# V5603. OWASP. The original exception object was swallowed. Stack of original exception could be lost.

The analyzer detected that the original object of a caught exception was not used properly when re-throwing from a catch block. This issue makes some errors hard to detect since the stack of the original exception is lost.

Further we will discuss a couple of examples of incorrect code. The first example:

    public Asn1Object ToAsn1Object()
    {
      try
      {
        return Foo(_constructed, _tagNumber);
      }
      catch (IOException e)
      {
        throw new ParsingException(e.Message);
      }
    }

In this code, the programmer wanted to transform the caught I/O exception into a new exception of type 'ParsingException'. However, only the message from the first exception is included, so some of the information is lost.

The fixed version of the code:

    public Asn1Object ToAsn1Object()
    {
      try
      {
        return Foo(_constructed, _tagNumber);
      }
      catch (IOException e)
      {
        throw new ParsingException(e.Message, e);
      }
    }

In the fixed version, the original exception is re-thrown as an inner one, so all the information about the original error is saved.

Here's the second example:

    private int ReadClearText(byte[] buffer, int offset, int count)
    {
      int pos = offset;
      try
      {
        ....
      }
      catch (IOException ioe)
      {
        if (pos == offset) throw ioe;
      }
      return pos - offset;
    }

In this case, the caught I/O exception is thrown again, completely erasing the stack of the original error. To avoid this defect, we just need to re-throw the original exception.

The fixed version of the code:

    private int ReadClearText(byte[] buffer, int offset, int count)
    {
      int pos = offset;
      try
      {
        ....
      }
      catch (IOException ioe)
      {
        if (pos == offset) throw;
      }
      return pos - offset;
    }

This diagnostic is classified as:

CWE-390 OWASP-11.1.8