CS 39006: Assignment 6 Non-blocking I/O


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The objective of this assignment is to implement a concurrent server where multiple clients can
requests for same or different services and the server serves them concurrently with the help of
nonblocking I/O operations. The implementation will help you to understand the functionality of the
fcntl() system call used for manipulating file descriptors.
Problem Statement:
The assignment statement is completely similar to the Assignment 3, except that you need to use
non-blocking I/O instead of the select() system call. Your task is to implement a server and two
clients with two different service requests. The server can receive two different service requests from
the clients as follows.
1. Request for a bag of words, where the server will forward a set of words from a file word.txt
one after another over a stream socket. The file word.txt contains a set of words, one each at
every line. Once the server receives a request for the words, it reads the words from the file and
forwards them one after another, each as a null terminated string. The end of service is marked
with an empty string (a string only with a null character). Once the client receives that empty
string, it prints the number of words received and exits. You need to set the stream socket as a
non-blocking socket using fcntl() system call with O_NONBLOCK using the file status flags
F_SETFL. Note that here you have to make the entire socket non-blocking as the socket will wait
over the accept() call. Once you accept a new connection, you will use a fork() to create a
child process and then the child process will handle the word transfers.
2. Request for the IP address corresponding to a domain name, where the client requests for the
IP address of a domain, say www.iitkgp.ac.in, over a datagram socket. The server looks up
for the IP address by using the system call gethostbyname(). The server returns this IP
address to the client. The client prints the IP address and exits. Here you can make the
recvfrom() call non-blocking by setting the MSG_DONTWAIT flag while receiving the data from
the other host.
You have to implement two clients, one corresponding to each of the services as mentioned above.
Note that the client requesting bag of words works over a stream socket, whereas the client requesting
for the IP address works on a datagram socket.
Submission Instruction:
You should write three C programs – nonblockingserver.c (contains the server program),
bowclient.c (for bag of words requests) and dnsclient.c (for IP address requests). Ideally, you
should not make any change in the client codes that you had done as a part of Assignment 3.
Keep these three files in a single compressed folder (zip or tar.gz) having the name _Assignment6.zip or _Assignment6.tar.gz. Upload this compressed folder at
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