Introduce a request throttler for limiting requests in mobile NTP.

components/ntp_snippets/request_counter.cc

+// 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_counter.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 {
+
+const char kQuotaParamPrefix[] = "quota_";
+const char kUMAHistogramRequestStatusFormat[] =
+    "NewTabPage.RequestCounter.RequestStatus_%s";
+const char kUMAHistogramPerDayFormat[] = "NewTabPage.RequestCounter.PerDay_%s";

[Alexei Svitkine (slow), 2016/07/21 14:13:29]

Nit: If you're only using these once and in the same file, I'd actually suggest
inlining the format string so it's easier when reading the code to understand
where the param goes and that it's the right number/types of params per the
format string.

[jkrcal, 2016/07/21 18:17:57]

Done.

+
+// 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
+
+RequestCounter::RequestCounter(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, kQuotaParamPrefix + GetRequestTypeAsString());
+  if (!base::StringToInt(quota, &quota_)) {
+    LOG_IF(WARNING, !quota.empty())
+        << "Invalid variation parameter for quota for "
+        << GetRequestTypeAsString();
+    quota_ = default_quota;
+  }
+
+  // Lookup the histograms.
+  int status_count = static_cast<int>(RequestStatus::REQUEST_STATUS_COUNT);
+  histogram_request_status_ = base::LinearHistogram::FactoryGet(

[Alexei Svitkine (slow), 2016/07/21 14:13:29]

For each of these, do you mind adding a comment about what histogram macro it
corresponds to?

[jkrcal, 2016/07/21 18:17:57]

Done.

+      base::StringPrintf(kUMAHistogramRequestStatusFormat,
+                         GetRequestTypeAsString().c_str()),
+      1, status_count, status_count + 1,
+      base::HistogramBase::kUmaTargetedHistogramFlag);
+
+  histogram_per_day_ = base::Histogram::FactoryGet(
+      base::StringPrintf(kUMAHistogramPerDayFormat,
+                         GetRequestTypeAsString().c_str()),
+      1, 100, 50, base::HistogramBase::kUmaTargetedHistogramFlag);
+}
+
+// static
+void RequestCounter::RegisterProfilePrefs(PrefRegistrySimple* registry) {
+  for (const RequestTypeInfo& info : kRequestTypeInfo) {
+    registry->RegisterIntegerPref(info.count_pref, 0);
+    registry->RegisterIntegerPref(info.day_pref, 0);
+  }
+}
+
+bool RequestCounter::DemandQuotaForRequest() {
+  ResetCounterIfDayChanged();
+
+  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 RequestCounter::ReportForcedRequest() const {
+  histogram_request_status_->Add(static_cast<int>(RequestStatus::FORCED));
+}
+
+void RequestCounter::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);
+  }
+}
+
+std::string RequestCounter::GetRequestTypeAsString() const {
+  return type_info_.name;
+}
+
+int RequestCounter::GetCount() const {
+  return pref_service_->GetInteger(type_info_.count_pref);
+}
+
+void RequestCounter::SetCount(int count) {
+  pref_service_->SetInteger(type_info_.count_pref, count);
+}
+
+int RequestCounter::GetDay() const {
+  return pref_service_->GetInteger(type_info_.day_pref);
+}
+
+void RequestCounter::SetDay(int day) {
+  pref_service_->SetInteger(type_info_.day_pref, day);
+}
+
+bool RequestCounter::HasDay() const {
+  return pref_service_->HasPrefPath(type_info_.day_pref);
+}
+
+}  // namespace ntp_snippets