hacker-proof-practices.md

Hacker proof practices

State Changes

Contract state modifying statements

• Setting the value in storage variable
• Emitting of events from the function
• Creating a new contract instance
• Sending Ethers
• Using low level calls OR EVM assembly
• Using selfdestruct
• Calling functions that modify the state with any of the above

View (Hacker proof practices)

View statements e.g. function getSomethingFixed() public view returns (uint)

• Allowed to read the
• NOT allowed to use any state change statement

Pure (Hacker proof practices)

Pure statements e.g. function returnConstantFixed() public pure returns (uint)

• NOT allowed to read the storage
• NOT allowed to use any state change statement

Examples of good and bad coding practices

GET function

Bad function getSomething() public returns(uint) { someValue = 10 // Shouldn't change the state of storage in GET function return someValue; }

Good function getSomethingFixed() public view returns(uint) { someValue = 10 // With view modifier, a state change in the function will cause compilation error, forcing developer to fix the error return someValue; }

RETURN a constant

Bad function returnConstant() public returns(uint) { return someValue + 100 // This is not a constant }

Good function returnConstantFixed() public pure returns(uint) { return someValue + 100 // With pure modifier, a state change in the function will cause compilation error, forcing developer to fix the error

return 100 // This will return constant }