instance.cs

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using System;
using System.Configuration;
using System.Web;

namespace BufferedUpload
{
	/// <summary>
	/// The chunked file upload is session-based and the Instance class acts as a manager for the upload.
	/// The object is fetched from session state for each method used in the upload.
	/// </summary>
	public sealed class Instance 
	{
		private long bytesReceived = 0;
		private string instanceId = "";
		public string tempFilename = "";
		private string targetFolder = "Uploads";

		public long BytesReceived { get { return this.bytesReceived; } set { this.bytesReceived = value; } }
		public string Id { get { return this.instanceId; } }
		public string TargetFolder { get { return this.targetFolder; } set { this.TargetFolder = value; } }

		public Instance() { }
		public Instance(string Filename, bool Overwrite) 
		{ 	
			this.tempFilename = HttpContext.Current.Server.MapPath(this.targetFolder + "/" + Filename);
			if (!System.IO.File.Exists(this.tempFilename) || Overwrite)
				System.IO.File.Create(this.tempFilename).Close(); 			
			else
				CustomSoapException("File Already Exists", Filename);
		}

		public Instance Initialize() 
		{
			System.Web.SessionState.HttpSessionState Session = System.Web.HttpContext.Current.Session;

			this.instanceId = Guid.NewGuid().ToString();
			Session.Add(this.instanceId, this);	
			return this; 
		}

		public void AppendChunk(byte[] buffer, long offset, int bufferSize) 
		{
			// make sure that the file exists
			if (!System.IO.File.Exists(this.tempFilename))
				CustomSoapException("Cannot Find Temp File", this.tempFilename);

			long tempFilesize = new System.IO.FileInfo(this.tempFilename).Length;

			// if the temp file size is not the same as the offset then something went wrong....
			if (tempFilesize != offset) 				
				CustomSoapException("Transfer Corrupted", String.Format("The file size is {0}, expected {1} bytes", tempFilesize, offset));
			else
			{

				// offset matches the filesize, so the chunk is to be inserted at the end of the file.
				System.IO.FileStream FileStream = new System.IO.FileStream(this.tempFilename, System.IO.FileMode.Append);
				FileStream.Write(buffer, 0, bufferSize);
				FileStream.Close();
			}		
		}

		public void RemoveFromSession() 
		{
			if (Instance.GetInstanceById(this.instanceId) != null)
				System.Web.HttpContext.Current.Session.Remove(this.instanceId);
		}

		public static Instance GetInstanceById(string InstanceId) 
		{
			object o = System.Web.HttpContext.Current.Session[InstanceId];
			if (o != null) 
				return o as Instance;
			else 
				return null; 
		}

		/// <summary>
		/// Throws a soap exception.  It is formatted in a way that is more readable to the client, after being put through the xml serialisation process
		/// Typed exceptions don't work well across web services, so these exceptions are sent in such a way that the client
		/// can determine the 'name' or type of the exception thrown, and any message that went with it, appended after a : character.
		/// </summary>
		/// <param name="exceptionName"></param>
		/// <param name="message"></param>
		public static void CustomSoapException(string exceptionName, string message)
		{
			throw new System.Web.Services.Protocols.SoapException(exceptionName + ": " + message, new System.Xml.XmlQualifiedName("BufferedUpload"));
		}
	}
}