using sigurg signal

Referring to the SIGURG signal  here is the sample server client application that I am presenting to see how SIGURG signal are being sent and received. For all this to see we need three files which are basically the simple client and server program and a code that I have presented earlier for the mkaddr subroutine. Please download all the files mentioned below and try to build them in the order I am suggesting otherwise there are chances you may get errors.

1. oobrecv.c
2. mkaddr.c
3. bindacpt.c
4. oobsend.c

[root@rhel54x64 sigurg]#

[root@rhel54x64 sigurg]# gcc -c -D_GNU_SOURCE -Wall -Wreturn-type -g oobrecv.c

[root@rhel54x64 sigurg]# gcc -c -D_GNU_SOURCE -Wall -Wreturn-type -g mkaddr.c

[root@rhel54x64 sigurg]# gcc -c -D_GNU_SOURCE -Wall -Wreturn-type -g bindacpt.c

[root@rhel54x64 sigurg]# gcc oobrecv.o mkaddr.o bindacpt.o -o oobrecv

[root@rhel54x64 sigurg]#

[root@rhel54x64 sigurg]#

[root@rhel54x64 sigurg]# gcc -c -D_GNU_SOURCE -Wall -Wreturn-type -g oobsend.c

[root@rhel54x64 sigurg]# gcc oobsend.o mkaddr.o bindacpt.o -o oobsend

[root@rhel54x64 sigurg]#

After the compile is complete, you have two executable programs:

• oobrecv is the receiving program (a server). 
• oobsend is the sending program (a client).

Now you are ready to invoke these programs.

Testing the oobrecv and oobsend Programs

It is best to run these programs in two completely different terminal sessions. Use either two different xterm windows, or two different console sessions. Start the receiving program first in the first terminal session:

Example

[root@rhel54x64 sigurg]#

[root@rhel54x64 sigurg]# ./oobrecv

[root@rhel54x64 sigurg]#

Both programs accept an optional address and port number pair if you want to specify your Ethernet address instead of the local loopback address ("127.0.0.1:9011" is assumed by default). For example, the following would work on a system with an NIC card addressed as 192.168.0.1:

Example

[root@rhel54x64 sigurg]#

[root@rhel54x64 sigurg]# ./oobrecv 192.168.0.1:9023

[root@rhel54x64 sigurg]#

This would start the server listening on 192.168.0.1 port number 9023. For the purposes of this demonstration, however, you can just run the program without arguments. Now start the sending program on the second terminal session, as follows:

Output

[root@rhel54x64 sigurg]#

[root@rhel54x64 sigurg]# ./oobsend

ib: 'In the beginning' (16)

ib: 'Linus begat Linux,' (18)

ib: 'and the Penguins' (16)

OOB 'rejoiced' (8)

ib: 'exceedingly.' (12)

[root@rhel54x64 sigurg]#

The lines starting with ib: indicate in-band data that was written. The line beginning with OOB indicates that 'rejoiced' was written as out-of-band data to the socket. If you were able to watch both sessions at the same time, you will notice that the receiving program reports the data shortly after it is sent by the sending program. Its session output should look like this:

Output

[root@rhel54x64 sigurg]# ./oobrecv

rcv 'In the beginning' (16)

rcv 'Linus begat Linux,' (18)

rcv 'and the Penguins' (16)

URG 'd' (1)

rcv 'rejoice' (7)

rcv 'exceedingly.' (12)

[root@rhel54x64 sigurg]#

The output lines shown in this terminal session that begin with rcv indicate normal in-band data that was received. The line starting with URG indicates that SIGURG was raised and the signal handler was called. Within the signal handler, the urgent data is read and reported. You should notice something peculiar— only the d byte was received as out-of-band data! What gives? Read on to find out.