Add control functions to PcmStream

-move json parsing to Server class
-improve error handling with the new ErrorCode object

common/error_code.hpp

@@ -0,0 +1,61 @@
+/***
+    This file is part of snapcast
+    Copyright (C) 2014-2021  Johannes Pohl
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#ifndef ERROR_CODE_HPP
+#define ERROR_CODE_HPP
+
+
+#include <optional>
+#include <string>
+#include <system_error>
+
+
+namespace snapcast
+{
+
+struct ErrorCode : public std::error_code
+{
+    ErrorCode() : std::error_code(), detail_(std::nullopt)
+    {
+    }
+
+    ErrorCode(const std::error_code& code) : std::error_code(code), detail_(std::nullopt)
+    {
+    }
+
+    ErrorCode(const std::error_code& code, std::string detail) : std::error_code(code), detail_(std::move(detail))
+    {
+    }
+
+    std::string detailed_message() const
+    {
+        if (detail_.has_value())
+            return message() + ": " + *detail_;
+        return message();
+    }
+
+private:
+    std::optional<std::string> detail_;
+};
+
+
+} // namespace snapcast
+
+
+
+#endif