CSS 432
FAQ on Program 1: Basic TCP Communication

Q1: Should we use C or C++?

A: Use C++.

Q2: May I use the code in the lecture slides from CSS432 and/or CSS434?

A: Yes, you can

Q3: Where is gnuplot?

A:/usr/bin/gnuplot

If you want to know how to use it, type "man gnuplot". Also, visit http://www.gnuplot.info

Q4: Should I use the "flush" system call?

A: No.

For data transfer, you should just use write and read system calls.

Q5: What header files should I inclulde for each system call?

A: Use man.

If you would like to know the usage and the header files required for the "write" system call, type 
man 2 write
where 2 means the section 2. In general, most system calls are described the section 2. The "man" page displays: 
SYNOPSIS
       #include 
 
       ssize_t write(int fd, const void *buf, size_t count);
...
So, what you need is to include the "unistd.h" file.

Q6. How can a server know the size of message it receives from the client?

A. You may hard-code the server in that you make sure to increment the message size in the same way in the server as we do in the client

Q7. I got a "Broken pipe" error.

A. Your client and server program didn't agree at the number of messages exchange and the message size, and thus one of them exited earlier than the other.

The client and server must agree how many bytes to send and read. If the client sends 100, 200, 300, and 400 bytes, the server must read 100, 200, 300, and 400 bytes. Since server sends back a 1-byte acknowledgment for every message, the client must read 1 byte after every message transfer. If either cleint or server exits and its counter part still tries to send a message, the socket (=pipe) has been already gone and you'll get a broekn error.

Q8. When I tried to compile the following program, I got a bunch of errors.

int main( void ) {
   write( 5, "Hi there!", 9 );
   return 0;
}

A. Include header files necessary to execute the "write" system call and open a file descriptor first.

Check the answer for Q5. Thereafter, you have to receive a file descriptor explicitly from OS with open. In the above code, you are using the file descriptor 5 without receiving this descriptor from OS. First open a file or a socket. Note that you can use the file descriptors 0, 1, and 2 without calling open( ). They are automatically opened and correspond to stdin, stdout, and stderr respectively.

Q9. The compiler complains about my usage of accept.

int len;
newSd = accept(sd, (strcute sockaddr *)&client, &len);

A. Use "socklen_t*" instead of "int*"

socklen_t len;
newSd = accept(sd, (strcute sockaddr *)&client, &len);

Q10. Do you want us to actually fill the message exchange between a client and a server?

A. You don't have to fill it out.