Read individual characters off socket?

[Ken D'Ambrosio]

Hi! I'm trying to read a character-at-a-time off a network socket;
while (say) getch kinda-sorta does that, it only does it once the remote
end has submitted the entire line via <CR>. Clearly, I'm missing
something where character-at-a-time interaction could occur.

Any pointers?

Thanks!

-Ken

E.g., "character-at-a-time," but only when <CR> is submitted:

require 'socket'
server_socket = Socket.new(Socket::AF_INET, Socket::SOCK_STREAM, 0)
pry(main)> sockaddr = Socket.pack_sockaddr_in( 2200, 'localhost' )
server_socket.bind( sockaddr )
server_socket.listen(5)
client, client_sockaddr = server_socket.accept
while (foo = client.getc)
puts foo
end

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[Eric Wong]

Hi! I'm trying to read a character-at-a-time off a network socket; while
(say) getch kinda-sorta does that, it only does it once the remote end has
submitted the entire line via <CR>. Clearly, I'm missing something where
character-at-a-time interaction could occur.
Any pointers?

What characters are you sending with the client?
If it's a multi-byte character, then maybe the "character" was
not finished?

require 'socket'
server_socket = Socket.new(Socket::AF_INET, Socket::SOCK_STREAM, 0)
pry(main)> sockaddr = Socket.pack_sockaddr_in( 2200, 'localhost' )
server_socket.bind( sockaddr )
server_socket.listen(5)
client, client_sockaddr = server_socket.accept
while (foo = client.getc)
puts foo
end

Which client are you using?
If it's the telnet command, telnet itself might not send write a
packet until the user hits "Enter" for <CR>.

Instead, try TCPSocket from another terminal:

conn = TCPSocket.new('localhost', 2200)
conn.write("a") # one TCP packet sent
# client.getc should return 1 byte


Keep in mind doing stuff one-byte-at-a-time is extremely
inefficient because of TCP/IP header overhead and your
network administrators will not be happy with you.

Normally Ruby servers and network clients use IO#readpartial or
IO#read_nonblock to read a bunch at once.

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[Diego Fernandez]

Fuck I’m too high for that

Post by Eric Wong

Hi! I'm trying to read a character-at-a-time off a network socket; while
(say) getch kinda-sorta does that, it only does it once the remote end

has

submitted the entire line via <CR>. Clearly, I'm missing something where
character-at-a-time interaction could occur.
Any pointers?

What characters are you sending with the client?
If it's a multi-byte character, then maybe the "character" was
not finished?

require 'socket'
server_socket = Socket.new(Socket::AF_INET, Socket::SOCK_STREAM, 0)
pry(main)> sockaddr = Socket.pack_sockaddr_in( 2200, 'localhost' )
server_socket.bind( sockaddr )
server_socket.listen(5)
client, client_sockaddr = server_socket.accept
while (foo = client.getc)
puts foo
end

Which client are you using?
If it's the telnet command, telnet itself might not send write a
packet until the user hits "Enter" for <CR>.
conn = TCPSocket.new('localhost', 2200)
conn.write("a") # one TCP packet sent
# client.getc should return 1 byte
Keep in mind doing stuff one-byte-at-a-time is extremely
inefficient because of TCP/IP header overhead and your
network administrators will not be happy with you.
Normally Ruby servers and network clients use IO#readpartial or
IO#read_nonblock to read a bunch at once.
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[ema gut]

can you send me information in spanish please thank you

Post by Diego Fernandez
Fuck I’m too high for that

Post by Eric Wong

Post by Ken D'Ambrosio
Hi! I'm trying to read a character-at-a-time off a network socket;

while

Post by Ken D'Ambrosio
(say) getch kinda-sorta does that, it only does it once the remote end

has

Post by Ken D'Ambrosio
submitted the entire line via <CR>. Clearly, I'm missing something

where

Post by Ken D'Ambrosio
character-at-a-time interaction could occur.
Any pointers?

What characters are you sending with the client?
If it's a multi-byte character, then maybe the "character" was
not finished?

Post by Ken D'Ambrosio
require 'socket'
server_socket = Socket.new(Socket::AF_INET, Socket::SOCK_STREAM, 0)
pry(main)> sockaddr = Socket.pack_sockaddr_in( 2200, 'localhost' )
server_socket.bind( sockaddr )
server_socket.listen(5)
client, client_sockaddr = server_socket.accept
while (foo = client.getc)
puts foo
end

Which client are you using?
If it's the telnet command, telnet itself might not send write a
packet until the user hits "Enter" for <CR>.
conn = TCPSocket.new('localhost', 2200)
conn.write("a") # one TCP packet sent
# client.getc should return 1 byte
Keep in mind doing stuff one-byte-at-a-time is extremely
inefficient because of TCP/IP header overhead and your
network administrators will not be happy with you.
Normally Ruby servers and network clients use IO#readpartial or
IO#read_nonblock to read a bunch at once.
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[Ken D'Ambrosio]

Post by Eric Wong
What characters are you sending with the client?
If it's a multi-byte character, then maybe the "character" was
not finished?

Just straight-up eight-bit ASCII. (Long story short, this is meant to
interact with an old-school bulletin board system. No fancy Unicode or
anything going on -- or, indeed, even supported.)

Post by Eric Wong
Which client are you using?
If it's the telnet command, telnet itself might not send write a
packet until the user hits "Enter" for <CR>.

Nah -- telnet is "realtime." I.e., when I use telnet to go to said
bulletin board, individual characters are immediately acted on.

Post by Eric Wong
Keep in mind doing stuff one-byte-at-a-time is extremely
inefficient because of TCP/IP header overhead and your
network administrators will not be happy with you.

Fortunately, I'm the network admin. ;-) And, yeah, crazy inefficient to
use a 1500-byte packet to send a one-byte payload, but such are the
vagaries of unbuffered interaction.

Post by Eric Wong
Normally Ruby servers and network clients use IO#readpartial or
IO#read_nonblock to read a bunch at once.

Hrmm... THIS, I will have to do some reading up on.

Thank you!!

-Ken

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[Ken D'Ambrosio]

Post by Ken D'Ambrosio

Post by Eric Wong
Which client are you using?
If it's the telnet command, telnet itself might not send write a
packet until the user hits "Enter" for <CR>.

Nah -- telnet is "realtime." I.e., when I use telnet to go to said
bulletin board, individual characters are immediately acted on.

GAH! I have learned something. Telnet apparently operates differently
depending on whether it's connecting to port 23 (the one the BBS is on),
or other ports (e.g., port 2200, which is what I was using, "because
privileged ports.") Once I connected, then did a "^]", typed "mode
character" -- setting character-at-a-time, and not LINEMODE -- the code
I posted originally worked fine.

That'll learn me to not give due thought to client-side considerations.

-Ken

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[Ken Ke]

Post by Eric Wong
What characters are you sending with the client?
If it's a multi-byte character, then maybe the "character" was
not finished?

Just straight-up eight-bit ASCII. (Long story short, this is meant to interact with an old-school bulletin board system. No fancy Unicode or anything going on -- or, indeed, even supported.)

Post by Eric Wong
Which client are you using?
If it's the telnet command, telnet itself might not send write a
packet until the user hits "Enter" for <CR>.

Nah -- telnet is "realtime." I.e., when I use telnet to go to said bulletin board, individual characters are immediately acted on.

Post by Eric Wong
Keep in mind doing stuff one-byte-at-a-time is extremely
inefficient because of TCP/IP header overhead and your
network administrators will not be happy with you.

Fortunately, I'm the network admin. ;-) And, yeah, crazy inefficient to use a 1500-byte packet to send a one-byte payload, but such are the vagaries of unbuffered interaction.

Post by Eric Wong
Normally Ruby servers and network clients use IO#readpartial or
IO#read_nonblock to read a bunch at once.

Hrmm... THIS, I will have to do some reading up on.
Thank you!!
-Ken
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[Greg Navis]

Interesting! It seems telnet is too smart for this kind of testing. I think
netcat might be a better tool. You can type in a character and hit ^D to
send it (otherwise it's line buffered).

Best regards
Greg

[Ken D'Ambrosio]

Nah; telnet's good. It's *me* that's broke. I've learned a lot more
about the telnet protocol, itself. E.g., the telnet server, itself, is
what requests character mode (or linemode). So, for example, the server
could do something like this:
socket.print(255.chr, 254.chr, 34.chr) # IAC [Interpret As Command],
DONT, Linemode

telnetd -- by default, at least -- issues just that as part of the
initial handshake. Opening a port and listening, though, not so much.

Now I know! And, by issuing just that command, was able to force the
telnet client into character mode. Yay!

-Ken

Interesting! It seems telnet is too smart for this kind of testing. I think netcat might be a better tool. You can type in a character and hit ^D to send it (otherwise it's line buffered).
Best regards
Greg
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[Ken D'Ambrosio]

Gosh darn it. I meant to send along a link for reference; here's a
decent one:

http://pcmicro.com/netfoss/telnet.html

socket.print(255.chr, 254.chr, 34.chr) # IAC [Interpret As Command], DONT, Linemode
telnetd -- by default, at least -- issues just that as part of the initial handshake. Opening a port and listening, though, not so much.
Now I know! And, by issuing just that command, was able to force the telnet client into character mode. Yay!
-Ken

Interesting! It seems telnet is too smart for this kind of testing. I think netcat might be a better tool. You can type in a character and hit ^D to send it (otherwise it's line buffered).
Best regards
Greg
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[Matthew Kerwin]

If you really want to dive into it, there's these:

* https://tools.ietf.org/html/rfc854
* https://www.iana.org/assignments/telnet-options/telnet-options.xhtml
* https://tools.ietf.org/html/rfc1184

Telnet was great fun, back in the day. I can't honestly say I miss it,
though.

But now I have to ask: are you implementing a telnet server, or just
reading bytes from a TCP stream? Because netcat might actually be a better
answer *in this instance *.

Matthew Kerwin

Gosh darn it. I meant to send along a link for reference; here's a decent
http://pcmicro.com/netfoss/telnet.html
Nah; telnet's good. It's *me* that's broke. I've learned a lot more
about the telnet protocol, itself. E.g., the telnet server, itself, is
what requests character mode (or linemode). So, for example, the server
socket.print(255.chr, 254.chr, 34.chr) # IAC [Interpret As Command], DONT, Linemode
telnetd -- by default, at least -- issues just that as part of the initial
handshake. Opening a port and listening, though, not so much.
Now I know! And, by issuing just that command, was able to force the
telnet client into character mode. Yay!
-Ken
Interesting! It seems telnet is too smart for this kind of testing. I
think netcat might be a better tool. You can type in a character and hit ^D
to send it (otherwise it's line buffered).
Best regards
Greg
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[Ken D'Ambrosio]

But now I have to ask: are you implementing a telnet server, or just reading bytes from a TCP stream? Because netcat might actually be a better answer *in this instance *.
Telnet was great fun, back in the day. I can't honestly say I miss it, though.

Well... it's like this. Our BBS -- running code from '88 and earlier --
is strictly telnet. (Well... probably some dialup code in there, too,
but that's so crufty it makes the '88 telnet stuff look new.) However,
that's not entirely true; there are two components to the BBS: the core
BBS code itself (which -- ah, the joys of legacy code -- actually runs
one instance/user), and a "connector" front end that accepts telnet
connections and then passes them through to the BBS code. All of which
worked for ~23 years or so terrifically.

Then came the Russians. More specifically, the Russian Dyn/DDoS attack.
It took us *down*. Now, you may say to yourself, "Who in their right
mind would DDoS a BBS used by a few-hundred old fogies?" And the answer
is "Nobody -- intentionally." But the way that the damn worm
*propagates* is through embedded devices with telnet as the admin
mechanism, and user "admin" as the user. So we've been *slammed* for
some two years straight with One Bajillion bogus login attempts over
telnet. And the connector happily accepts them -- they can't log in
(there's no user "admin", nor credentials for same), but they take up
lots and lots of sockets, causing the connector to die fairly often, and
exposing a few edge condition bugs in the core BBS code.

I'd like to set up something to replace the connector: a telnet proxy of
sorts. First and foremost would be to discard attempted "admin" logins.
After that, to just sit there and pass stuff through to the BBS code.

Regret you asked yet? ;-)

-Ken

Matthew Kerwin

http://pcmicro.com/netfoss/telnet.html
socket.print(255.chr, 254.chr, 34.chr) # IAC [Interpret As Command], DONT, Linemode
telnetd -- by default, at least -- issues just that as part of the initial handshake. Opening a port and listening, though, not so much.
Now I know! And, by issuing just that command, was able to force the telnet client into character mode. Yay!
-Ken
Interesting! It seems telnet is too smart for this kind of testing. I think netcat might be a better tool. You can type in a character and hit ^D to send it (otherwise it's line buffered).
Best regards
Greg
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[Matthew Kerwin]

Post by Ken D'Ambrosio
I'd like to set up something to replace the connector: a telnet proxy of
sorts. First and foremost would be to discard attempted "admin" logins.
After that, to just sit there and pass stuff through to the BBS code.

So, if you write a new gateway which can eagerly drop attempted
"admin" logins, you can save the BBS back-end from being flooded out.
But won't the gateway itself still run out of sockets? You can tweak
TCP parameters and stuff (e.g. reducing TIME_WAIT) but those have
their own risks.

If it's really Mirai (and variants) you're up against, why not just
have the telnet side of the gateway listen on a completely different
port? AFAIK Mirai attacks TCP/23 and TCP/2323. So set it to listen
on TCP/7777 or something.

Cheers

[Ken D'Ambrosio]

Post by Matthew Kerwin
So, if you write a new gateway which can eagerly drop attempted
"admin" logins, you can save the BBS back-end from being flooded out.
But won't the gateway itself still run out of sockets? You can tweak
TCP parameters and stuff (e.g. reducing TIME_WAIT) but those have
their own risks.

From the OS side, I don't think we're being hammered so hard that it
affects the availability of sockets. It just makes the connector app
get upset fairly frequently (e.g., it's down as I type this -- even
though it's still accepting connection attempts). I, myself, set up an
open telnet port on one of my VMs, and it was truly impressive how many
connection attempts got going, but it was more of a "boy, that's really
annoying" than "holy crow, port 23 is officially down."

Post by Matthew Kerwin
If it's really Mirai (and variants) you're up against, why not just
have the telnet side of the gateway listen on a completely different
port? AFAIK Mirai attacks TCP/23 and TCP/2323. So set it to listen
on TCP/7777 or something.

We thought about that -- but a number of people use clients, and not all
of them are terribly technically savvy in figuring out how to change
default port settings, etc. It's a shame -- there aren't many BBSes
left, and the botnet propagation mechanism took down a handful of them
permanently. (At least one threw in the towel and migrated to a Slack
channel.) But I'm taking this as a bit of a fun challenge, too: I'll
learn some, and help out the BBS. Win-win. I hope. ;-)

-Ken

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[Mikol Faro]

Have you tried to use something like iptables and fail2ban?
If you have a log about failed logins you should be able to ban bots by IP

Mikol

PS this is my first reply to this mailing list :-)

Post by Matthew Kerwin
So, if you write a new gateway which can eagerly drop attempted
"admin" logins, you can save the BBS back-end from being flooded out.
But won't the gateway itself still run out of sockets? You can tweak
TCP parameters and stuff (e.g. reducing TIME_WAIT) but those have
their own risks.

From the OS side, I don't think we're being hammered so hard that it affects the availability of sockets. It just makes the connector app get upset fairly frequently (e.g., it's down as I type this -- even though it's still accepting connection attempts). I, myself, set up an open telnet port on one of my VMs, and it was truly impressive how many connection attempts got going, but it was more of a "boy, that's really annoying" than "holy crow, port 23 is officially down."

Post by Matthew Kerwin
If it's really Mirai (and variants) you're up against, why not just
have the telnet side of the gateway listen on a completely different
port? AFAIK Mirai attacks TCP/23 and TCP/2323. So set it to listen
on TCP/7777 or something.

We thought about that -- but a number of people use clients, and not all of them are terribly technically savvy in figuring out how to change default port settings, etc. It's a shame -- there aren't many BBSes left, and the botnet propagation mechanism took down a handful of them permanently. (At least one threw in the towel and migrated to a Slack channel.) But I'm taking this as a bit of a fun challenge, too: I'll learn some, and help out the BBS. Win-win. I hope. ;-)
-Ken
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