lnwallet/lnrpc: Expose sync status to gRPC interface

This commit adds wallet_best_block_timestamp to the gRPC interface.
This is done in order to allow clients to calculate progress while
lnd syncs to the blockchain. wallet_best_block_timestamp is exposed
via the GetInfo() rpc call. Additionally, IsSynced() returns the
WalletBestBlockTimestamp as the second value in the tuple
that is returned, providing additional detail when querying about the
status of the sync. The BtcWallet interface has also been updated
accordingly.

This commit was created to support the issue to
[Add progress bar for chain sync] (lightninglabs/lightning-app#10) in
lightning-app

lnwallet/btcwallet/btcwallet.go

@@ -667,27 +667,32 @@ func (b *BtcWallet) SubscribeTransactions() (lnwallet.TransactionSubscription, e
 // it has fully synced to the current best block in the main chain.
 //
 // This is a part of the WalletController interface.
-func (b *BtcWallet) IsSynced() (bool, error) {
-	// Grab the best chain state the wallet is currently aware of.
+func (b *BtcWallet) IsSynced() (bool, int64, error) {
+	// Grab the best chain state the wallet is currently aware of. We'll
+	// also grab the timestamp of the best block to return for determining
+	// sync progress.
 	syncState := b.wallet.Manager.SyncedTo()
+	walletBestHeader, err := b.chain.GetBlockHeader(&syncState.Hash)
+	if err != nil {
+		return false, 0, err
+	}
 
 	var (
 		bestHash   *chainhash.Hash
 		bestHeight int32
-		err        error
 	)
 
 	// Next, query the chain backend to grab the info about the tip of the
 	// main chain.
 	bestHash, bestHeight, err = b.cfg.ChainSource.GetBestBlock()
 	if err != nil {
-		return false, err
+		return false, 0, err
 	}
 
 	// If the wallet hasn't yet fully synced to the node's best chain tip,
 	// then we're not yet fully synced.
 	if syncState.Height < bestHeight {
-		return false, nil
+		return false, walletBestHeader.Timestamp.Unix(), nil
 	}
 
 	// If the wallet is on par with the current best chain tip, then we
@@ -696,11 +701,11 @@ func (b *BtcWallet) IsSynced() (bool, error) {
 	// order to make a guess based on the current time stamp.
 	blockHeader, err := b.cfg.ChainSource.GetBlockHeader(bestHash)
 	if err != nil {
-		return false, err
+		return false, 0, err
 	}
 
 	// If the timestamp no the best header is more than 2 hours in the
 	// past, then we're not yet synced.
 	minus24Hours := time.Now().Add(-2 * time.Hour)
-	return !blockHeader.Timestamp.Before(minus24Hours), nil
+	return !blockHeader.Timestamp.Before(minus24Hours), walletBestHeader.Timestamp.Unix(), nil
 }

lnwallet/interface.go

@@ -198,7 +198,9 @@ type WalletController interface {
 
 	// IsSynced returns a boolean indicating if from the PoV of the wallet,
 	// it has fully synced to the current best block in the main chain.
-	IsSynced() (bool, error)
+	// It also returns an int64 indicating the timestamp of the best block
+	// known to the wallet, expressed in Unix epoch time
+	IsSynced() (bool, int64, error)
 
 	// Start initializes the wallet, making any necessary connections,
 	// starting up required goroutines etc.