I have an apply function that listeners for transfers to my contract from eosio.token. On notification of a transfer, a function (buy) is called within the contract. How do I ensure that this "buy" function cannot be called manually, by faking the transfer strut? I am concerned it is possible to supply a false ".from=eosio.token", when no tokens were actually transferred.
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1it's easy, don't add the buy to your abi, or don't add the buy to your EOSIO_ABI MACRO – Jimmy Guo Jul 31 '18 at 11:38
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I suspected as much. This means the action listener does not require the abi then. Thanks. – Phil Jul 31 '18 at 12:27
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There are two ways that you can prevent this:
- You remove the
buyfunction from the ABI, it can therefore never be called manually, but only through another function that is part of the ABI. - You restrict access to the
buyfunction to only be accessible by the contract itself, usingrequire_auth(_self).
Ideally do both, as you can never be too safe...
answered Aug 24 '18 at 8:00
The problem isn't the "buy" (you can just leave that out of the ABI), it is calling "transfer" directly - not by way of eosio.token. The "transfer" function must be part of the the ABI macro or it won't accept require_recipient calls from eosio.token - I just verified this to be sure.
So then the question I believe you are asking is how to I check that the require_recipient carbon copy actually came from eosio.token. I believe the answer is to check as follows:
require_auth(from);
require_auth2(N(eosio.token), N(eosio.code));
Also some discussion of this here worth reading:
