Programming

echoServAddr.sin_family      = AF_INET;             /* Internet address family */ 
    {
      struct in_addr a;
      struct hostent *h=gethostbyname(servIP);
      if(h == NULL)
        DieWithError("Unknown host");

      memcpy(&a, h->h_addr_list[0], sizeof(a));
 
      servIP=inet_ntoa(a);
    }    
    echoServAddr.sin_addr.s_addr = inet_addr(servIP);   /* Server IP address */

#include <stdio.h>      /* for printf() and fprintf() */
#include <sys/socket.h> /* for socket(), connect(), send(), and recv() */
#include <arpa/inet.h>  /* for sockaddr_in and inet_addr() */
#include <stdlib.h>     /* for atoi() and exit() */
#include <string.h>     /* for memset() */
#include <unistd.h>     /* for close() */
#include <netdb.h>

#define RCVBUFSIZE 64   /* Size of receive buffer */
#define PORT 80
#define USERAGENT "HTMLGET 1.0"

void DieWithError(char *errorMessage);  /* Error handling function */

int main(int argc, char *argv[])
{
    int sock;                        /* Socket descriptor */
    struct sockaddr_in echoServAddr; /* Echo server address */
    unsigned short echoServPort;     /* Echo server port */
    char *servIP;                    /* Server IP address (dotted quad) */
    char *echoString;                /* String to send to echo server */
    char echoBuffer[RCVBUFSIZE];     /* Buffer for echo string */
    unsigned int echoStringLen;      /* Length of string to echo */
    int bytesRcvd, totalBytesRcvd;   /* Bytes read in single recv() 
                                        and total bytes read */
   
   
    if ((argc < 3) || (argc > 4))    /* Test for correct number of arguments */
    {
      
      fprintf(stderr, "Usage: %s <servername> <message> <Echo Port>\n",
               argv[0]);
       exit(1);
    }


    servIP = argv[1];             /* First arg: server IP address (dotted quad) */
    

    if (argc == 4)
        echoServPort = atoi(argv[3]); /* Use given port, if any */
    else
        echoServPort = 7;  /* 7 is the well-known port for the echo service */

    /* Create a reliable, stream socket using TCP */
    if ((sock = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP)) < 0)
        DieWithError("socket() failed");

    /* If connected then send the message */
    if ( connect(sock, (struct sockaddr*)&echoServAddr, sizeof(echoServAddr)) == 0)
    {    char s[200];
        FILE *fp = fdopen(sock, "r+");       /* convert into stream */

        fprintf(fp, argv[2]);                     /* send request */
        fprintf(fp, "\n\n");                 /* add some newlines */
        fflush(fp);                          /* ensure it got out */
        while ( fgets(s, sizeof(s), fp) != 0 )/* while not EOF ...*/
            fputs(s, stdout);                /*... print the data */
        fclose(fp);                           /* close the socket */
    }
    
    /* Construct the server address structure */
    memset(&echoServAddr, 0, sizeof(echoServAddr));     /* Zero out structure */
    echoServAddr.sin_family      = AF_INET;             /* Internet address family */     
    echoServAddr.sin_addr.s_addr = inet_addr(servIP);   /* Server IP address */
    echoServAddr.sin_port        = htons(echoServPort); /* Server port */

    /* Establish the connection to the echo server */ 
    if (connect(sock, (struct sockaddr *) &echoServAddr, sizeof(echoServAddr)) < 0) 
        DieWithError("connect() failed"); 
    echoStringLen = strlen(echoString);          /* Determine input length */ 
 
    /* Send the string to the server */ 
    if (send(sock, echoString, echoStringLen, 0) != echoStringLen) 
        DieWithError("send() sent a different number of bytes than expected"); 
 
    /* Receive the same string back from the server */ 
    totalBytesRcvd = 0; 
    printf("Received: ");                /* Setup to print the echoed string */ 
    while (totalBytesRcvd < echoStringLen) 
    { 
        /* Receive up to the buffer size (minus 1 to leave space for 
           a null terminator) bytes from the sender */ 
        if ((bytesRcvd = recv(sock, echoBuffer, RCVBUFSIZE - 1, 0)) <= 0) 
            DieWithError("recv() failed or connection closed prematurely"); 
        totalBytesRcvd += bytesRcvd;   /* Keep tally of total bytes */ 
        echoBuffer[bytesRcvd] = '\0';  /* Terminate the string! */ 
        printf("%s", echoBuffer);      /* Print the echo buffer */ 
    } 
 
    printf("\n");    /* Print a final linefeed */ 
 
    close(sock); 
    exit(0); 
}//-- end main --// 
 
 
 
// 
//// 
// 
void DieWithError(char *errorMessage) 
{ 
    perror(errorMessage); 
    exit(1); 
}

fprintf(fp, argv[2]);                     /* send request */