Client Server Communication using SOCKET

TCP is a Connection-Oriented Protocol. The Communication can be done using Sockets. The System Calls used in the interaction of Client Server are in the library <sys/socket.h>

1) int socket(int family, int type, int protocol);

creates an entry in object/file descriptor table to allow I/O based on file descriptors and also returns the index in object description table.

2) int bind(int sockfd, const struct sockaddr *myaddr, socklen_t addrlen);

determines the local address and local process. It assigns a name to an unnamed socket. It informs system with its address that are dispatched to the process.

3) int listen(int sockfd, int backlog);

sets queue length for client process waiting to connect to socket.

4) int accept(int sockfd, const struct sockaddr *clientaddr, socklen_t addrlen);

waits for another process to connect to this socket after creating file descriptor for actual communication with client to read & write data.

5) int connect(int sockfd, const struct sockaddr *servaddr, socklen_t addrlen);

client tries to connect to waiting server process through

socket created.

6) size_t read(int filedes, void *buff, size_t nbytes);

7) size_t write(int filedes, void *buff, size_t nbytes);

8) int close(int sockfd);

CONSTANTS :

family

AF_INET IPv4 protocols

AF_INET6 IPv6 protocols

AF_LOCAL UNIX domain protocols

AF_ROUTE Routing protocols

AF_KEY Key protocols

type

SOCK_STREAM stream socket

SOCK_DGRAM datagram socket

SOCK_SEQPACKET sequenced packet socket

SOCK_RAW raw socket

protocol

IPROTO_TCP TCP transport protocol

IPROTO_UDP UDP transport protocol

IPROTO_SCTP SCTP transport protocol

CLIENT SERVER Communication Flow

server.c

#include <stdio.h>

#include <sys/types.h>

#include <sys/socket.h>

#include <netinet/in.h>

void error(char *msg)

{

perror(msg);

exit(1);

}

int main(int argc, char *argv[])

{

int sockfd, newsockfd, portno, clilen;

char buffer[256];

struct sockaddr_in serv_addr, cli_addr;

int n;

if (argc<2)

{

fprintf(stderr,"ERROR, no port provided\n");

exit(1);

}

sockfd = socket(AF_INET, SOCK_STREAM, 0);

if (sockfd<0)

error("ERROR opening socket");

bzero((char *) &serv_addr, sizeof(serv_addr));

portno = atoi(argv[1]);

serv_addr.sin_family = AF_INET;

serv_addr.sin_addr.s_addr = INADDR_ANY;

serv_addr.sin_port = htons(portno);

if (bind(sockfd, (struct sockaddr *) &serv_addr,

sizeof(serv_addr))<0)

error("ERROR on binding");

listen(sockfd,5);

clilen = sizeof(cli_addr);

newsockfd = accept(sockfd,(struct sockaddr *) &cli_addr,

&clilen);

if (newsockfd<0)

error("ERROR on accept");

bzero(buffer,256);

n = read(newsockfd,buffer,255);

if (n<0)

error("ERROR reading from socket");

printf("Here is the message: %s\n",buffer);

n = write(newsockfd,"SERVER : I got your message",18);

if (n<0)

error("ERROR writing to socket");

return 0;

}

client.c

#include <stdio.h>

#include <sys/types.h>

#include <sys/socket.h>

#include <netinet/in.h>

#include <netdb.h>

void error(char *msg)

{

perror(msg);

exit(1);

}

int main(int argc, char *argv[])

{

int sockfd, portno;

char buffer[256];

struct sockaddr_in serv_addr;

struct hostent *server;

int n;

if (argc<3)

{

fprintf(stderr,"ERROR, usage %s hostname port\n",argv[0]);

exit(0);

}

portno = atoi(argv[2]);

sockfd = socket(AF_INET, SOCK_STREAM, 0);

if (sockfd<0)

error("ERROR opening socket");

server = gethostbyname(argv[1]);

if (server == NULL)

{

fprintf(stderr,"ERROR, no such host\n");

exit(0);

}

bzero((char *) &serv_addr, sizeof(serv_addr));

portno = atoi(argv[1]);

serv_addr.sin_family = AF_INET;

bcopy((char *)server->h_addr,

(char *)&serv_addr.sin_addr.s_addr,

server->h_length);

serv_addr.sin_port = htons(portno);

if (connect(sockfd, (struct sockaddr *) &serv_addr,

sizeof(serv_addr))<0)

printf("Please Enter the message");

bzero(buffer,256);

fgets(buffer,255,stdin);

n = write(sockfd,buffer,255);

if (n<0)

error("ERROR writing to socket");

bzero(buffer,256);

n = read(sockfd,buffer,255);

if (n<0)

error("ERROR reading to socket");

printf("CLIENT : Here is the message: %s\n",buffer);

return 0;

}

OUTPUT :

$ ./server server 51222

$ ./client client manoj 51222

Please enter the message

you are going to be killed!

SERVER : I got the message

CLIENT : Here is the message: you are going to be killed!