code: function ClientWritableStream(call) {
    Writable.call(this, {objectMode: true});
    this.call = call;
    var self = this;
    this.on('finish', function() {
      self.call.halfClose();
    });
  }
docs: A stream that the client can write to. Used for calls that are streaming from
  the client side.
  @constructor grpc~ClientWritableStream
  @extends external:Writable
  @borrows grpc~ClientUnaryCall#cancel as grpc~ClientWritableStream#cancel
  @borrows grpc~ClientUnaryCall#getPeer as grpc~ClientWritableStream#getPeer
  @borrows grpc~ClientUnaryCall#event:metadata as
  grpc~ClientWritableStream#metadata
  @borrows grpc~ClientUnaryCall#event:status as
  grpc~ClientWritableStream#status
  @param {InterceptingCall} call Exposes gRPC request operations, processed by
  an interceptor stack.