add GetLatestTreeState() grpc

docs/rtd/index.html

@@ -1561,6 +1561,13 @@ <h3 id="cash.z.wallet.sdk.rpc.CompactTxStreamer">CompactTxStreamer</h3>
 The block can be specified by either height or hash.</p></td>
               </tr>
 
+              <tr>
+                <td>GetLatestTreeState</td>
+                <td><a href="#cash.z.wallet.sdk.rpc.Empty">Empty</a></td>
+                <td><a href="#cash.z.wallet.sdk.rpc.TreeState">TreeState</a></td>
+                <td><p></p></td>
+              </tr>
+
               <tr>
                 <td>GetAddressUtxos</td>
                 <td><a href="#cash.z.wallet.sdk.rpc.GetAddressUtxosArg">GetAddressUtxosArg</a></td>

frontend/service.go

@@ -242,6 +242,15 @@ func (s *lwdStreamer) GetTreeState(ctx context.Context, id *walletrpc.BlockID) (
 	}, nil
 }
 
+func (s *lwdStreamer) GetLatestTreeState(ctx context.Context, in *walletrpc.Empty) (*walletrpc.TreeState, error) {
+	latestHeight := s.cache.GetLatestHeight()
+
+	if latestHeight == -1 {
+		return nil, errors.New("Cache is empty. Server is probably not yet ready")
+	}
+	return s.GetTreeState(ctx, &walletrpc.BlockID{Height: uint64(latestHeight)})
+}
+
 // GetTransaction returns the raw transaction bytes that are returned
 // by the zcashd 'getrawtransaction' RPC.
 func (s *lwdStreamer) GetTransaction(ctx context.Context, txf *walletrpc.TxFilter) (*walletrpc.RawTransaction, error) {

walletrpc/service.proto

@@ -163,6 +163,7 @@ service CompactTxStreamer {
     // values also (even though they can be obtained using GetBlock).
     // The block can be specified by either height or hash.
     rpc GetTreeState(BlockID) returns (TreeState) {}
+    rpc GetLatestTreeState(Empty) returns (TreeState) {}
 
     rpc GetAddressUtxos(GetAddressUtxosArg) returns (GetAddressUtxosReplyList) {}
     rpc GetAddressUtxosStream(GetAddressUtxosArg) returns (stream GetAddressUtxosReply) {}