DB 0003

[Python] Credit Card Validation

2022-10-27T23:00:00+11:00

This is a credit card validation with Luhn’s Algorithm

Multiply every other digit by 2, starting with the number’s second-to-last digit, and then add those products’ digits together.
Add the sum to the sum of the digits that weren’t multiplied by 2.
If the total’s last digit is 0 (or, put more formally, if the total modulo 10 is congruent to 0), the number is valid.

Ex)

Card Number: 4003600000000014

Multiply each of the underlined digits by 2:

1•2 + 0•2 + 0•2 + 0•2 + 0•2 + 6•2 + 0•2 + 4•2

That gives us:

2 + 0 + 0 + 0 + 0 + 12 + 0 + 8

Now let’s add those products’ digits (i.e., not the products themselves) together:

2 + 0 + 0 + 0 + 0 + 1 + 2 + 0 + 8 = 13

Add that sum (13) to the sum of the digits that weren’t multiplied by 2 (starting from the end):

13 + 4 + 0 + 0 + 0 + 0 + 0 + 3 + 0 = 20

The last digit in that sum (20) is a 0, then the card number is valid.

from cs50 import get_int
import re

divider = 10000000000000


def main():
    card_number = get_int("Enter credit card number: ")
    size = validate_card_type(card_number)
    is_valid = validate_card_numbers(card_number)

    if size == 0 or is_valid > 0:
        print("INVALID")


def validate_card_type(card_number):
    size = is_amex(card_number)
    if size > 0:
        return size

    size = is_master(card_number)
    if size > 0:
        return size

    size = is_visa(card_number)
    if size > 0:
        return size

    return size


def validate_card_numbers(card_number):
    odds = str(card_number)[0::2]
    evens = str(card_number)[1::2]

    result = 0
    for num in odds:
        multiplied = int(num) * 2
        if (multiplied < 10):
            result += multiplied
        else:
            str_num = str(multiplied)
            result += int(str_num[0])
            result += int(str_num[1])

    for num in evens:
        result += int(num)

    return result % 10


def is_amex(card_number):
    number = int(card_number / divider)
    if number + 66 == 100 or number + 63 == 100:
        print("AMEX")
        return 15
    else:
        return 0


def is_master(card_number):
    # Master 16 digit and start 51,52,53,54, 55
    r = re.search("^[5][1-5]", str(card_number))

    if r:
        print("MASTERCARD")
        return 16
    else:
        return 0


def is_visa(card_number):
    # Visa 13 16 digit and start with 4
    r = re.match("^[4]", str(card_number))
    l = len(str(card_number))

    if r and (l == 16 or l == 13):
        print("VISA")
        return 16
    else:
        return 0


if __name__ == "__main__":
    main()
    

[Python] Readability

2022-10-27T23:00:00+11:00

Python version of Readability

The Coleman-Liau index of a text is designed to output that (U.S.) grade level that is needed to understand some text

Formula index = 0.0588 * L - 0.296 * S - 15.8

from cs50 import get_string
import re


def main():
    text = get_string("Text: ")

    cnt_l = len(re.findall("[a-zA-Z]", text))
    cnt_w = len(text.split())
    cnt_s = len(re.split('[.]|[?]|[!]', text))
    cnt_s -= 1

    # get avg of letters per 100 words
    L = round((cnt_l * 100) / cnt_w, 2)
    # get avg of sentences per 100 words
    S = round((cnt_s * 100) / cnt_w, 2)
    index = round(0.0588 * L - 0.296 * S - 15.8)
    print_grade(index)


def print_grade(index):
    if (index < 1):
        return print("Before Grade 1")
    if (index >= 16):
        return print("Grade 16+")
    print(f"Grade {index}")


main()

[JS] Promise Basics

2021-12-16T01:00:00+11:00

1. Resolve case

//resolve
var promise = new Promise(function (resolve, reject) {
  setTimeout(() => resolve('done!'), 1000);
});

promise.then(
  (result) => console.log('CASE 1', result),
  (error) => console.log('CASE 1',error.message)
);

2. Reject case

//reject
var promise = new Promise(function (resolve, reject) {
  setTimeout(() => reject(new Error('failed!')), 2000);
});

promise.then(
  (result) => console.log('CASE 2',result),
  (error) => console.log('CASE 2',error.message)
);

3. Handling only error with passing null in resolve

// handle only error
var promise = new Promise(function (resolve, reject) {
  setTimeout(() => reject(new Error('handle failed!')), 2000);
});

promise.then(null, (e) => console.log('CASE 3',e.message));

// or you can use catch
promise.catch((e) => console.log('CASE 3', e.message));

4. Finally - Execute always without result of resolve or reject

//finally (good for cleanup)
new Promise(function (resolve, reject) {
  setTimeout(() => resolve('Resolved'), 1000);
})
  .finally(() => console.log('CASE 4 Finally! I always run!'))
  .then(
    (result) => console.log('CASE 4', result),
    (error) => console.log('CASE 4', error.message)
  );

[Node.js] Koa Server initialization with formatter

2021-12-10T23:00:00+11:00

Step 1. Setup packages required

# generate package.json
yarn init -y

# add koa
yarn add koa

# add eslint
yarn add --dev eslint

yarn run esline --init # Answer the questions

Step 2. Create Prettier connfig file.

Change this settings upto your flavour.

// create .prettierrc file on the root of source folder
{
    "singleQuote": true,
    "trailingComma": "all",
    "semi": true,
    "useTabs": false,
    "tabWidth": 2,
    "printWidth": 80
}

# Set ESLint does not control prettier styled
$ yarn add eslint-config-prettier

// create .eslintrc.json on the root of source folder
{
  "env": {
    "commonjs": true,
    "node": true,
    "es6": true
  },
  "extends": ["eslint:recommended", "prettier"],
  "globals": {
    "Atomics": "readonly",
    "SharedArrayBuffer": "readonly"
  },
  "parserOptions": {
    "ecmaVersion": 2018
  },
  "rules": {
    "no-unused-vars": "warn",
  }
}

Step 3. Setup Koa server

Inital template of koa server running on port 4000. Two middle ware included as an example.

const Koa = require('koa');
const app = new Koa();

app.use(async (ctx, next) => {
  ctx.body = 'Hello World';
  console.log(1);
  await next();
  console.log('END')
});

app.use((ctx, next) => {
  console.log(2);
  next();
});

app.listen(4000, () => {
  console.log('server is running at http://localhost:4000');
});

Step 4. Run the server

$ node src

# Check on the browser - http://localhost:4000

[Java] Custom HTTP RequestURL XSS Filter

2021-12-10T06:00:00+11:00

Sample to show how to check requestURL and prevent Croos-Site-Script Attack Using common XSS Filter to convert URL to clean string.

package com.handler.filter;

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;

public class XSSFilter implements Filter {
	@Override
	public void init(FilterConfig filterConfig) throws ServletException {
	}

	@Override
	public void destroy() {
	}

	@Override
	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
		String requestURI = ((HttpServletRequest) request).getRequestURI();
		String newURI = cleanXSS(requestURI);
		request.getRequestDispatcher(newURI).forward(request, response);
		chain.doFilter(request, response);
	}

	private String cleanXSS(String value) {
		value = value.replaceAll("<", "& lt;").replaceAll(">", "& gt;");
		value = value.replaceAll("\\(", "& #40;").replaceAll("\\)", "& #41;");
		value = value.replaceAll("'", "& #39;");
		value = value.replaceAll("eval\\((.*)\\)", "");
		value = value.replaceAll("[\\\"\\\'][\\s]*javascript:(.*)[\\\"\\\']", "\"\"");
		value = value.replaceAll("script", "");
		return value;
	}

}

Then set filter in the web.xml

    XSSFilter
    com.handler.filter.XSSFilter


    XSSFilter
    /*

[JS] Slice Strings

2021-12-08T06:00:00+11:00

Example codes of String.slice()

let str = "stringify";
console.log(str.slice(0, 5) ); // 'strin', from 0 to 5
console.log(str.slice(0, 1) ); // 's', from 0 to 1

str = "stringify";
console.log(str.slice(2) ); // ringify, from 2 to end

str = 'stringify';

// from last 4 to last 1
console.log(str.slice(-4, -1) ); // gif
str = 'stringify';

Please aware that String.substring() and String.slice result is not same

// same value will be returned
console.log(str.substring(2, 6) ); // "ring"
console.log(str.substring(6, 2) ); // "ring"

// slice result is not same as substring
console.log(str.slice(2, 6) ); // "ring"
console.log(str.slice(6, 2) ); // ""

[JS] Cut string into limited length

2021-12-06T23:00:00+11:00

Sample function to cut string into desired limit value.

const limitTitle = (title, limit = 17) => {
  const newTitle = [];
  if(title.length > limit) {
    title.split(' ').reduce((acc, cur) => {
      if (acc + cur.length <= limit) {
        newTitle.push(cur);
      }
      return acc + cur.length
    }, 0);
    return `${newTitle.join(' ')} ...`;
  }
  return title;
}

console.log(limitTitle("This is an example title"));

[JS] Formatting console output

2021-12-03T23:00:00+11:00

You can pass arguments to the console.log like a C printf();

With %c and second parameter, you can inject CSS style to the text.

%s Formats the value as a string

%i or %d Formats the value as an integer

%f Formats the value as a floating point value

%o Formats the value as an expandable DOM element

%O Formats the value as an expandable JavaScript object

%c Applies CSS style rules to the output string as specified by the second parameter

console.log("%s is %i", "Pie", 3.1415926535);
// Pie is 3
console.log("%s is %f", "Pie", 3.1415926535);
// Pie is 3.1415926535

console.log("%c CSS text", "color: blue; font-size: 13px");
// Check out in the browser console

[React] Routing

2021-12-02T08:00:00+11:00

Example of React DOM Router usage.

Here assume that you already have Menu and Page Component to render.

Configure index.js to wrap in the

index.js

import React from "react";
import ReactDOM from "react-dom";
import App from "./App";
import { BrowserRouter } from "react-router-dom";

ReactDOM.render(
  <React.StrictMode>
    <BrowserRouter>
      <App />
    </BrowserRouter>
  </React.StrictMode>,
  document.getElementById("root")
);

Then place each path in the and declare the path and the element.

App.js

import { Routes, Route } from "react-router-dom";
import Menu from "./components/Menu";
import Page1 from "./pages/Page1";
import Page2 from "./pages/Page2";

function App() {
  return (
    <div>
      <Menu />
      <hr />
      <Routes>
        <Route path="/page1" element={<Page1/>} />
        <Route path="/page2" element={<Page2/>} />
      </Routes>
    </div>
  );
}

export default App;

[Python] Pandas export as a csv file

2021-11-30T02:00:00+11:00

Sample code that how to export data as a csv using pandas library. this function will create filename string with date as a actual filename.

from datetime import datetime
import pandas

def export_csv(_data, _headers, _filename):
	date = datetime.today().date()
	df = pandas.DataFrame(_data)
	path = 'C:\\download\\csv\\' + _filename + str(date) + '.csv'
	df.to_csv(path, header=_headers, index=False, encoding='utf-8-sig')

# Usage
headers = ['A', 'B', 'C'];
data = [];
export_csv(data, headers, 'sample');