InfoPath File Attachment Decoder

InfoPath-Attachment-Decoder.cs

using System;
using System.IO;
using System.Text;

namespace InfoPathAttachmentEncoding
{
   /// <summary>
   /// Decodes a file attachment and saves it to a specified path.
   /// </summary>
   public class InfoPathAttachmentDecoder
   {
      private const int SP1Header_Size = 20;
      private const int FIXED_HEADER = 16;
      private int fileSize;
      private int attachmentNameLength;
      private string attachmentName;
      private byte[] decodedAttachment;

      /// <summary>
      /// Accepts the Base64 encoded string
      /// that is the attachment.
      /// </summary>
      public InfoPathAttachmentDecoder(string theBase64EncodedString)
      {
         byte [] theData = Convert.FromBase64String(theBase64EncodedString);
         using(MemoryStream ms = new MemoryStream(theData))
         {
            BinaryReader theReader = new BinaryReader(ms);
            DecodeAttachment(theReader);
         }
      }

      private void DecodeAttachment(BinaryReader theReader)
      {
         //Position the reader to obtain the file size.
         byte[] headerData = new byte[FIXED_HEADER];
         headerData = theReader.ReadBytes(headerData.Length);
         fileSize = (int)theReader.ReadUInt32();
         attachmentNameLength = (int)theReader.ReadUInt32() * 2;
         byte[] fileNameBytes = theReader.ReadBytes(attachmentNameLength);
         //InfoPath uses UTF8 encoding.
         Encoding enc = Encoding.Unicode;
         attachmentName = enc.GetString(fileNameBytes, 0, attachmentNameLength - 2);
         decodedAttachment = theReader.ReadBytes(fileSize);
      }

      public void SaveAttachment(string saveLocation)
      {
         string fullFileName = saveLocation;
         if (!fullFileName.EndsWith(Path.DirectorySeparatorChar.ToString()))
         {
            fullFileName += Path.DirectorySeparatorChar;
         }
         fullFileName += attachmentName;
         if(File.Exists(fullFileName))
            File.Delete(fullFileName);
         FileStream fs = new FileStream(fullFileName, FileMode.CreateNew);
         BinaryWriter bw = new BinaryWriter(fs);
         bw.Write(decodedAttachment);
         bw.Close();
         fs.Close();
      }

      public string Filename
      {
         get{ return attachmentName; }
      }

      public byte[] DecodedAttachment
      {
         get{ return decodedAttachment; }
      }
   }
}