Implement an initial extension settings API.

chrome/browser/extensions/extension_settings_leveldb_storage.cc

+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "chrome/browser/extensions/extension_settings_leveldb_storage.h"
+
+#include "base/bind.h"
+#include "base/compiler_specific.h"
+#include "base/json/json_reader.h"
+#include "base/json/json_writer.h"
+#include "base/logging.h"
+#include "base/sys_string_conversions.h"
+#include "content/browser/browser_thread.h"
+#include "third_party/leveldb/include/leveldb/iterator.h"
+#include "third_party/leveldb/include/leveldb/write_batch.h"
+
+namespace {
+
+// Generic error message sent to extensions on failure.
+const char* kGenericOnFailureMessage = "Extension settings failed";
+
+// General closure type for computing a value on the FILE thread and calling
+// back on the UI thread.  The *OnFileThread methods should run on the file
+// thread, all others should run on the UI thread.
+//
+// Subclasses should implement RunOnFileThread(), manipulating settings_
+// or error_, then call either SucceedOnFileThread() or FailOnFileThread().
+class ResultClosure {
+ public:
+  // Ownership of callback is taken.
+  ResultClosure(leveldb::DB* db, ExtensionSettingsStorage::Callback* callback)
+      : db_(db),
+        settings_(new DictionaryValue()),
+        callback_(callback) {}
+
+  ~ResultClosure() {}
+
+  void Run() {
+    DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+    BrowserThread::PostTask(
+        BrowserThread::FILE,
+        FROM_HERE,
+        base::Bind(&ResultClosure::RunOnFileThread, base::Unretained(this)));
+  }
+
+ protected:
+  virtual void RunOnFileThread() = 0;
+
+  void SucceedOnFileThread() {
+    DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+    BrowserThread::PostTask(
+        BrowserThread::UI,
+        FROM_HERE,
+        base::Bind(&ResultClosure::Succeed, base::Unretained(this)));
+  }
+
+  void FailOnFileThread(std::string error) {
+    DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+    error_ = error;
+    BrowserThread::PostTask(
+        BrowserThread::UI,
+        FROM_HERE,
+        base::Bind(&ResultClosure::Fail, base::Unretained(this)));
+  }
+
+  // Helper for the Get() methods; reads a single key from the database using
+  // an existing leveldb options object.
+  // Returns whether the read was successful, in which case the given settings
+  // will have the value set.  Otherwise, error will be set.
+  bool ReadFromDb(
+      leveldb::ReadOptions options,
+      const std::string& key,
+      DictionaryValue* settings,
+      std::string* error) {
+    DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+    std::string value_as_json;
+    leveldb::Status s = db_->Get(options, key, &value_as_json);
+    if (s.ok()) {
+      base::JSONReader json_reader;
+      Value* value = json_reader.JsonToValue(value_as_json, false, false);
+      if (value != NULL) {
+        settings->Set(key, value);
+        return true;
+      } else {
+        // TODO(kalman): clear the offending non-JSON value from the database.
+        LOG(ERROR) << "Invalid JSON: " << value_as_json;
+        *error = "Invalid JSON";
+        return false;
+      }
+    } else if (s.IsNotFound()) {
+      // Despite there being no value, it was still a success.
+      return true;
+    } else {
+      LOG(ERROR) << "Error reading from database: " << s.ToString();
+      *error = s.ToString();
+      return false;
+    }
+  }
+
+  leveldb::DB* db_;

[Matt Perry, 2011/06/23 19:14:11]

beware of lifetime here. there's no guarantee that db_ will live longer than
ResultClosure. you need to use some sort of WeakPtr (careful, WeakPtr is not
thread safe), or a refptr.

[not at google - send to devlin, 2011/06/27 08:51:02]

Hm.  Well this actually should never happen.  The only way db_ could be deleted
is if
 1. DeleteSoon() called
 2. Get/Set/Clear/Remove whatever called
 3. FILE thread deletes this -> deletes db_
 4. FILE thead closure uses db_
However... (2) following (1) should never occur, unless the
ExtensionSettingsLeveldbStorave object is used after its GetStorage() callback
has run, which would be a programmer error.

I.e. it's just as incorrect to use the object after DeleteSoon() is called as it
is to use after delete is called.

So really -- DeleteSoon() should be flipping an about-to-be-deleted flag, and
all methods checking that this is false.

[Matt Perry, 2011/06/29 18:08:11]

I see. So you're saying RunOnFileThread is the only thing that touches db_, and
it is guaranteed to finish before the DeleteSoon task is processed. That makes
sense. Could you add a comment explaining that db_ should only be accessed from
within RunOnFileThread?

[not at google - send to devlin, 2011/08/03 06:36:51]

Done.

+  DictionaryValue* settings_;
+  std::string error_;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(ResultClosure);
+
+  void Succeed() {
+    DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+    callback_->OnSuccess(settings_);

[Matt Perry, 2011/06/23 19:14:11]

make settings_ a scoped_ptr, and use settings_.release() here instead. it's
better to have ptr ownership explicit.

[not at google - send to devlin, 2011/06/27 08:51:02]

Done.

+    delete this;
+  }
+
+  void Fail() {
+    DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+    delete settings_;
+    callback_->OnFailure(error_);
+    delete this;
+  }
+
+  scoped_ptr<ExtensionSettingsStorage::Callback> callback_;
+};
+
+// Result closure for Get(key).
+class Get1ResultClosure : public ResultClosure {
+ public:
+  Get1ResultClosure(
+      leveldb::DB* db,
+      ExtensionSettingsStorage::Callback* callback,
+      const std::string& key)
+      : ResultClosure(db, callback), key_(key) {}
+
+ protected:
+  virtual void RunOnFileThread() OVERRIDE {
+    DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+    if (ReadFromDb(leveldb::ReadOptions(), key_, settings_, &error_)) {
+      SucceedOnFileThread();
+    } else {
+      FailOnFileThread(kGenericOnFailureMessage);
+    }
+  }
+
+ private:
+  std::string key_;
+};
+
+// Result closure for Get(keys).
+class Get2ResultClosure : public ResultClosure {
+ public:
+  // Ownership of keys is taken.
+  Get2ResultClosure(
+      leveldb::DB* db,
+      ExtensionSettingsStorage::Callback* callback,
+      ListValue* keys)
+      : ResultClosure(db, callback), keys_(keys) {}
+
+ protected:
+  virtual void RunOnFileThread() OVERRIDE {
+    DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+    leveldb::ReadOptions options;
+    // All interaction with the db is done on the same thread, so snapshotting
+    // isn't strictly necessary.  This is just defensive.
+    options.snapshot = db_->GetSnapshot();
+    bool success = true;
+    std::string key;
+
+    for (ListValue::const_iterator it = keys_->begin();
+        success && it != keys_->end(); ++it) {
+      if ((*it)->GetAsString(&key)) {
+        if (!ReadFromDb(options, key, settings_, &error_)) {
+          success = false;
+        }
+      }
+    }
+    db_->ReleaseSnapshot(options.snapshot);
+
+    if (success) {
+      SucceedOnFileThread();
+    } else {
+      FailOnFileThread(kGenericOnFailureMessage);
+    }
+  }
+
+ private:
+  scoped_ptr<ListValue> keys_;
+};
+
+// Result closure for Get() .
+class Get3ResultClosure : public ResultClosure {
+ public:
+  Get3ResultClosure(
+      leveldb::DB* db,
+      ExtensionSettingsStorage::Callback* callback)
+      : ResultClosure(db, callback) {
+  }
+
+ protected:
+  virtual void RunOnFileThread() OVERRIDE {
+    DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+    base::JSONReader json_reader;
+    leveldb::ReadOptions options = leveldb::ReadOptions();
+    // All interaction with the db is done on the same thread, so snapshotting
+    // isn't strictly necessary.  This is just defensive.
+    options.snapshot = db_->GetSnapshot();
+    scoped_ptr<leveldb::Iterator> it(db_->NewIterator(options));
+
+    for (it->SeekToFirst(); it->Valid(); it->Next()) {
+      Value* value =
+          json_reader.JsonToValue(it->value().ToString(), false, false);
+      if (value != NULL) {
+        settings_->Set(it->key().ToString(), value);
+      } else {
+        // TODO(kalman): clear the offending non-JSON value from the database.
+        LOG(ERROR) << "Invalid JSON: " << it->value().ToString();
+      }
+    }
+    db_->ReleaseSnapshot(options.snapshot);
+
+    if (!it->status().ok()) {
+      LOG(ERROR) << "DB iteration failed: " << it->status().ToString();
+      FailOnFileThread(kGenericOnFailureMessage);
+    } else {
+      SucceedOnFileThread();
+    }
+  }
+};
+
+// Result closure for Set(key, value).
+class Set1ResultClosure : public ResultClosure {
+ public:
+  // Ownership of the value is taken.
+  Set1ResultClosure(
+      leveldb::DB* db,
+      ExtensionSettingsStorage::Callback* callback,
+      const std::string& key,
+      Value* value)
+      : ResultClosure(db, callback), key_(key), value_(value) {}
+
+ protected:
+  virtual void RunOnFileThread() OVERRIDE {
+    DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+    std::string value_as_json;
+    base::JSONWriter::Write(value_, false, &value_as_json);
+    leveldb::Status status =
+        db_->Put(leveldb::WriteOptions(), key_, value_as_json);
+    if (status.ok()) {
+      settings_->Set(key_, value_);
+      SucceedOnFileThread();
+    } else {
+      LOG(WARNING) << "DB write failed: " << status.ToString();
+      delete value_;
+      FailOnFileThread(kGenericOnFailureMessage);
+    }
+  }
+
+ private:
+  std::string key_;
+  Value* value_;

[Matt Perry, 2011/06/23 19:14:11]

see comment about settings_

[not at google - send to devlin, 2011/06/27 08:51:02]

Done.

+};
+
+// Result callback for Set(values).
+class Set2ResultClosure : public ResultClosure {
+ public:
+  // Ownership of values is taken.
+  Set2ResultClosure(
+      leveldb::DB* db,
+      ExtensionSettingsStorage::Callback* callback,
+      DictionaryValue* values)
+      : ResultClosure(db, callback), values_(values) {
+  }
+
+ protected:
+  virtual void RunOnFileThread() OVERRIDE {
+    DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+    // Gather keys since a dictionary can't be modified during iteration.
+    std::vector<std::string> keys;
+    for (DictionaryValue::key_iterator it = values_->begin_keys();
+        it != values_->end_keys(); ++it) {
+      keys.push_back(*it);
+    }
+    // Write values while transferring ownership from values_ to settings_.
+    std::string value_as_json;
+    leveldb::WriteBatch batch;
+    for (unsigned i = 0; i < keys.size(); ++i) {
+      Value* value = NULL;
+      values_->RemoveWithoutPathExpansion(keys[i], &value);
+      base::JSONWriter::Write(value, false, &value_as_json);
+      batch.Put(keys[i], value_as_json);
+      settings_->SetWithoutPathExpansion(keys[i], value);
+    }
+    DCHECK(values_->empty());
+
+    leveldb::Status status = db_->Write(leveldb::WriteOptions(), &batch);
+    if (status.ok()) {
+      SucceedOnFileThread();
+    } else {
+      LOG(WARNING) << "DB batch write failed: " << status.ToString();
+      FailOnFileThread(kGenericOnFailureMessage);
+    }
+  }
+
+ private:
+  scoped_ptr<DictionaryValue> values_; // will be empty on destruction
+};
+
+// Result closure for Remove(key).
+class Remove1ResultClosure : public ResultClosure {
+ public:
+  Remove1ResultClosure(
+      leveldb::DB* db,
+      ExtensionSettingsStorage::Callback* callback,
+      const std::string& key)
+      : ResultClosure(db, callback), key_(key) {
+  }
+
+ protected:
+  virtual void RunOnFileThread() OVERRIDE {
+    DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+    leveldb::Status status = db_->Delete(leveldb::WriteOptions(), key_);
+    if (status.ok() || status.IsNotFound()) {
+      SucceedOnFileThread();
+    } else {
+      LOG(WARNING) << "DB delete failed: " << status.ToString();
+      FailOnFileThread(kGenericOnFailureMessage);
+    }
+  }
+
+ private:
+  std::string key_;
+};
+
+// Result closure for Remove(keys).
+class Remove2ResultClosure : public ResultClosure {
+ public:
+  // Ownership of keys is taken.
+  Remove2ResultClosure(
+      leveldb::DB* db,
+      ExtensionSettingsStorage::Callback* callback,
+      ListValue* keys)
+      : ResultClosure(db, callback), keys_(keys) {
+  }
+
+ protected:
+  virtual void RunOnFileThread() OVERRIDE {
+    DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+    std::string key;
+    leveldb::WriteBatch batch;
+    for (ListValue::const_iterator it = keys_->begin();
+        it != keys_->end(); ++it) {
+      if ((*it)->GetAsString(&key)) {
+        batch.Delete(key);
+      }
+    }
+
+    leveldb::Status status = db_->Write(leveldb::WriteOptions(), &batch);
+    if (status.ok() || status.IsNotFound()) {
+      SucceedOnFileThread();
+    } else {
+      LOG(WARNING) << "DB batch delete failed: " << status.ToString();
+      FailOnFileThread(kGenericOnFailureMessage);
+    }
+  }
+
+ private:
+  scoped_ptr<ListValue> keys_;
+};
+
+// Result closure for Clear().
+class ClearResultClosure : public ResultClosure {
+ public:
+  ClearResultClosure(
+      leveldb::DB* db,
+      ExtensionSettingsStorage::Callback* callback)
+      : ResultClosure(db, callback) {
+  }
+
+ protected:
+  virtual void RunOnFileThread() OVERRIDE {
+    DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+    leveldb::ReadOptions options;
+    // All interaction with the db is done on the same thread, so snapshotting
+    // isn't strictly necessary.  This is just defensive.
+    options.snapshot = db_->GetSnapshot();
+    scoped_ptr<leveldb::Iterator> it(db_->NewIterator(options));
+    leveldb::WriteBatch batch;
+
+    for (it->SeekToFirst(); it->Valid(); it->Next()) {
+      batch.Delete(it->key());
+    }
+    db_->ReleaseSnapshot(options.snapshot);
+
+    if (it->status().ok()) {
+      leveldb::Status status = db_->Write(leveldb::WriteOptions(), &batch);
+      if (status.ok() || status.IsNotFound()) {
+        SucceedOnFileThread();
+      } else {
+        LOG(WARNING) << "Clear failed: " << status.ToString();
+        FailOnFileThread(kGenericOnFailureMessage);
+      }
+    } else {
+      LOG(WARNING) << "Clear iteration failed: " << it->status().ToString();
+      FailOnFileThread(kGenericOnFailureMessage);
+    }
+  }
+};
+
+// Deletes a storage area on the FILE thread.
+class DeleteStorageClosure {
+ public:
+  // Ownership of storage is taken.
+  explicit DeleteStorageClosure(ExtensionSettingsLeveldbStorage* storage)
+      : storage_(storage) {}
+
+  ~DeleteStorageClosure() {}
+
+  void Run() {
+    DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+    BrowserThread::PostTask(
+        BrowserThread::FILE,
+        FROM_HERE,
+        base::Bind(
+          &DeleteStorageClosure::RunOnFileThread, base::Unretained(this)));
+  }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(DeleteStorageClosure);
+
+  void RunOnFileThread() {
+    DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+    delete this;
+  }
+
+  scoped_ptr<ExtensionSettingsStorage> storage_;
+};
+
+}  // namespace
+
+/* static */
+ExtensionSettingsLeveldbStorage* ExtensionSettingsLeveldbStorage::Create(
+      const FilePath& base_path,
+      const std::string& extension_id) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+  FilePath path = base_path.AppendASCII(extension_id);
+
+#if defined(OS_POSIX)
+  std::string os_path(path.value());
+#elif defined(OS_WIN)
+  std::string os_path = base::SysWideToUTF8(path.value());
+#endif
+
+  leveldb::Options options;
+  options.create_if_missing = true;
+  leveldb::DB* db;
+  leveldb::Status status = leveldb::DB::Open(options, os_path, &db);
+  if (!status.ok()) {
+    LOG(WARNING) << "Failed to create leveldb at " << path.value() <<
+      ": " << status.ToString();
+    return NULL;
+  }
+  return new ExtensionSettingsLeveldbStorage(db);
+}
+
+void ExtensionSettingsLeveldbStorage::DestroyEventually() {
+  (new DeleteStorageClosure(this))->Run();

[Matt Perry, 2011/06/23 19:14:11]

we have BrowserThread::DeleteSoon to handle this case

[not at google - send to devlin, 2011/06/27 08:51:02]

Done.

+}
+
+void ExtensionSettingsLeveldbStorage::Get(
+    const std::string& key, ExtensionSettingsStorage::Callback* callback) {
+  (new Get1ResultClosure(db_.get(), callback, key))->Run();
+}
+
+void ExtensionSettingsLeveldbStorage::Get(
+    const ListValue& keys, ExtensionSettingsStorage::Callback* callback) {
+  (new Get2ResultClosure(db_.get(), callback, keys.DeepCopy()))->Run();
+}
+
+void ExtensionSettingsLeveldbStorage::Get(
+    ExtensionSettingsStorage::Callback* callback) {
+  (new Get3ResultClosure(db_.get(), callback))->Run();
+}
+
+void ExtensionSettingsLeveldbStorage::Set(
+    const std::string& key,
+    const Value& value,
+    ExtensionSettingsStorage::Callback* callback) {
+  (new Set1ResultClosure(db_.get(), callback, key, value.DeepCopy()))->Run();
+}
+
+void ExtensionSettingsLeveldbStorage::Set(
+    const DictionaryValue& values,
+    ExtensionSettingsStorage::Callback* callback) {
+  (new Set2ResultClosure(db_.get(), callback, values.DeepCopy()))->Run();
+}
+
+void ExtensionSettingsLeveldbStorage::Remove(
+    const std::string& key, ExtensionSettingsStorage::Callback *callback) {
+  (new Remove1ResultClosure(db_.get(), callback, key))->Run();
+}
+
+void ExtensionSettingsLeveldbStorage::Remove(
+    const ListValue& keys, ExtensionSettingsStorage::Callback *callback) {
+  (new Remove2ResultClosure(db_.get(), callback, keys.DeepCopy()))->Run();
+}
+
+void ExtensionSettingsLeveldbStorage::Clear(
+    ExtensionSettingsStorage::Callback* callback) {
+  (new ClearResultClosure(db_.get(), callback))->Run();
+}
+
+ExtensionSettingsLeveldbStorage::ExtensionSettingsLeveldbStorage(
+    leveldb::DB* db)
+    : db_(db) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+}
+
+ExtensionSettingsLeveldbStorage::~ExtensionSettingsLeveldbStorage() {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+}