The component is based on two technologies:

  • instead of relying on COM, foo_rpc uses Windows named pipe for the communication protocol, having the address \\.\pipe\foobar2000.
  • the parameters to the API methods, as well as the responses are serialized with msgpack.

The APIs are exported as qualified names, where the first part is the class to which the given method belongs and the second part is the actual method itself. For instance, for starting the playback, one can call the method PlaybackControl.start, while for sorting the current playlist by a specific criteria, one can use Playlist.activeplaylist_sort_by_format. For more informations, see foo_rpc API methods.

Due to implementation limitations, we cannot know a priori what parameters a method requires when dispatching the method. Due to this, the components needs to receive a two-packed object, containing the method to be called and its parameters. For example, to call the start method, one could call the API with this payload:

msgpack::sbuffer sbuf;
msgpack::pack(sbuf, std::make_tuple(0, false));
auto params =;

msgpack::sbuffer sbuf;
msgpack::pack(sbuf, std::make_tuple("PlaybackControl.start", params));
auto payload =;

In this case, the component will know the first element of the tuple is the method, while the second is the parameters. In case the method does not need any parameters, the second element will not be unpacked, meaning that the first packing is not necessary in this case.

Each API call returns a two-element tuple, where the first element designates the status of the request, while the second one represents the result or the error, in case the request failed. In case the request succeeds, the first element is 0.