Add new API function: feedbackPrivate.readLogSource

chrome/browser/extensions/api/feedback_private/log_source_access_manager.cc

+// Copyright 2017 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 "chrome/browser/extensions/api/feedback_private/log_source_access_manager.h"
+
+#include <algorithm>
+#include <utility>
+
+#include "base/bind.h"
+
+namespace extensions {
+
+LogSourceAccessManager::SourceAndExtension::SourceAndExtension(
+    api::feedback_private::LogSource source,
+    const std::string& extension_id)
+    : source(source), extension_id(extension_id) {}
+
+LogSourceAccessManager::LogSourceAccessManager(
+    const base::TimeDelta& min_time_between_reads)
+    : min_time_between_reads_(min_time_between_reads), weak_factory_(this) {}
+
+LogSourceAccessManager::~LogSourceAccessManager() {}
+
+bool LogSourceAccessManager::AddExtension(const SourceAndExtension& key) {
+  // emplace() returns a pair where the second element is a flag indicating
+  // whether the entry was newly added.
+  return active_keys_.emplace(key).second;
+}
+
+bool LogSourceAccessManager::RemoveExtension(const SourceAndExtension& key) {
+  auto iter = active_keys_.find(key);
+  if (iter == active_keys_.end())
+    return false;
+
+  active_keys_.erase(iter);
+  return true;
+}
+
+size_t LogSourceAccessManager::GetNumActiveExtensionsForSource(
+    api::feedback_private::LogSource source) const {
+  size_t count = 0;
+  // The stored entries are sorted first by source type, then by extension ID.
+  // We can take advantage of this fact to avoid iterating over all elements.
+  // Instead start from the first element that matches |source|, and end at the
+  // first element that does not match |source| anymore.
+  for (auto iter = active_keys_.lower_bound(SourceAndExtension(source, ""));
+       iter != active_keys_.end() && iter->source == source; ++iter) {
+    ++count;
+  }
+  return count;
+}
+
+bool LogSourceAccessManager::AccessSourceFromExtension(
+    const SourceAndExtension& key) {
+  base::Time last = GetLastExtensionAccessTime(key);
+  if (last.is_null() || base::Time::Now() > last + min_time_between_reads_) {

[tbarzic, 2017/05/25 22:46:45]

you should use TimeTicks (as Time is not guaranteed to increase monotonically)

Also, I'd add a TickClock as a member to this class - that way you can easily
mock passage of the time in tests.

E.g. in production, use DefaultTickClock, but enable test to inject a test tick
clock (e.g. SimpleTestTickClock -
https://cs.chromium.org/chromium/src/base/test/simple_test_tick_clock.h?type=...)

Then replace base::Time::Now() with tick_clock_->NowTicks();
And in tests use SimpleTestTickClock::Advance when required.

[Simon Que, 2017/05/26 04:34:38]

Done.

+    last_access_times_[key] = base::Time::Now();
+    return true;
+  }
+  return false;
+}
+
+base::Time LogSourceAccessManager::GetLastExtensionAccessTime(
+    const SourceAndExtension& key) const {
+  auto iter = last_access_times_.find(key);
+  if (iter == last_access_times_.end())
+    return base::Time();
+
+  return iter->second;
+}
+
+base::Closure LogSourceAccessManager::GetUnregisterCallback(
+    const SourceAndExtension& key) {
+  return base::Bind(&LogSourceAccessManager::RemoveExtensionNoReturn,
+                    weak_factory_.GetWeakPtr(), key);
+}
+
+void LogSourceAccessManager::RemoveExtensionNoReturn(
+    const SourceAndExtension& key) {
+  RemoveExtension(key);
+}
+
+}  // namespace extensions