Add error message

client/controller.cpp

@@ -59,6 +59,7 @@
 #include "browseZeroConf/browse_mdns.hpp"
 #include "common/aixlog.hpp"
 #include "common/message/client_info.hpp"
+#include "common/message/error.hpp"
 #include "common/message/hello.hpp"
 #include "common/message/time.hpp"
 #include "common/snap_exception.hpp"
@@ -299,6 +300,11 @@ void Controller::getNextMessage()
             player_->setVolume({serverSettings_->getVolume() / 100., serverSettings_->isMuted()});
             // }
         }
+        else if (response->type == message_type::kError)
+        {
+            auto error = msg::message_cast<msg::Error>(std::move(response));
+            LOG(ERROR, LOG_TAG) << "Received error: " << error->message << ", code: " << error->code << "\n";
+        }
         else
         {
             LOG(WARNING, LOG_TAG) << "Unexpected message received, type: " << response->type << "\n";

common/message/error.hpp

@@ -0,0 +1,68 @@
+/***
+    This file is part of snapcast
+    Copyright (C) 2014-2025  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/>.
+***/
+
+#pragma once
+
+
+// local headers
+#include "message.hpp"
+
+namespace msg
+{
+
+/**
+ * Generic error message
+ */
+class Error : public BaseMessage
+{
+public:
+    /// c'tor taking the @p code and @p message of error
+    explicit Error(uint32_t code, std::string message) : BaseMessage(message_type::kError), code(code), message(std::move(message))
+    {
+    }
+
+    Error() : Error(0, "")
+    {
+    }
+
+    void read(std::istream& stream) override
+    {
+        readVal(stream, code);
+        readVal(stream, message);
+    }
+
+    uint32_t getSize() const override{
+        return static_cast<uint32_t>(sizeof(uint32_t)   // code
+                                     + sizeof(uint32_t) // message len
+                                     + message.size());  // message;
+    }
+
+    /// error code
+    uint32_t code;
+    /// error message
+    std::string message;
+
+protected:
+    void doserialize(std::ostream& stream) const override
+    {
+        writeVal(stream, code);
+        writeVal(stream, message);
+    }
+};
+
+} // namespace msg

common/message/factory.hpp

@@ -21,6 +21,8 @@
 // local headers
 #include "client_info.hpp"
 #include "codec_header.hpp"
+#include "common/message/error.hpp"
+#include "error.hpp"
 #include "hello.hpp"
 #include "pcm_chunk.hpp"
 #include "server_settings.hpp"
@@ -79,6 +81,8 @@ static std::unique_ptr<BaseMessage> createMessage(const BaseMessage& base_messag
             return createMessage<PcmChunk>(base_message, buffer);
         case message_type::kClientInfo:
             return createMessage<ClientInfo>(base_message, buffer);
+        case message_type::kError:
+            return createMessage<msg::Error>(base_message, buffer);
         default:
             return nullptr;
     }

common/message/message.hpp

@@ -66,9 +66,10 @@ enum class message_type : uint16_t
     kHello = 5,
     // kStreamTags = 6,
     kClientInfo = 7,
+    kError = 8,
 
     kFirst = kBase,
-    kLast = kClientInfo
+    kLast = kError
 };
 
 /// Message type to string
@@ -97,6 +98,9 @@ static std::ostream& operator<<(std::ostream& os, const message_type& msg_type)
         case message_type::kClientInfo:
             os << "ClientInfo";
             break;
+        case message_type::kError:
+            os << "Error";
+            break;
         default:
             os << "Unknown";
     }

doc/binary_protocol.md

@@ -34,6 +34,7 @@ When a client joins a server, the following exchanges happen
 | 4                | [Time](#time)                        | C->S<br>S->C | Used for synchronizing time with the server                       |
 | 5                | [Hello](#hello)                      | C->S | Sent by the client when connecting with the server                        |
 | 7                | [Client Info](#client-info)          | C->S | Update the server when relevant information changes (e.g. client volume)  |
+| 8                | [Error](#error)                      | S->C | Error response, used e.g. for missing authentication                      |
 
 ### Base
 
@@ -144,3 +145,11 @@ Sample JSON payload (whitespace added for readability):
 ```
 
 - `volume` can have a value between 0-100 inclusive
+
+### Error
+
+| Field   | Type   | Description                                              |
+|---------|--------|----------------------------------------------------------|
+| code    | uint32 | Error code                                               |
+| size    | uint32 | Size of the following error message                      |
+| error   | char[] | string containing the error (not null terminated)        |