Np Lab 1p33n

NETWORK PROGRAMMING Lab Manual

IV / IV B.Tech. Ist Semester Information Technology LAKIREDDY BALIREDDY COLLEGE OF ENGINEERING(AUTONOMOUS) (d to JNTU, Hyderabad, Approved by AICTE, Accredited by NBA, New Delhi) LB REDDY NAGAR, MYLAVARAM – 521 230, KRISHNA(Dist), A.P. INDIA Website: www.lbrce.com

Fax: 08659-222931

Week1. Implement the following forms of IPC. a)Pipes b)FIFO Week2. Implement file transfer using Message Queue form of IPC Week3. Write a program to create an integer variable using shared memory concept and increment the variable simultaneously by two processes. Use semaphores to avoid race conditions Week4. Design T iterative Client and server application to reverse the given input sentence Week5. Design T iterative Client and server application to reverse the given input sentence Week6. Design T client and server application to transfer file Week7. Design a T concurrent server to convert a given text into upper case using multiplexing system call “select” Week8. Design a T concurrent server to echo given set of sentences using poll functions Week9. Design UDP Client and server application to reverse the given input sentence

Introduction The Internet is all about connecting machines together. One of the most exciting aspects of Java is that it incorporates an easy-to-use, cross-platform model for network communications that makes it possible to learn network programming without years of study. This opens up a whole new class of applications to programmers.

What is a Socket? Java's socket model is derived from BSD (UNIX) sockets, introduced in the early 1980s for interprocess communication using IP, the Internet Protocol. The Internet Protocol breaks all communications into packets, finite-sized chunks of data which are separately and individually routed from source to destination. IP allows routers, bridges, etc. to drop packets--there is no delivery guarantee. Packet size is limited by the IP protocol to 65535 bytes. Of this, a minimum of 20 bytes is needed for the IP packet header, so there is a maximum of 65515 bytes available for data in each packet. Sockets are a means of using IP to communicate between machines, so sockets are one major feature that allows Java to interoperate with legacy systems by simply talking to existing servers using their pre-defined protocol. Other common protocols are layered on top of the Internet protocol. The ones we discuss in this chapter are the Datagram Protocol (UDP) and the Transmission Control Protocol (T). Applications can make use of these two protocols to communicate over the network, commonly by building additional protocols on top of the T or UDP base.

Internet Addresses Internet addresses are manipulated in Java by the use of the InetAddress class. InetAddress takes care of the Domain Name System (DNS) look-up and reverse look-up; IP addresses can be specified by either the host name or the raw IPaddress. InetAddres provides methods to getByName(), getAllByName(),getLocalHost(), getAddress(), etc.

IP Addresses IP addresses are a 32-bit number, often represented as a "quad" of four 8-bit numbers separated by periods. They are organized into classes (A, B, C, D, and E) which are used to group varying numbers of hosts in a hierarchical numbering scheme.

Class A 1.0.0.0 to 126.255.255.255, inclusive. About 16 million IP addresses in a class A domain. Class B 128.1.0.0 to 191.254.255.255, inclusive. About 64 thousand IP addresses in a class B domain. Class C 192.0.1.0 to 223.255.254.255, inclusive. 256 IP addresses in a class C domain. Class D 224.0.0.1 to 239.255.255.255, inclusive, denote multicast groups. Class E 240.0.0.0 to 254.255.255.255, inclusive. Reserved for future use. The IP address 127.0.0.1 is special, and is reserved to represent the loopback or "localhost" address.

Port number The port number field of an IP packet is specified as a 16-bit unsigned integer. This means that valid port numbers range from 1 through 65535. (Port number 0 is reserved and can't be used).

Java does not have any unsigned data types; Java's short data type is 16 bits, but its range is -32768 to 32767 since it is a signed type. Thus, short is not large enough to hold a port number, so all classes which use or return a port number must represent the port number as an int. In the JDK 1.1, using an int with a value greater than 65535 will generate an IllegalArgumentException. In the JDK 1.0.2 and earlier, values greater than 65535 are truncated and only the loworder 16 bits are used.

Port numbers 1 through 255 are reserved by IP for well-known services. A well-known service is a service that is widely implemented which resides at a published, "well-known", port. If you connect to port 80 of a host, for instance, you may expect to find an HTTP server. On UNIX machines, ports less than1024 are privileged and can only be bound by the root . This is so an arbitrary on a multi system can't impersonate well-known services like TELNET (port 23), creating a security problem. Windows has no such restrictions, but you should program as if it did so that your applications will work cross-platform.

Client/Server Computing You can use the Java language to communicate with remote file systems using client/server model. A server listens for connection requests from clients across the network or even from the same machine. Clients know how to connect to the server via an IP address and port number. Upon connection, the server reads the request sent by the client and responds appropriately. In this way, applications can be broken down into specific tasks that are accomplished in separate locations. The data that is sent back and forth over a socket can be anything you like. Normally, the client sends a request for information or processing to the server, which performs a task or sends data back. You could, for example, place an SQL shell on the server and let people talk to it via a simple client "chat" program. The IP and port number of the server is generally well-known and d so the client knows where to find the service. In contrast, the port number on client the side is generally allocated automatically by the kernel. Many protocols used on the Internet (HTTP for example) are designed to be driven from the command line. They send their requests and responses across the net in plain text. One of the easiest ways to become familiar with network programming and/or specific protocols is to use the TELNET application to "talk “directly to a server from the command line.

Datagram Protocol (UDP) UDP provides an unreliable packet delivery system built on top of the IPprotocol. As with IP, each packet is an individual, and is handled separately. Because of this, the amount of data that can be sent in a UDP packet is limited to the amount that can be contained in a single IP packet. Thus, a UDP

packet can contain at most 65507 bytes (this is the 65535-byte IP packet size minus the minimum IP header of 20 bytes and minus the 8-byte UDP header). UDP packets can arrive out of order or not at all. No packet has any knowledge of the preceding or following packet. The recipient does not acknowledge packets, so the sender does not know that the transmission was successful. UDP has no provisions for flow control--packets can be received faster than they can be used. We call this type of communication connectionless because the packets have no relationship to each other and because there is no state maintained. The destination IP addresses and port number is encapsulated in each UDP packet. These two numbers together uniquely identify the recipient and are used by the underlying operating system to deliver the packet to a specific process(application). One way to think of UDP is by analogy to communications via a letter. You write the letter (this is the data you are sending); put the letter inside an envelope (the UDP packet); address the envelope (using an IP address and a port number); put your return address on the envelope (your local IP address and port number); and then you send the letter. Like a real letter, you have no way of knowing whether a UDP packet was received. If you send a second letter one day after the first, the second one may be received before the first. Or, the second one may never be received. So why use UDP if it unreliable? Two reasons: speed and overhead. UDP packets have almost no overhead--you simply send them then forget about them. And they are fast, since there is no acknowledgement required for each packet. Keep in mind the degree of unreliability we are talking about. For all practical purposes, an Ethernet breaks down if more than about 2 percent of all packets are lost. So, when we say unreliable, the worst-case loss is very small. UDP is appropriate for the many network services that do not require guaranteed delivery. An example of this is a network time service. Consider a time daemon that issues a UDP packet every second so computers on the LAN can synchronize their clocks. If a packet is lost, it's no big deal--the next one will be by in another second and will contain all necessary information to accomplish the task. Another common use of UDP is in networked, multi- games, where a player's position is sent periodically. Again, if one position update is lost, the next one will contain all the required information. A broad class of applications is built on top of UDP using streaming protocols. With streaming protocols, receiving data in real-time is far more important than guaranteeing delivery. Examples of real-time streaming protocols are RealAudio and Real Video which respectively deliver real-time streaming audio and video over the Internet. The reason a streaming protocol is desired in these cases is because if an audio or video packet is lost, it is much better for the client to see this as noise or "drop-out" in the sound or picture rather than having a long pause while the client software stops the playback, requests the missing data from the server. That would result in a very choppy, busty playback which most people find unacceptable, and which would place a heavy demand on the server.

Creating UDP Servers To create a server with UDP, do the following: 1. Create a Datagram Socket attached to a port.

int port = 1234; DatagramSocket socket = new DatagramSocket(port); 2. Allocate space to hold the incoming packet, and create an instance of

DatagramPacket to hold the incoming data. byte[] buffer = new byte[1024]; DatagramPacket packet =new DatagramPacket(buffer, buffer.length); 3. Block until a packet is received, then extract the information you need from the packet.

// Block on receive() socket.receive(packet); // Find out where packet came from // so we can reply to the same host/port InetAddress remoteHost = packet.getAddress(); int remotePort = packet.getPort(); // Extract the packet data byte[] data = packet.getData(); The server can now process the data it has received from the client, and issue an appropriate reply in response to the client's request.

Creating UDP Clients Writing code for a UDP client is similar to what we did for a server. Again, weneed a DatagramSocket and a DatagramPacket. The only real difference is thatwe must specify the destination address with each packet, so the form of theDatagramPacket constructor used here specifies the destination host and portnumber. Then, of course, we initially send packets instead of receiving.

1. First allocate space to hold the data we are sending and create an instance of

DatagramPacket to hold the data. byte[] buffer = new byte[1024]; int port = 1234; InetAddress host = InetAddress.getByName("magelang.com"); DatagramPacket packet = new DatagramPacket(buffer, buffer.length, host, port); 2. Create a DatagramSocket and send the packet using this socket.

DatagramSocket socket = new DatagramSocket(); socket.send(packet); The DatagramSocket constructor that takes no arguments will allocate a free local port to use. You can find out what local port number has been allocated for your socket, along with other information about your socket if needed. // Find out where we are sending from

InetAddress localHostname = socket.getLocalAddress(); int localPort = socket.getLocalPort(); The client then waits for a reply from the server. Many protocols require theserver to reply to the host and port number that the client used, so the client cannow invoke socket.receive() to wait for information from the server.

Transmission Control Protocol (T) We saw in the previous section that UDP provides an unreliable packet delivery system--each packet is an individual, and is handled separately. Packets can arrive out of order or not at all. The recipient does not acknowledge them, so the sender does not know that the transmission was successful. There is no provisions forflow control--packets can be received faster than they can be used. Packet size was limited by the underlying IP protocol. T, Transmission Control Protocol, was designed to address these problems.T packets are lost occasionally, just like UDP packets. The difference is that the T protocol takes care of requesting retransmits to ensure that all packets show up, and tracks packet sequence numbers to be sure that they are delivered in the correct order. While UDP required us to send packets of byte arrays, with T we can use streams along with the standard Java file I/O mechanism.

Unlike UDP, the Transmission Control Protocol, T, establishes a connection between the two endpoints. Negotiation is performed to establish a socket, and the socket remains open throughout the duration of the communications. The recipient acknowledges each packet, and packet retransmissions are performed by the protocol if packets are missed or arrive out of order. In this way T can allow an application to send as much data as it desires and not be subject to the IP packet size limit. T is responsible for breaking the data into packets, buffering the data, resending lost or out of order packets, acknowledging receipt, and controlling rate of data flow by telling the sender to speed up or slow down so that the application never receives more than it can handle. Again, unlike UDP, the destination host and port number is not sufficient to identify a recipient of a T connection. There are five distinct elements that make a T connection unique: IP address of the server IP address of the client Port number of the server Port number of the client Protocol (UDP, T/IP, etc...)

where each requested client socket is assigned a unique port number whereas the server port number is always the same. If any of these numbers is different, the socket is different. A server can thus listen to one and only one port, and talk to multiple clients at the same time. So a T connection is more like a telephone connection than a letter; you need to know not only the phone number (IP address), but since the phone may be shared by many people at that location, you also need the name of the you want to talk to at the other end (port number). The analogy can be taken a little further. If you don't hear what the other person has said, a simple request ("What?") will prompt the other end to resend or repeat the phrase. And, the connection remains open until someone hangs up.

Creating T Servers To create a T server, do the following: 1. Create a ServerSocket attached to a port number.

ServerSocket server = new ServerSocket(port); 2. Wait for connections from clients requesting connections to that port. // Block on accept()

Socket channel = server.accept(); You'll get a Socket object as a result of the connection. 3. Get input and output streams associated with the socket.

out = new PrintWriter (channel.getOutputStream()); reader = new InputStreamReader (channel.getInputStream()); in = new BufferedReader (reader); Now you can read and write to the socket, thus, communicating with the client. String data = in.readLine(); out.println("Hey! I heard you over this socket!"); When a server invokes the accept() method of the Server Socket instance, the main server thread blocks until a client connects to the server; it is then prevented from accepting further client connections until the server has processed the client's request. This is known as an iterative server, since the main server method handles each client request in its entirety before moving on to the next request. Iterative servers are good when the requests take a known, short period of time. For example, requesting the current day and time from a time-of-day server.

Creating T Clients To create a T client, do the following: 1. Create a Socket object attached to a remote host, port. Socket client = new Socket(host, port);

When the constructor returns, you have a connection. 2. Get input and output streams associated with the socket.

out = new PrintWriter

(client.getOutputStream()); reader = new InputStreamReader (client.getInputStream()); in = new BufferedReader (reader); Now you can read and write to the socket, thus, communicating with the server. out.println("Watson!" + "Come here...I need you!"); String data = in.readLine();

Servers Handling Multiple Clients While iterative servers are simple, they are severely limited in their performance since only one client at a time can be handled. In particular, when the amount of processing needed to handle a client request is unknown a priori (i.e., depends on the request itself), iterative servers are unacceptable. A TELNET session, for instance, can take an unbounded amount of time, so the server should not wait until that session is over before accepting new clients. To overcome this problem with iterative servers, a separate thread can handle each client session, allowing the server to deal with multiple clients simultaneously. This is known as a concurrent server-the main server method launches a thread to handle each client request, then continues to listen for additional clients. Here is an example server method called acceptClients() that listens for connections and handles multiple clients, each in a separate thread: public void acceptClients() { Socket socket = null; while (true) { // For each connection, start a new handler // in its own thread and keep on listening

try { socket = server.accept(); PrintWriter out = new PrintWriter(socket.getOutputStream()); InputStreamReader reader = new InputStreamReader(socket.getInputStream()); BufferedReader in = new BufferedReader(reader); // Create new client handler // and launch thread on it. Handler h = new Handler(in, out); (new Thread(h)).start(); } catch (IOException e) { System.err.println ("Error creating socket connection"); System.exit(1); } } } An enhancement to this server could be to pre-allocate a collection of Thread objects to be used for handling client requests. This will allow the server to handle the requests quicker by utilizing a thread from the pool rather than dynamically allocating one. In addition, it will allow the server to manage the client connections for the purpose of limiting number of clients or setting timeout values for the client connections.

Multithreaded Clients In the previous section we learned why we needed to use threads in our server if we wanted to simultaneously deal with multiple clients. It is not so clear why we would need more than one thread for our client, but we generally do. The reason for this is that the I/O operations we perform on a

socket generally block. So the client can read or write to the socket, but not both at the same time. This poses a problem when the client does not know ahead of time how much data the server is going to send back in response to the client's request. How many times should the client call readLine()? Having one thread to read and one thread to write, we can ensure that we never enter into a situation where the client fails to read the entire server response, or where the client is stuck waiting for too much data from the server. Instead of creating two threads within your client, a more common scenario would be to take advantage of the fact that the WT handles input in a separate thread; you can receive input and send data over the socket from an AWT event handling method, while your client class receives data in its run() method.

Sending Objects T is a stream protocol; we can do anything with socket streams that we can with file streams. One way we can greatly simplify communications between clients and servers written in Java is to use an ObjectInputStream andObjectOutputStream combination to read and write objects across the socket. This is a higher level of abstraction--we don't have to write int or float data types, but we can send a whole object. For example: 1. First, define an object to send. We'll define a class called Message to encapsulate our

communications. public class Message implements Serializable { private int senderID; private String messageText; public Message(int id, String text) { senderID = id; messageText = text; } public String getText() { return messageText; } }

2. Next, instantiate the object; wrap the socket's streams in object streams; and then send the message

across the socket. Message sayhey = new Message("123456789", "Hello"); out = new ObjectOutputStream(socket.getOutputStream()); in = new ObjectInputStream(socket.getInputStream()); out.writeObject(sayhey); 3. On the other side of the socket, the message can be retrieved and used by invoking methods on the

returned object. Message messageObject = (Message) in.readObject(); String messageText = messageObject.getText(); Network Programming Network Programming -12 © 1996-2003 jGuru.com. All Rights Reserved.

Socket APIs * socket: creates a socket of a given domain, type, protocol (buy a phone) * bind: assigns a name to the socket (get a telephone number) * listen: specifies the number of pending connections that can be queued for a server socket. (call waiting allowance) * accept: server accepts a connection request from a client (answer phone) * connect: client requests a connection request to a server (call) * send, sendto: write to connection (speak) * recv, recvfrom: read from connection (listen) * shutdown: end the call

Server performs the following actions * socket: create the socket * bind: give the address of the socket on the server * listen: specifies the maximum number of connection requests that can be pending for this process * accept: establish the connection with a specific client * send,recv: stream-based equivalents of read and write (repeated) * shutdown: end reading or writing * close: release kernel data structures

Client performs the following actions * socket: create the socket * connect: connect to a server * send,recv: (repeated) * shutdown * close

Week1: AIM:Implement the following forms of IPC. a) Pipes b) FIFO a)PIPES: PROGRAM: PIPE.c: #include #include <stdio.h> #define MSGSIZE 16 char *msg1 = "hello #1"; char *msg2 = "hello #2"; char *msg3 = "hello #3"; main() { char inbuf[MSGSIZE]; int p[2], j; /* open pipe */ if(pipe(p) == -1) { perror("pipe call error"); exit(1); } printf("read pipe fd=%d,write pipe fd= %d\n",p[0],p[1]); /* write down pipe */ write(p[1], msg1, MSGSIZE); write(p[1], msg2, MSGSIZE); write(p[1], msg3, MSGSIZE); /* read pipe */ for(j=0; j<3; j++) { read(p[0], inbuf, MSGSIZE); printf("%s\n", inbuf); }

exit(0); }

Output: :~$ cc PIPE.c :~$ ./a.out read pipe fd=3,write pipe fd= 4 hello #1 hello #2 hello #3

b) FIFO: PROGRAM: fullduplex.h: #define NP2 "/tmp/np2" #define MAX_BUF_SIZE 255 fd_server.c: #include <errno.h> #include #include <sys/types.h> #include <sys/stat.h> #include #include "fullduplex.h" /* For name of the named-pipe */ #include <stdlib.h> #include<string.h> int main(int argc, char *argv[]) { int rdfd, wrfd, ret_val, count, numread; char buf[MAX_BUF_SIZE]; /* Create the first named - pipe */ ret_val = mkfifo(NP1, 0666); if ((ret_val == -1) && (errno != EEXIST)) { perror("Error creating the named pipe"); exit (1);

} ret_val = mkfifo(NP2, 0666); if ((ret_val == -1) && (errno != EEXIST)) { perror("Error creating the named pipe"); exit (1); } /* Open the first named pipe for reading */ rdfd = open(NP1, O_RDONLY); /* Open the second named pipe for writing */ wrfd = open(NP2, O_WRONLY); /* Read from the first pipe */ numread = read(rdfd, buf, MAX_BUF_SIZE); buf[numread] = '0'; printf("Full Duplex Server : Read From the pipe : %s\n", buf); /* Convert to the string to upper case */ count = 0; while (count < numread) { buf[count] = toupper(buf[count]); count++; } write(wrfd, buf, strlen(buf)); } 7 fd_client.c: #include <errno.h> #include #include <sys/types.h> #include <sys/stat.h> #include #include "fullduplex.h" /* For name of the named-pipe */ #include <stdlib.h> #include<string.h> int main(int argc, char *argv[]) { int wrfd, rdfd, numread; char rdbuf[MAX_BUF_SIZE]; /* Check if an argument was specified. */ if (argc != 2) { printf("Usage : %s <string to be sent to the server>\n", argv[0]); exit (1);

} /* Open the first named pipe for writing */ wrfd = open(NP1, O_WRONLY); /* Open the second named pipe for reading */ rdfd = open(NP2, O_RDONLY); /* Write to the pipe */ write(wrfd, argv[1], strlen(argv[1])); /* Read from the pipe */ numread = read(rdfd, rdbuf, MAX_BUF_SIZE); rdbuf[numread] = '0'; printf("Full Duplex Client : Read From the Pipe : %s\n", rdbuf); }

Output: Run the server: :~$ cc fd_server.c :~$ ./a.out The server program will block here, and the shell will return control to the command line. Run the client: :~$ cc fd_client.c :~$ ./a.out lbrce The client program will send the string to server and block on the read to await the server's response. The server prints the following: Full Duplex Server : Read From the pipe : lbrce The client prints the following: Full Duplex Client : Read From the pipe : LBRCE

Week2: AIM:Implement file transfer using Message Queue form of IPC PROGRAM: message_send.c: #include <sys/types.h> #include <sys/ipc.h> #include <sys/msg.h> #include <stdio.h> #include <string.h> #define MSGSZ

128

typedef struct msgbuf { long mtype; char mtext[MSGSZ]; } message_buf; main() { int msqid; int msgflg = IPC_CREAT | 0666; key_t key; message_buf sbuf; size_t buf_length; key = 1234; if ((msqid = msgget(key, msgflg )) < 0) { perror("msgget"); exit(1); } else (void) fprintf(stderr,"msgget: msgget succeeded: msqid = %d\n", msqid); sbuf.mtype = 1; (void) stry(sbuf.mtext, "WELCOME TO LBRCE");

buf_length = strlen(sbuf.mtext) + 1 ; if (msgsnd(msqid, &sbuf, buf_length, IPC_NOWAIT) < 0) { printf ("%d, %d, %s, %d\n", msqid, sbuf.mtype, sbuf.mtext, buf_length); perror("msgsnd"); exit(1); } else printf("Message: \"%s\" Sent\n", sbuf.mtext); exit(0); }

message_rec.c: #include <sys/types.h> #include <sys/ipc.h> #include <sys/msg.h> #include <stdio.h> #define MSGSZ

128

typedef struct msgbuf { long mtype; char mtext[MSGSZ]; } message_buf;

main() { int msqid; key_t key; message_buf rbuf; key = 1234; if ((msqid = msgget(key, 0666)) < 0) { perror("msgget"); exit(1);

} if (msgrcv(msqid, &rbuf, MSGSZ, 1, 0) < 0) { perror("msgrcv"); exit(1); } printf("%s\n", rbuf.mtext); exit(0); }

Output: :~$ cc message_send.c :~$ ./a.out msgget: msgget succeeded: msqid = 0 Message: "WELCOME TO LBRCE" Sent

:~$ cc message_rec.c :~$ ./a.out WELCOME TO LBRCE

Week3: AIM:Write a program to create an integer variable using shared memory concept and increment the variable simultaneously by two processes. Use semaphores to avoid race conditions. PROGRAM: sheredserver.c: #include <string.h> #include <sys/ipc.h> #include <sys/sem.h> #include <sys/shm.h> #define SEMKEYPATH "/dev/null" /* Path used on ftok for semget key */ #define SEMKEYID 1 /* Id used on ftok for semget key */ #define SHMKEYPATH "/dev/null" /* Path used on ftok for shmget key */ #define SHMKEYID 1 /* Id used on ftok for shmget key */ #define NUMSEMS 2 /* Num of sems in created sem set */ #define SIZEOFSHMSEG 50 /* Size of the shared mem segment */ #define NUMMSG 2

/* Server only doing two "receives" on shm segment */

int main(int argc, char *argv[]) { int rc, semid, shmid, i; key_t semkey, shmkey; void *shm_address; struct sembuf operations[2]; struct shmid_ds shmid_struct; short sarray[NUMSEMS]; /* Generate an IPC key for the semaphore set and the shared */ /* memory segment. Typically, an application specific path and */ /* id would be used to generate the IPC key. */ semkey = ftok(SEMKEYPATH,SEMKEYID); if ( semkey == (key_t)-1 ) { printf("main: ftok() for sem failed\n");

return -1; } shmkey = ftok(SHMKEYPATH,SHMKEYID); if ( shmkey == (key_t)-1 ) { printf("main: ftok() for shm failed\n"); return -1; } semid = semget( semkey, NUMSEMS, 0666 | IPC_CREAT | IPC_EXCL ); if ( semid == -1 ) { printf("main: semget() failed\n"); return -1; } sarray[1] = 0; if(rc == -1) { printf("main: semctl() initialization failed\n"); return -1; } if (shmid == -1) { printf("main: shmget() failed\n"); return -1; } if ( shm_address==NULL ) { printf("main: shmat() failed\n"); return -1; } printf("Ready for client jobs\n"); /* Loop only a specified number of times for this example. for (i=0; i < NUMMSG; i++) { operations[0].sem_num = 1; /* Operate on the second sem */ operations[0].sem_op = -1;

*/

/* Decrement the semval by one */ operations[0].sem_flg = 0; /* Allow a wait to occur */ operations[1].sem_num = 0; /* Operate on the first sem */ operations[1].sem_op = 1; /* Increment the semval by 1 */ operations[1].sem_flg = IPC_NOWAIT; /* Do not allow to wait */ rc = semop( semid, operations, 2 ); if (rc == -1) { printf("main: semop() failed\n"); return -1; } /* Print the shared memory contents. */ printf("Server Received : \"%s\"\n", (char *) shm_address); /* Signal the first semaphore to free the shared memory. operations[0].sem_num = 0; operations[0].sem_op = -1; operations[0].sem_flg = IPC_NOWAIT; rc = semop( semid, operations, 1 ); if (rc == -1) { printf("main: semop() failed\n"); return -1; } } /* End of FOR LOOP */ if (rc==-1) { printf("main: semctl() remove id failed\n"); return -1; } rc = shmdt(shm_address); if (rc==-1) {

*/

printf("main: shmdt() failed\n"); return -1; } rc = shmctl(shmid, IPC_RMID, &shmid_struct); if (rc==-1) { printf("main: shmctl() failed\n"); return -1; } return 0; } sheredclient.c: #include <stdio.h> #include <string.h> #include <sys/ipc.h> #include <sys/sem.h> #include <sys/shm.h> #define SEMKEYPATH "/dev/null" /* Path used on ftok for semget key */ #define SEMKEYID 1 /* Id used on ftok for semget key */ #define SHMKEYPATH "/dev/null" /* Path used on ftok for shmget key */ #define SHMKEYID 1 /* Id used on ftok for shmget key */ #define NUMSEMS 2 #define SIZEOFSHMSEG 50 int main(int argc, char *argv[]) { struct sembuf operations[2]; void *shm_address; int semid, shmid, rc; key_t semkey, shmkey; /* Generate an IPC key for the semaphore set and the shared */ /* memory segment. Typically, an application specific path and */ /* id would be used to generate the IPC key. */ semkey = ftok(SEMKEYPATH,SEMKEYID); if ( semkey == (key_t)-1 ) { printf("main: ftok() for sem failed\n"); return -1;

} shmkey = ftok(SHMKEYPATH,SHMKEYID); if ( shmkey == (key_t)-1 ) { printf("main: ftok() for shm failed\n"); return -1; } if ( semid == -1 ) { printf("main: semget() failed\n"); return -1; } if (shmid == -1) { printf("main: shmget() failed\n"); return -1; } /* Attach the shared memory segment to the client process. shm_address = shmat(shmid, NULL, 0); if ( shm_address==NULL ) { printf("main: shmat() failed\n"); return -1; } /* Operate on the first sem */ operations[0].sem_op = 0; /* Wait for the value to be=0 */ operations[0].sem_flg = 0; /* Allow a wait to occur */ operations[1].sem_num = 0; /* Operate on the first sem */ operations[1].sem_op = 1; /* Increment the semval by one */ operations[1].sem_flg = 0; /* Allow a wait to occur */ rc = semop( semid, operations, 2 ); if (rc == -1)

*/

{ printf("main: semop() failed\n"); return -1; } stry((char *) shm_address, "Hello from Client"); /* Operate on the first sem */ operations[0].sem_op = -1; /* Decrement the semval by one */ operations[0].sem_flg = 0; /* Allow a wait to occur */ operations[1].sem_num = 1; /* Operate on the second sem */ operations[1].sem_op = 1; /* Increment the semval by one */ operations[1].sem_flg = 0; /* Allow a wait to occur */ rc = semop( semid, operations, 2 ); if (rc == -1) { printf("main: semop() failed\n"); return -1; } /* Detach the shared memory segment from the current process. rc = shmdt(shm_address); if (rc==-1) { printf("main: shmdt() failed\n"); return -1; } return 0; }

*/

Output: At server side: :~$ cc sheredserver.c Ready for client jobs Server Received : "Hello from Client" Server Received : "Hello from Client" At client side: :~$ cc sheredclient.c :~$ ./a.out :~$ cc sheredclient.c :~$ ./a.out

Week4: AIM:Design T iterative Client and server application to reverse the given input sentence PROGRAM: server2.c: #include<stdlib.h> #include<errno.h> #include<string.h> #include<sys/types.h> #include<sys/socket.h> #include<sys/un.h> #define SOCK_PATH "echo_socket" int main(void) { int s,s2,t,len,i,j; struct sockaddr_un local,remote; char str[100],str2[100],c; if((s=socket(AF_UNIX,SOCK_STREAM,0))==-1) { perror("socket"); exit(1); } local.sun_family=AF_UNIX; stry(local.sun_path,SOCK_PATH); unlink(local.sun_path); len=strlen(local.sun_path)+sizeof(local.sun_family); if(bind(s,(struct sockaddr *)&local,len)==-1) { perror("bind"); exit(1); } if(listen(s,5)==-1) { perror("listen"); exit(1); } for( ; ;) {

int done,n; printf("Waiting for a Connection...\n"); t=sizeof(remote); if((s2=accept(s,(struct sockaddr *)&remote,&t))==-1) { perror("accept"); exit(1); } printf("Connected....\n"); done=0; do { n=recv(s2,str,100,0); if(n<=0) { if(n<0) perror("recv"); done=1; } if(!done) i=0;j=n-1; while(i<=j) { c=str[i]; str[i]=str[j]; str[j]=c; i++; j--; } if(send(s2,str,n,0)<0) { perror("send"); done=1; } }while(!done); close(s2); } return 0; }

client2.c: #include #include<stdio.h> #include<stdlib.h> #include<errno.h> #include<string.h> #include<sys/types.h> #include<sys/socket.h> #include<sys/un.h> #define SOCK_PATH "echo_socket" int main(void) { int s,t,len; struct sockaddr_un remote; char str[100]; if((s=socket(AF_UNIX,SOCK_STREAM,0))==-1) { perror("Socket"); exit(1); } printf("Trying to connect...\n"); remote.sun_family=AF_UNIX; stry(remote.sun_path,SOCK_PATH); len=strlen(remote.sun_path)+sizeof(remote.sun_family); if(connect(s,(struct sockaddr *)&remote,len)==-1) { perror("connect"); exit(1); } printf("Connected.....\n");

while(printf(">"),fgets(str,100,stdin),!feof(stdin)) { if(send(s,str,strlen(str),0)==-1) { perror("send"); exit(1); } if((t=recv(s,str,100,0))>0) {

str[t]='\0'; printf("Reverse : %s \n",str); } else { if(t<0) perror("recv"); else printf("Server closed Connection..\n"); exit(1); } } close(s); return 0; }

Output: At server side: :~$ cc server2.c :~$ ./a.out Waiting for a Connection... Connected....

At Client side: :~$ cc client2.c :~$ ./a.out Trying to connect... Connected..... >lbrce Reverse : ecrbl >hello Reverse : olleh

Week5: AIM:Design T client and server application to transfer file PROGRAM: fserver.c: #include<sys/types.h> #include #include<arpa/inet.h> #include<stdio.h> #define PORT 2080 main(){ int sock1,sock2,clength; sock1=socket(AF_INET,SOCK_STREAM,0); struct sockaddr_in serv,cli; serv.sin_family=AF_INET; serv.sin_port=htons(PORT); serv.sin_addr.s_addr=inet_addr("127.0.0.1"); bind(sock1,(struct sockaddr *)&serv,sizeof(serv)); listen(sock1,5); clength=sizeof(cli); int i=0; char buf[50]; sock2=accept(sock1,(struct sockaddr *)&cli,&clength); printf("\n Client Connected..\n"); FILE* fp=fopen("server2.txt","r"); while(!feof(fp)) { //bzero(buf,sizeof(buf)); fread(buf,sizeof(char),50,fp); write(sock2,buf,50); } write(sock2,"quit1234",50); fclose(fp); return 0; }

fclient.c: #include<sys/socket.h> #include<sys/types.h> #include #include<arpa/inet.h> #include<stdio.h> #define PORT 2080 main() { int sock1; sock1=socket(AF_INET,SOCK_STREAM,0); struct sockaddr_in serv; serv.sin_port=htons(PORT); printf("%x %x\n",PORT,htons(PORT)); serv.sin_family=AF_INET; serv.sin_addr.s_addr=inet_addr("127.0.0.1"); printf("Client Connecting....."); connect(sock1,(struct sockaddr *)&serv,sizeof(serv)); char buf[50]; FILE* fp=fopen("client2.txt","w"); while(1) { //bzero(buf,sizeof(buf)); read(sock1,buf,50); if(strcmp(buf,"quit1234")==0) { break; } fprintf(fp,"%s",buf); } fclose(fp); }

Output: :~$vi server2.txt

Hello How r u Iam Fine....

At server side: :~$ cc fserver.c :~$ ./a.out Client Connected..

At client side: :~$ cc fclient.c :~$ ./a.out 820 2008 Client Connecting..... :~$ cat client2.txt Hello How r u Iam Fine....

Week6: AIM:a)Design a T iterative server to convert a given text into upper case using multiplexing system call “select” . PROGRAM: iservert_select.c: #include <stdio.h>

/* for standard I/O */

#include

/* for read() and write() */

#include <strings.h>

/* for bzero() */

#include <stdlib.h>

/* for atoi() */

#include <sys/types.h>

/* for accept() and connect() */

#include <sys/socket.h> #include <sys/errno.h>

/* for perror() */

#include <sys/select.h> /* for select() */ #include /* for htonl() */

#define FD_SETSIZE 1 #define LISTENQ 2 #define BSIZE 256 #define USAGE "./iservert_select portno\n"

void error(char *msg)

{ perror(msg); exit(1); }

int main(int argc, char *argv[]) { int listenfd, connfd;/* socket file descriptor */ int j; int portno; socklen_t clilen; char buffer[BSIZE]; struct sockaddr_in serv_addr, cli_addr; int n;

/* variable declarations for select() */ int i, maxi, maxfd, sockfd; int nready, client[FD_SETSIZE]; fd_set rset, allset; if (argc < 2) error(USAGE);

/* the bitmap */

/* create a listening socket */ listenfd = socket(PF_INET, SOCK_STREAM, 0); if (listenfd < 0) error("ERROR opening socket"); bzero((char *) &serv_addr, sizeof(serv_addr)); serv_addr.sin_family = AF_INET; serv_addr.sin_addr.s_addr = htonl(INADDR_ANY); portno = atoi(argv[1]); serv_addr.sin_port = htons(3456); if (bind(listenfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr)) < 0) error("ERROR on binding"); listen(listenfd, LISTENQ); maxfd = listenfd; maxi = -1;

/* the maximum fd so far */ /* index to the client[] array */

for (i=0; i<=FD_SETSIZE;i++)

/* initialize the client array */

client[i] = -1; FD_ZERO(&allset);

/* initialize the descriptor set */

FD_SET(listenfd, &allset);

/* set the corresponding bit to on */

while (1) { rset = allset;

/* reset rset (a dynamic bitmap) */

nready = select(maxfd+1, &rset, NULL, NULL, NULL);

if (FD_ISSET(listenfd, &rset)) { /* accept connections */ clilen = sizeof(cli_addr); connfd = accept(listenfd, (struct sockaddr *) &cli_addr, &clilen); if (connfd < 0) error("ERROR on accept");

for (i=0; i maxfd)

/* update the descriptor set (a static bitmap) */ /* maxfd always records the largest fd */

maxfd = connfd; if (i > maxi) maxi = i;

if (--nready <= 0) continue; } for (i=0; i<=maxi;i++) {

/* update the index to the client array */

if ((sockfd = client[i]) < 0) continue;

if (FD_ISSET(sockfd, &rset)) { bzero(buffer, BSIZE); n = read(sockfd, buffer, BSIZE-1); if (n < 0) error("ERROR reading from socket"); if (n == 0) { close(sockfd);

/* receives a FIN package, close connection */ /* close the socket */

FD_CLR(sockfd, &allset); client[i] = -1; } else {

/* clear off the descriptor set */

/* reset that entry in client array */ /* if n>0, echo back */

for(j=0;j<strlen(buffer);j++) { if(buffer[j]>=65&&buffer[j]<=90) { buffer[j]+=32; } else if(buffer[j]>=97&&buffer[j]<=122)

{ buffer[j]-=32; } } printf("Here is the message: %s\n", buffer); fflush(stdout); n = write(sockfd, "I got your message", 18); if (n < 0) error("ERROR writing to socket"); if (--nready <= 0) break; } } } }

return 0; }

iclientt.c: #include <stdio.h>

/* for standard I/O */

#include

/* for read() and write() */

#include <strings.h>

/* for bzero() */

#include <stdlib.h>

/* for atoi() */

#include <sys/socket.h> #include <sys/types.h>

/* for accept() and connect() */

#include <sys/errno.h>

/* for perror() */

#include /* for htonl() */ #include

/* for gethostbyname() */

#define BSIZE 256 #define USAGE "./iclientt server portno\n"

void error(char *msg) { perror(msg); exit(1); }

int main(int argc, char *argv[]) { int connfd; int portno;

/* socket file descriptor */

struct hostent *server; char buffer[BSIZE]; struct sockaddr_in serv_addr; int n; if (argc < 3) error(USAGE); connfd = socket(PF_INET, SOCK_STREAM, 0); if (connfd < 0) error("ERROR opening socket"); bzero((char *) &serv_addr, sizeof(serv_addr)); serv_addr.sin_family = AF_INET; server = gethostbyname(argv[1]); if (server == NULL) error("ERROR, no such host\n"); bcopy((char *)server->h_addr, (char *)&serv_addr.sin_addr.s_addr, server->h_length); portno = atoi(argv[2]); serv_addr.sin_port = htons(3456);

/* connect to server */ if (connect(connfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0) error("ERROR connecting");

/* start sending message */ while(1) {

/** just add a while loop here for iterative client **/

printf("Please enter the message: "); bzero(buffer, BSIZE); fgets(buffer, BSIZE-1, stdin); n = write(connfd, buffer, strlen(buffer)); if (n < 0) error("ERROR writing to socket");

bzero(buffer, BSIZE); n = read(connfd, buffer, BSIZE-1); if (n < 0) error("ERROR reading from socket"); printf("%s\n\n", buffer); fflush(stdout); }

return 0; }

Output: At server side: :~$ cc iservert_select.c :~$ ./a.out 3456 Here is the message: LBRCE

Here is the message: HELLO

Here is the message: HOW R U

Here is the message: IAM FINE HERE.....

At Client side: :~$ cc iclientt.c :~$ ./a.out 127.0.0.1 3456 Please enter the message: lbrce I got your message

Please enter the message: hello I got your message

Please enter the message: how r u I got your message

Please enter the message: iam fine here..... I got your message

6 b)AIM: Design a T concurrent server to convert a given text into upper case using multiplexing system call “select” . PROGRAM: tservselect01.c: #include <stdlib.h> #include #include <errno.h> #include <string.h> #include <sys/types.h> #include <sys/stat.h> #include <sys/select.h> #include <sys/time.h> #include <sys/socket.h> #include #include <arpa/inet.h> #include #define MAXLINE 100 #define SERV_PORT 13153 int main(int argc, char **argv) { int k, i, maxi, maxfd, listenfd, connfd, sockfd; int nready, client[FD_SETSIZE]; ssize_t n; fd_set rset, allset; char line[MAXLINE],buf[100]; socklen_t clilen; struct sockaddr_in cliaddr, servaddr; listenfd = socket(AF_INET, SOCK_STREAM, 0); if (listenfd < 0 ) { perror("socket" );

exit(1); } bzero(&servaddr, sizeof(servaddr)); servaddr.sin_family = AF_INET; servaddr.sin_addr.s_addr = htonl(INADDR_ANY); servaddr.sin_port = htons(SERV_PORT); bind(listenfd, (struct sockaddr *) &servaddr, sizeof(servaddr)); listen(listenfd,5); maxfd = listenfd; /* initialize */ maxi = -1; /* index into client[] array */ for (i = 0; i < FD_SETSIZE; i++) client[i] = -1; /* -1 indicates available entry */ FD_ZERO(&allset); FD_SET(listenfd, &allset); /* end fig01 */ /* include fig02 */ for ( ; ; ) { printf("\n\nServer:I am waiting-----\n"); rset = allset; /* structure assignment */ nready = select(maxfd+1, &rset, NULL, NULL, NULL); if (FD_ISSET(listenfd, &rset)) { /* new client connection */ clilen = sizeof(cliaddr); connfd = accept(listenfd, (struct sockaddr *) &cliaddr, &clilen); #ifdef NOTDEF printf("new client: %s, port %d\n", inet_ntop(AF_INET, &cliaddr.sin_addr, buf, NULL), ntohs(cliaddr.sin_port)); #endif for (i = 0; i < FD_SETSIZE; i++) if (client[i] < 0) { client[i] = connfd; /* save descriptor */ break; } if (i == FD_SETSIZE) { printf("too many clients"); exit(0); } FD_SET(connfd, &allset); /* add new descriptor to set */ if (connfd > maxfd) maxfd = connfd; /* for select */ if (i > maxi)

maxi = i; if (--nready <= 0) continue;

/* max index in client[] array */

/* no more readable descriptors

*/ } for (i = 0; i <= maxi; i++) { /* check all clients for data */ if ( (sockfd = client[i]) < 0) continue; if (FD_ISSET(sockfd, &rset)) { if ( (n = read(sockfd, line, MAXLINE)) == 0) { /*4connection closed by client */ close(sockfd); FD_CLR(sockfd, &allset); client[i] = -1; } else { printf("\n output at server\n"); for(k=0;line[k]!='\0';k++) printf("%c ",toupper(line[k])); write(sockfd, line, n); } if (--nready <= 0) break; /* no more readable descriptors */ } } } } tclient1.c: #include #include #include #include #include #include #include #include #include #include #include

<stdio.h> <stdlib.h> <errno.h> <string.h> <sys/types.h> <sys/stat.h> <sys/socket.h> <arpa/inet.h>

#define MAXBUFFER 1024 void sendstring(int , char *); int main( int C, char *V[] ) { int sd,fd; char c; struct sockaddr_in serveraddress; char text[100]; int i=0; sd = socket( AF_INET, SOCK_STREAM, 0 ); if( sd < 0 ) { perror( "socket" ); exit( 1 ); } if (V[1] == NULL ) { printf ("PL specfiy the server's IP Address \n"); exit(0); } if (V[2] == NULL ) { printf ("PL specify the server's Port No \n"); exit(0); } memset( &serveraddress, 0, sizeof(serveraddress) ); serveraddress.sin_family = AF_INET; serveraddress.sin_port = htons(atoi(V[2]));//PORT NO serveraddress.sin_addr.s_addr = inet_addr(V[1]);//ADDRESS if (connect(sd,(struct sockaddr*)&serveraddress, sizeof(serveraddress))<0) { printf("Cannot Connect to server"); exit(1); } printf("enter sentence to end enter #"); while(1) { c=getchar(); if(c=='#') break; text[i++]=c; } text[i]='\0'; sendstring(sd,text); close(sd);

return 0; } void sendstring( int sd, /*Socket Descriptor*/ char *fname) /*Array Containing the string */ { int n , byteswritten=0 , written ; char buffer[MAXBUFFER]; stry(buffer , fname); n=strlen(buffer); while (byteswritten sent to server \n",buffer); }

Output: At server side: :~$ cc tservselect01.c :~$ ./a.out Server:I am waiting----Server:I am waiting----output at server HELLO Server:I am waiting----Server:I am waiting-----

At Client Side: :~$ cc tclient1.c

:~$ ./a.out 127.0.0.1 13153 enter sentence to end enter #hello# String : hello -----> sent to server

Week7: AIM:Design a T concurrent server to echo given set of sentences using poll functions. PROGRAM: tservpoll01.c: #include <stdio.h> #include <string.h> #include <sys/types.h> #include <sys/stat.h> #include <sys/socket.h> #include #include <arpa/inet.h> #include #include /* for OPEN_MAX */ #include <poll.h> #include <errno.h> #define MAXLINE 100 #define SERV_PORT 13154 #define POLLRDNORM 5 #define INFTIM 5 #define OPEN_MAX 5 int main(int argc, char **argv) { int k, i, maxi, listenfd, connfd, sockfd; int nready; ssize_t n; char line[MAXLINE]; socklen_t clilen; struct pollfd client[OPEN_MAX]; struct sockaddr_in cliaddr, servaddr; listenfd = socket(AF_INET, SOCK_STREAM, 0); bzero(&servaddr, sizeof(servaddr)); servaddr.sin_family = AF_INET; servaddr.sin_addr.s_addr = htonl(INADDR_ANY); servaddr.sin_port = htons(SERV_PORT); bind(listenfd, (struct sockaddr *) &servaddr, sizeof(servaddr)); listen(listenfd, 5); client[0].fd = listenfd;

client[0].events = POLLRDNORM; for (i = 1; i < OPEN_MAX; i++) client[i].fd = -1; /* -1 indicates available entry */ maxi = 0; /* max index into client[] array */ for ( ; ; ) { nready = poll(client, maxi+1, INFTIM); if (client[0].revents & POLLRDNORM) { /* new client connection */ clilen = sizeof(cliaddr); connfd = accept(listenfd, (struct sockaddr *) &cliaddr, &clilen); #ifdef NOTDEF printf("new client: %s\n", sock_ntop((struct sockaddr *) &cliaddr, clilen)); #endif for (i = 1; i < OPEN_MAX; i++) if (client[i].fd < 0) { client[i].fd = connfd; /* save descriptor */ break; } if (i == OPEN_MAX) { printf("too many clients"); exit(0); } client[i].events = POLLRDNORM; if (i > maxi) maxi = i; /* max index in client[] array */ if (--nready <= 0) continue; /* no more readable descriptors */ } for (i = 1; i <= maxi; i++) { /* check all clients for data */ if ( (sockfd = client[i].fd) < 0) continue; if (client[i].revents & (POLLRDNORM | POLLERR)) { if ( (n = read(sockfd, line, MAXLINE)) < 0) { if (errno == ECONNRESET) { /*4connection reset by client */ #ifdef NOTDEF printf("client[%d] aborted connection\n", i); #endif close(sockfd); client[i].fd = -1;

} else printf("readline error"); } else if (n == 0) { /*4connection closed by client */ #ifdef NOTDEF printf("client[%d] closed connection\n", i); #endif close(sockfd); client[i].fd = -1; } else{ printf("\n data from client is \n"); k=strlen(line); printf(" length=%d data = %s\n", k,line); //write(sockfd, line, n); stry(line," "); } if (--nready <= 0) break; /* no more readable descriptors */ } } } }

democlient.c: #include <stdio.h> #include <stdlib.h> #include #include <errno.h> #include <string.h> #include <sys/types.h> #include <sys/stat.h> #include <sys/socket.h> #include #include <arpa/inet.h> #include #define MAXBUFFER 1024 void sendstring(int , char *); int main( int C, char *V[] ) { int sd,fd; char c;

struct sockaddr_in serveraddress; char text[100]; int i=0; sd = socket( AF_INET, SOCK_STREAM, 0 ); if( sd < 0 ) { perror( "socket" ); exit( 1 ); } if (V[1] == NULL ) { printf ("PL specfiy the server's IP Address \n"); exit(0); } if (V[2] == NULL ) { printf ("PL specify the server's Port No \n"); exit(0); } memset( &serveraddress, 0, sizeof(serveraddress) ); serveraddress.sin_family = AF_INET; serveraddress.sin_port = htons(atoi(V[2]));//PORT NO serveraddress.sin_addr.s_addr = inet_addr(V[1]);//ADDRESS if (connect(sd,(struct sockaddr*)&serveraddress, sizeof(serveraddress))<0) { printf("Cannot Connect to server"); exit(1); } printf("enter sentence to end enter #"); while(1) { c=getchar(); if(c=='#') break; text[i++]=c; } text[i]='\0'; sendstring(sd,text); close(sd); return 0; } void sendstring( int sd, /*Socket Descriptor*/ char *fname) /*Array Containing the string */ { int n , byteswritten=0 , written ;

char buffer[MAXBUFFER]; stry(buffer , fname); n=strlen(buffer); while (byteswritten sent to server :~$ cc democlient.c :~$ ./a.out 127.0.0.1 13154 enter sentence to end enter #lbrce# String : lbrce----> sent to server

Week8: AIM:Design UDP Client and server application to reverse the given input sentence PROGRAM: udp-string-rev-ser.c: #include <sys/socket.h> #include #include <arpa/inet.h> #include <stdio.h> #include #include <errno.h> #include <string.h> #include <stdlib.h> int main() { int sock,len,i; int addr_len, bytes_read; char recv_data[1024],buf[1024]; struct sockaddr_in server_addr , client_addr;

if ((sock = socket(AF_INET, SOCK_DGRAM, 0)) == -1) { perror("Socket"); exit(1); } server_addr.sin_family = AF_INET; server_addr.sin_port = htons(1223); server_addr.sin_addr.s_addr = INADDR_ANY; bzero(&(server_addr.sin_zero),8);

if (bind(sock,(struct sockaddr *)&server_addr, sizeof(struct sockaddr)) == -1) { perror("Bind"); exit(1); }

addr_len = sizeof(struct sockaddr); printf("\nUDPServer Waiting for client on port 1223"); fflush(stdout); while (1) { bytes_read = recvfrom(sock,recv_data,1024,0, (struct sockaddr *)&client_addr, &addr_len);

recv_data[bytes_read] = '\0'; printf("\n(%s , %d) Data : ",inet_ntoa(client_addr.sin_addr), ntohs(client_addr.sin_port)); printf("%s", recv_data); fflush(stdout); stry(buf,recv_data); len=strlen(recv_data); for(i=0;i
udp-string-rev-cli.c: #include <sys/types.h> #include <sys/socket.h> #include #include <arpa/inet.h> #include #include <stdio.h> #include #include <errno.h> #include <string.h>

#include <stdlib.h> int main() { int sock; int addr_len,bytes_read; struct sockaddr_in server_addr; struct hostent *host; char send_data[1024],recv_data[1024]; host= (struct hostent *) gethostbyname((char *)"127.0.0.1");

if ((sock = socket(AF_INET, SOCK_DGRAM, 0)) == -1) { perror("socket"); exit(1); } server_addr.sin_family = AF_INET; server_addr.sin_port = htons(1223); server_addr.sin_addr = *((struct in_addr *)host->h_addr); bzero(&(server_addr.sin_zero),8); while (1) { printf("\nType Something (q or Q to quit):"); gets(send_data); if ((strcmp(send_data , "q") == 0) || strcmp(send_data , "Q") == 0) break; else sendto(sock, send_data, strlen(send_data), 0, (struct sockaddr *)&server_addr, sizeof(struct sockaddr)); bytes_read = recvfrom(sock,recv_data,1024,0, (struct sockaddr *)&server_addr, &addr_len);

recv_data[bytes_read] = '\0'; printf("\necho> %s",recv_data); fflush(stdout);

} }

Output: At Server Side: :~$ cc udp-string-rev-ser.c :~$ ./a.out UDPServer Waiting for client on port 1223 (127.0.0.1 , 36636) said : phani (127.0.0.1 , 36636) said : sandeep (127.0.0.1 , 49097) said : vamsi (127.0.0.1 , 49097) said : santosh

At Client Side: :~$ cc udp-string-rev-cli.c :~$ ./a.out Type Something (q or Q to quit):phani echo> inahp Type Something (q or Q to quit):sandeep echo> peednas Type Something (q or Q to quit):vamsi echo> ismav Type Something (q or Q to quit):santosh echo> hsotnas