How can I tell who has called a function / contract?

Question

I am very new to Ethereum and don't really understand the problem spec very well, so bear with me.

There is a function named GetVotesCount() in the contract MordorVote which I must limit to only being called by a 'vote master'. How can I determine who is calling a function in the contract?

Also, when I invoke a function in Embark, I get a hex string returned, but not whatever the function returns. How can I find out what a function is returning?

Answer 1

1. msg.sender will have the address of the caller. In your function you can do if (msg.sender != addressOfVoteMaster) throw;.

See also: What's the difference between 'msg.sender' and 'tx.origin'?

2. You get a hex string, which is the transaction hash. Depending on the type of function, you could make it constant to get the function's return value. See What is the difference between a transaction and a call?