Implement IStreamAttributes when reading from host

This allows presets to contain meta data about file names and the type
of preset.

Even though the docs don't mention that this is also relevant for
`getState()`, we should also implement it there so plugins can write
their own meta data.

src/common/serialization/vst3/bstream.cpp

@@ -16,6 +16,8 @@
 
 #include "bstream.h"
 
+#include <pluginterfaces/vst/vstpresetkeys.h>
+
 #include <cassert>
 #include <stdexcept>
 
@@ -46,6 +48,50 @@ YaBStream::YaBStream(Steinberg::IBStream* stream) {
     assert(stream->read(buffer.data(), size, &num_bytes_read) ==
            Steinberg::kResultOk);
     assert(num_bytes_read == 0 || num_bytes_read == size);
+
+    // Starting at VST 3.6.0 streams provided by the host may contain context
+    // based meta data
+    if (Steinberg::FUnknownPtr<Steinberg::Vst::IStreamAttributes>
+            stream_attributes = stream) {
+        supports_stream_attributes = true;
+
+        Steinberg::Vst::String128 vst_string{0};
+        if (stream_attributes->getFileName(vst_string) ==
+            Steinberg::kResultOk) {
+            file_name.emplace(tchar_pointer_to_u16string(vst_string));
+        }
+
+        // Copy over all predefined meta data keys. `IAttributeList` does not
+        // offer any interface to enumerate over the stored keys.
+        // TODO: There's also
+        //       `Steinberg::Vst::PresetAttributes::kFilePathStringType`
+        //       This would require translating between Windows and Unix style
+        //       paths, which we can't easily do outside of Wine. If this ends
+        //       up being important, then we'll have to shell out to `winepath`
+        //       which is not ideal. On the Wine side we can just use the
+        //       `wine_get_dos_file_name` and `wine_get_unix_file_name`
+        //       functions instead. Requesting this should also use a 1024
+        //       character buffer.
+        attributes.emplace();
+        Steinberg::IPtr<Steinberg::Vst::IAttributeList> stream_attributes_list =
+            stream_attributes->getAttributes();
+        for (const auto& key :
+             {Steinberg::Vst::PresetAttributes::kPlugInName,
+              Steinberg::Vst::PresetAttributes::kPlugInCategory,
+              Steinberg::Vst::PresetAttributes::kInstrument,
+              Steinberg::Vst::PresetAttributes::kStyle,
+              Steinberg::Vst::PresetAttributes::kCharacter,
+              Steinberg::Vst::PresetAttributes::kStateType,
+              Steinberg::Vst::PresetAttributes::kName,
+              Steinberg::Vst::PresetAttributes::kFileName}) {
+            vst_string[0] = 0;
+            if (stream_attributes_list->getString(key, vst_string,
+                                                  sizeof(vst_string)) ==
+                Steinberg::kResultOk) {
+                attributes->setString(key, vst_string);
+            }
+        }
+    }
 }
 
 YaBStream::~YaBStream() {
@@ -64,6 +110,12 @@ tresult PLUGIN_API YaBStream::queryInterface(Steinberg::FIDString _iid,
     QUERY_INTERFACE(_iid, obj, Steinberg::ISizeableStream::iid,
                     Steinberg::ISizeableStream)
 
+    // TODO: We don't have any logging for this
+    if (supports_stream_attributes) {
+        QUERY_INTERFACE(_iid, obj, Steinberg::Vst::IStreamAttributes::iid,
+                        Steinberg::Vst::IStreamAttributes)
+    }
+
     *obj = nullptr;
     return Steinberg::kNoInterface;
 }
@@ -83,6 +135,11 @@ tresult YaBStream::write_back(Steinberg::IBStream* stream) const {
                static_cast<size_t>(num_bytes_written) == buffer.size());
     }
 
+    // TODO: Can plugins write their own meta data, and should we write those
+    //       back after `*::getState()`? I'd assume so, but the docs don't
+    //       mention this. If so then we need to always store whether the host
+    //       supports `IStreamAttributes`.
+
     return Steinberg::kResultOk;
 }
 
@@ -174,3 +231,22 @@ tresult PLUGIN_API YaBStream::setStreamSize(int64 size) {
     buffer.resize(size);
     return Steinberg::kResultOk;
 }
+
+tresult PLUGIN_API YaBStream::getFileName(Steinberg::Vst::String128 name) {
+    if (name && file_name) {
+        std::copy(file_name->begin(), file_name->end(), name);
+        name[file_name->size()] = 0;
+
+        return Steinberg::kResultOk;
+    } else {
+        return Steinberg::kResultFalse;
+    }
+}
+
+Steinberg::Vst::IAttributeList* PLUGIN_API YaBStream::getAttributes() {
+    if (attributes) {
+        return &*attributes;
+    } else {
+        return nullptr;
+    }
+}