cmd,eth: 16400 Add an option to stop geth once in sync. WIP for light mode (#17321)

* cmd, eth: Added in the flag to step geth once sync based on input

* cmd, eth: 16400 Add an option to stop geth once in sync.

* cmd: 16400 Add an option to stop geth once in sync. WIP

* cmd/geth/main, les/fletcher: added in light mode support

* cmd/geth/main, les/fletcher: Cleaned Comments and code for light mode

* cmd: 16400 Fixed formatting issue and cleaned code

* cmd, eth, les: 16400 Fixed formatting issues

* cmd, eth, les: Performed gofmt to update formatting

* cmd, eth, les: Fixed bugs resulting formatting

* cmd/geth, eth/, les: switched to downloader event

* eth: Fixed styling and gen_config

* eth/: Fix nil error in config file

* cmd/geth: Updated countdown log

* les/fetcher.go: Removed depcreated channel

* eth/downloader.go: Removed deprecated select

* cmd/geth, cmd/utils: Fixed minor issues

* eth: Reverted config files to proper format

* eth: Fixed typo in config file

* cmd/geth, eth/down: Updated code to use header time stamp

* eth/downloader: Changed the time threshold to 10 minutes

* cmd/geth, eth/downloader: Updated downloading event to pass latest header

* cmd/geth: Updated main to use right timer object

* cmd/geth: Removed unused failed event

* cmd/geth: added in correct time field with type assertion

* cmd/geth, cmd/utils: Updated flag to use boolean

* cmd/geth, cmd/utils, eth/downloader: Cleaned up code based on recommendations

* cmd/geth: Removed unneeded import

* cmd/geth, eth/downloader: fixed event field and suggested changes

* cmd/geth, cmd/utils: Updated flag and linting issue

3 files changed, 34 insertions, 1 deletions

diff --git a/cmd/geth/main.go b/cmd/geth/main.go
index 77c04ff36..0d9f733de 100644
--- a/cmd/geth/main.go
+++ b/cmd/geth/main.go
@@ -31,8 +31,10 @@ import (
 	"github.com/ethereum/go-ethereum/accounts"
 	"github.com/ethereum/go-ethereum/accounts/keystore"
 	"github.com/ethereum/go-ethereum/cmd/utils"
+	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/console"
 	"github.com/ethereum/go-ethereum/eth"
+	"github.com/ethereum/go-ethereum/eth/downloader"
 	"github.com/ethereum/go-ethereum/ethclient"
 	"github.com/ethereum/go-ethereum/internal/debug"
 	"github.com/ethereum/go-ethereum/log"
@@ -87,6 +89,7 @@ var (
 		utils.ULCTrustedNodesFlag,
 		utils.ULCMinTrustedFractionFlag,
 		utils.SyncModeFlag,
+		utils.ExitWhenSyncedFlag,
 		utils.GCModeFlag,
 		utils.LightServFlag,
 		utils.LightPeersFlag,
@@ -339,6 +342,32 @@ func startNode(ctx *cli.Context, stack *node.Node) {
 			}
 		}
 	}()
+
+	// Spawn a standalone goroutine for status synchronization monitoring,
+	// close the node when synchronization is complete if user required.
+	if ctx.GlobalBool(utils.ExitWhenSyncedFlag.Name) {
+		go func() {
+			sub := stack.EventMux().Subscribe(downloader.DoneEvent{})
+			defer sub.Unsubscribe()
+			for {
+				event := <-sub.Chan()
+				if event == nil {
+					continue
+				}
+				done, ok := event.Data.(downloader.DoneEvent)
+				if !ok {
+					continue
+				}
+				if timestamp := time.Unix(done.Latest.Time.Int64(), 0); time.Since(timestamp) < 10*time.Minute {
+					log.Info("Synchronisation completed", "latestnum", done.Latest.Number, "latesthash", done.Latest.Hash(),
+						"age", common.PrettyAge(timestamp))
+					stack.Stop()
+				}
+
+			}
+		}()
+	}
+
 	// Start auxiliary services if enabled
 	if ctx.GlobalBool(utils.MiningEnabledFlag.Name) || ctx.GlobalBool(utils.DeveloperFlag.Name) {
 		// Mining only makes sense if a full Ethereum node is running
diff --git a/cmd/geth/usage.go b/cmd/geth/usage.go
index de2a3d073..a19ad1094 100644
--- a/cmd/geth/usage.go
+++ b/cmd/geth/usage.go
@@ -75,6 +75,7 @@ var AppHelpFlagGroups = []flagGroup{
 			utils.TestnetFlag,
 			utils.RinkebyFlag,
 			utils.SyncModeFlag,
+			utils.ExitWhenSyncedFlag,
 			utils.GCModeFlag,
 			utils.EthStatsURLFlag,
 			utils.IdentityFlag,
diff --git a/cmd/utils/flags.go b/cmd/utils/flags.go
index 3109bf962..1d8c7f378 100644
--- a/cmd/utils/flags.go
+++ b/cmd/utils/flags.go
@@ -162,6 +162,10 @@ var (
 		Usage: "Document Root for HTTPClient file scheme",
 		Value: DirectoryString{homeDir()},
 	}
+	ExitWhenSyncedFlag = cli.BoolFlag{
+		Name:  "exitwhensynced",
+		Usage: "Exists syncing after block synchronisation",
+	}
 	ULCModeConfigFlag = cli.StringFlag{
 		Name:  "ulc.config",
 		Usage: "Config file to use for ultra light client mode",
@@ -178,7 +182,6 @@ var (
 		Name:  "ulc.trusted",
 		Usage: "List of trusted ULC servers",
 	}
-
 	defaultSyncMode = eth.DefaultConfig.SyncMode
 	SyncModeFlag    = TextMarshalerFlag{
 		Name:  "syncmode",