[net/dns] Watch configd notifications to detect DnsConfig changes on Mac.

net/dns/notify_watcher_mac.cc

+// Copyright (c) 2012 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 "net/dns/notify_watcher_mac.h"
+
+#include <notify.h>
+
+#include "base/eintr_wrapper.h"
+#include "base/logging.h"
+
+namespace net {
+
+NotifyWatcherMac::NotifyWatcherMac() : notify_fd_(-1), notify_token_(-1) {}
+
+NotifyWatcherMac::~NotifyWatcherMac() {
+  Cancel();
+}
+
+bool NotifyWatcherMac::Watch(const char* key, const CallbackType& callback) {
+  DCHECK(key);
+  DCHECK(!callback.is_null());
+  Cancel();
+  uint32_t status = notify_register_file_descriptor(
+      key, &notify_fd_, 0, &notify_token_);
+  if (status != NOTIFY_STATUS_OK)
+    return false;
+  DCHECK_GE(notify_fd_, 0);
+  if (!MessageLoopForIO::current()->WatchFileDescriptor(
+          notify_fd_,
+          true,
+          MessageLoopForIO::WATCH_READ,
+          &watcher_,
+          this)) {
+    Cancel();
+    return false;
+  }
+  callback_ = callback;
+  return true;
+}
+
+void NotifyWatcherMac::Cancel() {
+  if (notify_fd_ >= 0) {
+    notify_cancel(notify_token_);  // Also closes |notify_fd_|.
+    notify_fd_ = -1;
+    callback_.Reset();
+    watcher_.StopWatchingFileDescriptor();
+  }
+}
+
+void NotifyWatcherMac::OnFileCanReadWithoutBlocking(int fd) {
+  int token;
+  int status = HANDLE_EINTR(read(notify_fd_, &token, sizeof(token)));
+  if (status != sizeof(token)) {
+    Cancel();
+    callback_.Run(false);
+    return;
+  }
+  // Ignoring |token| value to avoid possible endianness mismatch:
+  // http://openradar.appspot.com/8821081
+  callback_.Run(true);
+}
+
+}  // namespace net