Tuesday, June 27, 2017

Ethereum Dev Chain - Private Chain

To develop and test an Ethereum smart contract we need a test network. The easiest way is go get spin off our own test chain with sufficient amount ethers. Below are the steps for spinning a development chain.

First download the latest Geth from the below URL

As I am using a windows machine, I downloaded the windows version. Install the Geth on your machine as per the installation guide.

Create a folder called DevChain where you can keep the chain data.

After that let’s create an account using command prompt. Specify the password when prompted.

Now create a genesis file to define the genesis block, which is the start of the block chain. Here is the genesis file (“genesis_dev.json”) I am using. Replace the account number with number you got in the previous step.

  "nonce": "0x0000000000000042",
  "difficulty": "0x200",
  "config": {
    "chainId": 15,
    "homesteadBlock": 0,
    "eip155Block": 0,
    "eip158Block": 0
  "alloc": {
    "0x0bd615694d433424c292599f080bda45b0c257fc": {
      "balance": "100000000000000000000000"
  "mixhash": "0x0000000000000000000000000000000000000000000000000000000000000000",
  "coinbase": "0x0000000000000000000000000000000000000000",
  "timestamp": "0x00",
  "parentHash": "0x0000000000000000000000000000000000000000000000000000000000000000",
  "gasLimit": "0x8000000"

Now create a batch file (“startgeth.bat”) which will initialize the network every time you run.

RD /S /Q %~dp0\devChain\geth

geth.exe --datadir=devChain init genesis_dev.json
geth.exe --mine --networkid=12345 --cache=2048 --maxpeers=0 --datadir=devChain --rpc --rpccorsdomain "*" --rpcapi "eth,web3,personal,net,miner,admin,debug" console 

Now run the batch file to initialize and start the test network.

Now our development network is ready to start deploying and testing smart contracts.

Wednesday, June 21, 2017

Hello World Ethereum Solidity Smart Contract

As we typically start every programming language with “Hello, World”, let start our first Ethereum Dapp with the same customary Hello World appp.

Ethereum uses Solidity to create smart contracts. As per definition “Solidity is a contract-oriented, high-level language whose syntax is similar to that of JavaScript and it is designed to target the Ethereum Virtual Machine (EVM)”

Here is our first Hello World smart contract
pragma solidity ^0.4.11;

contract FirstContract {

    function Greet() public constant returns (string) {
        return "Hello, World";

We can execute our very first contract using web based Remix Solidity IDE. Go to the below URL

Delete the default contract that comes with Remix. Create a new contract and write our first contract. Your browser should look like this:

Now click on the “Create” button. Remix will compile and deploy the contract. It will also shows you the output of our contract, which is “Hello, World” as shown below:

So we complete our traditional Hello World app using the browser based Remix Solidity IDE
Remis IDE is good for quick prototyping. If you need to build smart contracts and Dapps, you need the following tools. Please see my other blogs on this:

  • Visual Studio Code for compiling Contracts
  • Deploying and transacting with contracts using JavaScript Console
  • Development Test Chain during development phase
  • Rinkeby Test Chain for full node testing