[Feat] Zippers

[fubuloubu]

Add the ability to enable "Zippers" which implement pre-/post- transaction checks on the execution of certain callbacks (reminiscent of Safe's Guards)

Sketch: (update Purse.vy)

interface Zipper:
    def unzip(accessory: address, indata: Bytes[65535]): view
    def rezip(accessory: address, indata: Bytes[65535], outdata: Bytes[65535]): view


zippers: public(HashMap[bytes4, Zipper])


event ZipperUpdated:
    method: indexed(bytes4)
    old_zipper: indexed(Zipper)
    new_zipper: indexed(Zipper)

...

struct ZipperUpdate:
    method: bytes4
    zipper: Zipper


@external
# NOTE: Reentrancy guard ensures that `__default__` module calls can't call this
def update_zippers(updates: DynArray[ZipperUpdate, 100]):
    # NOTE: Can only work in a EIP-7702 context
    assert tx.origin == self and tx.origin == msg.sender, "Purse:!authorized"

    for update: ZipperUpdate in updates:
        old_zipper: Zipper = self.zippers[update.method]
        self.zippers[update.method] = update.zipper

        log ZipperUpdated(
            method=update.method,
            old_zipper=old_zipper,
            new_zipper=update.zipper,
        )

...

def __default__():
    ...  # Load accessory by `method`

    zipper: Zipper = self.zippers[method]
    if zipper.address != empty(address):
        staticcall zipper.unzip(accessory, msg.data)

    data: Bytes[65535] = ...  # Call accessory w/ `msg.data`

    if zipper.address != empty(address):
        staticcall zipper.rezip(accessory, msg.data, data)

    return data  # NOTE: Need to temporarily store return data

[fubuloubu]

Was thinking more about this, what about using a less cute system for checking access control from within an accessory?