How to do something when your contract is an action notification recipient (like when it receives funds)?

Question

The EOSIO_ABI macro seems to only forward actions meant for our contract. How do you also listen to all other contract actions (like the very common transfer action for the account "eosio.token")?

I tried not using the EOSIO_ABI macro and just use the C code, but then the .abi generation doesn't work anymore. So what's the best implementation to listen to all actions for all contracts while still being able to use the eosio toolset (which includes .abi creation)?

EDIT: I just talked to Daniel Larimer himself on Telegram and adding a better way to handle actions for other contracts is planned after june. Right now apparently it can only be done by sacrificing auto generation for .abi files with the eosiocpp toolset.

Answer 1

Extend EOSIO_ABI macro to handle eosio.token transfer notification. Please pay attention to if statements:

if( code == self || **code == N(eosio.token)** || action == N(onerror) )  
DO NOT USE THIS CODE ABOVE ANYMORE, OR YOU WILL BE ATTACKED! 

if( ((code == self  && action != N(transfer) ) || (code == N(eosio.token) && action == N(transfer)) || action == N(onerror)) )

// extend from EOSIO_ABI
#define EOSIO_ABI_EX( TYPE, MEMBERS ) \
extern "C" { \
   void apply( uint64_t receiver, uint64_t code, uint64_t action ) { \
      auto self = receiver; \
      if( action == N(onerror)) { \
         /* onerror is only valid if it is for the "eosio" code account and authorized by "eosio"'s "active permission */ \
         eosio_assert(code == N(eosio), "onerror action's are only valid from the \"eosio\" system account"); \
      } \
      if( ((code == self && action != N(transfer)) || (code == N(eosio.token) && action == N(transfer)) || action == N(onerror)) ) { \
         TYPE thiscontract( self ); \
         switch( action ) { \
            EOSIO_API( TYPE, MEMBERS ) \
         } \
         /* does not allow destructor of thiscontract to run: eosio_exit(0); */ \
      } \
   } \
}

EOSIO_ABI_EX(eosio::charity, (hi)(transfer))

Answer 2

The solution is to redefine EOSIO_ABI macro. @ofo's solution is correct for the code generation part but to make auto abi generation work EOSIO_ABI macro has to be used. To do this you first undefine macro and than define it again:

#undef EOSIO_ABI

#define EOSIO_ABI(TYPE, MEMBERS) \ ....