Question

currently the code contacts the server 1 time and exits. Modify the code so that the program contacts the server five times before exiting.

/* client.c - code for example client program that uses TCP */

#ifndef unix
#define WIN32
#include <windows.h>
#include <winsock.h>
#else
#define closesocket close
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#endif

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>

#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.
*
*------------------------------------------------------------------------
*/

int 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. */
// next line changed cast from (int) to (long) to remove warning. by streller
if ( ((long)(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);
n = recv(sd, buf, sizeof(buf), 0);
}

/* Close the socket. */

closesocket(sd);

/* Terminate the client program gracefully. */

return(0);
}

Answer 1

/* client.c - code for example client program that uses TCP */

#ifndef unix
#define WIN32
#include <windows.h>
#include <winsock.h>
#else
#define closesocket close
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#endif

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>

#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.
*
*------------------------------------------------------------------------
*/

int 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 */
int i =1; /* number of times socket should try connecting to server */
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. */
// next line changed cast from (int) to (long) to remove warning. by streller
if ( ((long)(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. */

while (i <=5)
{
   if (connect(sd, (struct sockaddr *)&sad, sizeof(sad)) < 0)
   {
   i += 1;
   }  
   else
   {
   break;
   }
}

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);
n = recv(sd, buf, sizeof(buf), 0);
}

/* Close the socket. */

closesocket(sd);

/* Terminate the client program gracefully. */

return(0);
}