buffer.byteLength(buf) === 9) { if (buf[0] === 0xff && buf[1] === 0x86) { const co2 = Number(buf[2].toString()) * 256 + Number(buf[3].toString()); log.info(`${co2}ppm`); } await app.utils.sleep(5000); app.serial.write(app.commands.READ_VALUE); } }); app.serial.write(app.commands.READ_VALUE).then(() => { }).catch(err => log.error(err.message)); }).catch(err => log.error(err.message));