Monday, 22 March 2010

In memory of Windows Telnet

There was a time when Windows Telnet came installed with every copy of Windows. Because of this, it was an easily accessible MUD client for anyone who might want to connect to one. However, times have changed. On one hand the most popular MUDs are making use of custom extensions to the telnet protocol that Windows Telnet will never be able to support, and on the other it no longer comes preinstalled with every copy of Windows.

This post is a recognition of Windows Telnet. That despite its problems as a MUD client, it is still an extremely capable and versatile telnet client. Please give less weight to the listed minuses (which are useful to know if you choose to adopt this client) and appreciate its plusses.

Plus: Superior terminal support

Back in the days before Putty was around, having a telnet client available with Windows that implemented ANSI/VT100 terminal support was extremely valuable. And Windows Telnet allows use of a wide range of the escape sequence that make up this terminal support.

The preceding screenshot is of a prototype of a roguelike that I attempted to implement for the recent 7DRL 2010 competition. Windows Telnet was as capable as Putty at displaying the arbitrary screen updates that my game makes.

Minus: Reduced availability

No longer coming preinstalled with every copy of Windows, installing it is now more complicated than just downloading any other MUD or telnet client which you stumble over a link to.

Minus: Negotiation support

If connecting to a server that does not engage in telnet negotiation, Windows Telnet echos what the user types back to them as it sends it. But should the server send any negotiation, this echoing is switched off and the server has no way to switch it back on. The only way it can be reenabled within the lifetime of the current connection is if the user enters the settings screen and explicitly reenables it. This leaves the server in a position of having to do the echoing of the input it receives, as it processes it.

Minus: The NEW-ENVIRON option

One of the options that can be negotiated between the server and the client is NEW-ENVIRON. It allows the server to query environment variables on the client. In practice, there is only one variable that Windows Telnet gives a useful value for and this is SYSTEMTYPE which always has the value WIN32. Now this is useful for identifying that Windows Telnet is in use, but when one of the reasons you might want to know that it is being used is to avoid negotiating and losing its local echo.. it's not really helpful.

Other than SYSTEMTYPE, another of the standard environment variables that is supported for this option is USER. But don't think about querying it if Windows Telnet is in use, because it will crash the user's client.

I guess if someone wanted to discourage use of Windows Telnet, they could detect it through this option's SYSTEMTYPE variable with a warning message about how it should be avoided due to instability. Then do another option request for the user variable and cement the truth of the claim by crashing the client. At this point, it is irrelevant to the user whether the client is echoing locally or not.

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