From 1201e7c4f83005f68ffbc65286e158e525b65f09 Mon Sep 17 00:00:00 2001
From: Austin Roberts <austin.roberts@openrelay.xyz>
Date: Fri, 7 Jan 2022 11:34:07 -0600
Subject: [PATCH] Avoid unnecessary RLP encoding

While looking for the source of a memory leak, I decided to optimize
the metatracer to avoid encoding values when there weren't any tracers
configured to received the encoded values.

I also avoided putting the EVM into debug mode when there weren't any
tracers configured.

None of these fixed the memory leak, but they still seem like good
practices. Memory leak fix is in the next commit.
---
 core/plugin_hooks.go    | 11 ++++++++---
 core/state_processor.go |  8 +++++---
 2 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/core/plugin_hooks.go b/core/plugin_hooks.go
index 77a5643ed..5ddde7437 100644
--- a/core/plugin_hooks.go
+++ b/core/plugin_hooks.go
@@ -190,6 +190,7 @@ type metaTracer struct {
 }
 
 func (mt *metaTracer) PreProcessBlock(block *types.Block) {
+	if len(mt.tracers) == 0 { return }
 	blockHash := core.Hash(block.Hash())
 	blockNumber := block.NumberU64()
 	encoded, _ := rlp.EncodeToBytes(block)
@@ -198,6 +199,7 @@ func (mt *metaTracer) PreProcessBlock(block *types.Block) {
 	}
 }
 func (mt *metaTracer) PreProcessTransaction(tx *types.Transaction, block *types.Block, i int) {
+	if len(mt.tracers) == 0 { return }
 	blockHash := core.Hash(block.Hash())
 	transactionHash := core.Hash(tx.Hash())
 	for _, tracer := range mt.tracers {
@@ -205,6 +207,7 @@ func (mt *metaTracer) PreProcessTransaction(tx *types.Transaction, block *types.
 	}
 }
 func (mt *metaTracer) BlockProcessingError(tx *types.Transaction, block *types.Block, err error) {
+	if len(mt.tracers) == 0 { return }
 	blockHash := core.Hash(block.Hash())
 	transactionHash := core.Hash(tx.Hash())
 	for _, tracer := range mt.tracers {
@@ -212,6 +215,7 @@ func (mt *metaTracer) BlockProcessingError(tx *types.Transaction, block *types.B
 	}
 }
 func (mt *metaTracer) PostProcessTransaction(tx *types.Transaction, block *types.Block, i int, receipt *types.Receipt) {
+	if len(mt.tracers) == 0 { return }
 	blockHash := core.Hash(block.Hash())
 	transactionHash := core.Hash(tx.Hash())
 	receiptBytes, _ := json.Marshal(receipt)
@@ -220,6 +224,7 @@ func (mt *metaTracer) PostProcessTransaction(tx *types.Transaction, block *types
 	}
 }
 func (mt *metaTracer) PostProcessBlock(block *types.Block) {
+	if len(mt.tracers) == 0 { return }
 	blockHash := core.Hash(block.Hash())
 	for _, tracer := range mt.tracers {
 		tracer.PostProcessBlock(blockHash)
@@ -258,7 +263,7 @@ func (mt *metaTracer) CaptureExit(output []byte, gasUsed uint64, err error) {
 	}
 }
 
-func PluginGetBlockTracer(pl *plugins.PluginLoader, hash common.Hash, statedb *state.StateDB) *metaTracer {
+func PluginGetBlockTracer(pl *plugins.PluginLoader, hash common.Hash, statedb *state.StateDB) (*metaTracer, bool) {
 	//look for a function that takes whatever the ctx provides and statedb and returns a core.blocktracer append into meta tracer
 	tracerList := plugins.Lookup("GetLiveTracer", func(item interface{}) bool {
 		_, ok := item.(func(core.Hash, core.StateDB) core.BlockTracer)
@@ -274,9 +279,9 @@ func PluginGetBlockTracer(pl *plugins.PluginLoader, hash common.Hash, statedb *s
 			}
 		}
 	}
-	return mt
+	return mt, (len(mt.tracers) > 0)
 }
-func pluginGetBlockTracer(hash common.Hash, statedb *state.StateDB) *metaTracer {
+func pluginGetBlockTracer(hash common.Hash, statedb *state.StateDB) (*metaTracer, bool) {
 	if plugins.DefaultPluginLoader == nil {
 		log.Warn("Attempting GetBlockTracer, but default PluginLoader has not been initialized")
 		return &metaTracer{}
diff --git a/core/state_processor.go b/core/state_processor.go
index 273815fae..a7903cb96 100644
--- a/core/state_processor.go
+++ b/core/state_processor.go
@@ -71,9 +71,11 @@ func (p *StateProcessor) Process(block *types.Block, statedb *state.StateDB, cfg
 		misc.ApplyDAOHardFork(statedb)
 	}
 	blockContext := NewEVMBlockContext(header, p.bc, nil)
-	blockTracer := pluginGetBlockTracer(header.Hash(), statedb)
-	cfg.Tracer = blockTracer
-	cfg.Debug = true
+	blockTracer, ok := pluginGetBlockTracer(header.Hash(), statedb)
+	if ok {
+		cfg.Tracer = blockTracer
+		cfg.Debug = true
+	}
 	vmenv := vm.NewEVM(blockContext, vm.TxContext{}, statedb, p.config, cfg)
 	// Iterate over and process the individual transactions
 	pluginPreProcessBlock(block)