Introduce a request throttler for limiting requests in mobile NTP.

components/ntp_snippets/request_throttler.cc

Index: components/ntp_snippets/request_throttler.cc
diff --git a/components/ntp_snippets/request_throttler.cc b/components/ntp_snippets/request_throttler.cc
new file mode 100644
index 0000000000000000000000000000000000000000..3055375aacbdc379101f1c12b6ec785c9e5a922d
--- /dev/null
+++ b/components/ntp_snippets/request_throttler.cc
@@ -0,0 +1,149 @@
+// Copyright 2016 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 "components/ntp_snippets/request_throttler.h"
+
+#include <vector>
+
+#include "base/metrics/histogram.h"
+#include "base/strings/string_number_conversions.h"
+#include "base/strings/string_split.h"
+#include "base/strings/stringprintf.h"
+#include "base/time/time.h"
+#include "components/ntp_snippets/ntp_snippets_constants.h"
+#include "components/ntp_snippets/pref_names.h"
+#include "components/prefs/pref_registry_simple.h"
+#include "components/prefs/pref_service.h"
+#include "components/variations/variations_associated_data.h"
+
+namespace ntp_snippets {
+
+// Used internally for working with a RequestType.
+struct RequestTypeInfo {
+  const char* name;
+  const char* count_pref;
+  const char* day_pref;
+};
+
+namespace {
+
+// Enumeration listing all possible outcomes for fetch attempts. Used for UMA
+// histogram, so do not change existing values. Insert new values at the end,
+// and update the histogram definition.
+enum class RequestStatus {
+  FORCED,
+  QUOTA_GRANTED,
+  QUOTA_EXCEEDED,
+  REQUEST_STATUS_COUNT
+};
+
+// When adding a new type here, extend also the "RequestCounterTypes"
+// <histogram_suffixes> in histograms.xml with the |name| string.
+const RequestTypeInfo kRequestTypeInfo[] = {
+    // RequestCounter::RequestType::CONTENT_SUGGESTION_FETCHER,
+    {"SuggestionFetcher", prefs::kSnippetFetcherQuotaCount,
+     prefs::kSnippetFetcherQuotaDay}};
+
+}  // namespace
+
+RequestThrottler::RequestThrottler(PrefService* pref_service,
+                               RequestType type,
+                               int default_quota)
+    : pref_service_(pref_service),
+      type_info_(kRequestTypeInfo[static_cast<int>(type)]) {
+  DCHECK(pref_service);
+
+  std::string quota = variations::GetVariationParamValue(
+      ntp_snippets::kStudyName,
+      base::StringPrintf("quota_%s", GetRequestTypeAsString()));
+  if (!base::StringToInt(quota, &quota_)) {
+    LOG_IF(WARNING, !quota.empty())
+        << "Invalid variation parameter for quota for "
+        << GetRequestTypeAsString();
+    quota_ = default_quota;
+  }
+
+  // Since the histogram names are dynamic, we cannot use the standard macros
+  // and we need to lookup the histograms, instead.
+  int status_count = static_cast<int>(RequestStatus::REQUEST_STATUS_COUNT);
+  // Corresponds to UMA_HISTOGRAM_ENUMERATION(name, sample, |status_count|).
+  histogram_request_status_ = base::LinearHistogram::FactoryGet(
+      base::StringPrintf("NewTabPage.RequestThrottler.RequestStatus_%s",
+                         GetRequestTypeAsString()),
+      1, status_count, status_count + 1,
+      base::HistogramBase::kUmaTargetedHistogramFlag);
+  // Corresponds to UMA_HISTOGRAM_COUNTS_100(name, sample).
+  histogram_per_day_ = base::Histogram::FactoryGet(
+      base::StringPrintf("NewTabPage.RequestThrottler.PerDay_%s",
+                         GetRequestTypeAsString()),
+      1, 100, 50, base::HistogramBase::kUmaTargetedHistogramFlag);
+}
+
+// static
+void RequestThrottler::RegisterProfilePrefs(PrefRegistrySimple* registry) {
+  for (const RequestTypeInfo& info : kRequestTypeInfo) {
+    registry->RegisterIntegerPref(info.count_pref, 0);
+    registry->RegisterIntegerPref(info.day_pref, 0);
+  }
+}
+
+bool RequestThrottler::DemandQuotaForRequest(bool forced_request) {
+  ResetCounterIfDayChanged();
+
+  if (forced_request) {
+    histogram_request_status_->Add(static_cast<int>(RequestStatus::FORCED));
+    return true;
+  }
+
+  int new_count = GetCount() + 1;
+  SetCount(new_count);
+  bool available = (new_count <= quota_);
+
+  histogram_request_status_->Add(
+      static_cast<int>(available ? RequestStatus::QUOTA_GRANTED
+                                 : RequestStatus::QUOTA_EXCEEDED));
+  return available;
+}
+
+void RequestThrottler::ResetCounterIfDayChanged() {
+  // The count of days since a fixed reference (the Unix epoch).
+  int now_day = (base::Time::Now() - base::Time::UnixEpoch()).InDays();
+
+  if (!HasDay()) {
+    // The counter is used for the first time in this profile.
+    SetDay(now_day);
+  } else if (now_day != GetDay()) {
+    // Day has changed - report the number of requests from the previous day.
+    histogram_per_day_->Add(GetCount());
+    // Reset the counter.
+    SetCount(0);
+    SetDay(now_day);
+  }
+}
+
+const char* RequestThrottler::GetRequestTypeAsString() const {
+  return type_info_.name;
+}
+
+int RequestThrottler::GetCount() const {
+  return pref_service_->GetInteger(type_info_.count_pref);
+}
+
+void RequestThrottler::SetCount(int count) {
+  pref_service_->SetInteger(type_info_.count_pref, count);
+}
+
+int RequestThrottler::GetDay() const {
+  return pref_service_->GetInteger(type_info_.day_pref);
+}
+
+void RequestThrottler::SetDay(int day) {
+  pref_service_->SetInteger(type_info_.day_pref, day);
+}
+
+bool RequestThrottler::HasDay() const {
+  return pref_service_->HasPrefPath(type_info_.day_pref);
+}
+
+}  // namespace ntp_snippets