Oracle integration (Chainlink) in Blockchain / Solidity - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the Chainlink client interface.

Blockchain / Solidity

import [1] from '@chainlink/contracts/src/v0.8/ChainlinkClient.sol';

Drag options to blanks, or click blank then click option'

AChainlinkOracle

BChainlinkClient

COracleClient

DChainlinkInterface

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect interface names like ChainlinkOracle or OracleClient.

Misspelling the import path or interface name.

The correct import is ChainlinkClient, which provides the functions to interact with Chainlink oracles.

2fill in blank

medium

Complete the code to set the Chainlink oracle address in the constructor.

Blockchain / Solidity

constructor() {
    setChainlinkOracle([1]);
}

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A0x0000000000000000000000000000000000000000

Bmsg.sender

Caddress(0)

DoracleAddress

Attempts:

3 left

💡 Hint

Common Mistakes

Passing zero address or msg.sender instead of the oracle address variable.

Forgetting to set the oracle address.

You need to pass the actual oracle address variable, usually named oracleAddress, to the setChainlinkOracle function.

3fill in blank

hard

Fix the error in the request function to correctly build the Chainlink request.

Blockchain / Solidity

function requestData() public returns (bytes32 requestId) {
    Chainlink.Request memory req = buildChainlinkRequest([1], address(this), this.fulfill.selector);
    return sendChainlinkRequest(req, fee);
}

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AjobId

Boracle

Cfulfill

DrequestId

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the oracle address instead of the job ID.

Using the wrong function selector.

The buildChainlinkRequest function requires the jobId as the first argument to specify the job to run on the oracle.

4fill in blank

hard

Fill both blanks to add a URL and a path to the Chainlink request.

Blockchain / Solidity

req.add([1], [2]);

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A"get"

B"https://api.example.com/data"

C"path"

D"data,results,0,value"

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the key and value arguments.

Using 'path' instead of 'get' for the first argument.

To request data, you add the 'get' key with the URL as value to the request.

5fill in blank

hard

Fill all three blanks to add the path and multiply the result in the Chainlink request.

Blockchain / Solidity

req.add([1], [2]);
req.addInt([3], 100);

Drag options to blanks, or click blank then click option'

A"path"

B"data,results,0,value"

C"times"

D"multiply"

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect keys like 'multiply' instead of 'times'.

Mixing up the order of arguments.

You add the 'path' key with the JSON path string, then add an integer 'times' to multiply the result.

Practice

1. What is the main purpose of using Chainlink oracles in smart contracts?

easy

A. To encrypt data stored on the blockchain

B. To fetch real-world data securely into the blockchain

C. To create new tokens automatically

D. To speed up transaction processing on the blockchain

Solution

1. Step 1: Understand what oracles do

   Oracles connect smart contracts to external data sources outside the blockchain.

2. Step 2: Identify the main use of Chainlink oracles

   Chainlink oracles securely fetch real-world data like prices or weather into smart contracts.

3. Final Answer:

   To fetch real-world data securely into the blockchain -> Option B

4. Quick Check:

   Oracle purpose = fetch external data [OK]

Hint: Oracles bring outside data inside smart contracts [OK]

Common Mistakes:

• Thinking oracles speed up blockchain transactions
• Confusing oracles with token creation
• Assuming oracles encrypt blockchain data

2. Which of the following is the correct way to declare a Chainlink request in Solidity?

easy

A. Chainlink.Request memory req = buildChainlinkRequest(jobId, address(this), this.fulfill.selector);

B. Chainlink.Request req = new Chainlink.Request(jobId, address(this), fulfill);

C. Request memory req = Chainlink.buildRequest(jobId, this, fulfill);

D. ChainlinkRequest req = buildRequest(jobId, this, fulfill.selector);

Solution

1. Step 1: Recall Chainlink request syntax

   The correct syntax uses Chainlink.Request memory and buildChainlinkRequest function.

2. Step 2: Match the correct parameters

   Parameters are jobId, contract address (address(this)), and fulfill function selector (this.fulfill.selector).

3. Final Answer:

   Chainlink.Request memory req = buildChainlinkRequest(jobId, address(this), this.fulfill.selector); -> Option A

4. Quick Check:

   Correct request syntax = Chainlink.Request memory req = buildChainlinkRequest(jobId, address(this), this.fulfill.selector); [OK]

Hint: Use buildChainlinkRequest with memory and fulfill.selector [OK]

Common Mistakes:

• Omitting 'memory' keyword
• Using 'new' keyword incorrectly
• Wrong function selector syntax

3. Given this Solidity snippet, what will be the value of data after fulfillment?

uint256 public data;

function fulfill(bytes32 _requestId, uint256 _value) public recordChainlinkFulfillment(_requestId) {
    data = _value;
}

// Assume fulfill is called with _value = 42

medium

A. 0

B. RequestId bytes32 value

C. Compilation error

D. 42

Solution

1. Step 1: Understand fulfill function behavior

   The fulfill function sets the contract's data variable to the passed _value.

2. Step 2: Apply given input value

   Since fulfill is called with _value = 42, data becomes 42.

3. Final Answer:

   42 -> Option D

4. Quick Check:

   fulfill sets data = _value = 42 [OK]

Hint: fulfill sets data to passed _value parameter [OK]

Common Mistakes:

• Confusing _requestId with _value
• Assuming data stays zero
• Thinking function causes error

4. Identify the error in this Chainlink oracle request code snippet:

Chainlink.Request memory req = buildChainlinkRequest(jobId, address(this), this.fulfill.selector);
req.add("get", "https://api.example.com/data");
req.add("path", "price");
sendChainlinkRequest(req, fee);

medium

A. Missing LINK token approval before sending request

B. Incorrect function name: should be sendChainlinkRequestTo

C. Missing import for Chainlink library

D. Using 'add' instead of 'addString' for parameters

Solution

1. Step 1: Review Chainlink request sending requirements

   Before sending a request, the contract must have LINK tokens approved to pay the oracle fee.

2. Step 2: Check code for LINK approval

   The snippet does not show LINK token approval, which is required to avoid failure.

3. Final Answer:

   Missing LINK token approval before sending request -> Option A

4. Quick Check:

   LINK approval needed before sendChainlinkRequest [OK]

Hint: Always approve LINK tokens before sending requests [OK]

Common Mistakes:

• Assuming sendChainlinkRequestTo is correct function
• Confusing add and addString methods
• Ignoring LINK token approval step

5. You want to fetch the current ETH/USD price using Chainlink in your smart contract. Which steps must you combine to do this correctly?

hard

A. Use Chainlink request but omit fulfill function to save gas

B. Directly call the price feed contract without Chainlink oracles

C. Build a Chainlink request with jobId and URL, send request with fee, implement fulfill to store price

D. Send request without specifying jobId and rely on default oracle

Solution

1. Step 1: Build and send Chainlink request

   Create a request specifying jobId and data source URL, then send it with the required fee.

2. Step 2: Implement fulfill function

   Define fulfill to receive the oracle response and store the ETH/USD price in your contract.

3. Final Answer:

   Build a Chainlink request with jobId and URL, send request with fee, implement fulfill to store price -> Option C

4. Quick Check:

   Request + fee + fulfill = correct Chainlink usage [OK]

Hint: Request data, pay fee, handle response in fulfill [OK]

Common Mistakes:

• Skipping fulfill function implementation
• Not specifying jobId in request
• Assuming default oracle without jobId