Listen for incoming secondary event requests

src/common/communication.h

@@ -16,6 +16,10 @@
 
 #pragma once
 
+#include <atomic>
+#include <iostream>
+#include <thread>
+
 #include <bitsery/adapter/buffer.h>
 #include <bitsery/bitsery.h>
 
@@ -331,18 +335,80 @@ class EventHandler {
      * the next audio buffer gets processed.
      *
      * @param logging A pair containing a logger instance and whether or not
-     * this is for sending `dispatch()` events or host callbacks. Optional since
-     * it doesn't have to be done on both sides.
+     *   this is for sending `dispatch()` events or host callbacks. Optional
+     *   since it doesn't have to be done on both sides.
      * @param callback The function used to generate a response out of an event.
      *
      * @tparam F A function type in the form of `EventResponse(Event)`.
      *
+     *         TODO: Add a boolean flag indicating that this is being called
+     *               from an off thread
+     *
      * @relates EventHandler::send
      * @relates passthrough_event
      */
     template <typename F>
     void receive(std::optional<std::pair<Logger&, bool>> logging, F callback) {
-        // TODO: Listen for new incoming connections
+        assert(acceptor.has_value());
+
+        // As described above we'll handle incoming requests for `socket` on
+        // this thread. We'll also listen for incoming connections on `endpoint`
+        // on another thread. For any incoming connection we'll spawn a new
+        // thread to handle the request. When `socket` closes and this loop
+        // breaks, the listener and any still active threads will be cleaned up
+        // before this function exits.
+        boost::asio::io_context secondary_context{};
+
+        // This works the exact same was as `active_plugins` and
+        // `next_plugin_id` in `GroupBridge`
+        std::map<size_t, std::jthread> active_secondary_requests{};
+        std::atomic_size_t next_request_id{};
+        std::mutex active_secondary_requests_mutex;
+        accept_requests(
+            *acceptor, logging,
+            [&](boost::asio::local::stream_protocol::socket secondary_socket) {
+                const size_t request_id = next_request_id.fetch_add(1);
+
+                std::lock_guard lock(active_secondary_requests_mutex);
+                active_secondary_requests[request_id] =
+                    std::jthread([&, request_id]() {
+                        // TODO: Factor this out
+                        auto event = read_object<Event>(secondary_socket);
+                        if (logging) {
+                            auto [logger, is_dispatch] = *logging;
+                            logger.log_event(is_dispatch, event.opcode,
+                                             event.index, event.value,
+                                             event.payload, event.option,
+                                             event.value_payload);
+                        }
+
+                        EventResult response = callback(event);
+                        if (logging) {
+                            auto [logger, is_dispatch] = *logging;
+                            logger.log_event_response(is_dispatch, event.opcode,
+                                                      response.return_value,
+                                                      response.payload,
+                                                      response.value_payload);
+                        }
+
+                        write_object(secondary_socket, response);
+
+                        // When we have processed this request, we'll join the
+                        // thread again with the thread that's handling
+                        // `secondary_context`.
+                        boost::asio::post(secondary_context, [&, request_id]() {
+                            std::lock_guard lock(
+                                active_secondary_requests_mutex);
+
+                            // The join is implicit because we're using
+                            // std::jthread
+                            active_secondary_requests.erase(request_id);
+                        });
+                    });
+            });
+
+        std::jthread secondary_requests_handler(
+            [&]() { secondary_context.run(); });
 
         while (true) {
             try {
@@ -369,9 +435,57 @@ class EventHandler {
                 break;
             }
         }
+
+        // When the socket gets terminated we'll stop accepting new connections
+        // and thus terminate `secondary_requests_handler`. Dropping
+        // `active_secondary_requests` will wait for all threads to join.
+        secondary_context.stop();
     }
 
    private:
+    /**
+     * Used in `receive()` to asynchronously listen for secondary socket
+     * connections. After `callback()` returns this function will continue to be
+     * called until the IO context gets stopped.
+     *
+     * @param acceptor The acceptor we will be listening on.
+     * @param logging A pair containing a logger instance and whether or not
+     *   this is for sending `dispatch()` events or host callbacks. Optional
+     *   since it doesn't have to be done on both sides.
+     * @param callback A function that handles the new socket connection.
+     *
+     * @tparam F A function in the form
+     *   `void(boost::asio::local::stream_protocol::socket)` to handle a new
+     *   incoming connection.
+     */
+    template <typename F>
+    void accept_requests(
+        boost::asio::local::stream_protocol::acceptor& acceptor,
+        std::optional<std::pair<Logger&, bool>> logging,
+        F callback) {
+        acceptor.async_accept(
+            [&](const boost::system::error_code& error,
+                boost::asio::local::stream_protocol::socket secondary_socket) {
+                //
+                if (error.failed()) {
+                    if (logging) {
+                        auto [logger, is_dispatch] = *logging;
+                        logger.log("Failure while accepting connections: " +
+                                   error.message());
+                    } else {
+                        std::cerr << "Failure while accepting connections: "
+                                  << error.message() << std::endl;
+                    }
+
+                    return;
+                }
+
+                callback(std::move(secondary_socket));
+
+                accept_requests(acceptor, logging, callback);
+            });
+    }
+
     /**
      * The main IO context. New sockets created during `send()` will be bound to
      * this context. In `receive()` we'll create a new IO context since we want
@@ -384,9 +498,9 @@ class EventHandler {
 
     /**
      * This acceptor will be used once synchronously on the listening side
-     * during `Sockets::connect()`. When `EventHandler::receive()` is called
-     * this will be replaced by a new acceptor bound to a new IO context to
-     * receive any additional incoming connections.
+     * during `Sockets::connect()`. When `EventHandler::receive()` is then
+     * called, we'll asynchronously listen for new incoming socket connections
+     * on `endpoint` using this same acceptor.
      */
     std::optional<boost::asio::local::stream_protocol::acceptor> acceptor;