Add a dynamic wrapper for VstSpeakerArrangement

Similar to `DynamicVstEvents`, so we can serialize the object to binary
data transfer it over our sockets.

src/common/serialization.cpp

@@ -32,9 +32,9 @@ VstEvents& DynamicVstEvents::as_c_events() {
     // First we need to allocate enough memory for the entire object. The events
     // are stored as pointers to objects in the `events` vector that we sent
     // over the socket.
-    static_assert(std::extent<decltype(VstEvents::events)>::value == 1);
+    static_assert(std::extent_v<decltype(VstEvents::events)> == 1);
     const size_t buffer_size =
-        sizeof(VstEvents) + (events.size() - 1) * sizeof(VstEvent*);
+        sizeof(VstEvents) + ((events.size() - 1) * sizeof(VstEvent*));
     vst_events_buffer.resize(buffer_size);
 
     // Now we can populate the VLA with pointers to the objects in the `events`
@@ -47,3 +47,40 @@ VstEvents& DynamicVstEvents::as_c_events() {
 
     return *vst_events;
 }
+
+DynamicSpeakerArrangement::DynamicSpeakerArrangement(
+    const VstSpeakerArrangement& speaker_arrangement)
+    : flags(speaker_arrangement.flags),
+      speakers(speaker_arrangement.num_speakers) {
+    using speaker_type =
+        std::remove_extent_t<decltype(speaker_arrangement.speakers)>;
+    static_assert(std::is_same_v<speaker_type, VstSpeaker>);
+
+    // Copy from the C-style array into a vector for serialization
+    speakers.assign(
+        speaker_arrangement.speakers,
+        speaker_arrangement.speakers +
+            (speaker_arrangement.num_speakers * sizeof(speaker_type)));
+}
+
+VstSpeakerArrangement& DynamicSpeakerArrangement::as_c_speaker_arrangement() {
+    // Just like in `DynamicVstEvents::as_c_events()`, we will use our buffer
+    // vector to allocate enough heap space and then reconstruct the original
+    // `VstSpeakerArrangement` object passed to the constructor.
+    static_assert(std::extent_v<decltype(VstSpeakerArrangement::speakers)> ==
+                  2);
+    const size_t buffer_size = sizeof(VstSpeakerArrangement) +
+                               ((speakers.size() - 2) * sizeof(VstSpeaker));
+    speaker_arrangement_buffer.resize(buffer_size);
+
+    // Now we'll just copy over the elements from our vector to the VLA in this
+    // struct
+    VstSpeakerArrangement* speaker_arrangement =
+        reinterpret_cast<VstSpeakerArrangement*>(
+            speaker_arrangement_buffer.data());
+    speaker_arrangement->flags = flags;
+    speaker_arrangement->num_speakers = speakers.size();
+    std::copy(speakers.begin(), speakers.end(), speaker_arrangement->speakers);
+
+    return *speaker_arrangement;
+}

src/common/serialization.h

@@ -190,8 +190,9 @@ class alignas(16) DynamicVstEvents {
 
    private:
     /**
-     * Some buffer we can build a `VstEvents`. This object can be populated with
-     * contents of the `VstEvents` vector using the `as_c_events()` method.
+     * Some buffer we can build a `VstEvents` object in. This object can be
+     * populated with contents of the `VstEvents` vector using the
+     * `as_c_events()` method.
      *
      * The reason why this is necessary is because the `VstEvents` struct is
      * actually a variable size object. In the definition in
@@ -204,6 +205,54 @@ class alignas(16) DynamicVstEvents {
     std::vector<uint8_t> vst_events_buffer;
 };
 
+/**
+ * A wrapper around `VstSpeakerArrangement` that works the same way as the above
+ * wrapper for `VstEvents`. This is needed because the `VstSpeakerArrangement`
+ * struct is actually a variable sized array. Even though it will be very
+ * unlikely that we'll encounter systems with more than 8 speakers, it is
+ * something we should be able to support.
+ *
+ * Before serialization the events are read from a C-style array into a vector
+ * using this class's constructor, and after deserializing the original struct
+ * can be reconstructed using the `as_c_speaker_arrangement()` method.
+ */
+class alignas(16) DynamicSpeakerArrangement {
+   public:
+    DynamicSpeakerArrangement(){};
+
+    explicit DynamicSpeakerArrangement(
+        const VstSpeakerArrangement& speaker_arrangement);
+
+    /**
+     * Construct a dynamically sized `VstSpeakerArrangement` struct based on
+     * this object.
+     */
+    VstSpeakerArrangement& as_c_speaker_arrangement();
+
+    /**
+     * The flags field from `VstSpeakerArrangement`
+     */
+    int flags;
+
+    /**
+     * Information about the speakers in a particular input or output
+     * configuration.
+     */
+    std::vector<VstSpeaker> speakers;
+
+   private:
+    /**
+     * Some buffer we can build a `VstSpeakerArrangement` object in. This object
+     * can be populated using the `as_c_speaker_arrangement()` method.
+     *
+     * This is necessary because the `VstSpeakerArrangement` struct contains a
+     * dynamically sized array of length `VstSpeakerArrangement::num_speakers`.
+     * We build this object in a byte sized vector to make allocating enough
+     * heap space easy and safe.
+     */
+    std::vector<uint8_t> speaker_arrangement_buffer;
+};
+
 /**
  * Marker struct to indicate that that the event writes arbitrary data into one
  * of its own buffers and uses the void pointer to store start of that data,
@@ -348,8 +397,8 @@ struct Event {
  *   gets passed along.
  * - A (short) string.
  * - Some binary blob stored as a byte vector. During `effGetChunk` this will
-     contain some chunk data that should be written to
-     `PluginBridge::chunk_data`.
+ *   contain some chunk data that should be written to
+ *   `PluginBridge::chunk_data`.
  * - A specific struct in response to an event such as `audioMasterGetTime` or
  *   `audioMasterIOChanged`.
  * - An X11 window pointer for the editor window.

src/common/vst24.h

@@ -80,6 +80,9 @@ struct VstSpeaker {
  * during `eff{Get,Set}SpeakerArrangement`. Reverse engineered from Renoise by
  * attaching gdb and dumping both the `value` and `data` pointers when the host
  * calls opcode 42.
+ *
+ * Use the `DynamicSpeakerArrangement` class to serialize and construct these
+ * objects.
  */
 struct VstSpeakerArrangement {
     int flags;
@@ -88,5 +91,5 @@ struct VstSpeakerArrangement {
      * Variable length array of speakers. Similar to how `VstEvents` works, but
      * with an array of objects instead of an array of pointers to objects.
      */
-    VstSpeaker speakers[8];
+    VstSpeaker speakers[2];
 };