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simple Telnet app, empty read buffer

Posted on 2010-08-25
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Last Modified: 2013-12-29
I am trying to write a Telnet interface to ICC, the Internet Chess Club.  Attached is the code I have so far.  Wireshark shows that when I run this program, the message "Welcome to the INTERNET CHESS CLUB" is sent across the wire, but the read buffer is empty at line 59.  Why is the buffer empty and/or how should I be reading from the socket?
Main.java
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Question by:blackfrancis75
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19 Comments
 
LVL 86

Expert Comment

by:CEHJ
ID: 33521823
What happens when you use a telnet app to do the same?
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Author Comment

by:blackfrancis75
ID: 33522329

telnet> open chessclub.com
Trying 207.99.83.228...
Connected to chessclub.com.
Escape character is '^]'.
Welcome to the INTERNET CHESS CLUB

web:   www.chessclub.com    email: icc@chessclub.com
phone: 1-412-521-5553

login:
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Expert Comment

by:CEHJ
ID: 33522578
So what gets printed - a solitary right angle bracket?
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Author Comment

by:blackfrancis75
ID: 33522713
yes.  I also checked the buffer (using Eclipse debugger) and it appears to be empty
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Expert Comment

by:CEHJ
ID: 33522959
Configure it to be blocking and you'll probably find it'll read something. If you want non-blocking, you should probably use a Selector
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Expert Comment

by:CEHJ
ID: 33523441
Another consideration is that a telnet stream contains control characters, so will not decode completely as text
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Author Comment

by:blackfrancis75
ID: 33523734
yeah, that's why I checked that the buffer was actually empty using the debugger.

I don't get it though - this is the documented nio.* way to open a socketchannel and read from it. I'd like to understand why it doesn't work.
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Expert Comment

by:CEHJ
ID: 33523866
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LVL 92

Accepted Solution

by:
objects earned 2000 total points
ID: 33527034
commons net supports telnet out of the box

http://commons.apache.org/net/

no need to reinvent the wheel
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Author Comment

by:blackfrancis75
ID: 33527328
CEHJ: If I run that program with parameters: chessclub.com 23
it hangs at line 52:  
mIn.read(buf);
indefinitely
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LVL 92

Expert Comment

by:objects
ID: 33527350
> Another consideration is that a telnet stream contains control characters, so will not decode completely as text

How would control chars cause it to "not decode completely"?
And how would that cause a read() to block anyway?
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Author Comment

by:blackfrancis75
ID: 33527503
CEHJ: objects really doesn't like you today
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Expert Comment

by:objects
ID: 33527536
his comments are getting a little questionable ;)
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Author Comment

by:blackfrancis75
ID: 33527606
perhaps you can comment on why my code wont work ;).  I looked at commons-net but would prefer to use my own basic implementation, if it can work.
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LVL 92

Expert Comment

by:objects
ID: 33527628
sorry don't have the time available. I only spend a small amount of time on EE these days.
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Expert Comment

by:CEHJ
ID: 33529044
Actually i've tried it with a telnet stream and it behaves weirdly with that too. I can only guess, at this point, that the server could be disallowing automation by screening for 'real' telnet clients.
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LVL 5

Author Comment

by:blackfrancis75
ID: 33549541
Using the example code for the Commons-net telnet works fine.  I wish someone could tell me why my original code doesn't work.
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Expert Comment

by:CEHJ
ID: 33550378
I used commons net telnet too - with weird results
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Expert Comment

by:CEHJ
ID: 33550487
Just tried it again - seemed ok that time. Possibly an intermittent problem..?
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