What other constants depend on the current call like msg.sender?

I recently noticed that msg.sender isn't always the original caller's address (see here). It's the address of the current call. So if foo() calls bar(), then msg.sender in bar() will be the address of the contract containing foo().

My questions are:

Are there any other constants that depend on the current call? Full list: https://solidity.readthedocs.io/en/latest/units-and-global-variables.html#special-variables-and-functions

What's the best way to get the original sender's address?

edited Jan 24 at 19:10

Rob Hitchens

28.8k74482

asked Jan 24 at 17:53

Justin Harris

1266

add a comment |

My questions are:

Are there any other constants that depend on the current call? Full list: https://solidity.readthedocs.io/en/latest/units-and-global-variables.html#special-variables-and-functions

What's the best way to get the original sender's address?

edited Jan 24 at 19:10

Rob Hitchens

28.8k74482

asked Jan 24 at 17:53

Justin Harris

1266

add a comment |

My questions are:

Are there any other constants that depend on the current call? Full list: https://solidity.readthedocs.io/en/latest/units-and-global-variables.html#special-variables-and-functions

What's the best way to get the original sender's address?

edited Jan 24 at 19:10

Rob Hitchens

28.8k74482

asked Jan 24 at 17:53

Justin Harris

1266

My questions are:

Are there any other constants that depend on the current call? Full list: https://solidity.readthedocs.io/en/latest/units-and-global-variables.html#special-variables-and-functions

What's the best way to get the original sender's address?

contract-design contract-invocation constant

edited Jan 24 at 19:10

Rob Hitchens

28.8k74482

asked Jan 24 at 17:53

Justin Harris

1266

edited Jan 24 at 19:10

Rob Hitchens

28.8k74482

asked Jan 24 at 17:53

Justin Harris

1266

edited Jan 24 at 19:10

Rob Hitchens

28.8k74482

edited Jan 24 at 19:10

Rob Hitchens

28.8k74482

edited Jan 24 at 19:10

Rob Hitchens

28.8k74482

asked Jan 24 at 17:53

Justin Harris

1266

asked Jan 24 at 17:53

Justin Harris

1266

asked Jan 24 at 17:53

Justin Harris

1266

add a comment |

3 Answers
3

active

oldest

votes

msg.data, msg.sender, msg.sig, and msg.value will depend on the current call.

tx.origin is the original sender of the transaction (EOA = Externally Owned Account).

Note that the msg.* variables are only changed if you have

 this.fn()

 someOtherContractRef.fn()

Internal calls within the contract (without this.) will not change msg.* variables.

edited Jan 24 at 19:10

answered Jan 24 at 18:49

ivicaa

5,4981938

add a comment |

Adding to @ivicaa's and @Lauri's answer.

What's the best way to get the original sender's address?

tx.origin is a security concern and not recommended. Relying on it also ensures that contracts cannot be clients of your contract since a contract can never be the tx.origin. This limitation seriously constrains your dapp since it includes multi-signature wallet contracts and since there are usually desirable use-cases where the "user" could be another contract.

It's not a simple issue. This thread may shed some light on the considerations: https://github.com/ethereum/solidity/issues/683

tx.origin is almost never useful. This is the most subjective point, but I have yet to come across a use of tx.origin that seemed legitimate to me. I welcome counter-examples, but I've written dozens or hundreds of smart contracts without needing it, and I have never heard of anyone else needing it either.

Instead, pass the msg.sender into functions that are concerned with the transaction signer. This implies that the called contract trusts the sending contract to tell the truth. The called contract should not naively listen to anything, but rather trust only whitelisted contracts that form part of your system.

function somethingOnBehalfOfSomeoneElse(address user) public onlyTrustedContracts {...

Hope it helps.

answered Jan 24 at 19:11

Rob Hitchens

28.8k74482

That's very helpful. How about doing stuff like: modifier onlyOwner() { require(msg.sender == owner || tx.origin == owner, "Sender is not the owner."); _; } ? Could that be a problem too?

– Justin Harris
Jan 28 at 16:25

My understanding is tx.origin can be overwritten by a determined adversary so I've learned to just disregard it and carry on as though it doesn't exist. I would call the example function with otherContact.somethingOnBehalfOfSomeoneElse(msg.sender) so my contract relies exclusively on values I believe are trustworthy.

– Rob Hitchens
Jan 28 at 17:00

add a comment |

All of the msg constants depend on the currenct scope (contract). Their value remains the same in the same contract (even in different functions) but if you call another contract the values change accordingly.

You can see them here in action:

pragma solidity ^0.5.0;

contract A {



    event Data(bytes a);

    event Sig(bytes4 a);

    event Val(uint a);



    function a() public payable {

        emit Data(msg.data);

        emit Sig(msg.sig);

        emit Val(msg.value);

        b();

        B b = new B();

        b.c();



    }



    function b() public payable {

        emit Data(msg.data);

        emit Sig(msg.sig);

        emit Val(msg.value);

    }

}



contract B {

    event Data(bytes a);

    event Sig(bytes4 a);

    event Val(uint a);



    function c() public payable {

        emit Data(msg.data);

        emit Sig(msg.sig);

        emit Val(msg.value);

    }

}

As for the original sender, you can simply use tx.origin. Note that this is very rarely used as using it may ruin functionality of some proxy contracts etc.

answered Jan 24 at 18:52

Lauri Peltonen

5,8232525

Thanks your answer is very good too but I accepted the other because it gave some details about the use of this.

– Justin Harris
Jan 24 at 19:06

add a comment |

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3 Answers
3

active

oldest

votes

3 Answers
3

active

oldest

votes

msg.data, msg.sender, msg.sig, and msg.value will depend on the current call.

tx.origin is the original sender of the transaction (EOA = Externally Owned Account).

Note that the msg.* variables are only changed if you have

 this.fn()

 someOtherContractRef.fn()

Internal calls within the contract (without this.) will not change msg.* variables.

edited Jan 24 at 19:10

answered Jan 24 at 18:49

ivicaa

5,4981938

add a comment |

msg.data, msg.sender, msg.sig, and msg.value will depend on the current call.

tx.origin is the original sender of the transaction (EOA = Externally Owned Account).

Note that the msg.* variables are only changed if you have

 this.fn()

 someOtherContractRef.fn()

Internal calls within the contract (without this.) will not change msg.* variables.

edited Jan 24 at 19:10

answered Jan 24 at 18:49

ivicaa

5,4981938

add a comment |

msg.data, msg.sender, msg.sig, and msg.value will depend on the current call.

tx.origin is the original sender of the transaction (EOA = Externally Owned Account).

Note that the msg.* variables are only changed if you have

 this.fn()

 someOtherContractRef.fn()

Internal calls within the contract (without this.) will not change msg.* variables.

edited Jan 24 at 19:10

answered Jan 24 at 18:49

ivicaa

5,4981938

msg.data, msg.sender, msg.sig, and msg.value will depend on the current call.

tx.origin is the original sender of the transaction (EOA = Externally Owned Account).

Note that the msg.* variables are only changed if you have

 this.fn()

 someOtherContractRef.fn()

Internal calls within the contract (without this.) will not change msg.* variables.

edited Jan 24 at 19:10

answered Jan 24 at 18:49

ivicaa

5,4981938

edited Jan 24 at 19:10

answered Jan 24 at 18:49

ivicaa

5,4981938

answered Jan 24 at 18:49

ivicaa

5,4981938

answered Jan 24 at 18:49

ivicaa

5,4981938

add a comment |

Adding to @ivicaa's and @Lauri's answer.

What's the best way to get the original sender's address?

It's not a simple issue. This thread may shed some light on the considerations: https://github.com/ethereum/solidity/issues/683

tx.origin is almost never useful. This is the most subjective point, but I have yet to come across a use of tx.origin that seemed legitimate to me. I welcome counter-examples, but I've written dozens or hundreds of smart contracts without needing it, and I have never heard of anyone else needing it either.

function somethingOnBehalfOfSomeoneElse(address user) public onlyTrustedContracts {...

Hope it helps.

answered Jan 24 at 19:11

Rob Hitchens

28.8k74482

That's very helpful. How about doing stuff like: modifier onlyOwner() { require(msg.sender == owner || tx.origin == owner, "Sender is not the owner."); _; } ? Could that be a problem too?

– Justin Harris
Jan 28 at 16:25

My understanding is tx.origin can be overwritten by a determined adversary so I've learned to just disregard it and carry on as though it doesn't exist. I would call the example function with otherContact.somethingOnBehalfOfSomeoneElse(msg.sender) so my contract relies exclusively on values I believe are trustworthy.

– Rob Hitchens
Jan 28 at 17:00

add a comment |

Adding to @ivicaa's and @Lauri's answer.

What's the best way to get the original sender's address?

It's not a simple issue. This thread may shed some light on the considerations: https://github.com/ethereum/solidity/issues/683

tx.origin is almost never useful. This is the most subjective point, but I have yet to come across a use of tx.origin that seemed legitimate to me. I welcome counter-examples, but I've written dozens or hundreds of smart contracts without needing it, and I have never heard of anyone else needing it either.

function somethingOnBehalfOfSomeoneElse(address user) public onlyTrustedContracts {...

Hope it helps.

answered Jan 24 at 19:11

Rob Hitchens

28.8k74482

That's very helpful. How about doing stuff like: modifier onlyOwner() { require(msg.sender == owner || tx.origin == owner, "Sender is not the owner."); _; } ? Could that be a problem too?

– Justin Harris
Jan 28 at 16:25

My understanding is tx.origin can be overwritten by a determined adversary so I've learned to just disregard it and carry on as though it doesn't exist. I would call the example function with otherContact.somethingOnBehalfOfSomeoneElse(msg.sender) so my contract relies exclusively on values I believe are trustworthy.

– Rob Hitchens
Jan 28 at 17:00

add a comment |

Adding to @ivicaa's and @Lauri's answer.

What's the best way to get the original sender's address?

It's not a simple issue. This thread may shed some light on the considerations: https://github.com/ethereum/solidity/issues/683

tx.origin is almost never useful. This is the most subjective point, but I have yet to come across a use of tx.origin that seemed legitimate to me. I welcome counter-examples, but I've written dozens or hundreds of smart contracts without needing it, and I have never heard of anyone else needing it either.

function somethingOnBehalfOfSomeoneElse(address user) public onlyTrustedContracts {...

Hope it helps.

answered Jan 24 at 19:11

Rob Hitchens

28.8k74482

Adding to @ivicaa's and @Lauri's answer.

What's the best way to get the original sender's address?

It's not a simple issue. This thread may shed some light on the considerations: https://github.com/ethereum/solidity/issues/683

tx.origin is almost never useful. This is the most subjective point, but I have yet to come across a use of tx.origin that seemed legitimate to me. I welcome counter-examples, but I've written dozens or hundreds of smart contracts without needing it, and I have never heard of anyone else needing it either.

function somethingOnBehalfOfSomeoneElse(address user) public onlyTrustedContracts {...

Hope it helps.

answered Jan 24 at 19:11

Rob Hitchens

28.8k74482

answered Jan 24 at 19:11

Rob Hitchens

28.8k74482

answered Jan 24 at 19:11

Rob Hitchens

28.8k74482

answered Jan 24 at 19:11

Rob Hitchens

28.8k74482

That's very helpful. How about doing stuff like: modifier onlyOwner() { require(msg.sender == owner || tx.origin == owner, "Sender is not the owner."); _; } ? Could that be a problem too?

– Justin Harris
Jan 28 at 16:25

My understanding is tx.origin can be overwritten by a determined adversary so I've learned to just disregard it and carry on as though it doesn't exist. I would call the example function with otherContact.somethingOnBehalfOfSomeoneElse(msg.sender) so my contract relies exclusively on values I believe are trustworthy.

– Rob Hitchens
Jan 28 at 17:00

add a comment |

That's very helpful. How about doing stuff like: modifier onlyOwner() { require(msg.sender == owner || tx.origin == owner, "Sender is not the owner."); _; } ? Could that be a problem too?

– Justin Harris
Jan 28 at 16:25

My understanding is tx.origin can be overwritten by a determined adversary so I've learned to just disregard it and carry on as though it doesn't exist. I would call the example function with otherContact.somethingOnBehalfOfSomeoneElse(msg.sender) so my contract relies exclusively on values I believe are trustworthy.

– Rob Hitchens
Jan 28 at 17:00

That's very helpful. How about doing stuff like:

modifier onlyOwner() {         require(msg.sender == owner || tx.origin == owner, "Sender is not the owner.");         _;     }

? Could that be a problem too?

– Justin Harris
Jan 28 at 16:25

That's very helpful. How about doing stuff like:

modifier onlyOwner() {         require(msg.sender == owner || tx.origin == owner, "Sender is not the owner.");         _;     }

? Could that be a problem too?

– Justin Harris
Jan 28 at 16:25

My understanding is tx.origin can be overwritten by a determined adversary so I've learned to just disregard it and carry on as though it doesn't exist. I would call the example function with otherContact.somethingOnBehalfOfSomeoneElse(msg.sender) so my contract relies exclusively on values I believe are trustworthy.

– Rob Hitchens
Jan 28 at 17:00

add a comment |

You can see them here in action:

pragma solidity ^0.5.0;

contract A {



    event Data(bytes a);

    event Sig(bytes4 a);

    event Val(uint a);



    function a() public payable {

        emit Data(msg.data);

        emit Sig(msg.sig);

        emit Val(msg.value);

        b();

        B b = new B();

        b.c();



    }



    function b() public payable {

        emit Data(msg.data);

        emit Sig(msg.sig);

        emit Val(msg.value);

    }

}



contract B {

    event Data(bytes a);

    event Sig(bytes4 a);

    event Val(uint a);



    function c() public payable {

        emit Data(msg.data);

        emit Sig(msg.sig);

        emit Val(msg.value);

    }

}

As for the original sender, you can simply use tx.origin. Note that this is very rarely used as using it may ruin functionality of some proxy contracts etc.

answered Jan 24 at 18:52

Lauri Peltonen

5,8232525

Thanks your answer is very good too but I accepted the other because it gave some details about the use of this.

– Justin Harris
Jan 24 at 19:06

add a comment |

You can see them here in action:

pragma solidity ^0.5.0;

contract A {



    event Data(bytes a);

    event Sig(bytes4 a);

    event Val(uint a);



    function a() public payable {

        emit Data(msg.data);

        emit Sig(msg.sig);

        emit Val(msg.value);

        b();

        B b = new B();

        b.c();



    }



    function b() public payable {

        emit Data(msg.data);

        emit Sig(msg.sig);

        emit Val(msg.value);

    }

}



contract B {

    event Data(bytes a);

    event Sig(bytes4 a);

    event Val(uint a);



    function c() public payable {

        emit Data(msg.data);

        emit Sig(msg.sig);

        emit Val(msg.value);

    }

}

As for the original sender, you can simply use tx.origin. Note that this is very rarely used as using it may ruin functionality of some proxy contracts etc.

answered Jan 24 at 18:52

Lauri Peltonen

5,8232525

Thanks your answer is very good too but I accepted the other because it gave some details about the use of this.

– Justin Harris
Jan 24 at 19:06

add a comment |

You can see them here in action:

pragma solidity ^0.5.0;

contract A {



    event Data(bytes a);

    event Sig(bytes4 a);

    event Val(uint a);



    function a() public payable {

        emit Data(msg.data);

        emit Sig(msg.sig);

        emit Val(msg.value);

        b();

        B b = new B();

        b.c();



    }



    function b() public payable {

        emit Data(msg.data);

        emit Sig(msg.sig);

        emit Val(msg.value);

    }

}



contract B {

    event Data(bytes a);

    event Sig(bytes4 a);

    event Val(uint a);



    function c() public payable {

        emit Data(msg.data);

        emit Sig(msg.sig);

        emit Val(msg.value);

    }

}

As for the original sender, you can simply use tx.origin. Note that this is very rarely used as using it may ruin functionality of some proxy contracts etc.

answered Jan 24 at 18:52

Lauri Peltonen

5,8232525

You can see them here in action:

pragma solidity ^0.5.0;

contract A {



    event Data(bytes a);

    event Sig(bytes4 a);

    event Val(uint a);



    function a() public payable {

        emit Data(msg.data);

        emit Sig(msg.sig);

        emit Val(msg.value);

        b();

        B b = new B();

        b.c();



    }



    function b() public payable {

        emit Data(msg.data);

        emit Sig(msg.sig);

        emit Val(msg.value);

    }

}



contract B {

    event Data(bytes a);

    event Sig(bytes4 a);

    event Val(uint a);



    function c() public payable {

        emit Data(msg.data);

        emit Sig(msg.sig);

        emit Val(msg.value);

    }

}

As for the original sender, you can simply use tx.origin. Note that this is very rarely used as using it may ruin functionality of some proxy contracts etc.

answered Jan 24 at 18:52

Lauri Peltonen

5,8232525

answered Jan 24 at 18:52

Lauri Peltonen

5,8232525

answered Jan 24 at 18:52

Lauri Peltonen

5,8232525

answered Jan 24 at 18:52

Lauri Peltonen

5,8232525

Thanks your answer is very good too but I accepted the other because it gave some details about the use of this.

– Justin Harris
Jan 24 at 19:06

add a comment |

Thanks your answer is very good too but I accepted the other because it gave some details about the use of this.

– Justin Harris
Jan 24 at 19:06

Thanks your answer is very good too but I accepted the other because it gave some details about the use of this.

– Justin Harris
Jan 24 at 19:06

add a comment |

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