Is it possible to print to a networked printer from a web app? Are there any POS or similar form factor printers which can be connected to the internet and printed to directly(given that a port is opened through the router)?
My ideal case would be a printer to which I could send XML and have it print without requiring a PC and hence no driver.
Another thing that would be good is creating an ssl connection to the printer, but that's not as critical.
Most thermal POS or label printers can be connected to a network with an add-on network card from the manufacturer. Big brand names are Zebra and Intermec.
The interesting thing is that most of these printers have a direct ASCII mode, so you just connect on a plain old TCP/IP connection and spit out some formatting commands, etc., written in a proprietary printer language that the manufacturer will give you. In the case of Intermec, it's called IPL (Intermec Printer Language).
You have two options... you can have the user click a button, do a page refresh, and on the server side just open a TCP/IP connection to the printer and print. This would also work for serial port printers and regular windows printers. In fact, this is how we implemented it in a recent project. Your second option is to write some client side code, in JavaScript or what-have-you, to open a connection to the printer and spit out the same printer message. Caveat: you'll probably run into security concerns doing that because the browser may not take kindly to your page initiating outbound connections to random IP addresses. If you're behind a corporate firewall and you can count on doing some tweaking to the client security models, this might be possible.
Personally, I prefer printing from the server side, not the client side.