Implement IComponent::getState()

With this the basic IComponent interface is fully implemented. Next will
be `IAudioProcessor` and `IConnectionPoint` as additions to IComponent.
We'll use the same `known_iids` mechanism as used in the plugin factory.

src/common/serialization/vst3.h

@@ -68,6 +68,7 @@ using ControlRequest = std::variant<YaComponent::Construct,
                                     YaComponent::ActivateBus,
                                     YaComponent::SetActive,
                                     YaComponent::SetState,
+                                    YaComponent::GetState,
                                     YaPluginFactory::Construct,
                                     YaPluginFactory::SetHostContext>;
 

src/common/serialization/vst3/base.cpp

@@ -175,15 +175,15 @@ tresult PLUGIN_API VectorStream::queryInterface(Steinberg::FIDString _iid,
     return Steinberg::kNoInterface;
 }
 
-tresult VectorStream::write_back(Steinberg::IBStream* stream) {
+tresult VectorStream::write_back(Steinberg::IBStream* stream) const {
     if (!stream) {
         return Steinberg::kInvalidArgument;
     }
 
     int32 num_bytes_written;
     assert(stream->seek(0, kIBSeekSet) == Steinberg::kResultOk);
-    assert(stream->write(buffer.data(), buffer.size(), &num_bytes_written) ==
-           Steinberg::kResultOk);
+    assert(stream->write(const_cast<uint8_t*>(buffer.data()), buffer.size(),
+                         &num_bytes_written) == Steinberg::kResultOk);
 
     assert(num_bytes_written == 0 ||
            static_cast<size_t>(num_bytes_written) == buffer.size());

src/common/serialization/vst3/base.h

@@ -140,7 +140,7 @@ class VectorStream : public Steinberg::IBStream,
      * Write the vector buffer back to an IBStream. After writing the seek
      * position will be left at the end of the stream.
      */
-    tresult write_back(Steinberg::IBStream* stream);
+    tresult write_back(Steinberg::IBStream* stream) const;
 
     /**
      * Return the buffer's, used in the logging messages.

src/common/serialization/vst3/component.h

@@ -371,6 +371,37 @@ class YaComponent : public Steinberg::Vst::IComponent {
 
     virtual tresult PLUGIN_API
     setState(Steinberg::IBStream* state) override = 0;
+
+    /**
+     * The response code and written state for a call to
+     * `IComponent::getState(state)`.
+     */
+    struct GetStateResponse {
+        UniversalTResult result;
+        VectorStream updated_state;
+
+        template <typename S>
+        void serialize(S& s) {
+            s.object(result);
+            s.object(updated_state);
+        }
+    };
+
+    /**
+     * Message to pass through a call to `IComponent::getState(state)` to the
+     * Wine plugin host.
+     */
+    struct GetState {
+        using Response = GetStateResponse;
+
+        native_size_t instance_id;
+
+        template <typename S>
+        void serialize(S& s) {
+            s.value8b(instance_id);
+        }
+    };
+
     virtual tresult PLUGIN_API
     getState(Steinberg::IBStream* state) override = 0;