eth, les: add new config field SyncFromCheckpoint (#22123)

This PR introduces a new config field SyncFromCheckpoint for light client.

In some special scenarios, it's required to start synchronization from some
arbitrary checkpoint or even from the scratch. So this PR offers this
flexibility to users so that the synchronization start point can be configured.

There are two relevant configs: SyncFromCheckpoint and Checkpoint.

- If the SyncFromCheckpoint is true, the light client will try to sync from the
  specified checkpoint.

- If the Checkpoint is not configured, then the light client will sync from the
  scratch(from the latest header if the database is not empty)

Additional notes: these two configs are not visible in the CLI flags but only
accessable in the config file.

Example Usage:

[Eth]
SyncFromCheckpoint = true

[Eth.Checkpoint]
SectionIndex = 100
SectionHead = "0xabc"
CHTRoot = "0xabc"
BloomRoot = "0xabc"

PS. Historical checkpoint can be retrieved from the synced full node or light
client via les_getCheckpoint API.

eth/config.go

@@ -127,11 +127,12 @@ type Config struct {
 	Whitelist map[uint64]common.Hash `toml:"-"`
 
 	// Light client options
-	LightServ    int  `toml:",omitempty"` // Maximum percentage of time allowed for serving LES requests
-	LightIngress int  `toml:",omitempty"` // Incoming bandwidth limit for light servers
-	LightEgress  int  `toml:",omitempty"` // Outgoing bandwidth limit for light servers
-	LightPeers   int  `toml:",omitempty"` // Maximum number of LES client peers
-	LightNoPrune bool `toml:",omitempty"` // Whether to disable light chain pruning
+	LightServ          int  `toml:",omitempty"` // Maximum percentage of time allowed for serving LES requests
+	LightIngress       int  `toml:",omitempty"` // Incoming bandwidth limit for light servers
+	LightEgress        int  `toml:",omitempty"` // Outgoing bandwidth limit for light servers
+	LightPeers         int  `toml:",omitempty"` // Maximum number of LES client peers
+	LightNoPrune       bool `toml:",omitempty"` // Whether to disable light chain pruning
+	SyncFromCheckpoint bool `toml:",omitempty"` // Whether to sync the header chain from the configured checkpoint
 
 	// Ultra Light client options
 	UltraLightServers      []string `toml:",omitempty"` // List of trusted ultra light servers

eth/gen_config.go

@@ -21,6 +21,7 @@ func (c Config) MarshalTOML() (interface{}, error) {
 		NetworkId               uint64
 		SyncMode                downloader.SyncMode
 		EthDiscoveryURLs        []string
+		SnapDiscoveryURLs       []string
 		NoPruning               bool
 		NoPrefetch              bool
 		TxLookupLimit           uint64                 `toml:",omitempty"`
@@ -30,6 +31,7 @@ func (c Config) MarshalTOML() (interface{}, error) {
 		LightEgress             int                    `toml:",omitempty"`
 		LightPeers              int                    `toml:",omitempty"`
 		LightNoPrune            bool                   `toml:",omitempty"`
+		SyncFromCheckpoint      bool                   `toml:",omitempty"`
 		UltraLightServers       []string               `toml:",omitempty"`
 		UltraLightFraction      int                    `toml:",omitempty"`
 		UltraLightOnlyAnnounce  bool                   `toml:",omitempty"`
@@ -62,6 +64,7 @@ func (c Config) MarshalTOML() (interface{}, error) {
 	enc.NetworkId = c.NetworkId
 	enc.SyncMode = c.SyncMode
 	enc.EthDiscoveryURLs = c.EthDiscoveryURLs
+	enc.SnapDiscoveryURLs = c.SnapDiscoveryURLs
 	enc.NoPruning = c.NoPruning
 	enc.NoPrefetch = c.NoPrefetch
 	enc.TxLookupLimit = c.TxLookupLimit
@@ -71,6 +74,7 @@ func (c Config) MarshalTOML() (interface{}, error) {
 	enc.LightEgress = c.LightEgress
 	enc.LightPeers = c.LightPeers
 	enc.LightNoPrune = c.LightNoPrune
+	enc.SyncFromCheckpoint = c.SyncFromCheckpoint
 	enc.UltraLightServers = c.UltraLightServers
 	enc.UltraLightFraction = c.UltraLightFraction
 	enc.UltraLightOnlyAnnounce = c.UltraLightOnlyAnnounce
@@ -107,6 +111,7 @@ func (c *Config) UnmarshalTOML(unmarshal func(interface{}) error) error {
 		NetworkId               *uint64
 		SyncMode                *downloader.SyncMode
 		EthDiscoveryURLs        []string
+		SnapDiscoveryURLs       []string
 		NoPruning               *bool
 		NoPrefetch              *bool
 		TxLookupLimit           *uint64                `toml:",omitempty"`
@@ -116,6 +121,7 @@ func (c *Config) UnmarshalTOML(unmarshal func(interface{}) error) error {
 		LightEgress             *int                   `toml:",omitempty"`
 		LightPeers              *int                   `toml:",omitempty"`
 		LightNoPrune            *bool                  `toml:",omitempty"`
+		SyncFromCheckpoint      *bool                  `toml:",omitempty"`
 		UltraLightServers       []string               `toml:",omitempty"`
 		UltraLightFraction      *int                   `toml:",omitempty"`
 		UltraLightOnlyAnnounce  *bool                  `toml:",omitempty"`
@@ -159,6 +165,9 @@ func (c *Config) UnmarshalTOML(unmarshal func(interface{}) error) error {
 	if dec.EthDiscoveryURLs != nil {
 		c.EthDiscoveryURLs = dec.EthDiscoveryURLs
 	}
+	if dec.SnapDiscoveryURLs != nil {
+		c.SnapDiscoveryURLs = dec.SnapDiscoveryURLs
+	}
 	if dec.NoPruning != nil {
 		c.NoPruning = *dec.NoPruning
 	}
@@ -186,6 +195,9 @@ func (c *Config) UnmarshalTOML(unmarshal func(interface{}) error) error {
 	if dec.LightNoPrune != nil {
 		c.LightNoPrune = *dec.LightNoPrune
 	}
+	if dec.SyncFromCheckpoint != nil {
+		c.SyncFromCheckpoint = *dec.SyncFromCheckpoint
+	}
 	if dec.UltraLightServers != nil {
 		c.UltraLightServers = dec.UltraLightServers
 	}