I've never really understood why it's a thing to use a telnet client for transmitting text on a socket for purposes other than telnet. My understanding is that telnet is a proper protocol with escape sequences/etc, and even that HTTP/SMTP/etc require things like \r\n for line breaks. Are these protocols just... close enough that it's not a problem in practice for text data?

▲ degamad 15 hours ago | parent | next [-]

Because for a long time, on most computers, the telnet client was the closest thing to an "open a tcp socket to this ip/port and connect the i/o from it to stdin/stdout" application you can get without installing something or coding it up yourself.

These days we have netcat/socat and others, but they're not reliably installed, while telnet used to be generally available because telnetting to another machine was more common.

These days, the answer would be to use a netcat variant. In the past, telnet was the best we could be confident would be there.

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SoftTalker 3 hours ago | parent | next [-]

In corporate environments, netcat was often banned as it was seen as a "hacking" tool. Having it installed would sometimes get the attention of the security folks, depending how tightly they controlled things.

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prmoustache 13 hours ago | parent | prev [-]

You don't even need netcat or socat for that, probing /dev/tcp/<host>/<port> from the shell is enough.

	▲	geocar 12 hours ago \| parent \| next [-]
		That's some gnu bash shenanigans. There is no /dev/tcp in unix Lots of shops didn't have gnu installed: telnet was what we had.
	▲	hibbelig 12 hours ago \| parent \| prev [-]
		Telnet was available in the 90s. I reckon /dev/tcp is way more recent. GP did say a long time ago.

▲ indymike 13 hours ago | parent | prev | next [-]

Same reason that people use vi. It's always there.

▲ teddyh 6 hours ago | parent | prev | next [-]

The telnet protocol with escapes, etc. is only used by the telnet client if you’re connecting to the telnet port. If you’re connecting to HTTP, SMTP or something else, the telnet protocol is not enabled.

▲ swinglock 15 hours ago | parent | prev | next [-]

Because it's there.

▲ prmoustache 13 hours ago | parent | next [-]

It hasn't for the most part of the last 2 decades.

▲ 1718627440 12 hours ago | parent [-]

The telnet client comes with MS Windows, Linux and macOS. The only platforms were you need to install some extra component are Android and iOS.

▲ prmoustache 8 hours ago | parent | next [-]

Many companies have been preventing its execution or removing the package by default for a number of years.

Also most linux containers do not ships with such binaries to save on img size and reduce vuln management overhead.

▲ 1718627440 7 hours ago | parent [-]

> to save on img size

    $ ls --human --size --dereference $(which telnet)
    144K /usr/bin/telnet

	▲	prmoustache 7 hours ago \| parent [-]
		The point is not that this particular binary is huge, the point is that we tend to strip images of anything that is not useful for the actual application shipped. So we strip everything. Also: small things adds up. On AI prompt can be handled reasonably by a single machine, millions of concurrent ones involve huge datacenters and whole energy plants being restarted/built. The point of reducing the amount of binaries shipped with the image is also to reduce the amount of CVEs/vulns in your reports that wouldn't be relevant for your app but woulld still be raised by their presence.

▲ alphager 5 hours ago | parent | prev | next [-]

Telnet client is an optional feature in Windows that needs to be enabled/installed.

▲ einr 4 hours ago | parent | prev [-]

telnet hasn’t shipped with macOS since 10.12 Sierra, ten years ago.

Debian also isn’t shipping telnet in the base install since Debian 11.

▲ 15 hours ago | parent | prev [-]

[deleted]

▲ linuxftw 10 hours ago | parent | prev [-]

In the days of yore, Windows had telnet installed. Most hackers used telnet in the 90's and early 2000's.