Solved

Intercepting print jobs by hooking createDCW and createDCA

Posted on 2006-06-09
3
1,192 Views
Last Modified: 2013-12-03
I have been trying to implement password protected printing by hooking createDCW and createDCA and either ‘doing nothing’ or passing the call onto the OS depending on whether the correct password has been entered.

‘doing nothing’ appeared to work, and prevent printing, for applications like Notepad, but caused problems with apps like MS Excel which would get stuck in a loop showing an error.

So in the hook I tried returning NULL, the value returned by createDCW and createDCA if they fail. This caused MS Excel to simply close after trying to print.

I then tried repeating the createDCW/ createDCA as normal, but following it with an AbortDoc, but this seems to allow the print job to get to the print queue, even though abortdoc returns 1.

Any suggestions to what is going wrong?
0
Comment
Question by:PeteMulford
  • 2
3 Comments
 
LVL 3

Expert Comment

by:Mikeh926
ID: 16886192
It sounds like Excel just can't handle the NULL returned from CreateDC. You really need to not change any return codes from the API so that applications think that everything is ok.

Can I suggest that you hook EndDoc()? Return a value that indicates success to the application, but if you want to prevent printing call AbortDoc() from inside your hook.

Mike.
0
 

Author Comment

by:PeteMulford
ID: 16893176
so allow the startdoc, startpage stuff to be sent, but when the enddoc is sent send an abortdoc as well?
0
 
LVL 3

Accepted Solution

by:
Mikeh926 earned 500 total points
ID: 16893196
Yes, allow the app to think that it's printed.

In your EndDoc() hook, call AbortDoc() and do not call the original EndDoc(). Instead just return the code for success to the app. The app will think it's printed, so no error messages will be displayed, but you can abort the print job.
0

Featured Post

Free Tool: Site Down Detector

Helpful to verify reports of your own downtime, or to double check a downed website you are trying to access.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
error email attachment VB2010 5 52
windbg taking it's time 32 100
Need an intro to -- .Net SQL Authorization Manager 7 95
SSRS troubles 4 82
In this article, I will show how to use the Ribbon IDs Tool Window to assign the built-in Office icons to a ribbon button.  This tool will help us to find the OfficeImageId that corresponds to our desired built-in Office icon. The tool is part of…
For most people, the WrapPanel seems like a magic when they switch from WinForms to WPF. Most of us will think that the code that is used to write a control like that would be difficult. However, most of the work is done by the WPF engine, and the W…
This is Part 3 in a 3-part series on Experts Exchange to discuss error handling in VBA code written for Excel. Part 1 of this series discussed basic error handling code using VBA. http://www.experts-exchange.com/videos/1478/Excel-Error-Handlin…
The Email Laundry PDF encryption service allows companies to send confidential encrypted  emails to anybody. The PDF document can also contain attachments that are embedded in the encrypted PDF. The password is randomly generated by The Email Laundr…

679 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question