libbrillo: Add dbus_utils::IntrospectableInterfaceHelper

dbus_utils::IntrospectableInterfaceHelper is a helper class that is
designed to work with chromeos-dbus-bindings tool to create
Introspectable DBus interface, a DBus standard interface.

BUG=none
TEST=manually with the following CL && FEATURES=test emerge-$BOARD libbrillo

Change-Id: I261e86de5b6a9c60c1f31c50dab68b142dd37aa2
Reviewed-on: https://chromium-review.googlesource.com/1797974
Tested-by: John L Chen <zuan@chromium.org>
Commit-Ready: John L Chen <zuan@chromium.org>
Legacy-Commit-Queue: Commit Bot <commit-bot@chromium.org>
Reviewed-by: Eric Caruso <ejcaruso@chromium.org>
Cr-Mirrored-From: https://chromium.googlesource.com/chromiumos/platform2
Cr-Mirrored-Commit: ca8cf7eaff618d97069beed3bfc1815eca94c8fd

3 files changed, 150 insertions, 0 deletions

diff --git a/BUILD.gn b/BUILD.gn
index dca735b..14922d5 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -100,6 +100,7 @@ libbrillo_sublibs = [
         "brillo/dbus/dbus_signal.cc",
         "brillo/dbus/exported_object_manager.cc",
         "brillo/dbus/exported_property_set.cc",
+        "brillo/dbus/introspectable_helper.cc",
         "brillo/dbus/utils.cc",
       ]
     }
diff --git a/brillo/dbus/introspectable_helper.cc b/brillo/dbus/introspectable_helper.cc
new file mode 100644
index 0000000..68ec78c
--- /dev/null
+++ b/brillo/dbus/introspectable_helper.cc
@@ -0,0 +1,81 @@
+// Copyright 2019 The Chromium OS 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 <brillo/dbus/introspectable_helper.h>
+
+#include <memory>
+
+#include <base/bind.h>
+#include <dbus/dbus-shared.h>
+
+namespace brillo {
+namespace dbus_utils {
+
+using base::Bind;
+using std::string;
+using std::unique_ptr;
+
+void IntrospectableInterfaceHelper::AddInterfaceXml(string xml) {
+  interface_xmls.push_back(xml);
+}
+
+void IntrospectableInterfaceHelper::RegisterWithDBusObject(DBusObject* object) {
+  DBusInterface* itf = object->AddOrGetInterface(DBUS_INTERFACE_INTROSPECTABLE);
+
+  itf->AddMethodHandler("Introspect", GetHandler());
+}
+
+IntrospectableInterfaceHelper::IntrospectCallback
+IntrospectableInterfaceHelper::GetHandler() {
+  return Bind(
+      [](const string& xml, StringResponse response) { response->Return(xml); },
+      GetXmlString());
+}
+
+string IntrospectableInterfaceHelper::GetXmlString() {
+  constexpr const char header[] =
+      "<!DOCTYPE node PUBLIC "
+      "\"-//freedesktop//DTD D-BUS Object Introspection 1.0//EN\"\n"
+      "\"http://www.freedesktop.org/standards/dbus/1.0/introspect.dtd\">\n"
+      "\n"
+      "<node>\n"
+      "  <interface name=\"org.freedesktop.DBus.Introspectable\">\n"
+      "    <method name=\"Introspect\">\n"
+      "      <arg name=\"data\" direction=\"out\" type=\"s\"/>\n"
+      "    </method>\n"
+      "  </interface>\n"
+      "  <interface name=\"org.freedesktop.DBus.Properties\">\n"
+      "    <method name=\"Get\">\n"
+      "      <arg name=\"interface\" direction=\"in\" type=\"s\"/>\n"
+      "      <arg name=\"propname\" direction=\"in\" type=\"s\"/>\n"
+      "      <arg name=\"value\" direction=\"out\" type=\"v\"/>\n"
+      "    </method>\n"
+      "    <method name=\"Set\">\n"
+      "      <arg name=\"interface\" direction=\"in\" type=\"s\"/>\n"
+      "      <arg name=\"propname\" direction=\"in\" type=\"s\"/>\n"
+      "      <arg name=\"value\" direction=\"in\" type=\"v\"/>\n"
+      "    </method>\n"
+      "    <method name=\"GetAll\">\n"
+      "      <arg name=\"interface\" direction=\"in\" type=\"s\"/>\n"
+      "      <arg name=\"props\" direction=\"out\" type=\"a{sv}\"/>\n"
+      "    </method>\n"
+      "  </interface>\n";
+  constexpr const char footer[] = "</node>\n";
+
+  size_t result_len = strlen(header) + strlen(footer);
+  for (const string& xml : interface_xmls) {
+    result_len += xml.size();
+  }
+
+  string result = header;
+  result.reserve(result_len + 1);  // +1 for null terminator
+  for (const string& xml : interface_xmls) {
+    result.append(xml);
+  }
+  result.append(footer);
+  return result;
+}
+
+}  // namespace dbus_utils
+}  // namespace brillo
diff --git a/brillo/dbus/introspectable_helper.h b/brillo/dbus/introspectable_helper.h
new file mode 100644
index 0000000..e1a398f
--- /dev/null
+++ b/brillo/dbus/introspectable_helper.h
@@ -0,0 +1,68 @@
+// Copyright 2019 The Chromium OS Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef LIBBRILLO_BRILLO_DBUS_INTROSPECTABLE_HELPER_H_
+#define LIBBRILLO_BRILLO_DBUS_INTROSPECTABLE_HELPER_H_
+
+#include <memory>
+#include <string>
+#include <vector>
+
+#include <brillo/brillo_export.h>
+#include <brillo/dbus/dbus_method_response.h>
+#include <brillo/dbus/dbus_object.h>
+
+namespace brillo {
+namespace dbus_utils {
+
+// Note that brillo/dbus/dbus_object.h include files that include this file, so
+// we'll need this forward declaration.
+// class DBusObject;
+
+// This is a helper class that is used for creating the DBus Introspectable
+// Interface. Each of the interfaces that is exported under a DBus Object will
+// add its dbus interface introspection XML to this class, and then the user of
+// this class will call RegisterWithDBusObject on the DBus object. Then this
+// class can be freed. Note that this class is usually used in conjunction with
+// the chromeos-dbus-bindings tool. Simply pass the string returned by
+// GetIntrospectionXML() of the generated adaptor. Usage example:
+// {
+//   IntrospectableInterfaceHelper helper;
+//   helper.AddInterfaceXML("<interface...> ...</interface>");
+//   helper.AddInterfaceXML("<interface...> ...</interface>");
+//   helper.AddInterfaceXML(XXXAdaptor::GetIntrospect());
+//   helper.RegisterWithDBusObject(object);
+// }
+class BRILLO_EXPORT IntrospectableInterfaceHelper {
+ public:
+  IntrospectableInterfaceHelper() = default;
+
+  // Add the Introspection XML for an interface to this class. The |xml| string
+  // should contain an interface XML tag and its content.
+  void AddInterfaceXml(std::string xml);
+
+  // Register the Introspectable Interface with a DBus object. Note that this
+  // class can be freed after registering with DBus object.
+  void RegisterWithDBusObject(DBusObject* object);
+
+ private:
+  // Internal alias for convenience.
+  using StringResponse = std::unique_ptr<DBusMethodResponse<std::string>>;
+  using IntrospectCallback = base::Callback<void(StringResponse)>;
+
+  // Create the method handler for Introspect method call.
+  IntrospectCallback GetHandler();
+
+  // Get the complete introspection XML.
+  std::string GetXmlString();
+
+  // Stores the list of introspection XMLs for each of the interfaces that was
+  // added to this class.
+  std::vector<std::string> interface_xmls;
+};
+
+}  // namespace dbus_utils
+}  // namespace brillo
+
+#endif  // LIBBRILLO_BRILLO_DBUS_INTROSPECTABLE_HELPER_H_