Get position in String from line number and line position

Question

I am using the XmlReader to parse XML data received over a socket. The data is sometimes broken into separate packets and when that happens, XmlReader will throw an XmlException for the incomplete XML. When this happens, I want to keep the partial XML message and concatenate it with the next data I receive which will contain the remaining XML. The problem I am having is keeping only the incomplete XML.

Here's sample XML (from Sample XML File) that illustrates the problem:

<book id="bk101">
  <author>Gambardella, Matthew</author>
  <title>XML Developer's Guide</title>
  <description>An in-depth look at creating applications 
  with XML.</description>
</book>
<book id="bk102">
  <author>Ralls, Kim</author>
  <title>Midnight Rain</title>
  <description>A former architect battles corporate zombies, 
  an evil sorceress, and her own childhood to become queen 
  of the world.</description>
</book>
<book id="bk103">
  <author>Corets, Eva</author>
  <title>Maeve Ascendant</title>
  <description>After the collapse of a nanotechnology 
  society in England, the young survivors lay the 
  foundation for a new society.</description>
</book>

Imagine 100 books were sold in one transaction and that the XML was divided in two packets. The 1st packet could end like this:

<book id="bk103">
  <author>Corets, Eva</author>
  <title>Maeve Ascendant</title>
  <description>After the collapse of a nano

and the following packet would contain the rest of the XML:

technology 
  society in England, the young survivors lay the 
  foundation for a new society.</description>
</book>

XmlReader will parse the first two books properly and I can get the XML using ReadOuterXml. It will then throw an exception on the 3rd book so I want to keep, from the original XML, only the substring starting at <book id="bk103">. XmlException gives me the LineNumber and LinePosition of the error but this is not the position I want. Instead, after each XML element XmlReader has read, I can cast my XmlReader as IXmlLineInfo and get the position of the reader after ReadOuterXml is called. This gives me a LineNumber and LinePosition again.

My question is: how can I convert LineNumber and LinePosition to an index within my original XML string. In the XML example I used, the XmlException would be at Line 17, Position 44. The position after the last valid element would be Line 13, Position 8. The position I am looking for is 440.

TL;DR

How do I get 440 from Line 13, Position 8. I am looking to use Substring on the original XML.

Answer 1

One simplistic way to do it is to loop to find the position of the 12th instance of System.Environment.NewLine, then add the value of LinePosition to that position:

string previousFragment = "";

while (!_cancellationToken.IsCancellationRequested)
{

    // Read from buffer
    string bufferData = _buffer.Take();
    string localBuffer = previousFragment + bufferData;

    // Clear out previous fragment
    previousFragment = "";

    using (TextReader textReader = new StringReader(localBuffer))
    {
        XmlReader xmlReader;
        xmlReader = XmlReader.Create(textReader, _xmlReaderSettings);

        int lastLine;
        int lastPosition;

        try
        {
            while (xmlReader.Read())
            {
                if (xmlReader.NodeType == XmlNodeType.Element)
                {
                    string validXml = xmlReader.ReadOuterXml;
                }

                IXmlLineInfo lineInfo = xmlReader;
                lastLine = lineInfo.LineNumber;
                lastPosition = lineInfo.LinePosition;
            }
        }
        catch (XmlException ex)
        {
            localBuffer = localBuffer.ReplaceLineEndings();
            int position = 0;

            for (int counter = 1; counter <= lastLine - 1; counter++)
                position = localBuffer.IndexOf(System.Environment.NewLine, position + 1);
            position += lastPosition + 1;

            previousFragment = localBuffer.Substring(position);
        }
    }
}

In this code:

1. _buffer is a BlockingCollection of String data received from socket.
2. _xmlReaderSettings is an XmlReaderSettings object with ValidationType set to ValidationType.None and ConformanceLevel set to ConformanceLevel.Fragment.
3. This code runs as a Task. When new XML arrives, it is added to _buffer.

Is there a better way to do this?

Answer 2

I use following code for reading huge xml files. I added exception handlers (code need to be added for exception) that I've never used before. See if this helps

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Xml;
using System.Xml.Linq;


namespace ConsoleApplication2
{
    class Program
    {
        const string URL = "URL";
        static void Main(string[] args)
        {
            XmlReader reader = XmlReader.Create(URL);

            while(!reader.EOF)
            {
                try
                {
                    if(reader.Name != "book")
                    {
                        reader.ReadToFollowing("book");
                    }
                }
                catch(Exception ex)
                {

                }
                try
                {
                    if(!reader.EOF)
                    {
                        XElement book = (XElement)XElement.ReadFrom(reader);
                    }
                }
                catch(Exception ex)
                {

                }
            }
        }
    }
 
}