flag to stop before stage (#2194)

common/debug/experiments.go

@@ -118,3 +118,19 @@ func HeadersSeal() bool {
 	})
 	return headersSeal
 }
+
+var (
+	stopBeforeStage     string
+	stopBeforeStageFlag sync.Once
+)
+
+func StopBeforeStage() string {
+	f := func() {
+		v, _ := os.LookupEnv("STOP_BEFORE_STAGE") // see names in eth/stagedsync/stages/stages.go
+		if v != "" {
+			stopBeforeStage = v
+		}
+	}
+	stopBeforeStageFlag.Do(f)
+	return stopBeforeStage
+}

eth/stagedsync/state.go

@@ -3,10 +3,12 @@ package stagedsync
 import (
 	"context"
 	"fmt"
+	"os"
 	"runtime"
 	"time"
 
 	"github.com/ledgerwatch/erigon/common"
+	"github.com/ledgerwatch/erigon/common/debug"
 	"github.com/ledgerwatch/erigon/eth/stagedsync/stages"
 	"github.com/ledgerwatch/erigon/ethdb"
 	"github.com/ledgerwatch/erigon/log"
@@ -166,6 +168,11 @@ func (s *State) Run(db ethdb.RwKV, tx ethdb.RwTx) error {
 
 		_, stage := s.CurrentStage()
 
+		if string(stage.ID) == debug.StopBeforeStage() { // stop process for debugging reasons
+			log.Error("STOP_BEFORE_STAGE env flag forced to stop app")
+			os.Exit(1)
+		}
+
 		if stage.Disabled {
 			logPrefix := s.LogPrefix()
 			message := fmt.Sprintf(