From 1b1ef4c7efa5f5116a851c23a6c34b68fab1393b Mon Sep 17 00:00:00 2001
From: Herr Seppia <seppia@dusk.network>
Date: Mon, 20 Jun 2022 14:53:45 +0200
Subject: [PATCH] Improve mempool extraction

Resolves #1421
---
 CHANGELOG.md                                  |  2 ++
 .../data/ipc/transactions/payload_decoded.go  | 14 ++++++++++
 pkg/core/mempool/mempool.go                   | 27 +++++++++++++++++++
 3 files changed, 43 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index dc6582729..671a86194 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -15,6 +15,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Mempool discards any transaction with repeated nullifier [#1388]
 
 ### Changed
+- Extraction from mempool consider Gas expenditure estimation [#1421]
 - Add GasLimit to the Block's header [#1416]
 - Reduce wire messages needed for propagating an Agreement vote
 - Improve fallback procedure to revert multiple ephemeral blocks [#1343]
@@ -30,6 +31,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 - Default configuration values loading [#1419] 
 
+[#1421]: (https://github.com/dusk-network/dusk-blockchain/issues/1421)
 [#1419]: (https://github.com/dusk-network/dusk-blockchain/issues/1419)
 [#1418]: (https://github.com/dusk-network/dusk-blockchain/issues/1418)
 [#1416]: (https://github.com/dusk-network/dusk-blockchain/issues/1416)
diff --git a/pkg/core/data/ipc/transactions/payload_decoded.go b/pkg/core/data/ipc/transactions/payload_decoded.go
index 715002db7..c66f52883 100644
--- a/pkg/core/data/ipc/transactions/payload_decoded.go
+++ b/pkg/core/data/ipc/transactions/payload_decoded.go
@@ -193,3 +193,17 @@ func UnmarshalTransactionPayloadDecoded(r *bytes.Buffer, f *TransactionPayloadDe
 
 	return nil
 }
+
+// EstimatedGasSpent return the estimated amount of Gas that a transaction will
+// spend. For now it uses `t.Call` to determine if it's a normal transfer or it
+// is an intercontract call.
+// TODO: further improvement should take care of the contractAddress to compare
+// it against historical data.
+func (p *TransactionPayloadDecoded) EstimatedGasSpent() uint64 {
+	if p.Call == nil {
+		// This is a normal transfer transaction
+		return 250_000_000
+	}
+	// This is an inter-contract call
+	return 1_200_000_000
+}
diff --git a/pkg/core/mempool/mempool.go b/pkg/core/mempool/mempool.go
index 81ef77a55..a16cf37a3 100644
--- a/pkg/core/mempool/mempool.go
+++ b/pkg/core/mempool/mempool.go
@@ -436,6 +436,7 @@ func (m Mempool) processGetMempoolTxsRequest(r rpcbus.Request) (interface{}, err
 // processGetMempoolTxsBySizeRequest returns a subset of verified mempool txs which
 // 1. contains only highest fee txs
 // 2. has total txs size not bigger than maxTxsSize (request param)
+// 3. has total txs EstimatedGasSpent not bigger than BlockGasLimit+10%
 // Called by BlockGenerator on generating a new candidate block.
 func (m Mempool) processGetMempoolTxsBySizeRequest(r rpcbus.Request) (interface{}, error) {
 	// Read maxTxsSize param
@@ -447,16 +448,42 @@ func (m Mempool) processGetMempoolTxsBySizeRequest(r rpcbus.Request) (interface{
 	}
 
 	txs := make([]transactions.ContractCall, 0)
+	gasLimit := config.Get().State.BlockGasLimit
+	// The slippageGasLimit is the threshold that consider the "estimated gas
+	// spent" acceptable even if it exceeds the strict GasLimit. This is
+	// required to avoid to iterate the whole meempol until it fit perfectly
+	// the block GasLimit
+	slippageGasLimit := gasLimit + gasLimit/10
 
 	var totalSize uint32
+	var totalGas uint64
 
 	err := m.verified.RangeSort(func(k txHash, t TxDesc) (bool, error) {
 		var done bool
+
+		decoded, err := t.tx.Decode()
+		if err != nil {
+			// Cannot decode, skip the tx.
+			// This should never happen, keeping `err` to log it properly`
+			return false, err
+		}
+
+		totalGas += decoded.EstimatedGasSpent()
+		if totalGas > slippageGasLimit {
+			// Total gas exceeded the slippage threshold, skip the tx
+			return false, nil
+		}
+
+		// If the totalGas exceeded the gasLimit (but still below the
+		// slippage threshold) stop to iterate the mempool
+		done = totalGas >= gasLimit
+
 		totalSize += uint32(t.size)
 
 		if totalSize <= maxTxsSize {
 			txs = append(txs, t.tx)
 		} else {
+			// it the totalSize exceeds the limit, stop to iterate the mempool
 			done = true
 		}