« Ruby Blockchain Week 2021, January 3rd to January 9th - 7 Days of Ruby (Crypto) Gems

Day 7 - centralbank Gem - Print Your Own Money / Cryptocurrency - Run Your Own Federated Central Bank Nodes on the Blockchain Peer-to-Peer over HTTP

Written by geraldb Gerald Bauer

A code monkey formerly at Big Korupto. Jobless no coiner having fun staying poor and wrong. Writing the Get Rich Quick “Business Blockchain” Bible - The Secrets of Free Easy Money.

What’s centralbank?

Use the centralbank command line tool. Try:

$ centralbank -h

resulting in:

Usage: centralbank [options]

  Wallet options:
    -n, --name=NAME                  Address name (default: Alice)

  Server (node) options:
    -o, --host HOST                  listen on HOST (default:
    -p, --port PORT                  use PORT (default: 4567)
    -h, --help                       Prints this help

To start a new (network) node using the default wallet address (that is, Alice) and the default server host and port settings use:

$ centralbank

Stand back ten feet :-) while starting up the machinery. Ready to print (mine) money on the blockchain? In your browser open up the page e.g. http://localhost:4567. Voila!

Note: You can start a second node on your computer - make sure to use a different port (use the -p/--port option) and (recommended) a different wallet address (use the -n/--name option). Example:

$ centralbank -p 5678 -n Bob

Happy mining!

Inside Mining - Printing Cryptos, Cryptos, Cryptos on the Blockchain

What happens when you hit the “Mine a block” button? Let’s follow the money code.

The form gets posted by the browser and hits the /mine route in centralbank network service:

class Service < Sinatra::Base
  # ...
  post '/mine' do
    redirect '/'
  # ...

(Source: lib/centralbank/service.rb

So the code mines a block and than redirects to (auto-)refresh the page. That’s it! Let’s dive into the on_mine! method in the network node:

class Node
  # ...
  def on_mine!
  # ...

(Source: lib/centralbank/node.rb)

So the code mines a block and sends the new blockchain (chain) to all peers (nodes). That’s it! Let’s dive into the mine_block! method for the centralbank machinery:

class Bank
  # ...
  def mine_block!
    @pending << Tx.new( Centralbank.config.coinbase,
                        Centralbank.config.mining_reward )

    ## add mined (w/ computed/calculated hash) block
    @chain << @pending.transactions
    @pending = Pool.new   ## clear out/ empty mem tx pool (just create a new one for now)

    ## update ledger (balances) with new confirmed transactions
    @ledger = Ledger.new( @chain )
  # ...

(Source: lib/centralbank/bank.rb)

So the code adds a “coinbase” transaction (tx) to the pending pool (of unconfirmed transactions). For mining a new block you will get a mining reward (e.g. $5). That’s the magic moment of printing new money on the blockchain out-of-thin-air. Next all pending (unconfirmed but validated) transactions get added to the blockchain (chain) as a new block. Done! Block mined! Let’s clear out the pending memory transaction pool and update all account balances in the wallet, that is, update the ledger book. Let’s dive into the << method for the blockchain (chain) machinery:

class Blockchain
  # ...
  def <<( txs )
    if @chain.size == 0
      block = Block.first( txs )
      block = Block.next( @chain.last, txs )
    @chain << block
  # ...

(Source: lib/centralbank/blockchain.rb)

So the code adds a block to the chain at the end and passes along the hash of the last block on the blockchain to the new block. That’s all the magic of printing money.

What about proof-of-work and the hashing power/rate? See the Day 2 - blockchain-lite Gem - Build Your Own Blockchains with Crypto Hashes article in the series.

Happy mining!

Bonus: Local Development Setup

For local development - clone or download (and unzip) the centralbank code repo. Next install all dependencies using bundler with a Gemfile e.g.:

# Gemfile

source "https://rubygems.org"

gem 'sinatra'
gem 'sass'
gem 'blockchain-lite'


$ bundle       ## will use the Gemfile (see above)

and now you’re ready to run your own centralbank server node. Use the config.ru script for rack:

# config.ru

$LOAD_PATH << './lib'

require 'centralbank'

run Centralbank::Service

and startup the money printing machine using rackup - the rack command line tool:

$ rackup       ## will use the config.ru - rackup configuration script (see above).

In your browser open up the page e.g. http://localhost:9292. Voila! Happy mining!

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