TSCD-021.md

Title

SmartPy - inadvertent meta-programmation with control statements

Description

Control statements in SmartPy may inadvertent lead to a wrong meta-programmation. See code example below

Remediation

It is recommended to carefully review SmartPy code containing control statements and to implement appropriate test cases to cover expected working of control statements.

References

Samples/Test cases

Code example for an sp.if control statement written in SmartPy. Can also be viewed in SmartPy IDE.

# Store Value - Example for illustrative purposes only.

import smartpy as sp

class StoreValue(sp.Contract):
    def __init__(self, value):
        self.init(storedValue = value, magic_one = True)

    @sp.entry_point
    def set(self):
        magic_data = 0
        sp.if self.data.magic_one:
            magic_data = 1
        sp.else:
            magic_data = 2
        self.data.storedValue = magic_data

if "templates" not in __name__:
    @sp.add_test(name = "StoreValue")
    def test():
        c1 = StoreValue(12)
        scenario = sp.test_scenario()
        scenario.h1("Store Value")
        scenario += c1
        scenario = c1.set()
        
    sp.add_compilation_target("storeValue", StoreValue(12))

Solution 1 with direct modification. See directly in SmartPy IDE.

# Store Value - Example for illustrative purposes only.

import smartpy as sp

class StoreValue(sp.Contract):
    def __init__(self, value):
        self.init(storedValue = value, magic_one = True)

    @sp.entry_point
    def set(self):
        sp.if self.data.magic_one:
            self.data.storedValue = 1
        sp.else:
            self.data.storedValue = 2

if "templates" not in __name__:
    @sp.add_test(name = "StoreValue")
    def test():
        c1 = StoreValue(12)
        scenario = sp.test_scenario()
        scenario.h1("Store Value")
        scenario += c1
        scenario = c1.set()
        
    sp.add_compilation_target("storeValue", StoreValue(12))

Solution 2 using locals. See directly in SmartPy IDE.

# Store Value - Example for illustrative purposes only.

import smartpy as sp

class StoreValue(sp.Contract):
    def __init__(self, value):
        self.init(storedValue = value, magic_one = True)

    @sp.entry_point
    def set(self):
        storedValue = sp.local("storedValue", self.data.storedValue)
        sp.if self.data.magic_one:
            storedValue.value = 1
        sp.else:
            storedValue.value = 2
        self.data.storedValue = storedValue.value

if "templates" not in __name__:
    @sp.add_test(name = "StoreValue")
    def test():
        c1 = StoreValue(12)
        scenario = sp.test_scenario()
        scenario.h1("Store Value")
        scenario += c1
        scenario = c1.set()

    sp.add_compilation_target("storeValue", StoreValue(12))