json_pref_store.cc revision 3345a6884c488ff3a535c2c9acdd33d74b37e311 
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::PrefReadError JsonPrefStore::ReadPrefs() {
34  if (path_.empty()) {
35    read_only_ = true;
36    return PREF_READ_ERROR_FILE_NOT_SPECIFIED;
37  }
38  JSONFileValueSerializer serializer(path_);
39
40  int error_code = 0;
41  std::string error_msg;
42  scoped_ptr<Value> value(serializer.Deserialize(&error_code, &error_msg));
43  if (!value.get()) {
44#if defined(GOOGLE_CHROME_BUILD)
45    // This log could be used for more detailed client-side error diagnosis,
46    // but since this triggers often with unit tests, we need to disable it
47    // in non-official builds.
48    PLOG(ERROR) << "Error reading Preferences: " << error_msg << " " <<
49        path_.value();
50#endif
51    PrefReadError error;
52    switch (error_code) {
53      case JSONFileValueSerializer::JSON_ACCESS_DENIED:
54        // If the file exists but is simply unreadable, put the file into a
55        // state where we don't try to save changes.  Otherwise, we could
56        // clobber the existing prefs.
57        error = PREF_READ_ERROR_ACCESS_DENIED;
58        read_only_ = true;
59        break;
60      case JSONFileValueSerializer::JSON_CANNOT_READ_FILE:
61        error = PREF_READ_ERROR_FILE_OTHER;
62        read_only_ = true;
63        break;
64      case JSONFileValueSerializer::JSON_FILE_LOCKED:
65        error = PREF_READ_ERROR_FILE_LOCKED;
66        read_only_ = true;
67        break;
68      case JSONFileValueSerializer::JSON_NO_SUCH_FILE:
69        // If the file just doesn't exist, maybe this is first run.  In any case
70        // there's no harm in writing out default prefs in this case.
71        error = PREF_READ_ERROR_NO_FILE;
72        break;
73      default:
74        error = PREF_READ_ERROR_JSON_PARSE;
75        // JSON errors indicate file corruption of some sort.
76        // Since the file is corrupt, move it to the side and continue with
77        // empty preferences.  This will result in them losing their settings.
78        // We keep the old file for possible support and debugging assistance
79        // as well as to detect if they're seeing these errors repeatedly.
80        // TODO(erikkay) Instead, use the last known good file.
81        FilePath bad = path_.ReplaceExtension(kBadExtension);
82
83        // If they've ever had a parse error before, put them in another bucket.
84        // TODO(erikkay) if we keep this error checking for very long, we may
85        // want to differentiate between recent and long ago errors.
86        if (file_util::PathExists(bad))
87          error = PREF_READ_ERROR_JSON_REPEAT;
88        file_util::Move(path_, bad);
89        break;
90    }
91    return error;
92  }
93
94  // Preferences should always have a dictionary root.
95  if (!value->IsType(Value::TYPE_DICTIONARY)) {
96    // See comment for the default case above.
97    read_only_ = true;
98    return PREF_READ_ERROR_JSON_TYPE;
99  }
100
101  prefs_.reset(static_cast<DictionaryValue*>(value.release()));
102
103  return PREF_READ_ERROR_NONE;
104}
105
106bool JsonPrefStore::WritePrefs() {
107  std::string data;
108  if (!SerializeData(&data))
109    return false;
110
111  // Lie about our ability to save.
112  if (read_only_)
113    return true;
114
115  writer_.WriteNow(data);
116  return true;
117}
118
119void JsonPrefStore::ScheduleWritePrefs() {
120  if (read_only_)
121    return;
122
123  writer_.ScheduleWrite(this);
124}
125
126bool JsonPrefStore::SerializeData(std::string* output) {
127  // TODO(tc): Do we want to prune webkit preferences that match the default
128  // value?
129  JSONStringValueSerializer serializer(output);
130  serializer.set_pretty_print(true);
131  scoped_ptr<DictionaryValue> copy(prefs_->DeepCopyWithoutEmptyChildren());
132  return serializer.Serialize(*(copy.get()));
133}
134