Define the Settings interface for a CrashReportDatabase and provide a Mac implementation.

client/settings.cc

+// Copyright 2015 The Crashpad Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "client/settings.h"
+
+#include <fcntl.h>
+#include <unistd.h>
+#include <uuid/uuid.h>
+
+#include "base/logging.h"
+#include "base/posix/eintr_wrapper.h"
+
+namespace crashpad {
+
+struct ALIGNAS(4) Settings::Data {

[Mark Mentovai, 2015/03/09 22:00:57]

#include "base/compiler_specific.h"

+  static const uint16_t kSettingsVersion = 1;
+
+  Data() : version(kSettingsVersion),
+           options(),

[Mark Mentovai, 2015/03/09 22:00:57]

Explicit 0 for uint32_t.

+           last_upload_attempt_time(0),
+           client_id() {}
+
+  enum Options : uint32_t {
+    kUploadsEnabled = 1 << 1,

[Mark Mentovai, 2015/03/09 22:00:58]

1 << 0

+  };
+
+  uint32_t version;
+  uint32_t options;
+  uint64_t last_upload_attempt_time;

[Mark Mentovai, 2015/03/09 22:00:58]

// time_t

+  UUID client_id;
+};
+
+Settings::Settings(const base::FilePath& file_path)
+    : file_path_(file_path) {
+}
+
+Settings::~Settings() {
+}
+
+bool Settings::Initialize() {
+  ScopedFileHandle handle(HANDLE_EINTR(
+      open(file_path(),
+           O_CREAT | O_EXCL | O_WRONLY | O_EXLOCK,
+           0644)));
+
+  // The file was created, so this is a new database that needs to be
+  // initialized with a client ID.
+  if (handle.is_valid()) {
+    return InitializeSettings(handle.get());
+  }
+
+  // The file wasn't created, try opening it for a write operation. If the file
+  // needs to be recovered, writing is necessary. This also ensures that the
+  // file has write permissions.

[Mark Mentovai, 2015/03/09 22:00:58]

process has permission to write the file.

+  handle.reset(OpenForReadingAndWriting().release());
+  if (!handle.is_valid()) {
+    return false;
+  }
+
+  // Ensure that the file is valid. If it fails to read, re-initialize the
+  // settings.
+  Data settings;
+  if (!ReadSettings(handle.get(), &settings)) {
+    return RecoverSettings(handle.get(), &settings);
+  }
+
+  return true;
+}
+
+bool Settings::GetClientID(UUID* client_id) {
+  Data settings;
+  if (!OpenAndReadSettings(&settings)) {
+    return false;
+  }
+
+  *client_id = settings.client_id;
+  return true;
+}
+
+bool Settings::GetUploadsEnabled(bool* enabled) {
+  Data settings;
+  if (!OpenAndReadSettings(&settings)) {
+    return false;
+  }
+
+  *enabled = (settings.options & Data::Options::kUploadsEnabled) != 0;
+  return true;
+}
+
+bool Settings::SetUploadsEnabled(bool enabled) {
+  Data settings;
+  ScopedFileHandle handle = OpenForWritingAndReadSettings(&settings);
+  if (!handle.is_valid())
+    return false;
+
+  if (enabled)
+    settings.options |= Data::Options::kUploadsEnabled;
+  else
+    settings.options &= ~Data::Options::kUploadsEnabled;
+
+  return WriteSettings(handle.get(), settings);
+}
+
+bool Settings::GetLastUploadAttemptTime(time_t* time) {
+  Data settings;
+  if (!OpenAndReadSettings(&settings))
+    return false;
+
+  *time = settings.last_upload_attempt_time;

[Mark Mentovai, 2015/03/09 22:00:57]

saturated_cast<time_t>()…
Perhaps with a LOG(WARNING) if !base::IsValueInRangeForNumericType<time_t>()

Actually, InRangeCast<time_t>(…, std::numeric_limits<time_t>::max()) will do
both of these for you (going from unsigned to signed, saturation would only
happen on the positive end).

+  return true;
+}
+
+bool Settings::SetLastUploadAttemptTime(time_t time) {
+  Data settings;
+  ScopedFileHandle handle = OpenForWritingAndReadSettings(&settings);
+  if (!handle.is_valid())
+    return false;
+
+  settings.last_upload_attempt_time = time;

[Mark Mentovai, 2015/03/09 22:00:57]

satured_cast<uint64_t>(), again perhaps with a warning. Or
InRangeCast<uint64_t>(…, 0) (going from signed to unsigned, saturation would
only happen on the negative end provided that time_t is an integral type no
wider than uint64_t).

+
+  return WriteSettings(handle.get(), settings);
+}
+
+ScopedFileHandle Settings::OpenForReading() {
+  ScopedFileHandle handle(HANDLE_EINTR(open(file_path(), O_RDONLY | O_SHLOCK)));
+  PLOG_IF(ERROR, !handle.is_valid()) << "open for reading";
+  return handle.Pass();
+}
+
+ScopedFileHandle Settings::OpenForReadingAndWriting() {
+  ScopedFileHandle handle(HANDLE_EINTR(
+      open(file_path(), O_RDWR | O_EXLOCK | O_CREAT)));
+  PLOG_IF(ERROR, !handle.is_valid()) << "open for writing";
+  return handle.Pass();
+}
+
+bool Settings::OpenAndReadSettings(Data* out_data) {
+  ScopedFileHandle handle = OpenForReading();
+  if (!handle.is_valid())
+    return false;
+
+  if (ReadSettings(handle.get(), out_data))
+    return true;
+
+  // The settings file is corrupt, so reinitialize it.
+  handle.reset();
+
+  // The settings failed to be read, so re-initialize them.
+  return RecoverSettings(kInvalidFileHandle, out_data);
+}
+
+ScopedFileHandle Settings::OpenForWritingAndReadSettings(Data* out_data) {
+  ScopedFileHandle handle = OpenForReadingAndWriting();
+  if (!handle.is_valid())
+    return ScopedFileHandle();
+
+  if (!ReadSettings(handle.get(), out_data)) {
+    if (!RecoverSettings(handle.get(), out_data))
+      return ScopedFileHandle();
+  }
+
+  return handle.Pass();
+}
+
+bool Settings::ReadSettings(FileHandle handle, Data* out_data) {
+  if (LoggingSeekFile(handle, 0, SEEK_SET) != 0)
+    return false;
+
+  if (!LoggingReadFile(handle, out_data, sizeof(*out_data)))
+    return false;
+
+  if (out_data->version != Data::kSettingsVersion) {
+    LOG(ERROR) << "Settings version is not " << Data::kSettingsVersion;
+    return false;
+  }
+
+  return true;
+}
+
+bool Settings::WriteSettings(FileHandle handle, const Data& data) {
+  if (LoggingSeekFile(handle, 0, SEEK_SET) != 0)
+    return false;
+
+  if (HANDLE_EINTR(ftruncate(handle, 0)) != 0) {
+    PLOG(ERROR) << "ftruncate settings file";
+    return false;
+  }
+
+  return LoggingWriteFile(handle, &data, sizeof(Data));
+}
+
+bool Settings::RecoverSettings(FileHandle handle, Data* out_data) {
+  LOG(INFO) << "Recovering settings file " << file_path();

[Mark Mentovai, 2015/03/09 22:00:57]

Move this to after the next conditional, since this doesn’t actually recover
anything if it finds that it’s already been recovered once it has the exclusive
write lock. It falsely implies that this function, if successful, generated a
new client ID.

+
+  ScopedFileHandle scoped_handle;
+  if (handle == kInvalidFileHandle) {
+    scoped_handle.reset(OpenForReadingAndWriting().release());
+    handle = scoped_handle.get();
+
+    // Test if the file has already been recovered.

[Mark Mentovai, 2015/03/09 22:00:57]

The critical thing here is that the test happens under the exclusive write lock.
The comment should point this out.

+    if (ReadSettings(handle, out_data))
+      return true;
+  }
+
+  if (handle == kInvalidFileHandle) {
+    LOG(ERROR) << "Invalid file handle";
+    return false;
+  }
+
+  if (!InitializeSettings(handle))
+    return false;
+
+  return ReadSettings(handle, out_data);
+}
+
+bool Settings::InitializeSettings(FileHandle handle) {
+  uuid_t uuid;
+  uuid_generate(uuid);
+
+  Data settings;
+  settings.client_id.InitializeFromBytes(uuid);
+
+  return WriteSettings(handle, settings);
+}
+
+}  // namespace crashpad