MemoryStream, XmlTextWriter and Warning 4 CA2202 : Microsoft.Usage

Question

The Run Code Analysis command in Visual Studio 2010 Ultimate returns a warning when seeing a certain pattern with MemoryStream and XmlTextWriter.

This is the warning:

Warning 7 CA2202 : Microsoft.Usage : Object 'ms' can be disposed more than once in method 'KinteWritePages.GetXPathDocument(DbConnection)'. To avoid generating a System.ObjectDisposedException you should not call Dispose more than one time on an object.: Lines: 421 C:\Visual Studio 2010\Projects\Songhay.DataAccess.KinteWritePages\KinteWritePages.cs 421 Songhay.DataAccess.KinteWritePages

This is the form:

static XPathDocument GetXPathDocument(DbConnection connection)
{
    XPathDocument xpDoc = null;
    var ms = new MemoryStream();
    try
    {
        using(XmlTextWriter writer = new XmlTextWriter(ms, Encoding.UTF8))
        {
            using(DbDataReader reader = CommonReader.GetReader(connection, Resources.KinteRssSql))
            {

                writer.WriteStartDocument();
                writer.WriteStartElement("data");

                do
                {
                    while(reader.Read())
                    {
                        writer.WriteStartElement("item");
                        for(int i = 0; i < reader.FieldCount; i++)
                        {
                            writer.WriteRaw(String.Format("<{0}>{1}</{0}>", reader.GetName(i), reader[i].ToString()));
                        }
                        writer.WriteFullEndElement();
                    }

                } while(reader.NextResult());

                writer.WriteFullEndElement();
                writer.WriteEndDocument();

                writer.Flush();
                ms.Position = 0;

                xpDoc = new XPathDocument(ms);
            }
        }

    }
    finally
    {
        ms.Dispose();
    }

    return xpDoc;
}

The same kind of warning is produced for this form:

XPathDocument xpDoc = null;
using(var ms = new MemoryStream())
{
    using(XmlTextWriter writer = new XmlTextWriter(ms, Encoding.UTF8))
    {
        using(DbDataReader reader = CommonReader.GetReader(connection, Resources.KinteRssSql))
        {
            //...
        }
    }

}

return xpDoc;

By the way, the following form produces another warning:

XPathDocument xpDoc = null;
var ms = new MemoryStream();
using(XmlTextWriter writer = new XmlTextWriter(ms, Encoding.UTF8))
{
    using(DbDataReader reader = CommonReader.GetReader(connection, Resources.KinteRssSql))
    {
        //...
    }
}

return xpDoc;

The above produces the warning:

Warning 7 CA2000 : Microsoft.Reliability : In method 'KinteWritePages.GetXPathDocument(DbConnection)', object 'ms' is not disposed along all exception paths. Call System.IDisposable.Dispose on object 'ms' before all references to it are out of scope. C:\Visual Studio 2010\Projects\Songhay.DataAccess.KinteWritePages\KinteWritePages.cs 383 Songhay.DataAccess.KinteWritePages

In addition to the following, what are my options?:

• Supress warning CA2202.
• Supress warning CA2000 and hope that Microsoft is disposing of MemoryStream (because Reflector is not showing me the source code).
• Rewrite my legacy code to recognize the wonderful XDocument and LINQ to XML.

Answer 1

First of all, you should never use new XmlTextWriter(). It has been deprecated since .NET 2.0. Use XmlWriter.Create() instead.

Secondly, the assignment to ms should be in a using block:

using (var ms = new MemoryStream())
{
    using (var writer = XmlWriter.Create(ms))
    {
        // ...
    }
}

I believe that the warning is correct. The MemoryStream could be disposed when the XmlTextWriter is disposed, then again in the "finally" block.