Add DBusMessage method for retrieving simple reply arguments

2 files changed, 81 insertions, 0 deletions

diff --git a/xbmc/linux/DBusMessage.cpp b/xbmc/linux/DBusMessage.cpp
index c674b11274..e5c4f1fd2f 100644
--- a/xbmc/linux/DBusMessage.cpp
+++ b/xbmc/linux/DBusMessage.cpp
@@ -169,3 +169,30 @@ void CDBusMessage::PrepareArgument()
 
   m_haveArgs = true;
 }
+
+bool CDBusMessage::InitializeReplyIter(DBusMessageIter* iter)
+{
+  if (!m_reply)
+  {
+    throw std::logic_error("Cannot get reply arguments of message that does not have reply");
+  }
+  if (!dbus_message_iter_init(m_reply.get(), iter))
+  {
+    CLog::Log(LOGWARNING, "Tried to obtain reply arguments from message that has zero arguments");
+    return false;
+  }
+  return true;
+}
+
+bool CDBusMessage::CheckTypeAndGetValue(DBusMessageIter* iter, int expectType, void* dest)
+{
+  const int haveType = dbus_message_iter_get_arg_type(iter);
+  if (haveType != expectType)
+  {
+    CLog::Log(LOGDEBUG, "DBus argument type mismatch: expected %d, got %d", expectType, haveType);
+    return false;
+  }
+
+  dbus_message_iter_get_basic(iter, dest);
+  return true;
+}
diff --git a/xbmc/linux/DBusMessage.h b/xbmc/linux/DBusMessage.h
index 510e1514ff..f3d65530ee 100644
--- a/xbmc/linux/DBusMessage.h
+++ b/xbmc/linux/DBusMessage.h
@@ -23,6 +23,7 @@
 #include <cstdint>
 #include <memory>
 #include <string>
+#include <type_traits>
 
 #include <dbus/dbus.h>
 
@@ -42,6 +43,9 @@ template<> struct ToDBusType<std::int64_t> { static constexpr int TYPE = DBUS_TY
 template<> struct ToDBusType<std::uint64_t> { static constexpr int TYPE = DBUS_TYPE_UINT64; };
 template<> struct ToDBusType<double> { static constexpr int TYPE = DBUS_TYPE_DOUBLE; };
 
+template<typename T>
+using ToDBusTypeFromPointer = ToDBusType<typename std::remove_pointer<T>::type>;
+
 struct DBusMessageDeleter
 {
   void operator()(DBusMessage* message) const;
@@ -76,6 +80,35 @@ public:
     AppendArguments(args...);
   }
 
+  /**
+   * Retrieve simple arguments from DBus reply message
+   *
+   * You MUST use the correct fixed-width integer typedefs (e.g. std::uint16_t)
+   * corresponding to the DBus types for the variables or you will get potentially
+   * differing behavior between architectures since the DBus argument type detection
+   * is based on the width of the type.
+   *
+   * Complex arguments (arrays, structs) are not supported.
+   *
+   * Returned pointers for strings are only valid until the instance of this class
+   * is deleted.
+   *
+   * \throw std::logic_error if the message has no reply
+   * \return whether all arguments could be retrieved (false on argument type
+   *         mismatch or when more arguments were to be retrieved than there are
+   *         in the message)
+   */
+  template<typename... TArgs>
+  bool GetReplyArguments(TArgs*... args)
+  {
+    DBusMessageIter iter;
+    if (!InitializeReplyIter(&iter))
+    {
+      return false;
+    }
+    return GetReplyArgumentsWithIter(&iter, args...);
+  }
+
   DBusMessage *SendSystem();
   DBusMessage *SendSession();
   DBusMessage *SendSystem(CDBusError& error);
@@ -93,6 +126,27 @@ private:
 
   void PrepareArgument();
 
+  bool InitializeReplyIter(DBusMessageIter* iter);
+  bool CheckTypeAndGetValue(DBusMessageIter* iter, int expectType, void* dest);
+  template<typename TFirst>
+  bool GetReplyArgumentsWithIter(DBusMessageIter* iter, TFirst* first)
+  {
+    // Recursion end
+    return CheckTypeAndGetValue(iter, ToDBusTypeFromPointer<TFirst>::TYPE, first);
+  }
+  template<typename TFirst, typename... TArgs>
+  bool GetReplyArgumentsWithIter(DBusMessageIter* iter, TFirst* first, TArgs*... args)
+  {
+    if (!CheckTypeAndGetValue(iter, ToDBusTypeFromPointer<TFirst>::TYPE, first))
+    {
+      return false;
+    }
+    // Ignore return value, if we try to read past the end of the message this
+    // will be catched by the type check (past-end type is DBUS_TYPE_INVALID)
+    dbus_message_iter_next(iter);
+    return GetReplyArgumentsWithIter(iter, args...);
+  }
+
   DBusMessagePtr m_message;
   DBusMessagePtr m_reply;
   DBusMessageIter m_args;