1// Copyright 2014 The Chromium OS Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5// DBusParamWriter::Append(writer, ...) provides functionality opposite
6// to that of DBusParamReader. It writes each of the arguments to D-Bus message
7// writer and return true if successful.
8
9// DBusParamWriter::AppendDBusOutParams(writer, ...) is similar to Append()
10// but is used to send out the D-Bus OUT (pointer type) parameters in a D-Bus
11// method response message. This method skips any non-pointer parameters and
12// only appends the data for arguments that are pointers.
13
14#ifndef LIBBRILLO_BRILLO_DBUS_DBUS_PARAM_WRITER_H_
15#define LIBBRILLO_BRILLO_DBUS_DBUS_PARAM_WRITER_H_
16
17#include <brillo/dbus/data_serialization.h>
18#include <dbus/message.h>
19
20namespace brillo {
21namespace dbus_utils {
22
23class DBusParamWriter final {
24 public:
25  // Generic writer method that takes 1 or more arguments. It recursively calls
26  // itself (each time with one fewer arguments) until no more is left.
27  template<typename ParamType, typename... RestOfParams>
28  static void Append(dbus::MessageWriter* writer,
29                     const ParamType& param,
30                     const RestOfParams&... rest) {
31    // Append the current |param| to D-Bus, then call Append() with one
32    // fewer arguments, until none is left and stand-alone version of
33    // Append(dbus::MessageWriter*) is called to end the iteration.
34    DBusType<ParamType>::Write(writer, param);
35    Append(writer, rest...);
36  }
37
38  // The final overload of DBusParamWriter::Append() used when no more
39  // parameters are remaining to be written.
40  // Does nothing and finishes meta-recursion.
41  static void Append(dbus::MessageWriter* /*writer*/) {}
42
43  // Generic writer method that takes 1 or more arguments. It recursively calls
44  // itself (each time with one fewer arguments) until no more is left.
45  // Handles non-pointer parameter by just skipping over it.
46  template<typename ParamType, typename... RestOfParams>
47  static void AppendDBusOutParams(dbus::MessageWriter* writer,
48                                  const ParamType& /* param */,
49                                  const RestOfParams&... rest) {
50    // Skip the current |param| and call Append() with one fewer arguments,
51    // until none is left and stand-alone version of
52    // AppendDBusOutParams(dbus::MessageWriter*) is called to end the iteration.
53    AppendDBusOutParams(writer, rest...);
54  }
55
56  // Generic writer method that takes 1 or more arguments. It recursively calls
57  // itself (each time with one fewer arguments) until no more is left.
58  // Handles only a parameter of pointer type and writes the data pointed to
59  // to the output message buffer.
60  template<typename ParamType, typename... RestOfParams>
61  static void AppendDBusOutParams(dbus::MessageWriter* writer,
62                                  ParamType* param,
63                                  const RestOfParams&... rest) {
64    // Append the current |param| to D-Bus, then call Append() with one
65    // fewer arguments, until none is left and stand-alone version of
66    // Append(dbus::MessageWriter*) is called to end the iteration.
67    DBusType<ParamType>::Write(writer, *param);
68    AppendDBusOutParams(writer, rest...);
69  }
70
71  // The final overload of DBusParamWriter::AppendDBusOutParams() used when no
72  // more parameters are remaining to be written.
73  // Does nothing and finishes meta-recursion.
74  static void AppendDBusOutParams(dbus::MessageWriter* /*writer*/) {}
75};
76
77}  // namespace dbus_utils
78}  // namespace brillo
79
80#endif  // LIBBRILLO_BRILLO_DBUS_DBUS_PARAM_WRITER_H_
81