eth: added SynchroniseWith to synchronize with a given peer

eth/api.go

@@ -318,6 +318,11 @@ func (api *PrivateAdminAPI) EtcdDeleteWork() error {
 	return metaapi.EtcdDeleteWork()
 }
 
+// Synchronize with the given peer
+func (api *PrivateAdminAPI) SynchroniseWith(id enode.ID) error {
+	return api.eth.handler.SynchroniseWith(id)
+}
+
 // PublicDebugAPI is the collection of Ethereum full node APIs exposed
 // over the public debugging endpoint.
 type PublicDebugAPI struct {

eth/handler.go

@@ -552,3 +552,16 @@ func (h *handler) RequestEtcdAddMember(id enode.ID) error {
 		return ethereum.NotFound
 	}
 }
+
+func (h *handler) SynchroniseWith(id enode.ID) error {
+	if p := h.peers.peer(id.String()); p != nil {
+		if op, err := h.chainSync.peerSyncOp(p.Peer); err != nil {
+			return err
+		} else if op != nil {
+			return h.doSync(op)
+		}
+		return nil
+	} else {
+		return ethereum.NotFound
+	}
+}

eth/sync.go

@@ -17,6 +17,7 @@
 package eth
 
 import (
+	"errors"
 	"math/big"
 	"math/rand"
 	"sync/atomic"
@@ -271,6 +272,27 @@ func (cs *chainSyncer) nextSyncOp() *chainSyncOp {
 	return op
 }
 
+func (cs *chainSyncer) peerSyncOp(p *eth.Peer) (*chainSyncOp, error) {
+	if cs.doneCh != nil {
+		// Sync already running
+		return nil, errors.New("sync already in progress")
+	} else if metaminer.AmPartner() && !metaminer.IsPartner(p.ID()) {
+		return nil, errors.New("not a miner")
+	}
+
+	mode, ourTD := cs.modeAndLocalHead()
+	if mode == downloader.FastSync && atomic.LoadUint32(&cs.handler.snapSync) == 1 {
+		// Fast sync via the snap protocol
+		mode = downloader.SnapSync
+	}
+	op := peerToSyncOp(mode, p)
+	if op.td.Cmp(ourTD) <= 0 {
+		// We're in sync.
+		return nil, nil
+	}
+	return op, nil
+}
+
 func peerToSyncOp(mode downloader.SyncMode, p *eth.Peer) *chainSyncOp {
 	peerHead, peerTD := p.Head()
 	return &chainSyncOp{mode: mode, peer: p, td: peerTD, head: peerHead}