Front-running awareness in Blockchain / Solidity - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to detect if a transaction is front-run by checking if the current gas price is higher than the previous one.

Blockchain / Solidity

if current_gas_price [1] previous_gas_price:
    print("Possible front-running detected")

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

A>

B<=

C==

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' causes the check to miss front-running.

Using '==' only checks equality, not increase.

The code checks if the current gas price is greater than the previous gas price, which can indicate front-running.

2fill in blank

medium

Complete the code to add a delay before sending a transaction to reduce front-running risk.

Blockchain / Solidity

import time

time.[1](5)  # wait 5 seconds before sending transaction

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

Await

Bsleep

Cdelay

Dpause

Attempts:

3 left

💡 Hint

Common Mistakes

Using non-existent functions like 'wait' or 'delay' causes errors.

Misspelling 'sleep' leads to runtime errors.

The time.sleep() function pauses the program for the given number of seconds.

3fill in blank

hard

Fix the error in the code that tries to check if a transaction nonce is less than the last confirmed nonce.

Blockchain / Solidity

if tx_nonce [1] last_confirmed_nonce:
    print("Transaction might be front-run")

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

A<

B<=

C>

D>=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>=' or '>' reverses the logic and misses front-running.

Using '<=' includes equal nonces which is not the intended check.

The code should check if the transaction nonce is less than the last confirmed nonce to detect replay or front-running.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that maps transaction hashes to their gas prices only if the gas price is higher than 100 gwei.

Blockchain / Solidity

tx_gas_prices = {tx_hash: tx[1] for tx_hash, tx in transactions.items() if tx['gas_price'] [2] 100}

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

A['gas_price']

B>

C<

D['nonce']

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong key like 'nonce' instead of 'gas_price'.

Using '<' instead of '>' reverses the filter logic.

The comprehension extracts the gas price from each transaction and includes only those with gas price greater than 100.

5fill in blank

hard

Fill both blanks to create a dictionary comprehension that maps user addresses to their transaction counts only if the count is greater than 10.

Blockchain / Solidity

user_tx_counts = {user[1]: tx_count for user, tx_count in user_transactions.items() if tx_count [2] 10}

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

A.lower()

C>

D.upper()

Attempts:

3 left

💡 Hint

Common Mistakes

Leaving the user address unchanged may cause inconsistent keys.

Using '<' instead of '>' filters the wrong transaction counts.

The comprehension converts user addresses to uppercase, keeps the transaction count as is, and filters counts greater than 10.