Improve mempool extraction

Resolves #1421

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)

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
+}

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
@@ -447,19 +448,41 @@ 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
-		totalSize += uint32(t.size)
+		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
+		}
+
+		totalSize += uint32(t.size)
 		if totalSize <= maxTxsSize {
 			txs = append(txs, t.tx)
-		} else {
-			done = true
 		}
 
+		// We stop to iterate the mempool if:
+		// 1. The totalGas exceeded the gasLimit (but still below the slippage
+		// threshold)
+		// 2. The totalSize exceeds the limit
+		done := totalGas >= gasLimit || totalSize >= maxTxsSize
+
 		return done, nil
 	})
 	if err != nil {