#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <sys/socket.h>
 
#define BUFFER_SIZE  1024
 
int serverfd;
int clientfd;
 
int n;
int addrSize;
int serverPort;
char clientIP[25];
char buffer[BUFFER_SIZE];
struct sockaddr_in serverAddr;
struct sockaddr_in clientAddr;
 
int main(int argc, char* argv[])
{
    if(argc < 2)
    {
        printf("Usage: ./server <port>\n");
        exit(0);
    }
    else
    {
        serverPort = atoi(argv[1]);
    }
 
    addrSize = sizeof(struct sockaddr);
 
    /* Create a TCP socket */
    serverfd = socket(AF_INET, SOCK_STREAM, 0);
 
    if(serverfd < 0)
        printf("Error creating server socket");
    serverAddr.sin_family = AF_INET; 
    serverAddr.sin_port = htons(serverPort); /* Specify a port */
    serverAddr.sin_addr.s_addr = INADDR_ANY; /* Accept connections from anywhere */
    memset(&(serverAddr.sin_zero), '\0', 8); /* This must be set to zero */
 
    /* Bind our server socket */
    if(bind(serverfd, (struct sockaddr*)&serverAddr, sizeof(struct sockaddr)) == -1)
        printf("Could not bind()\n");
 
    /* Start listening on socket for incoming connections */
    if(listen(serverfd, 10) == -1)
        printf("Could not listen()\n");
    fork();//this is the magical line...
    /* accept() accepts an incoming connection and fills a sockaddr_in structure with client information */
    clientfd = accept(serverfd, (struct sockaddr*)&clientAddr, &addrSize);
    
    /* inet_ntoa() converts an IP address to a displayable string */
    snprintf(clientIP, sizeof(clientIP), "%s", inet_ntoa(clientAddr.sin_addr));
    printf("Got connection from %s\n", clientIP);
 
    do
    {
        n = recv(clientfd, buffer, BUFFER_SIZE, 0); /* Receive message from client */
        buffer[n] = '\0'; /* terminate string */
 
        send(clientfd, buffer, BUFFER_SIZE, 0); /* Echo message back to client */
        printf("Client sent: %s\n" , buffer);
    }
    while(strncmp(buffer, "exit", 4) != 0); /* Exit when client sends "exit" */
 
    close(serverfd); /* Close socket */ 
    
    return 0;
}

 #include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include
<arpa/inet.h>
#include
<sys/types.h>
#include
<sys/socket.h>

#define
BUFFER_SIZE  1024

int sockfd;

int n;
int addrSize;
int serverPort;
char serverIP[25];
char
buffer[BUFFER_SIZE];
struct sockaddr_in serverAddr;

int main(int argc, char* argv[])
{
    if(argc < 3)
    {
        printf("Usage: ./client <server ip> <server port>\n");
        exit(0);
    }
    else
    {
        snprintf(serverIP, sizeof(serverIP), "%s", argv[1]);
        serverPort = atoi(argv[2]);
    }

    addrSize = sizeof(struct sockaddr);

      /* Create a TCP socket */
    sockfd = socket(AF_INET, SOCK_STREAM, 0);

    if(sockfd < 0)
        printf("Error creating socket");

    serverAddr.sin_family = AF_INET;
    serverAddr.sin_port = htons(serverPort); /* Server port */
    inet_pton(AF_INET, serverIP, &serverAddr.sin_addr); /* Server IP Address */
    memset(&(serverAddr.sin_zero), '\0', 8); /* This must be set to zero */

      /* Connect to server */
    if(connect(sockfd, (struct sockaddr*)&serverAddr, addrSize) != 0)
    {
        printf("Error: Could not connect to %s on port %d\n", serverIP, serverPort);
        exit(0);
    }
    else
        printf("Connected to %s on port %d\n\n", serverIP, serverPort);

    do
    {
        printf("> ");
        fgets(buffer, BUFFER_SIZE, stdin);
        send(sockfd, buffer, strlen(buffer), 0); /* Send message to server */

        n = recv(sockfd, buffer, BUFFER_SIZE, 0); /* Receive message from server */
        buffer[n] = '\0'; /* terminate string */
        printf("< %s\n", buffer);
    }
    while(strncmp(buffer, "exit", 4) != 0); /* Exit when message is "exit" */

    close(sockfd); /* Close socket */

    return 0;
}