Unix Network Programming: Simple Client Server using Sockets

To keep this program simple

1. The server accepts connection from a single client only
2. The server doesn't fork new process to handle client requst
3. Client sends only a single message to server and server replies back with another message

Algorithm

Server

1. Create socket
2. Bind
3. Listen
4. Accept connection
5. Read data sent by client
6. Send data back to client
7. Close socket descriptors

Client

1. Create socket
2. Connect to server
3. Send data to server
4. Receive data from server
5. Close socket descriptors

Program

server
#include<sys/types.h>
#include<sys/socket.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<stdio.h>
#include<string.h>
#include<malloc.h>
#define SERVERPORT 3098
#define SERVERIP "192.168.1.4"
#define SIZE 10
#define DEFAULT_FLAG 0
int main()
{
    int sockfd, newsockfd, n;
    int addrlen = sizeof(struct sockaddr_in);
    struct sockaddr_in *serveraddr = (struct sockaddr_in *)malloc(addrlen);
    struct sockaddr_in *clientaddr = (struct sockaddr_in *)malloc(addrlen);
    char buff[10];

    /* Create socket */
    if((sockfd = socket(AF_INET, SOCK_STREAM, DEFAULT_FLAG))<0)
    {
        printf("Error: Socket creation failed... Exiting...\n");
        return 0;
    }
  
    /* Bind */
    bzero(serveraddr,addrlen);                // Initailize serveraddr as null. defined in <string.h>
    serveraddr->sin_family = AF_INET;        // Set address family as INET
    serveraddr->sin_port = SERVERPORT;
    serveraddr->sin_addr.s_addr = inet_addr(SERVERIP);    // Convert character string to dotted decimal format. Defined in <arpa/inet.h>
    if(bind(sockfd, (struct sockaddr*) serveraddr, addrlen)<0)
    {
        printf("Error: Bind failed... Exiting...\n");
        return 0;
    }
  
    /* listen */
    listen(sockfd,4);
    printf("Server waiting for connection request . . .\n");
  
    /* Accept connection */
    if((newsockfd = accept(sockfd, (struct sockaddr*)clientaddr, &addrlen))<0)
        printf("Error: Accepting connection request failed\n");
    else
        printf("Connection Accepted \n");

    /* Read data sent by client */
    n = recv(newsockfd, buff, SIZE, DEFAULT_FLAG);
    buff[n] = '\0';
    printf("Message Received: %s\n",buff);
  
    /* Send replt to client */
    strcpy(buff,"Thank You");
    send(newsockfd, buff, strlen(buff), DEFAULT_FLAG);

    /* Close both socket descriptors*/
    close(newsockfd);
    close(sockfd);
    return 0;
}


client

#include<sys/types.h>
#include<sys/socket.h>
#include<netinet/in.h>
#include<stdio.h>
#include<string.h>
#include<malloc.h>
#define SERVERPORT 3098
#define SERVERIP "192.168.1.4"
#define SIZE 10
#define DEFAULT_FLAG 0
int main()
{
    int sockfd,n;
    int addrlen = sizeof(struct sockaddr_in);
    struct sockaddr_in *serveraddr = (struct sockaddr_in *)malloc(addrlen);
    char buff[10];

    /* Create socket */
    if((sockfd = socket(AF_INET, SOCK_STREAM, DEFAULT_FLAG))<0)
    {
        printf("Error: Socket creation failed... Exiting...\n");
        return 0;
    }
  
    /* Connect to server */
    bzero(serveraddr, addrlen);                // Initailize serveraddr as null. defined in <string.h>
    serveraddr->sin_family = AF_INET;        // Set address family as INET
    serveraddr->sin_port = SERVERPORT;
    serveraddr->sin_addr.s_addr = inet_addr(SERVERIP);    // Convert character string to dotted decimal format defined in <arpa/inet.h>
    if(connect(sockfd, (struct sockaddr*)serveraddr, addrlen)<0)
    {
        printf("Error: Connection failed... Exiting...\n");
        return 0;
    }else
        printf("Connection to server established successfully . . . \n");
  
    /* Send data to Server */
    printf("Enter Message to be sent ");
    scanf("%s",buff);
    send(sockfd, buff, strlen(buff), DEFAULT_FLAG);
  
    /* Read reply from server */
    n = recv(sockfd, buff, SIZE, DEFAULT_FLAG);
    buff[n] = '\0';
    printf("Message from Server: %s\n",buff);

    /* Close socket descriptor */
    close(sockfd);
    return 0;
}

Output

server window
Server waiting for connection request . . .
Connection Accepted
Message Received: Welcome

client window
Connection to server established successfully . . .
Enter Message to be sent Welcome
Message from Server: Thank You