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update sip-002 with tx-sender/contract-caller

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Aaron Blankstein
2019-07-29 12:58:42 -05:00
parent 108f339ef6
commit 3ccd3f1bfc
1 changed files with 15 additions and 17 deletions
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32
sip/sip-002-smart-contract-language.md
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@@ -149,30 +149,28 @@ smart contract transaction was signed by a particular
_principal_. Principals are a specific type in the smart contracting
language which represent a spending entity (roughly equivalent to a
Stacks address). The signature itself is not checked by the smart
contract, but by the VM. A smart contract function can use globally
defined variables to obtain the current principal:
contract, but by the VM. A smart contract function can use a globally
defined variable to obtain the current principal:
```scheme
tx-origin
tx-sender
```
The `tx-origin` variable does not change during inter-contract
The `tx-sender` variable does not change during inter-contract
calls. This means that if a transaction invokes a function in a given
smart contract, that function is able to make calls into other smart
contracts without that variable changing. This enables a wide variety
of applications, but it comes with some dangers for users of smart
contracts. However, as mentioned before, the static analysis
guarantees of our smart contracting language allow clients to know a
priori which functions a given smart contract will ever call. We plan
to include first-class support for including post-conditions on
transactions that ensure balances are not unintentionally modified for
users. The `tx-sender` variable _does_ change during inter-contract
calls, and will be either the contract principal that called the current
function or, if in the initial executing contract, it will be equal
to the `tx-origin`.
priori which functions a given smart contract will ever call.
Assets in the smart contracting language and blockchain will be
Another global variable, `contract-caller`, _does_ change during
inter-contract calls. In particular, `contract-caller` is the contract
principal corresponding to the most recent invocation of `contract-call!`.
In the case of a "top-level" invocation, this variable is equal to `tx-sender`.
Assets in the smart contracting language and blockchain are
"owned" by objects of the principal type, meaning that any object of
the principal type may own an asset. For the case of public-key hash
and multi-signature Stacks addresses, a given principal can operate on
@@ -189,11 +187,11 @@ contracts may use the special function:
(as-contract (...))
```
This function will execute the closure (passed as an argument) with the
`tx-origin` set to the _contract's_ principal, rather than the current
sender. It returns the return value of the provided closure. A smart
contract may use the special variable `contract-principal` to refer to
its own principal.
This function will execute the closure (passed as an argument) with
the `tx-sender` and `contract-caller` set to the _contract's_
principal, rather than the current sender. It returns the return value
of the provided closure. A smart contract may use the special variable
`contract-principal` to refer to its own principal.
For example, a smart contract that implements something like a "token
faucet" could be implemented as so: