Yeuk Hon Wong yeukhon

System Design Cheatsheet

Picking the right architecture = Picking the right battles + Managing trade-offs

User cases (description of sequences of events that, taken together, lead to a system doing something useful)
- Who is going to use it?
- How are they going to use it?

	I wasn't first to get the key. Nor was I second, third, or even fourth. I'm probably not even the
	10th to get it (ok, looks like I was the 8th.) But I'm happy that I was able to prove to myself
	that I too could do it.

	First, I have to admit I was a skeptic. Like the handful of other dissenters, I had initially
	believed that it would be highly improbable under normal conditions to obtain the private key
	through exploiting Heartbleed. So this was my motivation for participating in Cloudflare's
	challenge. I had extracted a lot of other things with Heartbleed, but I hadn't actually set out to
	extract private keys. So I wanted to see first-hand if it was possible or not.

	const { Task } = Cu.import("resource://gre/modules/Task.jsm", {});
	const { defer, all } = require("sdk/core/promise");
	const { setTimeout } = require("sdk/timers");

	Task.spawn(function *() {
	let item1 = yield getItem(1);
	let [item2, item3] = yield all([getItem(2), getItem(3)]);
	console.log(item1, item2, item3); // 1, 2, 3
	}).then(function () {
	console.log('all items processed')

	# to use:
	# 1. put this file in ~/callstatement/callstatement.py
	# 2. make a file ~/Library/Python/2.7/site-packages/derp.pth with this as the contents:
	# "/Users/USER/callstatement/\nimport callstatement\n"
	# 3. export PYTHONIOENCODING="callstatement_utf8"
	# warning: EXTREMELY NASTY DO NOT USE IN PRODUCTION CODE
	# WILL BREAK EVERYTHING I AM NOT RESPONSIBLE IF
	# YOU'RE FOOLISH ENOUGH TO ACTUALLY TRY TO USE
	# THIS

	#!/usr/bin/env python

	from __future__ import print_function
	import requests
	import sys
	import json


	def hipchat_notify(token, room, message, color='yellow', notify=False,
	format='text', host='api.hipchat.com'):

	# tcpdump -A -nn -s 0 'tcp dst port 9200 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)' -i lo
	tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
	listening on lo, link-type EN10MB (Ethernet), capture size 65535 bytes
	14:32:33.525122 IP 127.0.0.1.49777 > 127.0.0.1.9200: Flags [P.], seq 313752908:313753888, ack 2465010394, win 257, options [nop,nop,TS val 2684167067 ecr 2684167066], length 980
	E...^.@[email protected]#...}L...............
	..#...#.GET /index/_search HTTP/1.1
	Host: 127.0.0.1:9200
	Accept: /
	Content-Length: 845
	Content-Type: application/x-www-form-urlencoded

	# Install https://www.vaultproject.io/
	brew install vault

	# Start dev vault server in a separate terminal
	vault server -dev
	# ==> Vault server configuration:
	# ...
	# Unseal Key: 7ACQHhLZY5ivzNzhMruX9kSa+VXCah3y87hl3dPSWFk=
	# Root Token: 858a6658-682e-345a-e4c4-a6e14e6f7853

	import asyncio
	import itertools

	import aiohttp
	import async_timeout


	async def fetch_with_response_delay(session, delay):
	if not 0 <= delay <= 10:
	raise ValueError('Delay must be between 0 and 10 inclusive')