CS61065 Assignment 1- Ethereum Basics Solution

Assignment 1: Ethereum Basics
You need to submit the assignment as a group of maximum 4 members. Only one member of each group should submit the assignment.
In this assignment, you will get familiar with the basics of Ethereum. You will learn how to connect to the Ethereum main network, access test networks, manage your accounts, and execute transactions. You will also get started with Ethereum JavaScript API (web3.js) and do some basic operations in the test networks.
Submission Instructions
Submit the answers to the questions of Part A, Part B and Part C in the following Google Forms link: https://forms.gle/ejNJEPu11QvmnAtv7
Mark Distribution:
Part A
We recommend you install Geth by following the instructions on the documentation page and try it out: https://geth.ethereum.org/docs/install-and-build/installing-geth
For the rest of the assignment, create an account at https://infura.io/, and use it to connect to the goerli test network.
Infura provides you with JSON-RPC over the HTTP interface. Use JSON-RPC calls to answer the following questions in the Google form link provided above. Provide (a) the answer, (b) the JSON payload used in the JSON-RPC, and (c) the response from the RPC call for each question. [Note: Each question will need a single RPC call only].
A.1. Query the current gas price in wei. Give the answer as an integer (not in hex). Sample Answer:
I. Answer: 15877637594
II. JSON RPC payload:
{"jsonrpc":"2.0","method":"eth_gasPrice","params":
[],"id":1}
III. Response: {"jsonrpc":"2.0","id":1,"result":"0x3b26185da"}
A.2. Query the current latest block number (converted to decimal).
I. Answer, II. JSON RPC payload, III. Response
A3. Find the balance (In Integer) of the account of a given address.
0xBaF6dC2E647aeb6F510f9e318856A1BCd66C5e19 I. Answer, II. JSON RPC payload, III. Response
A.4. Query the information about a transaction requested by transaction hash “0xdcae4a84a5780f62f18a9afb07b3a7627b9a28aa128a76bfddec72de9a0c2606”. Find Out:
I. the number of transactions made by the sender prior to this one in the block. Give the answer as an integer.
II. value transferred in Wei(In Integer)
III. JSON RPC payload
IV. Response
A.5. Find the number of peers connected currently to your Geth client (in Infura).
I. Answer (Integer), II. JSON RPC payload, III. Response
A6. Query transaction receipt for the transaction with hash
“0x5d692282381c75786e5f700c297def496e8e54f0a96d5a4447035f75085933cb”.
Find out
I. the blockNumber (integer),
II. blockHash,
III. cumulativeGasUsed (integer), IV. transactionIndex (integer).
A7. Find out the number of transactions in the block with the given block: 0x1132aea
I. Answer (Integer), II. JSON RPC payload, III. Response
Part B
Use the Goerli faucet (https://goerlifaucet.com/) to obtain some Ethereum in your account.
Use web3.js to query and execute the following smart contract:
Smart Contract Address: 0xF98bFe8bf2FfFAa32652fF8823Bba6714c79eDd4
The smart contract stores your roll number corresponding to your Ethereum account address. Generate the ABI from the contract code. The code of the contract is as follows:
contract AddressRollMap {
mapping(address => string) public roll;
function update(string calldata newRoll) public
{ roll[msg.sender] = newRoll;
} function get(address addr) public view returns (string
memory)
{ return roll[addr];
} function getmine() public view returns (string memory)
{ return roll[msg.sender];
}
}
B.1. Query the roll for the address: 0x328Ff6652cc4E79f69B165fC570e3A0F468fc903
B.2. Input your own roll through the update function.
I. Submit your Ethereum account address from which you made the transaction,
II. The transaction id.
Part C: Movie Ticket Booking with Ethereum Smart Contract
Only one member from each group should submit the assignment in Moodle. Clearly mention your group details in the submission.
In this assignment, you will get familiar with Ethereum smart contracts in solidity language. You will learn how you can use blockchain to enforce certain rules in a distributed setting in order to construct applications where the users do not necessarily trust each other.
Description:
We want to develop a smart contract for Movie Ticket Booking. Using this contract the movie theater owner (seller) can sell tickets for a movie. People can purchase the movie tickets by sending transactions to the contract. You have to write an “TicketBooking” contract.

While deploying the smart contract, the owner of the contract specifies 2 parameters - the maxOccupancy (total number of tickets to sell) and the price of each ticket(in wei).
constructor(uint _quota, uint _price) {
owner = msg.sender;
numTicketsSold = 0;
quota = _quota;
price = _price;
}
function buyTicket(string memory email, uint numTickets) public
payable soldOut {
. . .
}
● It has a function modifier “soldOut”, which check if all the movie tickets are sold out.
modifier soldOut() {
require(numTicketsSold < quota, "All tickets have been
sold");
_;
}
● In the function, checks if the buyer is already bought a ticket for the movie.
○ If already bought, update the number of tickets purchased by the user and the total amount paid.
○ If not bought, add the user’s address to the “buyersPaid” list and store the user’s email address, the amount paid and the number of tickets purchased.
● If the value sent by the user is more than the total cost of the tickets, the balance should be refunded.
modifier onlyOwner() {
. .
}
function withdrawFunds() public onlyOwner {
. . .
}
function refundTicket(address buyer) public onlyOwner {
. . .
}
Additional Functions:
In addition to the function, also write the following functions to debug and test the smart contract:

Return the total amount paid by a buyer.
function kill() public onlyOwner
To kill the movie ticket booking event.
References
Solidity documentation: https://docs.soliditylang.org/en/v0.8.7/
Remix Editor: https://remix.ethereum.org/