Blog # 03 : TCP echo client-server [iterative]

An echo client-server performs the following steps:

1. The client reads a line of text from its standard input and writes the line to the server.
2. The server reads the line from its network input and echoes the line back to the client.
3. The client reads the echoed line and prints it on its standard output.

TCP echo Client

#include<sys/types.h>   

#include<sys/socket.h>       

#include<netinet/in.h>   

#include<stdlib.h>

#include<stdio.h>

#include<unistd.h>

#include<string.h>

#include<errno.h>

#define    SA struct sockaddr

#define    MAXLINE 4096   

#define    SERV_PORT 9877           

void str_cli(FILE *fp, int sockfd)

{

    char    sendline[MAXLINE], recvline[MAXLINE];

    while (fgets(sendline, MAXLINE, fp) != NULL) {

        write(sockfd, sendline, strlen(sendline));

        if (read(sockfd, recvline, MAXLINE) == 0){

            printf("str_cli: server terminated prematurely\n");

            return;

            }       

        fputs(recvline, stdout);

        bzero(sendline,strlen(sendline));

        bzero(recvline,strlen(recvline));

    }

}

int main(int argc, char **argv)

{

    int sockfd;

    struct sockaddr_in servaddr;

    if (argc != 2){

        printf("usage: tcpcli <IPaddress>");

        return -1;

        }

    sockfd = Socket(AF_INET, SOCK_STREAM, 0);

    bzero(&servaddr, sizeof(servaddr));

    servaddr.sin_family = AF_INET;

    servaddr.sin_port = htons(SERV_PORT);

    Inet_pton(AF_INET, argv[1], &servaddr.sin_addr);

    Connect(sockfd, (SA *) &servaddr, sizeof(servaddr));

    str_cli(stdin, sockfd);       

    exit(0);

}

TCP echo Server

#include<sys/types.h>   
#include<sys/socket.h>       
#include<netinet/in.h>       
#include<stdlib.h>
#include<stdio.h>
#include<unistd.h>
#include<string.h>
#include<pthread.h>
#include<errno.h>
#define    SA struct sockaddr
#define    LISTENQ    1024
#define    MAXLINE    4096
#define    SERV_PORT 9877

void str_echo(int sockfd)
{
    ssize_t    n;
    char line[MAXLINE];
    for ( ; ; ) {
        if ( (n = read(sockfd, line, MAXLINE)) == 0)
            return;
        Writen(sockfd, line, n);
    }
}
int main(int argc, char **argv)
{
    int listenfd, connfd;
    pid_t childpid;
    socklen_t clilen;
    struct sockaddr_in cliaddr, servaddr;
    listenfd = Socket(AF_INET, SOCK_STREAM, 0);
    bzero(&servaddr, sizeof(servaddr));
    servaddr.sin_family      = AF_INET;
    servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
    servaddr.sin_port        = htons(SERV_PORT);
   
    Bind(listenfd, (SA *) &servaddr, sizeof(servaddr));
    Listen(listenfd, LISTENQ);
    for ( ; ; ) {
        clilen = sizeof(cliaddr);
        connfd = Accept(listenfd, (SA *) &cliaddr, &clilen);   
            str_echo(connfd);   
           
        Close(connfd);           
    }
    Close(listenfd);
}