Rendering in-memory images from UNC file share

[Eric]

I have this same problem, and I've *half-way* resolved it. It turns
out that this is not exactly an IO problem; it's actually a security
issue and maybe even an ASP.NET bug. Here is what I've done so far...

1. Learned from this post that there are problems with the FromFile
method when using a UNC share as the source directory:
http://tinyurl.com/8exos.

2. Adapted the code in the post to:
'\\\
Dim objStream As New FileStream(SourcePath, _
FileMode.Open, FileAccess.Read)
Dim bmp As Bitmap = Bitmap.FromStream(objStream)
bmp.Save(ms, System.Drawing.Imaging.ImageFormat.Tiff)

' Send out through response.
With ParentPage
'.Response.ContentType = "image/jpeg"
.Response.ContentType = "image/tiff"
.Response.BinaryWrite(ms.GetBuffer)
.Response.End()
End With

objStream.Close()
'///

3. Added the relevant URLs to Internet Explorer's list of Trusted Sites
(http://localhost, http://127.0.0.1, etc.).

4. Removed anonymous authentication within IIS for the application's
directory.

5. Added the <identity impersonate="true" /> tag to the Web.config to
enable NT integrated security with impersonation.

THE RESULT

My application now works as expected when I am physically on the box
that hosts my application (i.e., when I RDP into the server). However,
when I try to access it from my workstation, I still get the
FileNotFoundException (even after adding the server's URL to my local
list of Trusted Sites).

It is as if ASP.NET "loses" the NT authentication token when servicing
the client's request for a remote file.

Any ASP.NET security gurus have an idea on this one??

Thanks,

Eric

I'm having a strange error message with ASP.NET image function.
Basically sometimes it will find the image path, sometimes it won't.
The logic here is that the script iterates through an access table,
pulls the image file name from the database, appends a subdirectory
path to this name, and then writes some html to display the image. But,
like, half the time I get the included error message, and I have no
idea why. When I was developing the page, I could get it to work by,
get this, copying all the relevant files to a new directory and then
restarting the web matrix web server, using that new path. Now, the
webmaster and myself are trying to put this on the actual web server
running IIS, and this message won't go away. If you want to see my code
you can actually look at it here when I posted it for critique, hehe:
http://groups-beta.google.com/group...738c7/6c674a830f9b23ca?hl=en#6c674a830f9b23ca

Anyways, TIA. Here is the error message:


Server Error in '/' Application.
--------------------------------------------------------------------------------

thumbnails/_DSC0833.JPG
Description: An unhandled exception occurred during the execution of
the current web request. Please review the stack trace for more
information about the error and where it originated in the code.

Exception Details: System.IO.FileNotFoundException:
thumbnails/_DSC0833.JPG

Source Error:

Line 182: id = objDR("id")
Line 183: name = objDR("name")
Line 184: currentImage =
System.Drawing.Image.FromFile(path)
Line 185: imgHeight = currentImage.Height/2
Line 186: imgWidth = currentImage.Width/2


Source File: E:\Webs\SPDemo\webimages\logo\index.aspx Line: 184

Stack Trace:

[FileNotFoundException: thumbnails/_DSC0833.JPG]
System.Drawing.Image.FromFile(String filename, Boolean
useEmbeddedColorManagement) +205
System.Drawing.Image.FromFile(String filename) +7
ASP.index_aspx.Draw_index() in
E:\Webs\SPDemo\webimages\logo\index.aspx:184
ASP.index_aspx.Page_Load(Object Source, EventArgs E) in
E:\Webs\SPDemo\webimages\logo\index.aspx:530
System.Web.UI.Control.OnLoad(EventArgs e) +67
System.Web.UI.Control.LoadRecursive() +35
System.Web.UI.Page.ProcessRequestMain() +750

 

[Dominick Baier [DevelopMentor]]

Hello Eric,

thats a double hop problem. You are impersonating AND accessing a remote
resource. This is called delegation. Check the info here:
http://www.leastprivilege.com/TroubleshootingKerberosDelegation.aspx

Is this IIS5 or 6??

Why do you impersonate??

---------------------------------------
Dominick Baier - DevelopMentor
http://www.leastprivilege.com

I have this same problem, and I've *half-way* resolved it. It turns
out that this is not exactly an IO problem; it's actually a security
issue and maybe even an ASP.NET bug. Here is what I've done so far...

1. Learned from this post that there are problems with the FromFile
method when using a UNC share as the source directory:
http://tinyurl.com/8exos.

2. Adapted the code in the post to:
'\\\
Dim objStream As New FileStream(SourcePath, _
FileMode.Open, FileAccess.Read)
Dim bmp As Bitmap = Bitmap.FromStream(objStream)
bmp.Save(ms, System.Drawing.Imaging.ImageFormat.Tiff)

' Send out through response.
With ParentPage
'.Response.ContentType = "image/jpeg"
.Response.ContentType = "image/tiff"
.Response.BinaryWrite(ms.GetBuffer)
.Response.End()
End With
objStream.Close()
'///
3. Added the relevant URLs to Internet Explorer's list of Trusted
Sites (http://localhost, http://127.0.0.1, etc.).

4. Removed anonymous authentication within IIS for the application's
directory.

5. Added the <identity impersonate="true" /> tag to the Web.config to
enable NT integrated security with impersonation.

THE RESULT

My application now works as expected when I am physically on the box
that hosts my application (i.e., when I RDP into the server).
However, when I try to access it from my workstation, I still get the
FileNotFoundException (even after adding the server's URL to my local
list of Trusted Sites).

It is as if ASP.NET "loses" the NT authentication token when servicing
the client's request for a remote file.

Any ASP.NET security gurus have an idea on this one??

Thanks,

Eric

I'm having a strange error message with ASP.NET image function.

Basically sometimes it will find the image path, sometimes it won't.

The logic here is that the script iterates through an access table,

pulls the image file name from the database, appends a subdirectory

path to this name, and then writes some html to display the image.
But,

like, half the time I get the included error message, and I have no

idea why. When I was developing the page, I could get it to work by,

get this, copying all the relevant files to a new directory and then

restarting the web matrix web server, using that new path. Now, the

webmaster and myself are trying to put this on the actual web server

running IIS, and this message won't go away. If you want to see my
code

you can actually look at it here when I posted it for critique, hehe:

http://groups-beta.google.com/group/asp-net/browse_thread/thread/1c2b
916ae11738c7/6c674a830f9b23ca?hl=en#6c674a830f9b23ca

Anyways, TIA. Here is the error message:

Server Error in '/' Application.
---------------------------------------------------------------------
-----------
thumbnails/_DSC0833.JPG
Description: An unhandled exception occurred during the execution of
the current web request. Please review the stack trace for more
information about the error and where it originated in the code.
Exception Details: System.IO.FileNotFoundException:
thumbnails/_DSC0833.JPG

Source Error:

Line 182: id = objDR("id")
Line 183: name = objDR("name")
Line 184: currentImage =
System.Drawing.Image.FromFile(path)
Line 185: imgHeight = currentImage.Height/2
Line 186: imgWidth = currentImage.Width/2
Source File: E:\Webs\SPDemo\webimages\logo\index.aspx Line: 184

Stack Trace:

[FileNotFoundException: thumbnails/_DSC0833.JPG]
System.Drawing.Image.FromFile(String filename, Boolean
useEmbeddedColorManagement) +205 System.Drawing.Image.FromFile(String
filename) +7 ASP.index_aspx.Draw_index() in
E:\Webs\SPDemo\webimages\logo\index.aspx:184
ASP.index_aspx.Page_Load(Object Source, EventArgs E) in
E:\Webs\SPDemo\webimages\logo\index.aspx:530
System.Web.UI.Control.OnLoad(EventArgs e) +67
System.Web.UI.Control.LoadRecursive() +35
System.Web.UI.Page.ProcessRequestMain() +750