json_pref_store.cc revision 21d179b334e59e9a3bfcaed4c4430bef1bc5759d 
1// Copyright (c) 2010 The Chromium 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#include "chrome/common/json_pref_store.h"
6
7#include <algorithm>
8
9#include "base/file_util.h"
10#include "base/values.h"
11#include "chrome/common/json_value_serializer.h"
12
13namespace {
14
15// Some extensions we'll tack on to copies of the Preferences files.
16const FilePath::CharType* kBadExtension = FILE_PATH_LITERAL("bad");
17
18}  // namespace
19
20JsonPrefStore::JsonPrefStore(const FilePath& filename,
21                             base::MessageLoopProxy* file_message_loop_proxy)
22    : path_(filename),
23      prefs_(new DictionaryValue()),
24      read_only_(false),
25      writer_(filename, file_message_loop_proxy) {
26}
27
28JsonPrefStore::~JsonPrefStore() {
29  if (writer_.HasPendingWrite() && !read_only_)
30    writer_.DoScheduledWrite();
31}
32
33PrefStore::ReadResult JsonPrefStore::GetValue(const std::string& key,
34                                              Value** result) const {
35  return prefs_->Get(key, result) ? READ_OK : READ_NO_VALUE;
36}
37
38void JsonPrefStore::AddObserver(PrefStore::Observer* observer) {
39  observers_.AddObserver(observer);
40}
41
42void JsonPrefStore::RemoveObserver(PrefStore::Observer* observer) {
43  observers_.RemoveObserver(observer);
44}
45
46void JsonPrefStore::SetValue(const std::string& key, Value* value) {
47  DCHECK(value);
48  scoped_ptr<Value> new_value(value);
49  Value* old_value = NULL;
50  prefs_->Get(key, &old_value);
51  if (!old_value || !value->Equals(old_value)) {
52    prefs_->Set(key, new_value.release());
53    FOR_EACH_OBSERVER(PrefStore::Observer, observers_, OnPrefValueChanged(key));
54  }
55}
56
57void JsonPrefStore::SetValueSilently(const std::string& key, Value* value) {
58  DCHECK(value);
59  scoped_ptr<Value> new_value(value);
60  Value* old_value = NULL;
61  prefs_->Get(key, &old_value);
62  if (!old_value || !value->Equals(old_value))
63    prefs_->Set(key, new_value.release());
64}
65
66void JsonPrefStore::RemoveValue(const std::string& key) {
67  if (prefs_->Remove(key, NULL)) {
68    FOR_EACH_OBSERVER(PrefStore::Observer, observers_, OnPrefValueChanged(key));
69  }
70}
71
72bool JsonPrefStore::ReadOnly() const {
73  return read_only_;
74}
75
76PersistentPrefStore::PrefReadError JsonPrefStore::ReadPrefs() {
77  if (path_.empty()) {
78    read_only_ = true;
79    return PREF_READ_ERROR_FILE_NOT_SPECIFIED;
80  }
81  JSONFileValueSerializer serializer(path_);
82
83  int error_code = 0;
84  std::string error_msg;
85  scoped_ptr<Value> value(serializer.Deserialize(&error_code, &error_msg));
86  if (!value.get()) {
87#if defined(GOOGLE_CHROME_BUILD)
88    // This log could be used for more detailed client-side error diagnosis,
89    // but since this triggers often with unit tests, we need to disable it
90    // in non-official builds.
91    PLOG(ERROR) << "Error reading Preferences: " << error_msg << " " <<
92        path_.value();
93#endif
94    PrefReadError error;
95    switch (error_code) {
96      case JSONFileValueSerializer::JSON_ACCESS_DENIED:
97        // If the file exists but is simply unreadable, put the file into a
98        // state where we don't try to save changes.  Otherwise, we could
99        // clobber the existing prefs.
100        error = PREF_READ_ERROR_ACCESS_DENIED;
101        read_only_ = true;
102        break;
103      case JSONFileValueSerializer::JSON_CANNOT_READ_FILE:
104        error = PREF_READ_ERROR_FILE_OTHER;
105        read_only_ = true;
106        break;
107      case JSONFileValueSerializer::JSON_FILE_LOCKED:
108        error = PREF_READ_ERROR_FILE_LOCKED;
109        read_only_ = true;
110        break;
111      case JSONFileValueSerializer::JSON_NO_SUCH_FILE:
112        // If the file just doesn't exist, maybe this is first run.  In any case
113        // there's no harm in writing out default prefs in this case.
114        error = PREF_READ_ERROR_NO_FILE;
115        break;
116      default:
117        error = PREF_READ_ERROR_JSON_PARSE;
118        // JSON errors indicate file corruption of some sort.
119        // Since the file is corrupt, move it to the side and continue with
120        // empty preferences.  This will result in them losing their settings.
121        // We keep the old file for possible support and debugging assistance
122        // as well as to detect if they're seeing these errors repeatedly.
123        // TODO(erikkay) Instead, use the last known good file.
124        FilePath bad = path_.ReplaceExtension(kBadExtension);
125
126        // If they've ever had a parse error before, put them in another bucket.
127        // TODO(erikkay) if we keep this error checking for very long, we may
128        // want to differentiate between recent and long ago errors.
129        if (file_util::PathExists(bad))
130          error = PREF_READ_ERROR_JSON_REPEAT;
131        file_util::Move(path_, bad);
132        break;
133    }
134    return error;
135  }
136
137  // Preferences should always have a dictionary root.
138  if (!value->IsType(Value::TYPE_DICTIONARY)) {
139    // See comment for the default case above.
140    read_only_ = true;
141    return PREF_READ_ERROR_JSON_TYPE;
142  }
143
144  prefs_.reset(static_cast<DictionaryValue*>(value.release()));
145
146  return PREF_READ_ERROR_NONE;
147}
148
149bool JsonPrefStore::WritePrefs() {
150  std::string data;
151  if (!SerializeData(&data))
152    return false;
153
154  // Lie about our ability to save.
155  if (read_only_)
156    return true;
157
158  writer_.WriteNow(data);
159  return true;
160}
161
162void JsonPrefStore::ScheduleWritePrefs() {
163  if (read_only_)
164    return;
165
166  writer_.ScheduleWrite(this);
167}
168
169bool JsonPrefStore::SerializeData(std::string* output) {
170  // TODO(tc): Do we want to prune webkit preferences that match the default
171  // value?
172  JSONStringValueSerializer serializer(output);
173  serializer.set_pretty_print(true);
174  scoped_ptr<DictionaryValue> copy(prefs_->DeepCopyWithoutEmptyChildren());
175  return serializer.Serialize(*(copy.get()));
176}
177