Nick’s Lounge

I am currently working on an ASP.Net web project, which allows client to download a well structured submission package. Due to security reason, web server can not create folder and write file on client side. Web server can generate a well structured zipped file and push to the client.

There could be two ways to achieve that;

Fist way:

1. Create folders and copy files into each folder
2. Use 3^rd party tool, eg winrar, 7zip to zip the whole folder to one zipped file
3. Send back download web address, and let client download the zipped file

If the zipped file is small and web server is powerful enough, client won’t feel any delay. However if the file is big, client side will get no any response until zip file is ready. We can put similar message, eg “Please wait… ”. But client side still don’t know how long would take. If zip file is not ready within time out period, server will get reset. This is a really awful user experience.

Second way:

1. Create folder and zip the files on the fly (on web server’s memory)
2. Send back zipped stream to client through Response
3. Client download  zipping file one by one

Client can clearly feel the progress of downloading.

Here is the code for 2^nd solution:

//prepare response header
Response.Clear();
//set Response Content Type
Response.ContentType = "application/x-zip-compressed";
Response.AddHeader("Content-Disposition", "attachment; filename=Download.zip");
ZipOutputStream zipOutput = new ZipOutputStream(Response.OutputStream);
try
{
            zipOutput.IsStreamOwner = false;
            //set compress level
            zipOutput.SetLevel(9);

            ArrayList fileList = functions.GetFileList();
            foreach (string fileName in fileList)
            {
                string folderName = "folder1" + @"";

                zipEntry = new ZipEntry(folderName + fileName);
                zipOutput.PutNextEntry(zipEntry);
                            
                byte[] file = functions.GetFile(fileName);
                //zip file
                zipOutput.Write(file, 0, file.Length);
                 //send to client for downloading
                Response.Flush();
            }
        }
        catch (Exception ex)
        {
            Response.Write(ex.ToString());
        }
        finally
        {
            zipOutput.Finish();
            zipOutput.Close();
            Response.End();
        }

This post originated from my previous question. In previous question, I was asking how to create a circular list box control. A list box, if scroll down to the last element and continue scroll down, it will appear first element; if scroll up to the first element and keep scroll up, it will appear last element. It looks like IPhone alarm setting function. Here is my solution.

public class CircularListBox : System.Windows.Forms.ListBox
{
    private System.ComponentModel.Container components = null;
    const int WM_VSCROLL = 0x0115;
    const int WM_KEYDOWN = 0x0100;

    const int SB_LINEUP = 0x0000;
    const int SB_LINEDOWN = 0x0001;

    const int VK_DOWN = 0x0028;
    const int VK_UP = 0x0026;
    const int VK_NEXT = 0x0022;
    const int VK_PRIOR = 0x0021;

    public CircularListBox()
    {
        // This call is required by the Windows.Forms Form Designer.
        InitializeComponent();

        // TODO: Add any initialization after the InitializeComponent call

    }

    /// 
 
    /// Clean up any resources being used.
    /// 
    protected override void Dispose(bool disposing)
    {
        if (disposing)
        {
            if (components != null)
            {
                components.Dispose();
            }
        }
        base.Dispose(disposing);
    }

    #region Component Designer generated code
    /// 
 
    /// Required method for Designer support - do not modify 
    /// the contents of this method with the code editor.
    /// 
    private void InitializeComponent()
    {
        components = new System.ComponentModel.Container();
    }
    #endregion
    protected int offset = 0;

    public new int TopIndex
    {
        get { return (this.Items.Count + offset + base.TopIndex) % this.Items.Count; }
        set
        {
            if (value > this.Items.Count - 1)
                return;
            Message m = new Message();
            m.Msg = WM_KEYDOWN;
            m.WParam = (System.IntPtr)VK_DOWN;
            while (value != this.TopIndex)
                WndProc(ref m);
        }
    }

    protected override void WndProc(ref Message m)
    {
        if (m.Msg == WM_VSCROLL || m.Msg == WM_KEYDOWN)
        {
            if (this.SelectedIndex == -1)
                this.SelectedIndex = 0;

            switch ((int)m.WParam)
            {
                case VK_PRIOR:
                case VK_UP:
                case SB_LINEUP:
                    if (this.SelectedIndex == 0)
                    {
                        offset = (this.Items.Count + offset - 1) % this.Items.Count;
                        this.Items.Insert(0, this.Items[this.Items.Count - 1]);
                        this.Items.RemoveAt(this.Items.Count - 1);
                        this.SelectedIndex = 0;
                    }
                    else
                    {
                        this.SelectedIndex--;
                    }
                    break;
                case VK_DOWN:
                case SB_LINEDOWN:
                case VK_NEXT:
                    if (this.SelectedIndex == this.Items.Count - 1)
                    {
                        offset = ++offset % this.Items.Count;
                        this.Items.Add(this.Items[0]);
                        this.Items.RemoveAt(0);
                        this.SelectedIndex = this.Items.Count - 1;
                    }
                    else
                    {
                        this.SelectedIndex++;
                    }
                    break;
                default:
                    base.WndProc(ref m);
                    break;
            }
        }
        else
            base.WndProc(ref m);
    }
}