Send null to socket

Dev Shed Forums Sponsor:

May 14th, 2006, 05:58 AM

tombell

Contributing User

Join Date: Jun 2002

Posts: 423

Time spent in forums: 1 Week 23 h 35 m 46 sec
Reputation Power: 13

Send null to socket

Hi to all

I would like to know how can I send null to a socket, so that I can evaluate it to null in Java.

My knowledge of C is limited.

Thanks for any help

May 14th, 2006, 10:54 AM

animatronic

Contributing User

Join Date: Jan 2004

Posts: 287

Time spent in forums: 2 Weeks 6 m 56 sec
Reputation Power: 13

Your question is a little unclear about your intent, perhaps you could post the Java code of what your trying to acheive.

May 14th, 2006, 11:04 AM

tombell

Contributing User

Join Date: Jun 2002

Posts: 423

Time spent in forums: 1 Week 23 h 35 m 46 sec
Reputation Power: 13

What I am doing is that the client (Java) sends a command to the server (C).
The server processes the command and sends back some data.
Most of the time, the response of the server is a single line (terminated by \n).

My problem is with a particular command which the server sends back multiple lines.
To read this in Java, I use readLine in a while loop.
The problem is that I have no way of breaking out of the loop.

Someone suggested that I should have the server send null to the socket as soon as he is done sending the actual data, so that I can evaluate it and break out of the loop.

Thanks

May 14th, 2006, 11:06 AM

jafet

Redpill

Dev Shed Intermediate (1500 - 1999 posts)

Join Date: Nov 2005

Posts: 1,660

Time spent in forums: 1 Week 6 Days 11 h 19 m 55 sec
Reputation Power: 150

Is this a C question, or Java question? What socket? What do you mean by "send NULL"? Please elaborate.

[edit] Whoops, 2 minutes late. Oh well.

__________________

Code:

#include <stdio.h>
int main(int o,char**O){return o>-1?o-2||!main(-1,1+O)?!!fprintf(stderr,"%s [0-"
"9]{81}\n",*O):main(-83,++O):o>-83?(*O)[-1-o]?81==(o=-o-1)||o[*O]<'0'||'9'<o[*O]
?0:main(-2-o,O):o==-82:o>-164?(*O)[-83-o]<'1'?main(o-82,O):main(--o,O):o+164?o>-
246?(*O)[-165-o]<'1'?main(o-82,O):main(--o,O):o+246?o>-328?(*O)[o=-o-247]<='8'?(
main(-328-o,(++o[*O],O)),main(-247-o,O)):!(o[*O]='0'):(o=-o-328)<729?(o%9/3*3-o%
27+o/243*9+o/81%3&&(*O)[o%81]==(*O)[o%81-o%27+o%9/3*3+o/243*9+o/81%3])||(o%81-o%
9-o/81*9&&(*O)[o%81]==(*O)[o%9+o/81*9])||(o/81-o%9&&(*O)[o%81]==(*O)[o%81-o%9+o/
81])?0:main(-409-o,O):main(-165-o%81,O):!puts(*O):0                           ;}

Last edited by jafet : May 14th, 2006 at 12:25 PM.

May 14th, 2006, 11:49 AM

animatronic

Contributing User

Join Date: Jan 2004

Posts: 287

Time spent in forums: 2 Weeks 6 m 56 sec
Reputation Power: 13

(guessing) the server is in Java and the cilent is in C?

May 14th, 2006, 12:09 PM

tombell

Contributing User

Join Date: Jun 2002

Posts: 423

Time spent in forums: 1 Week 23 h 35 m 46 sec
Reputation Power: 13

No.
It is the other way around
See post 3

May 14th, 2006, 07:19 PM

ptr2void

I haz teh codez!

Join Date: Dec 2003

Posts: 2,477

Time spent in forums: 1 Month 2 Weeks 2 Days 7 h 35 m 10 sec
Reputation Power: 2194

Assuming you're done with the socket on the server, just close it:

c Code:

Original - c Code
close(socket_file_descriptor);

close(socket_file_descriptor);

I'm guessing that would have the effect for which you're looking.

May 14th, 2006, 09:10 PM

dwise1_aol

Contributing User

Dev Shed God 2nd Plane (6000 - 6499 posts)

Join Date: Jan 2003

Location: USA

Posts: 6,142

Time spent in forums: 2 Months 2 Weeks 4 Days 33 m 48 sec
Reputation Power: 1974

I guess part of the question is the overall effect you want.

When you break out of that loop, do you want to close the connection? If so, then ptr2void's suggestion would be a way.

If you are wanting to keep the connection (for more commands, I would think), then close() is not the solution.

Take that suggestion of sending null figuratively as meaning that you need to send some special character or string that indicates end-of-data. In C, "null" means a zero value (actually, it refers to a pointer value of zero), which has special meaning in C because you make the end of a string with a NIL (a byte containing the ASCII value of zero). Would the client expect any empty strings in that data? If not, then that could be your "null". If an empty string would be acceptable data, then use a control character; ie, characters of ASCII code from 0 to 31. Can Java handle control characters in an input stream?
sendn

May 15th, 2006, 05:23 AM

tombell

Contributing User

Join Date: Jun 2002

Posts: 423

Time spent in forums: 1 Week 23 h 35 m 46 sec
Reputation Power: 13

Thank you for the replies.

Quote:

close(socket_file_descriptor);

Well, I need the socket to remain open.

dwise1_aol, thank you for the good explanation.
I will try sending the ASCII value of zero.

#10

May 16th, 2006, 11:46 AM

dwise1_aol

Contributing User

Join Date: Jan 2003

Location: USA

Posts: 6,142

Time spent in forums: 2 Months 2 Weeks 4 Days 33 m 48 sec
Reputation Power: 1974

An additional idea (which came to me as I was falling asleep last night): Or you could open a second socket for the actual data transfer and keep the original one open for commands and responses.

This is what FTP does. You start the session and issue commands and receive responses through port 21, but the actual transfer of files is through port 20 (designated ftp-data in your services file).

While embedding an end-of-data character (eg, a null character or ^D ('\x04') ) will work for text data, it won't work for binary data which could easily have your end-of-data values as valid data. So I'm just tossing this out as an idea for the future even though you should already have the remedy for your immediate problem.

#11

May 17th, 2006, 01:14 AM

tombell

Contributing User

Join Date: Jun 2002

Posts: 423

Time spent in forums: 1 Week 23 h 35 m 46 sec
Reputation Power: 13

Thanks for the idea.

However, I am concentrating on the client part to solve my problem.
Nice idea though, for future reference
Thanks

#12

May 19th, 2006, 08:27 AM

ripunjaytripath

Registered User

Join Date: Jun 2004

Posts: 9

Time spent in forums: 1 h 41 m 38 sec
Reputation Power: 0

Another Probability....

In such cases we can create a message header that contains the length of data followed by the data itself. The reading process first reads the length of the out put and then the out put itself. After that it calculates, the size and resumes processing.

You can modify the overall sceme to suit ur purpose.

Send null to socket

Developer Shed Advertisers and Affiliates