This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
I only read the magic cookie before opening the file to find out the file is correct or not.
Checking the file corruption is beyond the scope (if your instruction didn't require you to do so) and I think you'll not get an extra point if you do the things that didn't required by the instruction.