I see many tutorials expainging cliant side validation, but I'm not sure what is the best way to validate image file in server side.

I have this upload script, but I would like to allow only image files.

Could you show me how to add validation? (or link to web site )

Thank you

If FileField.HasFile Then
            Dim myfilename As String
            Dim strExtension As String
            Dim strTimeStamp As String
            strTimeStamp = DateTime.Now.ToString("yyyyMMddhhmmss")
            myfilename = System.IO.Path.GetFileNameWithoutExtension(FileField.FileName)
            strExtension = System.IO.Path.GetExtension(FileField.FileName)
            Dim fullname As String = myfilename + strTimeStamp + strExtension
           
            Dim originalBMP As New System.Drawing.Bitmap(FileField.FileContent)
            Dim thumbnailSize As Integer = 20
            Dim newWidth As Integer, newHeight As Integer

            If originalBMP.Width > originalBMP.Height Then
                newWidth = thumbnailSize
                newHeight = originalBMP.Height * thumbnailSize / originalBMP.Width
            Else
                newWidth = originalBMP.Width * thumbnailSize / originalBMP.Height
                newHeight = thumbnailSize
            End If

            Dim newBMP As New System.Drawing.Bitmap(originalBMP, newWidth, newHeight)
            Dim oGraphics As System.Drawing.Graphics = System.Drawing.Graphics.FromImage(newBMP)

            oGraphics.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias
            oGraphics.InterpolationMode = Drawing.Drawing2D.InterpolationMode.HighQualityBicubic
            oGraphics.DrawImage(originalBMP, 0, 0, newWidth, newHeight)
            Try
                newBMP.Save(Server.MapPath("~/blog/" + fullname))
                Span1.InnerHtml = "File upload successful."
            Catch ex As Exception
                Span1.InnerHtml = "There was an error. No file uploaded."
            End Try

            originalBMP.Dispose()
            newBMP.Dispose()
            oGraphics.Dispose()
End If

aibip:

I have this upload script, but I would like to allow only image files.

This may help you:

http://forums.asp.net/p/1051895/2171502.aspx

Hi,

you can check the file extention on server side.

If System.IO.Path.GetExtension(FileField.FullName).ToLower() = ".jpg" OrElse System.IO.Path.GetExtension(FileField.FullName).ToLower() = ".png" OrElse System.IO.Path.GetExtension(FileField.FullName).ToLower() = ".bmp" OrElse System.IO.Path.GetExtension(FileField.FullName).ToLower() = ".gif" Then

End If

mohd786hussain:

you can check the file extention on server side.

If System.IO.Path.GetExtension(FileField.FullName).ToLower() = ".jpg" OrElse System.IO.Path.GetExtension(FileField.FullName).ToLower() = ".png" OrElse System.IO.Path.GetExtension(FileField.FullName).ToLower() = ".bmp" OrElse System.IO.Path.GetExtension(FileField.FullName).ToLower() = ".gif" Then

End If

I don't think if this would be a good idea.. what if I rename a word file to image file like x.doc to x.jpg?

vinz:

I don't think if this would be a good idea.. what if I rename a word file to image file like x.doc to x.jpg?

Hi vinz,

could you provide me code that can check whether the file is renamed or not as suggested by you above that will be a lot more useful for me.

Second i think this is the best we can trap whether file uploaded is image fiel or not .

I read the article that vinz posted.

http://forums.asp.net/p/1051895/2171502.aspx

Did anyone try "peeking into the stream" method? or Zeerover's method?

mcmcomasp said there are gliches in the last post...

What would be the best way?

aibip:

I see many tutorials expainging cliant side validation, but I'm not sure what is the best way to validate image file in server side.

I have this upload script, but I would like to allow only image files.

Could you show me how to add validation? (or link to web site )

Hi,

Here is way to detect the real extension of files. Please have a try at the demo below. It runs a function called IsAllowedExtension to judge if the uploaded is an image. Also, it can detect other kinds of files according to the file list in the comments.

protected void btnSubmit_Click(object sender, EventArgs e)
{
    if (FileUpload.HasFile)
    {
        HttpPostedFile upFile = FileUpload.PostedFile;
        if (IsAllowedExtension(upFile))
        {
            upFile.SaveAs("path");
        }
    }
}
protected bool IsAllowedExtension(HttpPostedFile file)
{
    bool ret = false;
    System.IO.FileStream fs = new System.IO.FileStream(file.FileName, System.IO.FileMode.Open, System.IO.FileAccess.Read);
    System.IO.BinaryReader r = new System.IO.BinaryReader(fs);
    string fileclass = "";
    byte buffer;
    try
    {
        buffer = r.ReadByte();
        fileclass = buffer.ToString();
        buffer = r.ReadByte();
        fileclass += buffer.ToString();
    }
    catch
    {
        return false;
    }
    r.Close();
    fs.Close();

    /*extension list for files
     * 
     *7173        gif 
     *255216      jpg
     *13780       png
     *6677        bmp
     *239187      txt,aspx,asp,sql
     *208207      xls.doc.ppt
     *6063        xml
     *6033        htm,html
     *4742        js
     *8075        xlsx,zip,pptx,mmap,zip
     *8297        rar   
     *01          accdb,mdb
     *7790        exe,dll           
     *64101       bat 
     */

    //only allow images    jpg       gif     bmp     png      
    String[] fileType = { "255216", "7173", "6677", "13780" };
    for (int i = 0; i < fileType.Length; i++)
    {
        if (fileclass == fileType[i])
        {
            ret = true;
            break;
        }
    }
    return ret;
}

If I have misunderstood you, please feel free to let me know.

Best Regards,
Shengqing Yang

 Hi Shengqing Yang,

I have one question

In sample you are  allow images  with extension of  jpg , gif, bmp, png 

for example if i am uploading a zip file, in that zip file how can i check weather zip file contains only allowed extensions

if zip file contains onther than allowed extensions that file is not allowed.

Thanks in Advance

maverickhyd:

for example if i am uploading a zip file, in that zip file how can i check weather zip file contains only allowed extensions

if zip file contains onther than allowed extensions that file is not allowed.

Hi,

As far as I know, to handle such an issue, we can only unzip the zip file and then check files compressed in it one by one.

Thanks & Regards,
Shengqing Yang