Writing Server Applications (TCP/SOCK_STREAM): How can I read only one character at a time?
This question is usually asked by people who are testing their server with
telnet, and want it to process their keystrokes one character at a time.
Without special direction from the server telnet will buffer each line of
text that you type, so when you press a key, telnet won't send it until you
press enter. The correct way to read a single character is (as you would expect):
read(s,buf,1) or recv(s,buf,1,flags)
The rest of this answer assumes that you want to force telnet to send
individual characters and not do line buffering.
According to Roger Espel Llima (email@example.com), you can have your server
send a sequence of control characters:
0xff 0xfb 0x01 0xff 0xfb 0x03 0xff 0xfd 0x0f3,
which translates to
IAC WILL ECHO IAC WILL SUPPRESS-GO-AHEAD IAC DO SUPPRESS-GO-AHEAD.
For more information on what this means, check out std8, std28 and std29.
Roger also gave the following tips:
This code will suppress echo, so you'll have to send the characters the user
types back to the client if you want the user to see them.
Carriage returns will be followed by a null character, so you'll have to
If you get a 0xff, it will be followed by two more characters. These are telnet escapes.
Thanks to Cyrus Patel (firstname.lastname@example.org) for emailing me some pointers on clarifying this answer.