Proj 12: Making an Ethereum Contract (15 pts.)

What You Need

A Linux machine running a private Ethereum blockchain. You prepared one in the previous project. I assume you are using Ubuntu 16.04 64-bit in the instructions below.

Purpose

To set up an Ethereum Smart Contract. The ability to run programs like this is the main feature that distinguishes Ethereum from Bitcoin.

Task 1: Building and Installing Ethereum Compilers

To make a contract, we need a compiler. We'll install two compilers: Solidity and LLC.

Installing Dependencies

On your Linux machine, in a Terminal window, execute this command. Enter your password when you are prompted to.

sudo apt-get update

Execute these commands to install dependencies, fetch the source code, and compile it:

sudo apt install -y build-essential cmake libboost-all-dev cd git clone --recursive https://github.com/ethereum/solidity.git cd solidity mkdir build && cd build cmake .. make

This will take a few minutes. To complete the installation, execute this command:

sudo make install

Execute this command to set the PATH environment variable.

nano ~/.profile

At the end of this file, add this line, as shown below.

export LD_LIBRARY_PATH="$LD_LIBRARY_PATH:/usr/local/lib"

Save the file with Ctrl+X, Y, Enter.

Execute this command to restart the machine:

sudo reboot

Test the Installation

Execute these commands:

solc --version lllc --version

You should see information about both compilers, as shown below. This shows that they are installed and working.

Task 2: Compile a Solidity Contract

There are two compilers available to us: LLC and Solidity. Solidity is the easier one, so we'll use it.

Making an Identity Function

Execute these commands:

cd nano identity.sol

In nano, paste in the code shown below. This is a simple function that takes an integer as input and returns it as output.

pragma solidity ^0.4.0; contract IdentityFunction { function identity (uint value) returns (uint) { return value; } }

Save the file with Ctrl+x, y, Enter.

Compiling the Identity Function

Execute this command:

solc --optimize --bin identity.sol

The compiled code appears, in an ASCII representation of bytecode, as shown below.

Viewing the Assembly Code

Execute this command:

solc --optimize --asm identity.sol

The assembly code appears, as shown in the two images below.

This code looks strange at first, but it's a lot like other assembly code, with opcodes including ADD, XOR, and NOT, as listed here.

Task 3: Preparing for Deployment

To deploy code, we need some more tools.

Installing node.js

We must install node.js from source, because the Ubuntu repositories contain a version that is too old.

Execute these commands:

cd wget https://nodejs.org/dist/v8.1.0/node-v8.1.0-linux-x64.tar.gz tar xvf node-v8.1.0-linux-x64.tar.gz sudo chown -R root.root node-v8.1.0-linux-x64 sudo mv node-v8.1.0-linux-x64 /opt/node sudo ln -s /opt/node/bin/node /usr/bin/node sudo ln -s /opt/node/lib/node_modules/npm/bin/npm-cli.js /usr/bin/npm

Testing the Installation

Execute these commands:

node -v npm -v

You see version numbers, as shown below.

Installing web3.js

This library is used to interact with local or remote Ethereum nodes.

Execute this command:

npm install web3

There are a few warning messages, but no errors, as shown below.

Installing testrpc

The testrpc utility simulates an Ethereum blockchain so we can easily test deployment at no cost.

It also executes transactions immediately, without waiting for blocks to be mined.

Execute these commands:

sudo npm install --unsafe-perm -g scrypt sudo npm install --unsafe-perm -g ethereumjs-testrpc cd /opt/node/lib/node_modules/ethereumjs-testrpc/node_modules/scrypt sudo ln -s /opt/node/lib/node_modules/scrypt/build

Testing the Installation

Execute this command:

testrpc

You see two lists of addresses, and then the message "Listening on localhost:8545", as shown below.

Leave this window open and running.

Saving a Screen Image

Make sure you can see the message "Listening on localhost:8545", as shown above.

Capture a full-screen image.

YOU MUST SUBMIT A FULL-SCREEN IMAGE FOR FULL CREDIT!

Save the image with the filename "YOUR NAME Proj 12a", replacing "YOUR NAME" with your real name.

Task 4: Deploying the Contract

You have one Terminal window running testrpc. Leave that window alone.

Open a second Terminal window and execute this command:

node

This starts node.js and shows a > prompt. This is an interactive console to run JavaScript commands.

At the > prompt, execute these commands to connect the web3 library to our testrpc Ethereum node:

var Web3 = require('web3'); var web3 = new Web3(new Web3.providers.HttpProvider("http://localhost:8545"));

These commands have no output, so Node replies with "undefined", as shown below.

Making a Contract ABI

The Contract is in binary bytecode, but we need to interact with it via JavaScript. To do that, we need an ABI (Application Binary Interface).

We'll use an online Solidity compiler named "remix" to do that.

In a Web browser, open:

https://remix.ethereum.org/

The online compiler opens, showing sample code titled "ballot.sol", as shown below.

At the top left, click the first icon, which shows a white plus sign in a black circle.

A new pane opens, titled "Untitled.sol". Paste in this code, as shown below.

pragma solidity ^0.4.0; contract IdentityFunction { function identity (uint256 input) constant returns (uint256); }

On the right side of the compiler page, on the Contract tab, at the bottom, click the "Contract details (bytecode, interface etc.)" link.

JavaScript code appears in the Interface field. Highlight this code and copy it, as shown below.

In your Terminal window, at the > prompt, type this:

var abi =

Then paste in the JavaScript code you copied, and press Enter. The reply is "undefined" again, as shown below.

We have now stored the JavaScript in a variable named "abi".

The next step is to create an "Identity" object from that JavaScript code.

In your Terminal window, at the > prompt, type this:

var Identity = web3.eth.contract(abi);

Once again, the reply is "undefined".

Next we need to insert the bytecode we created earlier in this project.

In your Terminal window, at the > prompt, paste in this long line of text:

var bin = '60606040523415600b57fe5b5b608e8061001a6000396000f300606060405263ffffffff7c0100000000000000000000000000000000000000000000000000000000600035041663ac37eebb81146039575bfe5b3415604057fe5b6049600435605b565b60408051918252519081900360200190f35b805b9190505600a165627a7a72305820f7b2ec8f7a81287fa09c3bf1cdf6590ffd9ff4548907f8ab36a15aa131f1922f0029';

Once again, the reply is "undefined", as shown below.

Specifying the Sender's Address

We need to specify which account is sending the transaction that deploys the contract on the blockchain. We'll use the first account, which is called the "coinbase".

In your Terminal window, at the > prompt, type this:

var account = web3.eth.coinbase;

Once again, the reply is "undefined".