Add a new macro to detect transport error in core_mqtt_serializer.h

source/core_mqtt_serializer.c

@@ -135,6 +135,13 @@
  */
 #define MQTT_REMAINING_LENGTH_INVALID ( ( size_t ) 268435456 )
 
+/**
+ * @brief A value that represents transport layer error while retreiving the remaining length.
+ *
+ * This value is greater than what is allowed by the MQTT specification.
+ */
+#define MQTT_REMAINING_LENGTH_TRANSPORT_ERROR ( ( size_t ) 268435457 )
+
 /**
  * @brief The minimum remaining length for a QoS 0 PUBLISH.
  *
@@ -822,22 +829,22 @@ static size_t getRemainingLength( TransportRecv_t recvFunc,
  }
  else if( bytesReceived < 0)
  {
- remainingLength = -1;
+ remainingLength = MQTT_REMAINING_LENGTH_TRANSPORT_ERROR;
  }
  else
  {
  remainingLength = MQTT_REMAINING_LENGTH_INVALID;
  }
  }
 
- if( remainingLength == MQTT_REMAINING_LENGTH_INVALID || remainingLength < 0)
+ if( remainingLength == MQTT_REMAINING_LENGTH_INVALID || remainingLength == MQTT_REMAINING_LENGTH_TRANSPORT_ERROR)
  {
  break;
  }
  } while( ( encodedByte & 0x80U ) != 0U );
 
  /* Check that the decoded remaining length conforms to the MQTT specification. */
- if( (remainingLength != MQTT_REMAINING_LENGTH_INVALID) && (remainingLength >=0) )
+ if( (remainingLength != MQTT_REMAINING_LENGTH_INVALID) && (remainingLength != MQTT_REMAINING_LENGTH_TRANSPORT_ERROR) )
  {
  expectedSize = remainingLengthEncodedSize( remainingLength );
 
@@ -2595,7 +2602,7 @@ MQTTStatus_t MQTT_GetIncomingPacketTypeAndLength( TransportRecv_t readFunc,
  LogError( ( "Incoming packet remaining length invalid." ) );
  status = MQTTBadResponse;
  } 
- else if( pIncomingPacket->remainingLength < 0)
+ else if( pIncomingPacket->remainingLength == MQTT_REMAINING_LENGTH_TRANSPORT_ERROR)
  {
  /* MQTT Connection status cannot be updated here hence bubble up
  * MQTTStatusDisconnectPending status to the calling API that can update it. */