input/tidal: parse and report userMessage from error responses

src/input/plugins/TidalTrackRequest.hxx

@@ -27,9 +27,11 @@
 #include "lib/yajl/Handle.hxx"
 
 #include <exception>
+#include <memory>
 #include <string>
 
 class CurlRequest;
+class TidalErrorParser;
 
 /**
  * Callback class for #TidalTrackRequest.
@@ -54,6 +56,8 @@ class TidalTrackRequest final : CurlResponseHandler {
 
 	CurlRequest request;
 
+	std::unique_ptr<TidalErrorParser> error_parser;
+
 	Yajl::Handle parser;
 
 	enum class State {