Vaccine-Registration

Command Line Development Management Tools for creating a DAPP project:

• Truffle
• Embark
• Dapple

Browser based IDE to get instant feedback for solidity code:

• ReMix
• EthFiddle

Wallet clients to connect a ethereum wallet

• Metamask
• MyEtherWallet

Network

The smart contracts are deployed on the ethereum network on the EVM. But any transaction executed on this network requires ether to be spent, hence its not advicable for development.

Some testnets are :

• Testrpc – This is a local network running on your compuetr. 10 free wallet accounts with test ether is allocated.
• Ropsten – This is a global testnet with free test ether.
• Rinkeby – Another global testnet with free ether.

Wallet

Wallets are very important part of a smart contract. It serves 2 purposes:

• It serves as client to ethereum wallet. To make a transaction on network ether has to be spent and you can authorize these payments using this.
• To communicate with a blockchain and to deploy, you need to either have a full node or a wallet client of the network. A wallet can facilitate the communication with the network.

Deployment

To deploy a contract the following steps are to be taken:

• Compile the code and get necessary bytecodes and ABIcodes
• Select a network to migrate to
• Make a deployment with a wallet address as transaction sender
• Authenticate the transaction form the wallet and pay the transaction cost.

Your contract will be deployed and will be assigned a public address which can be used to access it.

Web Interface

A web app can be used to work with the contract. A backend javascript framework, web3.js, can intract with the blockchain. It can connect to the network, identify the contract and perform transactions. There are two kinds of transaction operation on a contract:

1.Call

A call is a local invocation of a contract function that does not broadcast or publish anything on the blockchain. It is a read-only operation and will not consume any Ether. It simulates what would happen in a transaction, but discards all the state changes when it is done. It is synchronous and the return value of the contract function is returned immediately.

2.Transaction

A transaction is broadcasted to the network, processed by miners, and if valid, is published on the blockchain. It is a write-operation that will affect other accounts, update the state of the blockchain, and consume Ether (unless a miner accepts it with a gas price of zero). It is asynchronous, because it is possible that no miners will include the transaction in a block (for example, the gas price for the transaction may be too low). Since it is asynchronous, the immediate return value of a transaction is always the transaction's hash.

The **web3js framework **works in the following way:

• Connect to a network using ‘web3Provider’ to a localhost(local testnet) or a global network
• Create a contract instance using the ABI code and Contract address. Contract address identifies the particular contract on the network to interact with and the ABI code specifies how to access each function.
• Use the instance to call contract functions like javascript.

Steps:

Pre requistes

• Nodejs v12+
• Docker
• ganache-cli (npm i -g ganache-cli)
• truffle (npm i -g truffle)
• yarn (npm i -g yarn)

Install MetaMask

1. Go to https://metamask.io/ and install the browser plugin.

2. Setup a password and open the wallet. Select the network as ‘Rinkeby Test Network’ / ‘Ropsten Test Network’ .

3. Click on ‘CREATE ACCOUNT’ to create a new wallet account and click ‘Copy Address to clipboard’ to copy your public address for the wallet.

4. Go to https://faucet.rinkeby.io/ to get free test ether to the address. Check your account on metamask and verify the balance. You can also make use of ropsten network, there will be a faucet option available in metamask to get test ethereum.

5. Repeat steps 3 and 4 to create more accounts.

Deploying contract

1.Create .env file with the following format in the root of the cloned repo

INFURA_KEY="<paste you infura key>"
MNEMONIC="<Mnemonics>"

Please make sure that addresses generated from the mnemonics have some funds in the network you are trying to deploy also is the same mnemonics loaded in metamask for the ease of testing

2. Execute "yarn install

3. Execute "yarn compile"

4. Execute "yarn deploy:ropsten" // or rinkeby

5. Your contract will get deployed to the network

6. Open src/js/app.js file. This is the javascript file that interacts with the contract.

7. Paste your contract address replacing 'contract_address' in **“web3.eth.Contract(abi, ”)

8. Run "yarn serve" to serve the web app locally

9. Connect your metamask to the web app and interact with the Dapp