Add basic communication with a child process

src/common/events.h

@@ -0,0 +1,40 @@
+#pragma once
+
+#include <cinttypes>
+#include <msgpack.hpp>
+#include <optional>
+
+/**
+ * An event as dispatched by the VST host. These events will get forwarded to
+ * the VST host process running under Wine. The fields here mirror those
+ * arguments sent to the `AEffect::dispatch` function.
+ */
+struct Event {
+    int32_t opcode;
+    int32_t parameter;
+    // TODO: This is an intptr_t, is this actually a poitner that should be
+    //       dereferenced?
+    intptr_t value;
+    float option;
+
+    MSGPACK_DEFINE(opcode, parameter, value, option)
+};
+
+/**
+ * AN instance of this should be sent back as a response to an incoming event.
+ */
+struct EventResult {
+    /**
+     * The result that should be returned from the dispatch function.
+     */
+    intptr_t return_value;
+    /**
+     * If present, this should get written into the void pointer passed to the
+     * dispatch function.
+     */
+    std::optional<std::string> result;
+
+    // TODO: Add missing return value fields;
+
+    MSGPACK_DEFINE(return_value, result)
+};