#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <stdlib.h>
#include <string.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <unistd.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;
     char *result1 = "Ian G. Harris";
     char *result2 = "Joe Smith";
     char *result3 = "Jane Smith";

     if (argc < 2) {
         fprintf(stderr,"ERROR, no port providedn");
         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");
     printf("Address server startedn");
     while (strcmp(buffer, "+++n") != 0)
     {
         bzero(buffer,256);
         n = read(newsockfd,buffer,255);
         if (n < 0) error("ERROR reading from socket");
         if (strcmp(buffer, "harris@ics.uci.edun") == 0)
         {
             printf("%sn", result1);
             n = write(newsockfd,"harris@ics.uci.edu",18);
             if (n < 0) error("ERROR writing to socket");
         }
         else if(strcmp(buffer, "joe@cnn.comn") == 0)
         {
             printf("%sn", result2);
             n = write(newsockfd,"joe@cnn.com",18);
             if (n < 0) error("ERROR writing to socket");
         }
         else if(strcmp(buffer, "jane@slashdot.orgn")==0)
         {
             printf("%sn", result3);
             n = write(newsockfd,"jane@slashdot.org",18);
             if (n < 0) error("ERROR writing to socket");
         }
     }
     return 0;
}

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <stdlib.h>
#include <string.h>
#include <arpa/inet.h>
#include <unistd.h>

void error(char *msg)
{
    perror(msg);
    exit(0);
}

int main(int argc, char *argv[])
{
    int sockfd, portno, n;
    struct sockaddr_in serv_addr;
    struct hostent *server;

    char buffer[256];
    if (argc < 3) {
       fprintf(stderr,"usage %s hostname portn", 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 hostn");
        exit(0);
    }
    bzero((char *) &serv_addr, sizeof(serv_addr));
    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)
        error("ERROR connecting");
    while (strcmp(buffer, "+++n") != 0)
    {
        printf("> ");
        bzero(buffer,256);
        fgets(buffer,255,stdin);
        n = write(sockfd,buffer,strlen(buffer));
        if (n < 0)
             error("ERROR writing to socket");
        if (strcmp(buffer, "+++n") == 0)
        {
             exit(0);
        }
        bzero(buffer,256);
        n = read(sockfd,buffer,255);
        if (n < 0)
              error("ERROR reading from socket");
        printf("%sn",buffer);
    }
    return 0;
}

> harris@ics.uci.edu
Ian G. Harris
> joe@cnn.com
Joe Smith
>

Address server started
harris@ics.uci.edu
joe@cnn.com