code: function ServerDuplexStream(call, metadata, serialize, deserialize) {
    Duplex.call(this, {objectMode: true});
    this.call = call;
    setUpWritable(this, serialize);
    setUpReadable(this, deserialize);
    /**
     * Indicates if the call has been cancelled
     * @member {boolean} grpc~ServerReadableStream#cancelled
     */
    this.cancelled = false;
    /**
     * The request metadata from the client
     * @member {grpc.Metadata} grpc~ServerReadableStream#metadata
     */
    this.metadata = metadata;
  }
docs: A stream that the server can read from or write to. Used for calls with
  duplex streaming.
  @constructor grpc~ServerDuplexStream
  @extends external:Duplex
  @borrows grpc~ServerUnaryCall#sendMetadata as
  grpc~ServerDuplexStream#sendMetadata
  @borrows grpc~ServerUnaryCall#getPeer as grpc~ServerDuplexStream#getPeer
  @param {grpc.internal~Call} call Call object to proxy
  @param {grpc.Metadata} metadata The request metadata from the client
  @param {grpc~serialize} serialize Serialization function for requests
  @param {grpc~deserialize} deserialize Deserialization function for
  responses