Prevent file corruption when saving xml file

Question

Next line sometimes is corrupting xml file and creating a zero length xml, when OutOfMemoryException has been thrown. How to prevent file corruption?

xmlDoc.Save(filename)

Save-Exception of type 'System.OutOfMemoryException' was thrown. Save-at System.IO.FileStream.Write(Byte[] array, Int32 offset, Int32 count) at System.IO.StreamWriter.Flush(Boolean flushStream, Boolean flushEncoder) at System.IO.StreamWriter.Write(Char value) at System.Xml.XmlTextWriter.Indent(Boolean beforeEndElement) at System.Xml.XmlTextWriter.AutoComplete(Token token) at System.Xml.XmlTextWriter.WriteStartElement(String prefix, String localName, String ns) at System.Xml.XmlDOMTextWriter.WriteStartElement(String prefix, String localName, String ns) at System.Xml.XmlElement.WriteTo(XmlWriter w) at System.Xml.XmlElement.WriteContentTo(XmlWriter w) at System.Xml.XmlElement.WriteTo(XmlWriter w) at System.Xml.XmlDocument.WriteContentTo(XmlWriter xw) at System.Xml.XmlDocument.WriteTo(XmlWriter w) at System.Xml.XmlDocument.Save(String filename) at MainOptions.Save(String filename, ItemOptions options)

Answer 1

You're overwritting the file as you save it to filename. To backup the old copy,

• move it to another location (like filename.bak) before saving and delete it afterwards or
• save the new file as another file (like filename.new) and rename it on success

When an exception is thrown, you can easily restore the old/previous version of the xml file.

Answer 2

Agree with Matten. Alternative solution can be generating xml string before saving it to a file:

Using ms As New MemoryStream
    xmlDoc.Save(ms)
    Using outStream As FileStream = File.Open(filename,
                 FileMode.Create, FileAccess.Write, FileShare.Read)
        ms.WriteTo(outStream)
    End Using
End Using

Use stream to match xmlDoc.Save(filename)