Nisman Coin

Smart Contract running on the Ethereum network using Solidity.

References

• A Guide to Private Ethereum Mining with Geth (Go-Ethereum)
• Deploy your first private Ethereum smart contract using Geth and Web3.js
• Using the Compiler
• web3.eth.Contract
• SPDX License List
• Deploying Solidity Smart Contracts to Moonbeam Using Web3 and JavaScript
• Solidity by Example
• web3js-quorum
• Canceling a pending transaction
• How do I sign transactions with Web3?
• web3.eth.personal
• gas required exceeds allowance or always failing transaction
• Writing Tests in Solidity

Installation

Geth is a command-line tool written in Go for creating a node and miners on a private chain.

sudo yum -y update
sudo dnf install snapd
sudo ln -s /var/lib/snapd/snap /snap
sudo snap install geth
npm install

Genesis Block

Every chain and network has a genesis block or the first block. This block does not have any parent and is the first block of the chain. A genesis.json file is required to create this first block.

{
    "config": {
        # The Chain ID 1 represents a Homestead public network.
        # The Chain ID 2 represents Morden (not used anymore).
        # The chain ID 3 represents Ropsten.
        # The chain ID 4 represents Rinkeby.
        # Any chain ID above 4 represents a private network.
        "chainId": 152389429837498234,
        "homesteadBlock": 0,
        "eip155Block": 0,
        "eip158Block": 0
    },  
    "nonce": "0x0000000000000042",
    "timestamp": "0x0",
    "parentHash": "0x0000000000000000000000000000000000000000000000000000000000000000",
    "gasLimit": "0xffffffff",
    "difficulty": "0x200",
    "mixhash": "0x0000000000000000000000000000000000000000000000000000000000000000",
    "coinbase": "0x0000000000000000000000000000000000000000",
    "alloc": {}
}

Starting a Geth node

npm run start

The preceding command runs as a service. Additional commands can not be executed through it. To manage existing running Geth nodes, open another terminal on the same computer and type:

npm run attach

Read the genesis block

eth.getBlock(0)

Creating accounts

After connecting to a Geth node, it's sime to set up the coinbase or etherbase account. For this, a new account should be created first.

personal.newAccount()

This will return an Account ID such as:

0x2cd40613fea30b90e81980673ab1dc0f657ac88b

Creating a new account to receive transactions:

personal.newAccount()

Listing all accounts available.

eth.accounts

It will return the 2 created accounts:

["0x2cd40613fea30b90e81980673ab1dc0f657ac88b", "0x6b69c123392e0b4184e479b732b96ab9480f16a0"]

Mining new tokens

Crypto currencies and blockchains in general allow you to work with arbitrarily many accounts at the same time. However often people want to have a default/primary account (e.g. miners have a designated mining address, average users will usually use one particular account even if they have multiple one for other purposes). [...] Coinbase or etherbase (they are the same thing) is just this. However to keep it simple and less surprising, your coinbase account is actually the first account in your keystore (i.e. in theory the first account you ever created).

miner.setEtherbase(eth.accounts[0])

With the coinbase set with a valid account and Geth node up and running, now mining can get started and, since we just have one miner, all rewards will go to this miner and its coinbase account will be credited with Ethers.

eth.coinbase

To begin mining on our private blockchain, we simply need to run:

miner.start()

If you aren't sure that your node is mining, please execute eth.hashrate to check, if the return value is greater than zero, it is mining, otherwise, it is not.

miner.getHashrate()

This command will return true if there is at least 1 active miner:

eth.mining

Get the latest mined block:

eth.getBlock("latest")
eth.getBlock("latest").number

Allow the miner to run for a while and then stop the process with:

miner.stop()

Notice that you’ve been rewarded with some tokens (depending on how long you left it running) for mining new blocks, this can be verified by checking the balance.

eth.getBalance(eth.accounts[0])

geth cannot provide any information about accounts or contracts until the sync is fully complete. When your sync is fully complete, syncing will return false, like:

eth.syncing

Sending Tokens (Wei) from one account to another

By default, your accounts in Geth are "locked," which means that you can't send transactions from them. You need to unlock an account in order to send transactions from it through Geth directly or via RPC (though web3 does not support this). In order to unlock an account, you'll need to provide the password, which is used to decrypt the private key associated with your account, hence allowing you to sign transactions.

personal.unlockAccount(eth.accounts[0])

To transfer tokens, we simply use eth.sendTransaction() which accepts a bunch of parameters but most are optional and can be left out as reasonable defaults are used under the hood.

eth.sendTransaction({from: eth.accounts[0], to: eth.accounts[1], value: 1000})

At this point, the transaction has been created but has not been mined.

eth.pendingTransactions

Remember we ran miner.stop() just before creating this transaction, what happens under the hood is that this transaction is added to the mempool (queue) of transactions waiting to be added to a block by a miner, and given that we are the only miners on this network, we will have to mine this transaction ourselves

miner.start()

Give it a couple of seconds then run:

miner.stop()

You can verify that some tokens were sent to the receiving account by running:

eth.getBalance(eth.accounts[0])
eth.getBalance(eth.accounts[1])

Importing an existing Wallet

Imports the given private key into the key store, encrypting it with the passphrase.

personal.importRawKey('private-key', 'encryption-password')

Check the account has been imported:

eth.accounts[eth.accounts.length - 1]

Add some tokens to the recently added account.

miner.setEtherbase(eth.accounts[eth.accounts.length - 1])

Start mining some blocks.

miner.start()

Wait for some blocks to be added to the Blockchain and stop the worker.

miner.stop()

Fetch the balance of the new account:

eth.getBalance(eth.accounts[eth.accounts.length - 1])

Transferring Ether between accounts.

Before transfering Ether, the account must be unlocked:

personal.unlockAccount(eth.accounts[0])

Transfer Ether from the miner to the seconary account:

node run send

At this point, the transaction should be pending:

eth.pendingTransactions

Start the miner so that the transaction is processed:

miner.start()

Give it a couple of seconds then run:

miner.stop()

List the balance of all the accounts:

Balance: 0 0x3dbc3f8DF17dc60F27494b53dc91150289D9f61c 5789998386453999997000
Balance: 1 0x7950880AE32E0E1A64e42b4E9EDd43057A33f443 2000

Deploying a Smart Contract

Deploying a contract requires unlocking an account.

personal.unlockAccount(eth.accounts[0])

Compiling and deploying the contract using web3.js:

npm run deploy

At this point, the transaction has been created but has not been mined.

eth.pendingTransactions

Start the miner so that the transaction that deploys the Contract is added to the Blockchain.

miner.start()

Give it a couple of seconds then run:

miner.stop()

The address of the contract is stored in token.txt.

cat token.txt

Interacting with the Contract

Reading data does not require gas:

npm run balance

Gas Price: 1000000000
Estimated Gas: 21782
Current Killer: 0x3dbc3f8DF17dc60F27494b53dc91150289D9f61c
Contract Balance: 2000
Balance: 0 0x3dbc3f8DF17dc60F27494b53dc91150289D9f61c Kills: 0 Balance: 5789996429870997960000
Balance: 1 0x7950880AE32E0E1A64e42b4E9EDd43057A33f443 Kills: 1 Balance: 34999977320002037000

For updating the state of the Contract, an account must be unlocked:

personal.unlockAccount(eth.accounts[0])

Now, the state of the contract can be updated:

npm run update

At this point, the transaction should be pending:

eth.pendingTransactions

Start the miner so that the transaction is processed:

miner.start()

Give it a couple of seconds then run:

miner.stop()

Now check the balance again:

Gas Price: 1000000000
Estimated Gas: 21782
Current Killer: 0x7950880AE32E0E1A64e42b4E9EDd43057A33f443
Contract Balance: 0
Balance: 0 0x3dbc3f8DF17dc60F27494b53dc91150289D9f61c Kills: 1 Balance: 5789996364575997957000
Balance: 1 0x7950880AE32E0E1A64e42b4E9EDd43057A33f443 Kills: 2 Balance: 34999866742002042000

Cancelling a pending transaction

Canceling a transaction requires unlocking your private key.

personal.unlockAccount(eth.accounts[0])

Send a new transaction with the same nonce but with a higher gas price.

eth.sendTransaction({
	from: eth.coinbase,
	to: eth.coinbase,
	value: 0,
	gasPrice: 4234545335244,
	gasLimit: 44000,
	nonce: eth.pendingTransactions[0].nonce
});

Testing the Contract

Run unit tests

npm run test