No length check on bytes and string arrays

[iamdefinitelyahuman]

Version Information

• vyper Version (output of vyper --version): 0.1.0b16
• OS: linux
• Python: 3.8

What's your issue about?

When a contract expects to receive a fixed length bytes or string array, there is no check on the length of the received data. In the following example, calling Bar.bar(Foo.address) returns b"foobar".

Contract Foo:

@public
def foo() -> bytes[6]:
    return b"foobar"

Contract Bar:

contract Foo:
    def foo() -> bytes[3]: constant

a: bytes[3]

@public
def bar(_addr: address) -> bytes[3]:
    self.a = Foo(_addr).foo()
    return self.a

This is an issue because Vyper does not allow dynamic arrays but Solidity does. If a Vyper contract is interacting with a Solidity contract that returns bytes or string it must give an upper bound on the expected bytes length.

How can it be fixed?

Check the length of the returned data when receiving a bytes or string array. If the length exceeds the given upper bound, truncate it.

[iamdefinitelyahuman]

Possibly related to #1602