Update MQTT_GetSubAckStatusCodes

Author: AniruddhaKanhere

docs/doxygen/include/size_table.md

@@ -24,7 +24,7 @@
     </tr>
     <tr>
         <td>core_mqtt_serializer_private.c</td>
-        <td><center>0.7K</center></td>
+        <td><center>0.8K</center></td>
         <td><center>0.7K</center></td>
     </tr>
     <tr>
@@ -39,7 +39,7 @@
     </tr>
     <tr>
         <td><b>Total estimates</b></td>
-        <td><b><center>20.8K</center></b></td>
+        <td><b><center>20.9K</center></b></td>
         <td><b><center>17.5K</center></b></td>
     </tr>
 </table>

source/core_mqtt.c

@@ -4918,6 +4918,7 @@ MQTTStatus_t MQTT_GetSubAckStatusCodes( const MQTTPacketInfo_t * pSubackPacket,
                                         size_t * pPayloadSize )
 {
     MQTTStatus_t status = MQTTSuccess;
+    uint32_t propertyLength = 0;
 
     if( pSubackPacket == NULL )
     {
@@ -4948,23 +4949,39 @@ MQTTStatus_t MQTT_GetSubAckStatusCodes( const MQTTPacketInfo_t * pSubackPacket,
         status = MQTTBadParameter;
     }
 
-    /* A SUBACK must have a remaining length of at least 3 to accommodate the
-     * packet identifier and at least 1 return code. */
-    else if( pSubackPacket->remainingLength < 3U )
+    /* A SUBACK must have a remaining length of at least 4 to accommodate the
+     * packet identifier, atleast 1 byte for the property length and at least 1 return code. */
+    else if( pSubackPacket->remainingLength < 4U )
     {
         LogError( ( "Invalid parameter: Packet remaining length is invalid: "
-                    "Should be greater than 2 for SUBACK packet: InputRemainingLength=%lu",
+                    "Should be greater than or equal to 4 for SUBACK packet: InputRemainingLength=%lu",
                     ( unsigned long ) pSubackPacket->remainingLength ) );
         status = MQTTBadParameter;
     }
     else
     {
-        /* According to the MQTT 3.1.1 protocol specification, the "Remaining Length" field is a
-         * length of the variable header (2 bytes) plus the length of the payload.
-         * Therefore, we add 2 positions for the starting address of the payload, and
-         * subtract 2 bytes from the remaining length for the length of the payload. */
-        *pPayloadStart = &pSubackPacket->pRemainingData[ sizeof( uint16_t ) ];
-        *pPayloadSize = pSubackPacket->remainingLength - sizeof( uint16_t );
+        /* According to the MQTT 5.0 specification, the "Remaining Length" field represents the
+         * combined length of the variable header and the payload. In a SUBACK packet, the variable
+         * header consists of the Packet Identifier (2 bytes) followed by the properties.
+         *
+         * To locate the start of the payload:
+         * - Skip the 2-byte Packet Identifier.
+         * - Then skip the properties, whose total length is decoded using the
+         *   decodeSubackPropertyLength() function.
+         *
+         * The payload starts immediately after the properties.
+         * Its size is calculated by subtracting the size of the variable header
+         * (2 bytes for Packet ID + property length) from the remaining length.
+         */
+        status = decodeSubackPropertyLength( &pSubackPacket->pRemainingData[ sizeof( uint16_t ) ],
+                                             pSubackPacket->remainingLength,
+                                             &propertyLength );
+
+        if( status == MQTTSuccess )
+        {
+            *pPayloadStart = &pSubackPacket->pRemainingData[ sizeof( uint16_t ) + propertyLength ];
+            *pPayloadSize = pSubackPacket->remainingLength - sizeof( uint16_t ) - propertyLength;
+        }
     }
 
     return status;

source/core_mqtt_serializer_private.c

@@ -585,3 +585,28 @@ uint8_t * serializeDisconnectFixed( uint8_t * pIndex,
 }
 
 /*-----------------------------------------------------------*/
+
+MQTTStatus_t decodeSubackPropertyLength( const uint8_t * pIndex,
+                                         uint32_t remainingLength,
+                                         uint32_t * subackPropertyLength )
+{
+    MQTTStatus_t status;
+    const uint8_t * pLocalIndex = pIndex;
+    uint32_t propertyLength = 0U;
+
+    status = decodeVariableLength( pLocalIndex, remainingLength - sizeof( uint16_t ), &propertyLength );
+
+    if( status == MQTTSuccess )
+    {
+        *subackPropertyLength = ( propertyLength + variableLengthEncodedSize( propertyLength ) );
+
+        if( *subackPropertyLength > ( remainingLength - sizeof( uint16_t ) ) )
+        {
+            status = MQTTBadResponse;
+        }
+    }
+
+    return status;
+}
+
+/*-----------------------------------------------------------*/

source/include/core_mqtt.h

@@ -1361,7 +1361,17 @@ MQTTStatus_t MQTT_MatchTopic( const char * pTopicName,
  *  - 0x00 - Success - Maximum QoS 0
  *  - 0x01 - Success - Maximum QoS 1
  *  - 0x02 - Success - Maximum QoS 2
- *  - 0x80 - Failure
+ *  These are the reason codes when the server refuses the request-
+ *  - 0x80 - Topic Filter Refused
+ *  - 0x83 - Implementation specific error.
+ *  - 0x87 - Not authorized.
+ *  - 0x8F - Invalid Topic Filter.
+ *  - 0x91 - Packet identifier in use.
+ *  - 0x97 - Quota exceeded.
+ *  - 0x9E - Shared subscriptions not supported.
+ *  - 0xA1 - Subscription identifiers not supported.
+ *  - 0xA2 - Wildcard subscriptions not supported.
+ *
  * Refer to #MQTTSubAckStatus_t for the status codes.
  *
  * @param[in] pSubackPacket The SUBACK packet whose payload is to be parsed.
@@ -1372,8 +1382,8 @@ MQTTStatus_t MQTT_MatchTopic( const char * pTopicName,
  * SUBACK status is present in the packet.
  *
  * @return Returns one of the following:
- * - #MQTTBadParameter if the input SUBACK packet is invalid.
- * - #MQTTSuccess if parsing the payload was successful.
+ * - #MQTTBadParameter if the input SUBACK packet is invalid.<br>
+ * - #MQTTSuccess if parsing the payload was successful.<br>
  *
  * <b>Example</b>
  * @code{c}
@@ -1384,10 +1394,13 @@ MQTTStatus_t MQTT_MatchTopic( const char * pTopicName,
  *
  * // MQTT_GetSubAckStatusCodes is intended to be used from the application
  * // callback that is called by the library in MQTT_ProcessLoop or MQTT_ReceiveLoop.
- * void eventCallback(
+ * bool eventCallback(
  *      MQTTContext_t * pContext,
  *      MQTTPacketInfo_t * pPacketInfo,
  *      MQTTDeserializedInfo_t * pDeserializedInfo
+ *      MQTTSuccessFailReasonCode_t * pReasonCode,
+ *      MQTTPropBuilder_t * pSendPropsBuffer,
+ *      MQTTPropBuilder_t * pGetPropsBuffer
  * )
  * {
  *      MQTTStatus_t status = MQTTSuccess;

source/include/private/core_mqtt_serializer_private.h

@@ -446,6 +446,20 @@ uint8_t * serializeAckFixed( uint8_t * pIndex,
                              size_t remainingLength,
                              MQTTSuccessFailReasonCode_t reasonCode );
 
+/**
+ * @brief Decodes the property length field in a SUBACK packet.
+ *
+ * @param[in] pIndex Pointer to the start of the properties in the SUBACK packet.
+ * @param[in] remainingLength The remaining length of the MQTT packet being parsed, without Packet ID.
+ * @param[out] subackPropertyLength The decoded property length including the size of its encoded representation.
+ *
+ * @return #MQTTSuccess if the property length is successfully decoded;
+ *         #MQTTBadResponse if the decoded property length is greater than the remaining length.
+ */
+MQTTStatus_t decodeSubackPropertyLength( const uint8_t * pIndex,
+                                         uint32_t remainingLength,
+                                         uint32_t * subackPropertyLength );
+
 /**
  * @brief Serialize the fixed size part of the disconnect packet header.
  *