Prevent library direct code execution

delegatecall.sol

/**

This code snippet aims to show how to prevent library methods from being executed directly.

That's achieved by baking in the address of the library before it's deployed, then comparing `address(this)` against the saved address within a modifier.

A contract/library address is deterministic, so one could inject that in: keccak256(creator_address, nonceValue).

Thanks to @pirapira, @chriseth and @arachnid for the idea.
*/

pragma solidity ^0.4.18;

library SafeDelegateCall {
  // npm packages required: web3 ethereumjs-util
  // eth.generateAddress(web3.eth.accounts[0], web3.eth.getTransactionCount(web3.eth.accounts[0])
  address public constant bakedAddr = 0x5afede1e6a7eca11000000000000000000000000;

  // 
  // This modifier prevents library functions to be called directly
  //
  modifier only_if_delegatecalled {
    require(this != bakedAddr);
    _;
  }

  function kill () only_if_delegatecalled public {
    selfdestruct(msg.sender);
  }
}

library UnsafeDelegateCall {  
  // 
  // kill() can be called both as delegatecall and directly, messing up contracts that rely on this one.
  // 
  function kill() public {
    selfdestruct(msg.sender);
  }
}


contract SafeDelegateCallTest {
  //
  // Simply put, it calls selfdestruct on SafeDelegateCallTest instances.
  //
  function kill(address from) public returns (bool){
    return from.delegatecall(bytes4(keccak256("suicide()")));
  }
    
}