clap-rpc

Easily add Remote Procedure Call(s) to your CLAP audio plugin(s).

Motivation

I wanted a fast and reliable way to enable out-of-process communication for plugins. This setup allows any executable to connect as a client and start interacting with the plugin — whether on the same machine or over a private network. It provides the flexibility to communicate freely with these clients, which can be written in any of the many supported languages

Introduction

The protobuf messages in clapservice.proto defines the exposed interface. In combination with gRPC, we exchange messages between clients and plugins through (long-lived) streams. A client can connect to any plugin in the CLAP bundle. The server runs on the plugin side and should be shared across plugin instances.

API Example

#include <clap-rpc/server.hpp>

std::unique_ptr<clap::rpc::Server> Server;
inline static size_t PluginCount = 0;

Plugin::Plugin(const clap_host *host)
{
    ++PluginCount;
    if (!Server) // Share the server across plugin instances within the same process
        Server = std::make_unique<clap::rpc::Server>("localhost:50552");
    mStreamHandler = Server->createStreamHandler(); // access streams
}
Plugin::~Plugin()
{
    if (--PluginCount == 0)
        Server.reset();
}

bool activate(double sampleRate, uint32_t minFrames, uint32_t maxFrames) noexcept override
{
    api::ServerMessage message;
    message.mutable_plugin()->set_plugin_api(api::plugin::Server::ACTIVATE);
    auto *act = message.mutable_plugin()->mutable_args()->mutable_activate();
    act->set_sample_rate(sampleRate);
    act->set_min_frames_count(minFrames);
    act->set_max_frames_count(maxFrames);
    mStreamHandler->pushMessage(std::move(message));
    return true;
}

Prerequisite

gRPC is a required dependency of this project.

Client Implementations

• qtcleveraudioplugin