msg.sender functionality

[drinkcoffee]

Ethereum contracts allow allow the caller to be determined by looking at msg.sender. This can be used to check that a contract is being called by a specific other contract. This functionality could be emulated in the GPACT system by having a function that returns the blockchain id and address of the contract that called the current contract.

The Cross-Blockchain Control contract could have functions to return these values. The contract could look at the call graph to determine these values, plus to the entry point contract for this blockchain.

[drinkcoffee]

A function has been added to the Crosschain Control Contract to allow for this functionality.

function whoCalledMe() external view override returns (uint256 targetBlockchainId, address targetContract)
in https://github.com/ConsenSys/gpact/blob/master/contracts/solidity/crossblockchaincontrol/src/main/solidity/CrosschainControl.sol
can be used to determine which blockchain and contract was the entry point at the root or segment above the active segment.