command/albumart: add "file" field with the artwork path

NEWS

@@ -4,6 +4,7 @@ ver 0.25 (not yet released)
   - new command "stringnormalization"
   - show detailed seek errors
   - support filename "cover.jxl" for "albumart" command
+  - "albumart" response includes a "file" field with the artwork path
 * decoder
   - faad: implement seeking
   - faad: output 32 bit floating point samples instead of 16 bit integer

doc/protocol.rst

@@ -1115,14 +1115,15 @@ The music database
     resides in for a file called :file:`cover.png`, :file:`cover.jpg`,
     :file:`cover.jxl`, or :file:`cover.webp`.
 
-    Returns the file size and actual number
-    of bytes read at the requested offset, followed
-    by the chunk requested as raw bytes (see :ref:`binary`), then a
-    newline and the completion code.
+    Returns the path of the artwork file (``file``), the file size
+    (``size``) and actual number of bytes read at the requested
+    offset, followed by the chunk requested as raw bytes (see
+    :ref:`binary`), then a newline and the completion code.
 
     Example::
 
      albumart foo/bar.ogg 0
+     file: foo/cover.png
      size: 1024768
      binary: 8192
      <8192 bytes>

src/command/FileCommands.cxx

@@ -161,6 +161,7 @@ find_stream_art(std::string_view directory, Mutex &mutex)
 
 static CommandResult
 read_stream_art(Response &r, const std::string_view art_directory,
+		const std::string_view display_directory,
 		size_t offset)
 {
 	// TODO: eliminate this const_cast
@@ -215,7 +216,11 @@ read_stream_art(Response &r, const std::string_view art_directory,
 			read_size += is->Read(lock, {buffer.get() + read_size, buffer_size - read_size});
 	}
 
-	r.Fmt("size: {}\n", art_file_size);
+	r.Fmt("file: {}\n"
+	      "size: {}\n",
+	      PathTraitsUTF8::Build(display_directory,
+				    PathTraitsUTF8::GetBase(is->GetUriView())),
+	      art_file_size);
 
 	r.WriteBinary({buffer.get(), read_size});
 
@@ -228,37 +233,43 @@ read_stream_art(Response &r, const std::string_view art_directory,
  * Attempt to locate the "real" directory where the given song is
  * stored.  This attempts to resolve "virtual" directories/songs,
  * e.g. expanded CUE sheet contents.
+ *
+ * Walks the relative (database) directory and the resolved (storage)
+ * directory in lockstep, so the caller has both forms available.
  */
 [[gnu::pure]]
-static std::string_view
+static std::pair<std::string_view, std::string_view>
 RealDirectoryOfSong(Client &client, const std::string_view song_uri,
-		    std::string_view directory_uri) noexcept
+		    std::string_view relative_directory,
+		    std::string_view resolved_directory) noexcept
 try {
 	const auto *db = client.GetDatabase();
 	if (db == nullptr)
-		return directory_uri;
+		return {relative_directory, resolved_directory};
 
 	const auto *song = db->GetSong(song_uri);
 	if (song == nullptr)
-		return directory_uri;
+		return {relative_directory, resolved_directory};
 
 	AtScopeExit(db, song) { db->ReturnSong(song); };
 
 	if (song->real_uri == nullptr)
-		return directory_uri;
+		return {relative_directory, resolved_directory};
 
 	const char *real_uri = song->real_uri;
 
 	/* this is a simplification which is just enough for CUE
 	   sheets (but may be incomplete): for each "../", go one
 	   level up */
-	while ((real_uri = StringAfterPrefix(real_uri, "../")) != nullptr)
-		directory_uri = PathTraitsUTF8::GetParent(directory_uri);
+	while ((real_uri = StringAfterPrefix(real_uri, "../")) != nullptr) {
+		relative_directory = PathTraitsUTF8::GetParent(relative_directory);
+		resolved_directory = PathTraitsUTF8::GetParent(resolved_directory);
+	}
 
-	return directory_uri;
+	return {relative_directory, resolved_directory};
 } catch (...) {
 	/* ignore all exceptions from Database::GetSong() */
-	return directory_uri;
+	return {relative_directory, resolved_directory};
 }
 
 static CommandResult
@@ -271,12 +282,13 @@ read_db_art(Client &client, Response &r, std::string_view uri, const uint64_t of
 	}
 	std::string uri2 = storage->MapUTF8(uri);
 
-	std::string_view directory_uri =
+	const auto [relative_directory, resolved_directory] =
 		RealDirectoryOfSong(client,
 				    uri,
+				    PathTraitsUTF8::GetParent(uri),
 				    PathTraitsUTF8::GetParent(uri2.c_str()));
 
-	return read_stream_art(r, directory_uri, offset);
+	return read_stream_art(r, resolved_directory, relative_directory, offset);
 }
 #endif
 
@@ -296,10 +308,11 @@ handle_album_art(Client &client, Request args, Response &r)
 
 	switch (located_uri.type) {
 	case LocatedUri::Type::ABSOLUTE:
-	case LocatedUri::Type::PATH:
-		return read_stream_art(r,
-				       PathTraitsUTF8::GetParent(located_uri.canonical_uri),
-				       offset);
+	case LocatedUri::Type::PATH: {
+		const auto directory =
+			PathTraitsUTF8::GetParent(located_uri.canonical_uri);
+		return read_stream_art(r, directory, directory, offset);
+	}
 
 	case LocatedUri::Type::RELATIVE:
 #ifdef ENABLE_DATABASE