Kevin Mitchell Jr klmitchell2

ANNOUNCEMENT

I have moved this over to the Tech Interview Cheat Sheet Repo and has been expanded and even has code challenges you can run and practice against!

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The introduction to Reactive Programming you've been missing

(by @andrestaltz)

This tutorial as a series of videos

If you prefer to watch video tutorials with live-coding, then check out this series I recorded with the same contents as in this article: Egghead.io - Introduction to Reactive Programming.

File Magic Numbers

Magic numbers are the first bits of a file which uniquely identify the type of file. This makes programming easier because complicated file structures need not be searched in order to identify the file type.

For example, a jpeg file starts with ffd8 ffe0 0010 4a46 4946 0001 0101 0047 ......JFIF.....G ffd8 shows that it's a JPEG file, and ffe0 identify a JFIF type structure. There is an ascii encoding of "JFIF" which comes after a length code, but that is not necessary in order to identify the file. The first 4 bytes do that uniquely.

This gives an ongoing list of file-type magic numbers.

Image Files

Apple Real Devices Debugging

What you need

certificate--which tells your devices that Apple trust you
a app id
a test device
a provisioning profile

Change default shell

Editing /etc/passwd won't work in iOS, so in order to change default shell in iOS you need to edit /etc/master.passwd. You can change root's default shell to bash like this -- root:/smx7MYTQIi2M:0:0::0:0:System Administrator:/var/root:/bin/bash.

	package com.darmasoft.parental_informant;

	import java.io.IOException;
	import java.net.InetAddress;
	import java.net.InetSocketAddress;
	import java.net.Socket;
	import java.net.UnknownHostException;

	import javax.net.ssl.SSLContext;
	import javax.net.ssl.SSLSocket;

	"use strict";
	var crypto = require("crypto");

	var EncryptionHelper = (function () {

	function getKeyAndIV(key, callback) {

	crypto.pseudoRandomBytes(16, function (err, ivBuffer) {

	var keyBuffer = (key instanceof Buffer) ? key : new Buffer(key) ;

	# You must first install apktool (https://github.com/iBotPeaches/Apktool) and android SDK
	# and decompile apk using it
	# apktool d -rf my-app.apk

	# then generate a key for sign in:
	# keytool -genkey -v -keystore my-release-key.keystore -alias alias_name -keyalg RSA -keysize 2048 -validity 10000
	rm signed-app.apk
	apktool b -f -d com.myapp
	jarsigner -verbose -sigalg SHA1withRSA -digestalg SHA1 -keystore my-release-key.keystore com.myapp/dist/com.myapp.apk alias_name
	zipalign -v 4 com.myapp/dist/com.myapp.apk signed-app.apk

	import Cocoa
	import Foundation

	var str = "Hello, playground"

	var task:NSTask = NSTask()
	var pipe:NSPipe = NSPipe()

	task.launchPath = "/bin/ls"
	task.arguments = ["-la"]

	// To check if a number is between a range, don't do
	if number >=0 && number <= 100 {

	}
	// Use range and news operators instead :
	if 0...100 ~= number {

	}