Developers need to understand the difference between tx.origin
and msg.sender
in Solidity. These two global variables often need clarification with each other despite their fundamental differences. While they may appear similar at first glance, tx.origin
and msg.sender
represent distinct addresses in the context of a transaction. In this blog post, we will delve deeper into the meanings of each of these variables.
What is tx.origin
?
In Solidity, tx.origin
identifies the original sender of a transaction. It points to the external account initiating the transaction and remains constant throughout subsequent smart contract interactions (full call chain).
When a transaction is initiated through the MetaMask wallet, the address of the user's MetaMask wallet is stored in tx.origin
. This address remains the same, even if the transaction passes through multiple contracts. The consistency of this address is essential for tracing the initial sender of the transaction.
What is msg.sender
?
In smart contract development, msg.sender
identifies the sender of the current call. This variable is dynamic and can change throughout the transaction process.
When a transaction moves through several smart contracts, the msg.sender
value changes to indicate the most recent contract address in the call chain. For example, if Contract A calls Contract B, then the msg.sender
value within Contract B will be recognized as Contract A.
Coding it up
To demonstrate how the tx.origin
and msg.sender
change between smart contract calls, we will create an EntryContract
smart contract that references the UnderlyingContract
contract.
Let's add a printTxOriginAndMsgSender
function that prints each address.
Here we have the Entry
smart contract:
contract EntryContract {
IUnderlyingContract private underlyingContract;
constructor(IUnderlyingContract _underlyingContract) {
underlyingContract = _underlyingContract;
}
function printTxOriginAndMsgSender() public view {
console.log("tx.origin", tx.origin);
console.log("msg.sender", msg.sender);
}
function callUnderlyingContract() external {
underlyingContract.printTxOriginAndMsgSender();
}
}
Now let's define the UnderlyingContract
and it's interface:
interface IUnderlyingContract {
function printTxOriginAndMsgSender() external ;
}
contract UnderlyingContract is IUnderlyingContract {
function printTxOriginAndMsgSender() external view {
console.log("tx.origin", tx.origin);
console.log("msg.sender", msg.sender);
}
}
To execute the test, we must first deploy the UnderlyingContract
and use its address when deploying the EntryContract
.
When we call the printTxOriginAndMsgSender
function of the EntryContract
contract, we see that both addresses are the same.
Let's call the callUnderlyingContract
function on the EntryContract
contract. We can see that tx.origin
and msg.sender
are different now. tx.origin
is the original caller address and msg.sender
is the EntryContract
smart contract address.
TL;DR
In Solidity, tx.origin
and msg.sender
are two variables that serve different but crucial purposes. tx.origin
always refers to the address that initially initiated the transaction and remains constant throughout the transaction chain. On the other hand, msg.sender
represents the sender of the current message or contract interaction and changes with each call. It is crucial to be cautious when using msg.sender
, as it may not always represent the initial caller of the transaction.
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