Posted: October 27th, 2022

Socket programming with c

  

In the provided client.c and server.c program (please download from the folder socket programming), after the client receives “This server has been contacted 1 time” from the server, the client process exits.

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Modify the client.c and server.c in this way: after the client receives “This server has been contacted 1 times”, instead of exit, the client sends back “This client has been contacted 1 times” to the server. The server then sends back “This server has been contacted 2 times”, the client sends back “This client has been contacted 2 times” to the server, and so on. That is, both the client and the server do not exit. They alternatively send messages to each other.

/* client.c – code for example client program that uses TCP */
#ifndef unix
#define WIN32
#include
#include
#else
#define closesocket close
#include
#include
#include
#include
#include
#endif
#include
#include
#define PROTOPORT 5193 /* default protocol port number */
extern int errno;
char localhost[] = “localhost”; /* default host name */
/*————————————————————————
* * Program: client
* *
* * Purpose: allocate a socket, connect to a server, and print all output
* * Syntax: client [ host [port] ]
* *
* * host – name of a computer on which server is executing
* * port – protocol port number server is using
* *
* * Note: Both arguments are optional. If no host name is specified,
* * the client uses “localhost”; if no protocol port is
* * specified, the client uses the default given by PROTOPORT.
* *
* *————————————————————————
* */
main(argc, argv)
int argc;
char *argv[];
{
struct hostent *ptrh; /* pointer to a host table entry */
struct protoent *ptrp; /* pointer to a protocol table entry */
struct sockaddr_in sad; /* structure to hold an IP address */
int sd; /* socket descriptor */
int port; /* protocol port number */
char *host; /* pointer to host name */
int n; /* number of characters read */
char buf[1000]; /* buffer for data from the server */
#ifdef WIN32
WSADATA wsaData;
WSAStartup(0x0101, &wsaData);
#endif
memset((char *)&sad,0,sizeof(sad)); /* clear sockaddr structure */
sad.sin_family = AF_INET; /* set family to Internet */
/* Check command-line argument for protocol port and extract */
/* port number if one is specified. Otherwise, use the default */
/* port value given by constant PROTOPORT */
if (argc > 2) { /* if protocol port specified */
port = atoi(argv[2]); /* convert to binary */
} else {
port = PROTOPORT; /* use default port number */
}
if (port > 0) /* test for legal value */
sad.sin_port = htons((u_short)port);
else { /* print error message and exit */
fprintf(stderr,”bad port number %s\n”,argv[2]);
exit(1);
}
/* Check host argument and assign host name. */
if (argc > 1) {
host = argv[1]; /* if host argument specified */
} else {
host = localhost;
}
/* Convert host name to equivalent IP address and copy to sad. */
ptrh = gethostbyname(host);
if ( ((char *)ptrh) == NULL ) {
fprintf(stderr,”invalid host: %s\n”, host);
exit(1);
}
memcpy(&sad.sin_addr, ptrh->h_addr, ptrh->h_length);
/* Map TCP transport protocol name to protocol number. */
if ( ((int)(ptrp = getprotobyname(“tcp”))) == 0) {
fprintf(stderr, “cannot map \”tcp\” to protocol number”);
exit(1);
}
/* Create a socket. */
sd = socket(PF_INET, SOCK_STREAM, ptrp->p_proto);
if (sd < 0) { fprintf(stderr, "socket creation failed\n"); exit(1); } /* Connect the socket to the specified server. */ if (connect(sd, (struct sockaddr *)&sad, sizeof(sad)) < 0) { fprintf(stderr,"connect failed\n"); exit(1); } /* Repeatedly read data from socket and write to user.s screen. */ n = recv(sd, buf, sizeof(buf), 0); while (n > 0) {
write(1,buf,n);
printf(“n: %d\n”, n);
n = recv(sd, buf, sizeof(buf), 0);
}
printf(“n: %d\n”, n);
/* Close the socket. */
closesocket(sd);
/* Terminate the client program gracefully. */
exit(0);
}

/* server.c – code for example server program that uses TCP */
#ifndef unix
#define WIN32
#include
#include
#else
#define closesocket close
#include
#include
#include
#include
#endif
#include
#include
#define PROTOPORT 5193 /* default protocol port number */
#define QLEN 6 /* size of request queue */
int visits = 0; /* counts client connections */
/*————————————————————————
* * Program: server
* *
* * Purpose: allocate a socket and then repeatedly execute the following:
* * (1) wait for the next connection from a client
* * (2) send a short message to the client
* * (3) close the connection
* * (4) go back to step (1)
* * Syntax: server [ port ]
* *
* * port – protocol port number to use
* *
* * Note: The port argument is optional. If no port is specified,
* * the server uses the default given by PROTOPORT.
* *
* *————————————————————————
* */
main(argc, argv)
int argc;
char *argv[];
{
struct hostent *ptrh; /* pointer to a host table entry */
struct protoent *ptrp; /* pointer to a protocol table entry */
struct sockaddr_in sad; /* structure to hold server.s address */
struct sockaddr_in cad; /* structure to hold client.s address */
int sd, sd2; /* socket descriptors */
int port; /* protocol port number */
int alen; /* length of address */
char buf[1000]; /* buffer for string the server sends */
#ifdef WIN32
WSADATA wsaData;
WSAStartup(0x0101, &wsaData);
#endif
memset((char *)&sad,0,sizeof(sad)); /* clear sockaddr structure */
sad.sin_family = AF_INET; /* set family to Internet */
sad.sin_addr.s_addr = INADDR_ANY; /* set the local IP address */
/* Check command-line argument for protocol port and extract */
/* port number if one is specified. Otherwise, use the default */
/* port value given by constant PROTOPORT */
if (argc > 1) { /* if argument specified */
port = atoi(argv[1]); /* convert argument to binary */
} else {
port = PROTOPORT; /* use default port number */
}
if (port > 0) /* test for illegal value */
sad.sin_port = htons((u_short)port);
else { /* print error message and exit */
fprintf(stderr,”bad port number %s\n”,argv[1]);
exit(1);
}
/* Map TCP transport protocol name to protocol number */
if ( ((int)(ptrp = getprotobyname(“tcp”))) == 0) {
fprintf(stderr, “cannot map \”tcp\” to protocol number”);
exit(1);
}
/* Create a socket */
sd = socket(PF_INET, SOCK_STREAM, ptrp->p_proto);
if (sd < 0) { fprintf(stderr, "socket creation failed\n"); exit(1); } /* Bind a local address to the socket */ if (bind(sd, (struct sockaddr *)&sad, sizeof(sad)) < 0) { fprintf(stderr,"bind failed\n"); exit(1); } /* Specify size of request queue */ if (listen(sd, QLEN) < 0) { fprintf(stderr,"listen failed\n"); exit(1); } /* Main server loop - accept and handle requests */ while (1) { alen = sizeof(cad); if ( (sd2=accept(sd, (struct sockaddr *)&cad, &alen)) < 0) { fprintf(stderr, "accept failed\n"); exit(1); } visits++; sprintf(buf,"This server has been contacted %d time%s\n", visits,visits==1?".":"s."); send(sd2,buf,strlen(buf),0); closesocket(sd2); } }

#include
#include
#include
#include
#include
#define SERVER_PORT 5432
#define MAX_PENDING 5
#define MAX_LINE 256
int main()
{
struct sockaddr_in sin;
char buf[MAX_LINE];
int len;
int s, new_s;
/* build address data structure */
bzero((char *)&sin, sizeof(sin));
sin.sin_family = AF_INET;
sin.sin_addr.s_addr = INADDR_ANY;
sin.sin_port = htons(SERVER_PORT);
/* setup passive open */
if ((s = socket(PF_INET, SOCK_STREAM, 0)) < 0) { perror("simplex-talk: socket"); exit(1); } if ((bind(s, (struct sockaddr *)&sin, sizeof(sin))) < 0) { perror("simplex-talk: bind"); exit(1); } listen(s, MAX_PENDING); /* wait for connection, then receive and print text */ while(1) { if ((new_s = accept(s, (struct sockaddr *)&sin, &len)) < 0) { perror("simplex-talk: accept"); exit(1); } while (len = recv(new_s, buf, sizeof(buf), 0)) fputs(buf, stdout); close(new_s); } }

#include
#include
#include
#include
#include
#define SERVER_PORT 5432
#define MAX_LINE 256
int main(int argc, char * argv[])
{
FILE *fp;
struct hostent *hp;
struct sockaddr_in sin;
char *host;
char buf[MAX_LINE];
int s;
int len;
if (argc==2) {
host = argv[1];
}
else {
fprintf(stderr, “usage: simplex-talk host\n”);
exit(1);
}
/* translate host name into peer’s IP address */
hp = gethostbyname(host);
if (!hp) {
fprintf(stderr, “simplex-talk: unknown host: %s\n”, host);
exit(1);
}
/* build address data structure */
bzero((char *)&sin, sizeof(sin));
sin.sin_family = AF_INET;
bcopy(hp->h_addr, (char *)&sin.sin_addr, hp->h_length);
sin.sin_port = htons(SERVER_PORT);
/* active open */
if ((s = socket(PF_INET, SOCK_STREAM, 0)) < 0) { perror("simplex-talk: socket"); exit(1); } if (connect(s, (struct sockaddr *)&sin, sizeof(sin)) < 0) { perror("simplex-talk: connect"); close(s); exit(1); } /* main loop: get and send lines of text */ while (fgets(buf, sizeof(buf), stdin)) { buf[MAX_LINE-1] = '\0'; len = strlen(buf) + 1; send(s, buf, len, 0); } }

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