Can not unpack data from received eosio.token::transfer action

Question

v1.0.6

I am trying to make my contract react to the token transfer. The code compiles fine, but I get the error when I do

>cleos set contract accountsale . accountsale.wast accountsale.abi
Reading WAST/WASM from accountsale.wast...
Assembling WASM...
Publishing contract...
1648512ms thread-0   main.cpp:2712                 main                 
] Failed with error: Assert Exception (10)

nodeos log:

1648511ms thread-0   http_plugin.cpp:405           handle_exception     
] FC Exception encountered while processing chain.push_transaction
1648511ms thread-0   http_plugin.cpp:406           handle_exception     
] Exception Details: 10 assert_exception: Assert Exception
!"unresolvable": env.free
{"module":"env","export":"free"}
thread-0  wasm_interface.hpp:41 resolve

{"mod_name":"env","export_name":"free"}
thread-0  wasm_interface.hpp:43 resolve

{"_pending_console_output.str()":""}
thread-0  apply_context.cpp:62 exec_one

accountsale.abi

{
  "____comment": "This file was generated by eosio-abigen. DO NOT EDIT - 2018-06-24T18:15:05",
  "version": "eosio::abi/1.0",
  "types": [],
  "structs": [{
      "name": "hi",
      "base": "",
      "fields": [{
          "name": "username",
          "type": "name"
        }
      ]
    }
  ],
  "actions": [{
      "name": "hi",
      "type": "hi",
      "ricardian_contract": ""
    }
  ],
  "tables": [],
  "ricardian_clauses": [],
  "error_messages": [],
  "abi_extensions": []
}

accountsale.cpp

#include <eosiolib/eosio.hpp>
#include <eosiolib/asset.hpp>
#include <eosiolib/types.hpp>
#include <eosiolib/currency.hpp>

#include <math.h>
#include <eosiolib/dispatcher.hpp>

using namespace eosio;

class accountsale : eosio::contract {
  public:
      using contract::contract;

      accountsale(account_name self_account_name):contract(self_account_name){
      }

      /// @abi action
      void hi(account_name username){
        print( "Selling account ",name{username});  
      }

      void on(const currency::transfer& t){
         print("on\n");
      }

      void apply( account_name contract, account_name act ){
         print( "apply to contract ",name{contract}," act ",name{act}," \n");   
         switch(act){
            case N(transfer):
               print( " action transfer");
               on(unpack_action_data<currency::transfer>());
               break;
            case N(sellaccount):
               print( " call sellaccount");
               break;
            default:
            return;
         };
         if( act == N(transfer) ) {

            return;
         }
      }
};

// add extern C api?
extern "C" {
   void apply( uint64_t receiver, uint64_t code, uint64_t action ) {
      accountsale  as( receiver );
      as.apply( code, action );
      eosio_exit(0);
   }
}

Answer 1

Please take a look at MonsterEOS.io contract, I use an extended macro to support the token::transfer detection. This is the function that listens for the transfer action: https://github.com/leordev/monstereos/blob/master/contracts/pet/pet.cpp#L197-L234

The above code just add funds to an accounts table with the deposited amount.

This is the ABI extension that you need to add to your code: https://github.com/leordev/monstereos/blob/master/contracts/pet/pet.cpp#L308-L347 - You will need to keep alternating by commenting/uncommenting this macro if you want to generate ABI with eosiocpp -g