Implement rate limited free transactions feature #603

libraries/chain/account_object.cpp

@@ -110,6 +110,32 @@ void account_statistics_object::pay_fee( share_type core_fee, share_type cashbac
       pending_vested_fees += core_fee;
 }
 
+fc::uint128_t account_statistics_object::compute_coin_seconds_earned(const asset& balance, fc::time_point_sec now)const
+{
+   if( now <= coin_seconds_earned_last_update )
+      return coin_seconds_earned;
+   int64_t delta_seconds = (now - coin_seconds_earned_last_update).to_seconds();
+
+   fc::uint128_t delta_coin_seconds = balance.amount.value;
+   delta_coin_seconds *= delta_seconds;
+
+   return (coin_seconds_earned + delta_coin_seconds);
+}
+
+void account_statistics_object::update_coin_seconds_earned(const asset& balance, fc::time_point_sec now)
+{
+   if( now <= coin_seconds_earned_last_update )
+      return;
+   coin_seconds_earned = compute_coin_seconds_earned(balance, now);
+   coin_seconds_earned_last_update = now;
+}
+
+void account_statistics_object::set_coin_seconds_earned(const fc::uint128_t new_coin_seconds, fc::time_point_sec now)
+{
+   coin_seconds_earned = new_coin_seconds;
+   coin_seconds_earned_last_update = now;
+}
+
 set<account_id_type> account_member_index::get_account_members(const account_object& a)const
 {
    set<account_id_type> result;

libraries/chain/committee_member_evaluator.cpp

@@ -77,6 +77,18 @@ void_result committee_member_update_global_parameters_evaluator::do_evaluate(con
 { try {
    FC_ASSERT(trx_state->_is_proposed_trx);
 
+   database& d = db();
+
+   // #603 hard fork check
+   if( d.head_block_time() <= HARDFORK_603_TIME )
+   {
+      for( const auto& e : o.new_parameters.extensions )
+      {
+         FC_ASSERT( e.which() != chain_parameters::parameter_extension::tag<chain_parameters::ext::coin_seconds_as_fees_options>::value,
+                    "New parameters contain an extension which requires hardfork #603." );
+      }
+   }
+
    return void_result();
 } FC_CAPTURE_AND_RETHROW( (o) ) }
 

libraries/chain/db_balance.cpp

@@ -68,12 +68,36 @@ void database::adjust_balance(account_id_type account, asset delta )
          b.asset_type = delta.asset_id;
          b.balance = delta.amount.value;
       });
+      // Update coin_seconds_earned and etc
+      if( head_block_time() > HARDFORK_603_TIME )
+      {
+         // TODO how to deal with smart coins?
+         if( delta.asset_id == asset_id_type() )
+         {
+            modify( account(*this).statistics(*this), [&](account_statistics_object& s) {
+               s.set_coin_seconds_earned( 0, head_block_time() );
+            });
+         }
+      }
    } else {
       if( delta.amount < 0 )
          FC_ASSERT( itr->get_balance() >= -delta, "Insufficient Balance: ${a}'s balance of ${b} is less than required ${r}", ("a",account(*this).name)("b",to_pretty_string(itr->get_balance()))("r",to_pretty_string(-delta)));
+      const asset original_balance = itr->get_balance();
       modify(*itr, [delta](account_balance_object& b) {
          b.adjust_balance(delta);
       });
+      // Update coin_seconds_earned and etc
+      if( head_block_time() > HARDFORK_603_TIME )
+      {
+         // TODO how to deal with smart coins?
+         if( delta.asset_id == asset_id_type() )
+         {
+            modify( account(*this).statistics(*this), [&](account_statistics_object& s) {
+               //TODO will coin_seconds_earned expire? seems hard to calculate
+               s.update_coin_seconds_earned( original_balance, head_block_time() );
+            });
+         }
+      }
    }
 
 } FC_CAPTURE_AND_RETHROW( (account)(delta) ) }

libraries/chain/evaluator.cpp

@@ -79,6 +79,35 @@ database& generic_evaluator::db()const { return trx_state->db(); }
       }
    }
 
+   void generic_evaluator::prepare_fee_from_coin_seconds(const operation& o)
+   {
+      const auto& fee_options = db().get_global_properties().parameters.get_coin_seconds_as_fees_options();
+      const auto& max_op_fee = fee_options.max_fee_from_coin_seconds_by_operation;
+      if( max_op_fee.size() > o.which() && max_op_fee[o.which()] > 0 ) // if fee can be paid with coin seconds
+      {
+         const asset& core_balance = db().get_balance( fee_paying_account->get_id(), asset_id_type() );
+         const auto payer_membership = fee_paying_account->get_membership( db().head_block_time() );
+         coin_seconds_earned = fee_paying_account_statistics->compute_coin_seconds_earned(
+                                       core_balance, db().head_block_time() );
+         if( coin_seconds_earned > 0 ) // if payer have some coin seconds to pay
+         {
+            coin_seconds_as_fees_rate = fee_options.coin_seconds_as_fees_rate[payer_membership];
+            fc::uint128_t coin_seconds_to_fees = coin_seconds_earned;
+            coin_seconds_to_fees /= coin_seconds_as_fees_rate.value;
+            fees_accumulated_from_coin_seconds = coin_seconds_to_fees.to_uint64();
+
+            share_type max_fees_allowed = fee_options.max_accumulated_fees_from_coin_seconds[payer_membership];
+            if( fees_accumulated_from_coin_seconds > max_fees_allowed ) // if accumulated too many coin seconds, truncate
+            {
+               fees_accumulated_from_coin_seconds = max_fees_allowed;
+               coin_seconds_earned = fc::uint128_t( max_fees_allowed.value );
+               coin_seconds_earned *= coin_seconds_as_fees_rate.value;
+            }
+            max_fees_payable_with_coin_seconds = std::min( fees_accumulated_from_coin_seconds, max_op_fee[o.which()] );
+         }
+      }
+   }
+
    void generic_evaluator::convert_fee()
    {
       if( !trx_state->skip_fee ) {
@@ -128,4 +157,19 @@ database& generic_evaluator::db()const { return trx_state->db(); }
      db().adjust_balance(fee_payer, fee_from_account);
    }
 
+   void generic_evaluator::pay_fee_with_coin_seconds()
+   { try {
+      if( !trx_state->skip_fee ) {
+         database& d = db();
+         // deduct fees from coin_seconds_earned
+         if( fees_paid_with_coin_seconds > 0 )
+         {
+            fc::uint128_t coin_seconds_consumed( fees_paid_with_coin_seconds.value );
+            coin_seconds_consumed *= coin_seconds_as_fees_rate.value;
+            d.modify(*fee_paying_account_statistics, [&](account_statistics_object& o) {
+               o.set_coin_seconds_earned( coin_seconds_earned - coin_seconds_consumed, d.head_block_time() );
+            });
+         }
+      }
+   } FC_CAPTURE_AND_RETHROW() }
 } }

libraries/chain/hardfork.d/603.hf

@@ -0,0 +1,4 @@
+// #603 simple rate limited free transaction
+#ifndef HARDFORK_603_TIME
+#define HARDFORK_603_TIME (fc::time_point_sec( 1450378800 ))
+#endif

libraries/chain/include/graphene/chain/account_object.hpp

@@ -22,6 +22,7 @@
  * THE SOFTWARE.
  */
 #pragma once
+#include <graphene/chain/hardfork.hpp>
 #include <graphene/chain/protocol/operations.hpp>
 #include <graphene/db/generic_index.hpp>
 #include <boost/multi_index/composite_key.hpp>
@@ -78,13 +79,48 @@ namespace graphene { namespace chain {
           */
          share_type pending_vested_fees;
 
+         /**
+          * Tracks the coin-seconds earned by this account. Lazy updating.
+          * actual_coin_seconds_earned = coin_seconds_earned + current_balance * (now - coin_seconds_earned_last_update)
+          */
+         // TODO maybe better to use a struct to store coin_seconds_earned and coin_seconds_earned_last_update
+         //      and related functions e.g. compute_coin_seconds_earned and update_coin_seconds_earned
+         fc::uint128_t                  coin_seconds_earned;
+
+         /**
+          * Tracks the most recent time when @ref coin_seconds_earned was updated.
+          */
+         fc::time_point_sec             coin_seconds_earned_last_update = HARDFORK_603_TIME;
+
          /// @brief Split up and pay out @ref pending_fees and @ref pending_vested_fees
          void process_fees(const account_object& a, database& d) const;
 
          /**
           * Core fees are paid into the account_statistics_object by this method
           */
          void pay_fee( share_type core_fee, share_type cashback_vesting_threshold );
+
+         /**
+          * Compute coin_seconds_earned.  Used to
+          * non-destructively figure out how many coin seconds
+          * are available.
+          */
+         // TODO use a public funtion to do this job as well as same job in vesting_balance_object
+         fc::uint128_t compute_coin_seconds_earned(const asset& balance, fc::time_point_sec now)const;
+
+         /**
+          * Update coin_seconds_earned and
+          * coin_seconds_earned_last_update fields due to passing of time
+          */
+         // TODO use a public funtion to do this job and same job in vesting_balance_object
+         void update_coin_seconds_earned(const asset& balance, fc::time_point_sec now);
+
+         /**
+          * Update coin_seconds_earned and
+          * coin_seconds_earned_last_update fields with new data
+          */
+         void set_coin_seconds_earned(const fc::uint128_t new_coin_seconds, fc::time_point_sec now);
+
    };
 
    /**
@@ -257,6 +293,13 @@ namespace graphene { namespace chain {
          {
             return !is_basic_account(now);
          }
+         /// @return membership status of the account.
+         account_membership get_membership(time_point_sec now)const
+         {
+            if( is_basic_account( now ) ) return basic_account;
+            if( is_lifetime_member() ) return lifetime_member;
+            return annual_member;
+         }
 
          account_id_type get_id()const { return id; }
    };
@@ -388,5 +431,6 @@ FC_REFLECT_DERIVED( graphene::chain::account_statistics_object,
                     (total_core_in_orders)
                     (lifetime_fees_paid)
                     (pending_fees)(pending_vested_fees)
+                    (coin_seconds_earned)(coin_seconds_earned_last_update)
                   )
 

libraries/chain/include/graphene/chain/evaluator.hpp

@@ -25,6 +25,7 @@
 #include <graphene/chain/exceptions.hpp>
 #include <graphene/chain/transaction_evaluation_state.hpp>
 #include <graphene/chain/protocol/operations.hpp>
+#include <graphene/chain/hardfork.hpp>
 
 namespace graphene { namespace chain {
 
@@ -95,6 +96,16 @@ namespace graphene { namespace chain {
        */
       void convert_fee();
 
+      /**
+       * Compute how much can be paid with coin-seconds, need to call after prepare_fee().
+       */
+      void prepare_fee_from_coin_seconds(const operation& o);
+
+      /**
+       * Pay fee with coin-seconds
+       */
+      void pay_fee_with_coin_seconds();
+
       object_id_type get_relative_id( object_id_type rel_id )const;
 
       /**
@@ -115,6 +126,13 @@ namespace graphene { namespace chain {
       const asset_object*              fee_asset          = nullptr;
       const asset_dynamic_data_object* fee_asset_dyn_data = nullptr;
       transaction_evaluation_state*    trx_state;
+      // fields for computing fees paid with coin seconds
+      share_type                       max_fees_payable_with_coin_seconds = 0;
+      share_type                       fees_accumulated_from_coin_seconds = 0;
+      share_type                       fees_paid_with_coin_seconds        = 0;
+      share_type                       coin_seconds_as_fees_rate          = 0;
+      fc::uint128_t                    coin_seconds_earned                = 0;
+
    };
 
    class op_evaluator
@@ -147,13 +165,21 @@ namespace graphene { namespace chain {
          const auto& op = o.get<typename DerivedEvaluator::operation_type>();
 
          prepare_fee(op.fee_payer(), op.fee);
+
+         if( db().head_block_time() > HARDFORK_603_TIME )
+            prepare_fee_from_coin_seconds(o);
+
          if( !trx_state->skip_fee_schedule_check )
          {
             share_type required_fee = calculate_fee_for_operation(op);
-            GRAPHENE_ASSERT( core_fee_paid >= required_fee,
+            GRAPHENE_ASSERT( core_fee_paid + max_fees_payable_with_coin_seconds >= required_fee,
                        insufficient_fee,
                        "Insufficient Fee Paid",
+                       ("payable_from_coin_seconds", max_fees_payable_with_coin_seconds)
                        ("core_fee_paid",core_fee_paid)("required", required_fee) );
+            // if some fees are paid with coin seconds
+            if( core_fee_paid < required_fee )
+               fees_paid_with_coin_seconds = required_fee - core_fee_paid;
          }
 
          return eval->do_evaluate(op);
@@ -166,6 +192,7 @@ namespace graphene { namespace chain {
 
          convert_fee();
          pay_fee();
+         pay_fee_with_coin_seconds();
 
          auto result = eval->do_apply(op);
 

libraries/chain/include/graphene/chain/protocol/chain_parameters.hpp

@@ -36,7 +36,6 @@ namespace fc {
 
 namespace graphene { namespace chain {
 
-   typedef static_variant<>  parameter_extension; 
    struct chain_parameters
    {
       /** using a smart ref breaks the circular dependency created between operations and the fee schedule */
@@ -69,14 +68,80 @@ namespace graphene { namespace chain {
       uint16_t                accounts_per_fee_scale              = GRAPHENE_DEFAULT_ACCOUNTS_PER_FEE_SCALE; ///< number of accounts between fee scalings
       uint8_t                 account_fee_scale_bitshifts         = GRAPHENE_DEFAULT_ACCOUNT_FEE_SCALE_BITSHIFTS; ///< number of times to left bitshift account registration fee at each scaling
       uint8_t                 max_authority_depth                 = GRAPHENE_MAX_SIG_CHECK_DEPTH;
+
+      /**
+       * struct for override extensions
+       */
+      struct ext
+      {
+         /** container of coin_seconds to fees parameters */
+         struct coin_seconds_as_fees_options
+         {
+             /**
+              * Rates of converting coin_seconds to core asset to pay fees,
+              * indexed by membership type: [basic_account, lifetime_member, annual_member]
+              */
+             //
+             // Theoretically, 100 tps means 8.64M transactions a day.
+             // Total quantity of core asset is 3.7BB, so 1 transaction = 3.7BB/8.64M ~= 428 core assets,
+             // which means with 428 core assets you can do 1 transaction a day.
+             // If we set conversion rate to 5000, and set transaction fee to 1, then about 1/10 of network
+             // capacity can be used freely. A whale with 10M core assets can accumulate same value as
+             // 1 core asset of coin seconds in 43.2 seconds. An average user with 10K core assets can
+             // accumulate same value as 1 core asset of coin seconds in 43200 seconds = half a day.
+             //
+             // TODO consider nonlinear conversion?
+             std::vector<share_type> coin_seconds_as_fees_rate { 86400*20000,
+                                                                 86400*5000,
+                                                                 86400*10000
+                                                               };
+             /**
+              * Maximum values of accumulated fees which can be paid with accumulated coin_seconds,
+              * indexed by membership type: [basic_account, lifetime_member, annual_member]
+              */
+             std::vector<share_type> max_accumulated_fees_from_coin_seconds { GRAPHENE_BLOCKCHAIN_PRECISION * 10,
+                                                                              GRAPHENE_BLOCKCHAIN_PRECISION * 40,
+                                                                              GRAPHENE_BLOCKCHAIN_PRECISION * 20
+                                                                            };
+             /**
+              * Maximum values of fees can be paid with coin_seconds, indexed by operation_id.
+              * Default value is all 0.
+              */
+             std::vector<share_type> max_fee_from_coin_seconds_by_operation;
+         };
+      };
+
+      typedef static_variant<ext::coin_seconds_as_fees_options>  parameter_extension;
+      typedef flat_set<parameter_extension> extensions_type;
       extensions_type         extensions;
 
       /** defined in fee_schedule.cpp */
       void validate()const;
+
+      /** @return the coin_seconds_as_fee_options object set in extensions, or default values if not set */
+      const ext::coin_seconds_as_fees_options get_coin_seconds_as_fees_options()const
+      {
+         if( extensions.size() > 0 )
+         {
+            for( const parameter_extension& e : extensions )
+            {
+               if( e.which() == parameter_extension::tag<ext::coin_seconds_as_fees_options>::value )
+                  return e.get<ext::coin_seconds_as_fees_options>();
+            }
+         }
+         return ext::coin_seconds_as_fees_options();
+      }
    };
 
 } }  // graphene::chain
 
+FC_REFLECT( graphene::chain::chain_parameters::ext::coin_seconds_as_fees_options,
+            (coin_seconds_as_fees_rate)
+            (max_accumulated_fees_from_coin_seconds)
+            (max_fee_from_coin_seconds_by_operation)
+          )
+FC_REFLECT_TYPENAME( graphene::chain::chain_parameters::parameter_extension )
+FC_REFLECT_TYPENAME( graphene::chain::chain_parameters::extensions_type )
 FC_REFLECT( graphene::chain::chain_parameters,
             (current_fees)
             (block_interval)