add server api for downloader

syncing/downloader/server.go

@@ -0,0 +1,48 @@
+package downloader
+
+import (
+	"context"
+	"fmt"
+	"net"
+
+	"github.com/harmony-one/harmony/node"
+	pb "github.com/harmony-one/harmony/syncing/downloader/proto"
+	"google.golang.org/grpc"
+)
+
+// Server ...
+type Server struct {
+	node *node.Node
+}
+
+// Query returns the feature at the given point.
+func (s *Server) Query(ctx context.Context, request *pb.DownloaderRequest) (*pb.DownloaderResponse, error) {
+	res := &pb.DownloaderResponse{}
+	if request.Type == pb.DownloaderRequest_HEADER {
+	} else {
+		res.Payload = append(res.Payload, []byte{1})
+	}
+	return res, nil
+}
+
+// Start ...
+func (s *Server) Start(port string) error {
+	if s.node == nil {
+		return ErrDownloaderWithNoNode
+	}
+	lis, err := net.Listen("tcp", fmt.Sprintf("localhost:%s", port))
+	if err != nil {
+
+	}
+	var opts []grpc.ServerOption
+	grpcServer := grpc.NewServer(opts...)
+	pb.RegisterDownloaderServer(grpcServer, s)
+	grpcServer.Serve(lis)
+	return nil
+}
+
+// NewServer ...
+func NewServer(node *node.Node) *Server {
+	s := &Server{node: node}
+	return s
+}