[Chromoting] GetHostAttributes with tests

remoting/host/host_attributes.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 "remoting/host/host_attributes.h"
+
+#include <type_traits>
+
+#include "base/atomicops.h"
+#include "base/logging.h"
+#include "base/macros.h"
+#include "build/build_config.h"
+
+#if defined(OS_WIN)
+#include "third_party/webrtc/modules/desktop_capture/win/screen_capturer_win_directx.h"
+#endif
+
+namespace remoting {
+
+namespace {
+static constexpr char kSeparator[] = ",";
+
+struct Attribute {
+  const char* name;
+  bool(* get_value_func)();
+};
+
+inline constexpr bool IsDebug() {
+#if defined(NDEBUG)
+  return false;
+#else
+  return true;
+#endif
+}
+
+// By using arraysize() macro in base/macros.h, it's illegal to have empty
+// arrays.
+//
+// error: no matching function for call to 'ArraySizeHelper'
+// note: candidate template ignored: substitution failure
+// [with T = const remoting::StaticAttribute, N = 0]:
+// zero-length arrays are not permitted in C++.
+//
+// So we need IsDebug() function, and "Debug-Build" Attribute.
+
+static constexpr Attribute kAttributes[] = {
+  { "Debug-Build", &IsDebug },
+#if defined(OS_WIN)
+  { "DirectX-Capturer", &webrtc::ScreenCapturerWinDirectx::IsSupported },
+  // TODO(zijiehe): Add DirectX version attributes. Blocked by change
+  // https://codereview.chromium.org/2468083002/.
+#endif
+};
+
+}  // namespace
+
+static_assert(std::is_pod<Attribute>::value, "Attribute should be POD.");
+
+std::string GetHostAttributes() {
+  std::string result;
+  // By using ranged for-loop, MSVC throws error C3316:
+  // 'const remoting::StaticAttribute [0]':
+  // an array of unknown size cannot be used in a range-based for statement.
+  for (size_t i = 0; i < arraysize(kAttributes); i++) {
+    const auto& attribute = kAttributes[i];
+    DCHECK_EQ(std::string(attribute.name).find(kSeparator), std::string::npos);
+    if (attribute.get_value_func()) {
+      if (!result.empty()) {
+        result.append(kSeparator);
+      }
+      result.append(attribute.name);
+    }
+  }
+
+  return result;
+}
+
+}  // namespace remoting