Rate limiting search prefetch

The rate limiting is based on the number of attempted prefetches in the
last minute (technically, it is the number of prefetches in the caching
limit that were not served).

Bug: 1138650
Change-Id: I0ed6108a8f065c2fb7acc5a90521d978dca0f830
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2490551Reviewed-by: Robert Ogden <robertogden@chromium.org>
Commit-Queue: Ryan Sturm <ryansturm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#819894}

chrome/browser/prefetch/search_prefetch/field_trial_settings.cc

@@ -35,3 +35,9 @@ base::TimeDelta SearchPrefetchCachingLimit() {
                                              "prefetch_caching_limit_ms",
                                              60000));
 }
+
+size_t SearchPrefetchMaxAttemptsPerCachingDuration() {
+  return base::GetFieldTrialParamByFeatureAsInt(
+      kSearchPrefetchServicePrefetching, "max_attempts_per_caching_duration",
+      2);
+}

chrome/browser/prefetch/search_prefetch/field_trial_settings.h

@@ -20,4 +20,8 @@ bool SearchPrefetchServicePrefetchingIsEnabled();
 // The amount of time a response is considered valid after the prefetch starts.
 base::TimeDelta SearchPrefetchCachingLimit();
 
+// The number of prefetches that can be initiated (but not served) within a time
+// period as long as |SearchPrefetchCachingLimit()|
+size_t SearchPrefetchMaxAttemptsPerCachingDuration();
+
 #endif  // CHROME_BROWSER_PREFETCH_SEARCH_PREFETCH_FIELD_TRIAL_SETTINGS_H_

chrome/browser/prefetch/search_prefetch/search_prefetch_service.cc

@@ -149,6 +149,9 @@ bool SearchPrefetchService::MaybePrefetchURL(const GURL& url) {
   if (search_terms.size() == 0)
     return false;
 
+  if (prefetches_.size() >= SearchPrefetchMaxAttemptsPerCachingDuration())
+    return false;
+
   // Don't prefetch the same search terms twice within the expiry duration.
   if (prefetches_.find(search_terms) != prefetches_.end()) {
     return false;

chrome/browser/prefetch/search_prefetch/search_prefetch_service_browsertest.cc

@@ -293,6 +293,35 @@ IN_PROC_BROWSER_TEST_F(SearchPrefetchServiceEnabledBrowserTest,
             prefetch_status.value());
 }
 
+IN_PROC_BROWSER_TEST_F(SearchPrefetchServiceEnabledBrowserTest,
+                       PrefetchRateLimiting) {
+  auto* search_prefetch_service =
+      SearchPrefetchServiceFactory::GetForProfile(browser()->profile());
+  EXPECT_NE(nullptr, search_prefetch_service);
+
+  EXPECT_TRUE(search_prefetch_service->MaybePrefetchURL(
+      GetSearchServerQueryURL("prefetch_1")));
+  EXPECT_TRUE(search_prefetch_service->MaybePrefetchURL(
+      GetSearchServerQueryURL("prefetch_2")));
+  EXPECT_FALSE(search_prefetch_service->MaybePrefetchURL(
+      GetSearchServerQueryURL("prefetch_3")));
+
+  auto prefetch_status =
+      search_prefetch_service->GetSearchPrefetchStatusForTesting(
+          base::ASCIIToUTF16("prefetch_1"));
+  ASSERT_TRUE(prefetch_status.has_value());
+  EXPECT_EQ(SearchPrefetchStatus::kInFlight, prefetch_status.value());
+
+  prefetch_status = search_prefetch_service->GetSearchPrefetchStatusForTesting(
+      base::ASCIIToUTF16("prefetch_2"));
+  ASSERT_TRUE(prefetch_status.has_value());
+  EXPECT_EQ(SearchPrefetchStatus::kInFlight, prefetch_status.value());
+
+  prefetch_status = search_prefetch_service->GetSearchPrefetchStatusForTesting(
+      base::ASCIIToUTF16("prefetch_3"));
+  EXPECT_FALSE(prefetch_status.has_value());
+}
+
 IN_PROC_BROWSER_TEST_F(SearchPrefetchServiceEnabledBrowserTest,
                        502PrefetchFunctionality) {
   auto* search_prefetch_service =
@@ -480,3 +509,22 @@ IN_PROC_BROWSER_TEST_F(SearchPrefetchServiceZeroCacheTimeBrowserTest,
   EXPECT_FALSE(prefetch_status.has_value());
   EXPECT_TRUE(search_prefetch_service->MaybePrefetchURL(prefetch_url));
 }
+
+IN_PROC_BROWSER_TEST_F(SearchPrefetchServiceZeroCacheTimeBrowserTest,
+                       PrefetchRateLimitingClearsAfterRemoval) {
+  auto* search_prefetch_service =
+      SearchPrefetchServiceFactory::GetForProfile(browser()->profile());
+  EXPECT_NE(nullptr, search_prefetch_service);
+
+  EXPECT_TRUE(search_prefetch_service->MaybePrefetchURL(
+      GetSearchServerQueryURL("prefetch_1")));
+  EXPECT_TRUE(search_prefetch_service->MaybePrefetchURL(
+      GetSearchServerQueryURL("prefetch_2")));
+  EXPECT_FALSE(search_prefetch_service->MaybePrefetchURL(
+      GetSearchServerQueryURL("prefetch_3")));
+
+  WaitUntilStatusChanges(base::ASCIIToUTF16("prefetch_1"));
+
+  EXPECT_TRUE(search_prefetch_service->MaybePrefetchURL(
+      GetSearchServerQueryURL("prefetch_4")));
+}