How to restrict function to only callable from one external contract?

Question

I have a Reputation contract which has a function foo() that sets some point.

In another contract called Market I want to use the foo() function. But I don't want any one to be able to call foo() outside Market.

the problem is I need to deploy Reputation first and make instance of it in market. I have no idea how to make modifier in Reputation to restrict foo() before deploying Market.

Answer 1

Check msg.sender and reject unacceptable actors.

In Market to protect foo() - make sure msg.sender == reputation.

Also in Market - a function to update reputation when you know the address.

Here's a little scribble to give you some ideas.

contract Market {

  address reputation;

  modifier onlyReputation {
    require(msg.sender == reputation, "403");
    _;
  }

  constructor(address reputation_) {
    reputation = reputation_;
  }

  function foo() public onlyReputation {
    // carry on
  }
}

That is the general idea. You can add functions to edit/update the acceptable reputation from time to time. You would want another variable, e.g. address owner to specify who is allowed to do that.

Finally, if you want to coordinate the deployment and there is one Market for each Reputation, use the constructors to configure everything on the fly.

In Reputation:

Market market;);

constructor () {
   market = new Market();
}

That way it will create one and know where it is. In Market, recognize "the creator" as the one to trust.

address reputation;

constructor () {
  reputation = msg.sender;
}

Hope it helps.