chain: Wait for dcrd to sync before starting RPC sync

This prevents the wallet from syncing from blockConnected messages when
it is connected to a dcrd instance that is not yet as synced as the one
the wallet has used in the past. This improves performance by batching
the sync work in the initial getHeaders stage and prevents wallet misuse
by ensuring the underlying dcrd is also synced to recent blocks.

Note that the the case of a new wallet (with recorded tip height 0)
connected to a network isolated dcrd instance (header and block height
both 0) is explicitly allowed to proceed without waiting. This handles
the use-cases of airgapped and empty simnet wallets.

Author: matheusd

chain/sync.go

@@ -14,6 +14,7 @@ import (
 	"runtime/trace"
 	"sync"
 	"sync/atomic"
+	"time"
 
 	"decred.org/dcrwallet/v4/errors"
 	"decred.org/dcrwallet/v4/rpc/client/dcrd"
@@ -460,6 +461,43 @@ func normalizeAddress(addr string, defaultPort string) (hostport string, err err
 	return addr, nil
 }
 
+// waitRPCSync waits until the underlying node is synced up to (at least) the
+// passed height and that is has all blockchain data up to its target header
+// height.
+func (s *Syncer) waitRPCSync(ctx context.Context, minHeight int64) error {
+	for {
+		info, err := s.rpc.GetBlockchainInfo(ctx)
+		if err != nil {
+			return err
+		}
+
+		if info.Headers > minHeight {
+			minHeight = info.Headers
+		}
+		if info.Blocks >= minHeight && !info.InitialBlockDownload {
+			// dcrd is synced.
+			return nil
+		}
+
+		log.Infof("Waiting dcrd instance to catch up to minimum block "+
+			"height %d (%d blocks, %d headers, IBS=%v)",
+			minHeight, info.Blocks, info.Headers, info.InitialBlockDownload)
+
+		// Determine when to make the next check. When there are less
+		// than 100 blocks to go, use a lower check interval.
+		nextDelay := 10 * time.Second
+		if minHeight-info.Blocks < 100 {
+			nextDelay = time.Second
+		}
+
+		select {
+		case <-time.After(nextDelay):
+		case <-ctx.Done():
+			return ctx.Err()
+		}
+	}
+}
+
 // hashStop is a zero value stop hash for fetching all possible data using
 // locators.
 var hashStop chainhash.Hash
@@ -570,6 +608,11 @@ func (s *Syncer) Run(ctx context.Context) (err error) {
 		log.Infof("Transactions synced through block %v height %d", &tipHash, tipHeight)
 	}
 
+	err = s.waitRPCSync(ctx, int64(tipHeight))
+	if err != nil {
+		return err
+	}
+
 	if s.wallet.VotingEnabled() {
 		err = s.rpc.Call(ctx, "notifywinningtickets", nil)
 		if err != nil {