cib eos demo: Track incoming funds

main.abi

{
    "structs": [{
        "name": "withdraw",
        "base": "",
        "fields": [
            {"name":"user", "type":"account_name"}
        ]
    },{
        "name": "balance",
        "base": "",
        "fields": [
            {"name":"funds", "type":"asset"}
        ]
    }],
    "actions": [{
        "name": "withdraw",
        "type": "withdraw"
    }],
    "tables": [{
        "name": "balance",
        "type": "balance",
        "index_type": "i64",
        "key_names": "key",
        "key_types": "i64"
    }]
}

main.cpp

// Todd Fleming 2018

#include <eosiolib/eosio.hpp>
#include <eosiolib/action.hpp>
#include <eosiolib/currency.hpp>
#include <eosiolib/multi_index.hpp>

using eosio::action;
using eosio::asset;
using eosio::currency;
using eosio::name;
using eosio::permission_level;
using eosio::print;
using eosio::require_auth;
using eosio::string_to_symbol;
using eosio::symbol_type;
using eosio::unpack_action_data;

struct balance {
    asset funds;
    uint64_t primary_key() const { return funds.symbol; }
};
using table = eosio::multi_index<N(balance), balance>;

struct withdraw {
    uint64_t user;
};

void transferAction(uint64_t self, uint64_t code) {
    eosio_assert(code == N(eosio.token), "I reject your non-eosio.token deposit");
    auto data = unpack_action_data<currency::transfer>();
    if(data.from == self || data.to != self)
        return;
    eosio_assert(data.quantity.symbol == string_to_symbol(4, "EOS"), 
        "I think you're looking for another contract");
    eosio_assert(data.quantity.is_valid(), "Are you trying to corrupt me?");
    eosio_assert(data.quantity.amount > 0, "When pigs fly");

    table balances(self, data.from);
    asset new_balance;
    auto it = balances.find(data.quantity.symbol);
    if(it != balances.end())
        balances.modify(it, data.from, [&](auto& bal){
            // Assumption: total currency issued by eosio.token will not overflow asset
            bal.funds += data.quantity;
            new_balance = bal.funds;
        });
    else
        balances.emplace(data.from, [&](auto& bal){
            bal.funds = data.quantity;
            new_balance = bal.funds;
        });

    print(name{data.from}, " deposited:       ", data.quantity, "\n");
    print(name{data.from}, " funds available: ", new_balance);
}

void withdrawAction(uint64_t self, uint64_t code) {
    if (code != self)
        return;
    auto data = unpack_action_data<withdraw>();
    require_auth(data.user);

    table balances(self, data.user);
    auto it = balances.find(string_to_symbol(4, "EOS"));
    if(it == balances.end()) {
        print(name{data.user}, " has no funds to withdraw.\n");
        print("no transfer needed.\n");
        return;
    }

    print(name{data.user}, " has ", it->funds, " available\n");
    print("returning everything");

    action{
        permission_level{self, N(active)},
        N(eosio.token),
        N(transfer),
        currency::transfer{
            .from=self, .to=data.user, .quantity=it->funds, .memo=""}
    }.send();
    balances.erase(it);
}

extern "C" void apply(uint64_t receiver, uint64_t code, uint64_t action) {
    switch(action) {
        case N(transfer): return transferAction(receiver, code);
        case N(withdraw): return withdrawAction(receiver, code);
    }
}

transaction

{
    "actions": [{
        "account": "eosio.token",
        "name": "transfer",
        "authorization": [{
            "actor": "user.a",
            "permission": "active"
        }],
        "data": {
            "from": "user.a",
            "to": "funds.holder",
            "quantity":"0.0001 EOS",
            "memo":"m"
        }
    },{
        "account": "eosio.token",
        "name": "transfer",
        "authorization": [{
            "actor": "user.a",
            "permission": "active"
        }],
        "data": {
            "from": "user.a",
            "to": "funds.holder",
            "quantity":"0.0200 EOS",
            "memo":"m"
        }
    },{
        "account": "funds.holder",
        "name": "withdraw",
        "authorization": [{
            "actor": "user.a",
            "permission": "active"
        }],
        "data": {
            "user": "user.a"
        }
    },{
        "account": "funds.holder",
        "name": "withdraw",
        "authorization": [{
            "actor": "user.a",
            "permission": "active"
        }],
        "data": {
            "user": "user.a"
        }
    }]
}