1//
2// Copyright (C) 2009 The Android Open Source Project
3//
4// Licensed under the Apache License, Version 2.0 (the "License");
5// you may not use this file except in compliance with the License.
6// You may obtain a copy of the License at
7//
8//      http://www.apache.org/licenses/LICENSE-2.0
9//
10// Unless required by applicable law or agreed to in writing, software
11// distributed under the License is distributed on an "AS IS" BASIS,
12// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13// See the License for the specific language governing permissions and
14// limitations under the License.
15//
16
17#ifndef UPDATE_ENGINE_COMMON_ACTION_PIPE_H_
18#define UPDATE_ENGINE_COMMON_ACTION_PIPE_H_
19
20#include <stdio.h>
21
22#include <map>
23#include <memory>
24#include <string>
25
26#include <base/logging.h>
27#include <base/macros.h>
28
29// The structure of these classes (Action, ActionPipe, ActionProcessor, etc.)
30// is based on the KSAction* classes from the Google Update Engine code at
31// http://code.google.com/p/update-engine/ . The author of this file sends
32// a big thanks to that team for their high quality design, implementation,
33// and documentation.
34
35// This class serves as a temporary holding area for an object passed out
36// from one Action and into another Action. It's templated so that it may
37// contain any type of object that an Action outputs/inputs. Actions
38// cannot be bonded (i.e., connected with a pipe) if their output/input
39// object types differ (a compiler error will result).
40//
41// An ActionPipe is generally created with the Bond() method and owned by
42// the two Action objects. a shared_ptr is used so that when the last Action
43// pointing to an ActionPipe dies, the ActionPipe dies, too.
44
45namespace chromeos_update_engine {
46
47// Used by Actions an InputObjectType or OutputObjectType to specify that
48// for that type, no object is taken/given.
49class NoneType {};
50
51template<typename T>
52class Action;
53
54template<typename ObjectType>
55class ActionPipe {
56 public:
57  virtual ~ActionPipe() {}
58
59  // This should be called by an Action on its input pipe.
60  // Returns a reference to the stored object.
61  const ObjectType& contents() const { return contents_; }
62
63  // This should be called by an Action on its output pipe.
64  // Stores a copy of the passed object in this pipe.
65  void set_contents(const ObjectType& contents) { contents_ = contents; }
66
67  // Bonds two Actions together with a new ActionPipe. The ActionPipe is
68  // jointly owned by the two Actions and will be automatically destroyed
69  // when the last Action is destroyed.
70  template<typename FromAction, typename ToAction>
71  static void Bond(FromAction* from, ToAction* to) {
72    std::shared_ptr<ActionPipe<ObjectType>> pipe(new ActionPipe<ObjectType>);
73    from->set_out_pipe(pipe);
74
75    to->set_in_pipe(pipe);  // If you get an error on this line, then
76    // it most likely means that the From object's OutputObjectType is
77    // different from the To object's InputObjectType.
78  }
79
80 private:
81  ObjectType contents_;
82
83  // The ctor is private. This is because this class should construct itself
84  // via the static Bond() method.
85  ActionPipe() {}
86  DISALLOW_COPY_AND_ASSIGN(ActionPipe);
87};
88
89// Utility function
90template<typename FromAction, typename ToAction>
91void BondActions(FromAction* from, ToAction* to) {
92  static_assert(
93      std::is_same<typename FromAction::OutputObjectType,
94                   typename ToAction::InputObjectType>::value,
95      "FromAction::OutputObjectType doesn't match ToAction::InputObjectType");
96  ActionPipe<typename FromAction::OutputObjectType>::Bond(from, to);
97}
98
99}  // namespace chromeos_update_engine
100
101#endif  // UPDATE_ENGINE_COMMON_ACTION_PIPE_H_
102