Indeed it was a mystery since:
- I have no idea where he lives and have never been there.
- We live far apart and never frequent each other's neighborhoods, so wireless access is not plausible.
- My colleague is provably competent and thus the printer is not available from outside his LAN.
- We didn't go to see Wall-E together, nor did I forward the tickets to him.
- He also doesn't have access to my email-account (not that I am aware of at least :-))
After establishing the above I pondered what had taken place for a moment and experienced a real Sherlock Holmes moment: "what brand and model printer do you have?". "A Canon i850" he responded.
Here is what I think happened:
- My printer is attached to one of my home machines. The printer is shared out to my local network. It is shared out using the default name the setup process came up with.
- I got the tickets via email and printed them, from my laptop on my shared printer at home. It didn't work so I printed the file from my Mac Mini instead.
- Meanwhile the tickets stay queued on the laptop.
- I take my laptop to work.
- My colleague has an identical printer at home. Attached to his Airport Extreme (I think) His laptop is set up to re-share out this printer. Under the default name.
- He brings his laptop to work.
- My laptop sees the shared printer turn up on the network, thinks oh goodie, and forwards the printout to his laptop.
- Since he is at work, and not near his printer, nothing much happens.
- He goes home, pops his laptop onto his LAN, the laptop sees the printer and hey presto: out comes my ticket.
There are still some mysteries that need to be solved. I don't really understand why it would take 27 days for the planets to align, but I have some suspicions. Among other things, I suspect that a third laptop may have been involved. You see, I changed laptops a couple of weeks ago. And I think I printed this on my old laptop. This means that the printout may have migrated from my old to my new laptop at some point.
I am too lazy to check my logs, but I think that this is a plausible explanation since I only recently powered up the old laptop in order to migrate some files I'd forgotten on it to the new laptop. I am not too sure about how the printer and sharing configurations have changed, but I know I've fiddled with them.
So I suspect the printout migrated from my laptop A to my laptop B, then on to my colleague's laptop and then finally got printed via his Airport Extreme to which his printer is attached.
I guess the moral of this story is that you should be careful about default values and that you do need authentication even for accessing devices like printers.
It would be interesting to see what happened if you wrote a program to automatically generate printer setups for all printers known by the CUPS printing system, shared them out without requiring any authentication and then took the laptop to places where people bring their laptops. Like airports, trains, libraries etc.
You could, of course, do the opposite: enqueue a printout of a document (say, this blog posting) to all of the names and then see what happened.
So if you found this blog post in your printout-tray, you now know how it may have gotten there :-)