Printing from a Service...

We've been working on adding the ability to create PDF files on the server side of our application. This sounds much easier than it is. Our server base is IBM UniVerse (how many people can say they are familiar with that?), an older multivalued database system. On top of being a multivalued database, it is also, essentially, a runtime environment.

To complicate this, the items that need to be printed are HTML documents, with some custom javascript that needs to run before the file can be printed (mostly to correct faulty HTML mistakes by people who have no clue about HTML -- but that's another topic for another day). So that means we need to run it through Internet Explorer. But wait, the complications are still not done! We use MeadCo's ScriptX to do the actual printing, since printing through IE's own engine is both complex and unreliable.

So, add all this together to try printing from a single source location.

Several "easy" solutions were tried first, some killed by the boss (due to too much interaction required from users, most of whom are quite unskilled with computers), some killed due to their technical limitations (IBM UniVerse offers the ability to shell out to DOS, but this lacks a windows context, so IE doesn't run properly -- ie: no javascript can be fired off).

So we came up with several proposals, of which one was approved by management for moving forward: build a window service that could print these pdf documents by running a small program that encapsulates the IE engine, thus providing a windows context for the printing.

Seemed so simple then. From that point on, things went all over the place.

Getting IE to run with a windows context was easy enough. Getting our ScriptX related javascript to run took a little more effort, but was manageable. Then came the brick wall. Sure, it works fine on XP running from the service account. What about Server 2k3? Or Vista?

Sure enough, changes to the way the service account runs starting in 2k3 meant that our solution no longer worked that well... Services in 2k3/Vista run in session 0, same as XP. However, that level is now isolated from users. In other words, only certain resources are now available to the service account. And, sure enough, Printers aren't one of them.

MSDN notes that the printing namespace isn't available from windows services (or at least not supproted) [1]. I'm obviously not the first person who's run into issues with printing from a service (StackOverflow questions: 1, 2, 3).

So, for now, we've gotten around it by creating a local account that has the printer available to it. This is far from an ideal solution and I continue to look for a solution that allows me to see printers from a 2k3/Vista windows service...