[net/dns] Suppress multiple DnsConfig withdrawals after timeout.

BUG=132110
TEST=net_unittests --gtest_filter=DnsConfigServiceTest.Timeout


Review URL: https://chromiumcodereview.appspot.com/10537106

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@141715 0039d316-1c4b-4281-b951-d872f2087c98

net/dns/dns_config_service.cc

@@ -75,7 +75,8 @@ base::Value* DnsConfig::ToValue() const {
 DnsConfigService::DnsConfigService()
     : have_config_(false),
       have_hosts_(false),
-      need_update_(false) {}
+      need_update_(false),
+      last_sent_empty_(true) {}
 
 DnsConfigService::~DnsConfigService() {
   // Must always clean up.
@@ -146,6 +147,10 @@ void DnsConfigService::OnHostsRead(const DnsHosts& hosts) {
 
 void DnsConfigService::StartTimer() {
   DCHECK(CalledOnValidThread());
+  if (last_sent_empty_) {
+    DCHECK(!timer_.IsRunning());
+    return;  // No need to withdraw again.
+  }
   timer_.Stop();
 
   // Give it a short timeout to come up with a valid config. Otherwise withdraw
@@ -167,19 +172,22 @@ void DnsConfigService::StartTimer() {
 
 void DnsConfigService::OnTimeout() {
   DCHECK(CalledOnValidThread());
+  DCHECK(!last_sent_empty_);
   // Indicate that even if there is no change in On*Read, we will need to
   // update the receiver when the config becomes complete.
   need_update_ = true;
   // Empty config is considered invalid.
+  last_sent_empty_ = true;
   callback_.Run(DnsConfig());
 }
 
 void DnsConfigService::OnCompleteConfig() {
   timer_.Stop();
-  if (need_update_) {
-    need_update_ = false;
-    callback_.Run(dns_config_);
-  }
+  if (!need_update_)
+    return;
+  need_update_ = false;
+  last_sent_empty_ = false;
+  callback_.Run(dns_config_);
 }
 
 }  // namespace net

net/dns/dns_config_service.h

@@ -135,6 +135,8 @@ class NET_EXPORT_PRIVATE DnsConfigService
   bool have_hosts_;
   // True if receiver needs to be updated when the config becomes complete.
   bool need_update_;
+  // True if the last config sent was empty (instead of |dns_config_|).
+  bool last_sent_empty_;
 
   // Started in Invalidate*, cleared in On*Read.
   base::OneShotTimer<DnsConfigService> timer_;

net/dns/dns_config_service_unittest.cc

@@ -114,6 +114,7 @@ TEST_F(DnsConfigServiceTest, FirstConfig) {
 TEST_F(DnsConfigServiceTest, Timeout) {
   DnsConfig config = MakeConfig(1);
   config.hosts = MakeHosts(1);
+  ASSERT_TRUE(config.IsValid());
 
   service_->OnConfigRead(config);
   service_->OnHostsRead(config.hosts);
@@ -131,6 +132,14 @@ TEST_F(DnsConfigServiceTest, Timeout) {
   WaitForConfig(TestTimeouts::action_timeout());
   EXPECT_FALSE(last_config_.IsValid());
 
+  service_->InvalidateConfig();
+  // We don't expect an update. This should time out. If we get an update,
+  // we'll detect unchanged config.
+  WaitForConfig(base::TimeDelta::FromMilliseconds(100) +
+                TestTimeouts::tiny_timeout());
+  EXPECT_FALSE(last_config_.IsValid());
+
+  service_->OnConfigRead(config);
   service_->OnHostsRead(config.hosts);
   EXPECT_TRUE(last_config_.Equals(config));
 }