Ethereum Cookbook

How to do it...

1. There are multiple ways a contract can interact with other contracts. Making validations around these interactions cannot be trusted, and the destination contract can manipulate them:

require(<external_contract_call>);

2. It is recommended not to depend on untrusted third-party contracts for validations. The external call can make the contract useless.

3. A place where this can be easily overlooked is while transferring Ether. If the destination address is an externally owned account, then the transfer will be successful. If it is a contract address, then the transfer will call the fallback function of that contract and execute the code written inside it.

4. Write a fallback function that always cancels the transaction. This ...