Avoid doing concurrent DNS resolves of the same hostname

net/base/host_cache_unittest.cc

+// Copyright (c) 2009 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/base/host_cache.h"
+
+#include "base/stl_util-inl.h"
+#include "base/string_util.h"
+#include "net/base/net_errors.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace net {
+
+namespace {
+static const int kMaxCacheEntries = 10;
+static const int kCacheDurationMs = 10000;  // 10 seconds.
+}
+
+TEST(HostCacheTest, Basic) {
+  HostCache cache(kMaxCacheEntries, kCacheDurationMs);
+
+  // Start at t=0.
+  base::TimeTicks now;
+
+  const HostCache::Entry* entry1 = NULL;  // Entry for foobar.com.
+  const HostCache::Entry* entry2 = NULL;  // Entry for foobar2.com.
+
+  EXPECT_EQ(0U, cache.size());
+
+  // Add an entry for "foobar.com" at t=0.
+  EXPECT_EQ(NULL, cache.Lookup("foobar.com", base::TimeTicks()));
+  cache.Set("foobar.com", OK, AddressList(), now);
+  entry1 = cache.Lookup("foobar.com", base::TimeTicks());
+  EXPECT_FALSE(NULL == entry1);
+  EXPECT_EQ(1U, cache.size());
+
+  // Advance to t=5.
+  now += base::TimeDelta::FromSeconds(5);
+
+  // Add an entry for "foobar2.com" at t=5.
+  EXPECT_EQ(NULL, cache.Lookup("foobar2.com", base::TimeTicks()));
+  cache.Set("foobar2.com", OK, AddressList(), now);
+  entry2 = cache.Lookup("foobar2.com", base::TimeTicks());
+  EXPECT_FALSE(NULL == entry1);
+  EXPECT_EQ(2U, cache.size());
+
+  // Advance to t=9
+  now += base::TimeDelta::FromSeconds(4);
+
+  // Verify that the entries we added are still retrievable, and usable.
+  EXPECT_EQ(entry1, cache.Lookup("foobar.com", now));
+  EXPECT_EQ(entry2, cache.Lookup("foobar2.com", now));
+
+  // Advance to t=10; entry1 is now expired.
+  now += base::TimeDelta::FromSeconds(1);
+
+  EXPECT_EQ(NULL, cache.Lookup("foobar.com", now));
+  EXPECT_EQ(entry2, cache.Lookup("foobar2.com", now));
+
+  // Update entry1, so it is no longer expired.
+  cache.Set("foobar.com", OK, AddressList(), now);
+  // Re-uses existing entry storage.
+  EXPECT_EQ(entry1, cache.Lookup("foobar.com", now));
+  EXPECT_EQ(2U, cache.size());
+
+  // Both entries should still be retrievable and usable.
+  EXPECT_EQ(entry1, cache.Lookup("foobar.com", now));
+  EXPECT_EQ(entry2, cache.Lookup("foobar2.com", now));
+
+  // Advance to t=20; both entries are now expired.
+  now += base::TimeDelta::FromSeconds(10);
+
+  EXPECT_EQ(NULL, cache.Lookup("foobar.com", now));
+  EXPECT_EQ(NULL, cache.Lookup("foobar2.com", now));
+}
+
+// Try caching entries for a failed resolve attempt.
+TEST(HostCacheTest, NegativeEntry) {
+  HostCache cache(kMaxCacheEntries, kCacheDurationMs);
+
+  // Set t=0.
+  base::TimeTicks now;
+
+  EXPECT_EQ(NULL, cache.Lookup("foobar.com", base::TimeTicks()));
+  cache.Set("foobar.com", ERR_NAME_NOT_RESOLVED, AddressList(), now);
+  EXPECT_EQ(1U, cache.size());
+
+  // We disallow use of negative entries.
+  EXPECT_EQ(NULL, cache.Lookup("foobar.com", now));
+
+  // Now overwrite with a valid entry, and then overwrite with negative entry
+  // again -- the valid entry should be kicked out.
+  cache.Set("foobar.com", OK, AddressList(), now);
+  EXPECT_FALSE(NULL == cache.Lookup("foobar.com", now));
+  cache.Set("foobar.com", ERR_NAME_NOT_RESOLVED, AddressList(), now);
+  EXPECT_EQ(NULL, cache.Lookup("foobar.com", now));
+}
+
+TEST(HostCacheTest, Compact) {
+  // Initial entries limit is big enough to accomadate everything we add.
+  net::HostCache cache(kMaxCacheEntries, kCacheDurationMs);
+
+  EXPECT_EQ(0U, cache.size());
+
+  // t=10
+  base::TimeTicks now = base::TimeTicks() + base::TimeDelta::FromSeconds(10);
+
+  // Add five valid entries at t=10.
+  for (int i = 0; i < 5; ++i) {
+    std::string hostname = StringPrintf("valid%d", i);
+    cache.Set(hostname, OK, AddressList(), now);
+  }
+  EXPECT_EQ(5U, cache.size());
+
+  // Add 3 expired entries at t=0.
+  for (int i = 0; i < 3; ++i) {
+    std::string hostname = StringPrintf("expired%d", i);
+    base::TimeTicks t = now - base::TimeDelta::FromSeconds(10);
+    cache.Set(hostname, OK, AddressList(), t);
+  }
+  EXPECT_EQ(8U, cache.size());
+
+  // Add 2 negative entries at t=10
+  for (int i = 0; i < 2; ++i) {
+    std::string hostname = StringPrintf("negative%d", i);
+    cache.Set(hostname, ERR_NAME_NOT_RESOLVED, AddressList(), now);
+  }
+  EXPECT_EQ(10U, cache.size());
+
+  EXPECT_TRUE(ContainsKey(cache.entries_, "valid0"));
+  EXPECT_TRUE(ContainsKey(cache.entries_, "valid1"));
+  EXPECT_TRUE(ContainsKey(cache.entries_, "valid2"));
+  EXPECT_TRUE(ContainsKey(cache.entries_, "valid3"));
+  EXPECT_TRUE(ContainsKey(cache.entries_, "valid4"));
+  EXPECT_TRUE(ContainsKey(cache.entries_, "expired0"));
+  EXPECT_TRUE(ContainsKey(cache.entries_, "expired1"));
+  EXPECT_TRUE(ContainsKey(cache.entries_, "expired2"));
+  EXPECT_TRUE(ContainsKey(cache.entries_, "negative0"));
+  EXPECT_TRUE(ContainsKey(cache.entries_, "negative1"));
+
+  // Shrink the max constraints bound and compact. We expect the "negative"
+  // and "expired" entries to have been dropped.
+  cache.max_entries_ = 5;
+  cache.Compact(now, NULL);
+  EXPECT_EQ(5U, cache.entries_.size());
+
+  EXPECT_TRUE(ContainsKey(cache.entries_, "valid0"));
+  EXPECT_TRUE(ContainsKey(cache.entries_, "valid1"));
+  EXPECT_TRUE(ContainsKey(cache.entries_, "valid2"));
+  EXPECT_TRUE(ContainsKey(cache.entries_, "valid3"));
+  EXPECT_TRUE(ContainsKey(cache.entries_, "valid4"));
+  EXPECT_FALSE(ContainsKey(cache.entries_, "expired0"));
+  EXPECT_FALSE(ContainsKey(cache.entries_, "expired1"));
+  EXPECT_FALSE(ContainsKey(cache.entries_, "expired2"));
+  EXPECT_FALSE(ContainsKey(cache.entries_, "negative0"));
+  EXPECT_FALSE(ContainsKey(cache.entries_, "negative1"));
+
+  // Shrink further -- this time the compact will start dropping valid entries
+  // to make space.
+  cache.max_entries_ = 3;
+  cache.Compact(now, NULL);
+  EXPECT_EQ(3U, cache.size());
+}
+
+// Add entries while the cache is at capacity, causing evictions.
+TEST(HostCacheTest, SetWithCompact) {
+  net::HostCache cache(3, kCacheDurationMs);
+
+  // t=10
+  base::TimeTicks now =
+      base::TimeTicks() + base::TimeDelta::FromMilliseconds(kCacheDurationMs);
+
+  cache.Set("host1", OK, AddressList(), now);
+  cache.Set("host2", OK, AddressList(), now);
+  cache.Set("expired", OK, AddressList(),
+      now - base::TimeDelta::FromMilliseconds(kCacheDurationMs));
+
+  EXPECT_EQ(3U, cache.size());
+
+  // Should all be retrievable except "expired".
+  EXPECT_FALSE(NULL == cache.Lookup("host1", now));
+  EXPECT_FALSE(NULL == cache.Lookup("host2", now));
+  EXPECT_TRUE(NULL == cache.Lookup("expired", now));
+
+  // Adding the fourth entry will cause "expired" to be evicted.
+  cache.Set("host3", OK, AddressList(), now);
+  EXPECT_EQ(3U, cache.size());
+  EXPECT_EQ(NULL, cache.Lookup("expired", now));
+  EXPECT_FALSE(NULL == cache.Lookup("host1", now));
+  EXPECT_FALSE(NULL == cache.Lookup("host2", now));
+  EXPECT_FALSE(NULL == cache.Lookup("host3", now));
+
+  // Add two more entries. Something should be evicted, however "host5"
+  // should definitely be in there (since it was last inserted).
+  cache.Set("host4", OK, AddressList(), now);
+  EXPECT_EQ(3U, cache.size());
+  cache.Set("host5", OK, AddressList(), now);
+  EXPECT_EQ(3U, cache.size());
+  EXPECT_FALSE(NULL == cache.Lookup("host5", now));
+}
+
+TEST(HostCacheTest, NoCache) {
+  // Disable caching.
+  HostCache cache(0, kCacheDurationMs);
+  EXPECT_TRUE(cache.caching_is_disabled());
+
+  // Set t=0.
+  base::TimeTicks now;
+
+  // Lookup and Set should have no effect.
+  EXPECT_EQ(NULL, cache.Lookup("foobar.com", base::TimeTicks()));
+  cache.Set("foobar.com", OK, AddressList(), now);
+  EXPECT_EQ(NULL, cache.Lookup("foobar.com", base::TimeTicks()));
+
+  EXPECT_EQ(0U, cache.size());
+}
+
+}  // namespace net