music source and client for subsonic

test fixture setup for navidrome

lib/sources/subsonic/xml.dart

@@ -0,0 +1,40 @@
+import 'package:xml/xml.dart';
+
+enum Status {
+  ok('ok'),
+  failed('failed');
+
+  const Status(this.value);
+  final String value;
+}
+
+class SubsonicResponse {
+  SubsonicResponse(XmlDocument xml) {
+    this.xml = xml.getElement('subsonic-response')!;
+    status = Status.values.byName(this.xml.getAttribute('status')!);
+  }
+
+  late Status status;
+  late XmlElement xml;
+}
+
+class SubsonicException implements Exception {
+  SubsonicException(this.xml) {
+    try {
+      final error = xml.getElement('error')!;
+      code = int.parse(error.getAttribute('code')!);
+      message = error.getAttribute('message')!;
+    } catch (err) {
+      code = -1;
+      message = 'Unknown error.';
+    }
+  }
+
+  final XmlElement xml;
+
+  late int code;
+  late String message;
+
+  @override
+  String toString() => 'SubsonicException [$code]: $message';
+}