TCP Client Server Communication Using Sockets

Algorithms

Client

Step 1: Create Socket

• Create a TCP client socket using socket(AF_INET, SOCK_STREAM, 0).
• If socket creation fails, terminate the program.

Step 2: Define Server Address

• Set the address family to AF_INET.
• Set the port number to 5555.
• Set the IP address to 127.0.0.1.

Step 3: Connect to Server

• Connect the client socket to the server using connect().
• Display a message if the connection is successful.

Step 4: Send Message

• Send a message to the server using send().

Step 5: Receive Reply

• Receive the server’s reply using recv().
• Display the received message.

Step 6: Close Socket

• Close the client socket using close().

Server

Step 1: Create Socket

• Create a TCP server socket using socket(AF_INET, SOCK_STREAM, 0).
• If socket creation fails, terminate the program.

Step 2: Define Server Address

• Set the address family to AF_INET.
• Set the port number to 5555.
• Set the IP address to 127.0.0.1.

Step 3: Bind Socket

• Bind the socket to the specified IP address and port using bind().

Step 4: Listen for Connections

• Put the server in listening mode using listen().

Step 5: Accept Client

• Accept a client connection using accept().

Step 6: Receive Message

• Receive data from the client using recv().
• Display the received message.

Step 7: Send Reply

• Send a response message to the client using send().

Step 8: Close Connection

• Close the client socket.
• Repeat the process for the next client.

Programs

Client

#include <arpa/inet.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#define PORT 5555
#define BUF_SIZE 1024

int main() {
  int sock;
  struct sockaddr_in server_addr;
  char buffer[BUF_SIZE];
  int n;

  sock = socket(AF_INET, SOCK_STREAM, 0);
  if (sock < 0) {
    perror("socket error");
    exit(1);
  }
  printf("[CLIENT] TCP socket created\n");

  memset(&server_addr, 0, sizeof(server_addr));
  server_addr.sin_family = AF_INET;
  server_addr.sin_port = htons(PORT);
  server_addr.sin_addr.s_addr = inet_addr("127.0.0.1");

  if (connect(sock, (struct sockaddr *)&server_addr, sizeof(server_addr)) < 0) {
    perror("connect error");
    exit(1);
  }
  printf("[CLIENT] Connected to server\n");

  strcpy(buffer, "HELLO FROM TCP CLIENT");
  send(sock, buffer, strlen(buffer), 0);
  printf("[CLIENT] Sent: %s\n", buffer);

  memset(buffer, 0, BUF_SIZE);
  n = recv(sock, buffer, BUF_SIZE - 1, 0);
  if (n > 0) {
    buffer[n] = '\0';
    printf("[CLIENT] Received: %s\n", buffer);
  }

  close(sock);
  printf("[CLIENT] Disconnected from server\n");

  return 0;
}

Server

#include <arpa/inet.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#define PORT 5555
#define BUF_SIZE 1024

int main() {
  int server_sock, client_sock;
  struct sockaddr_in server_addr, client_addr;
  socklen_t addr_size;
  char buffer[BUF_SIZE];
  int n;

  server_sock = socket(AF_INET, SOCK_STREAM, 0);
  if (server_sock < 0) {
    perror("socket error");
    exit(1);
  }
  printf("[SERVER] TCP socket created\n");

  memset(&server_addr, 0, sizeof(server_addr));
  server_addr.sin_family = AF_INET;
  server_addr.sin_port = htons(PORT);
  server_addr.sin_addr.s_addr = inet_addr("127.0.0.1");

  if (bind(server_sock, (struct sockaddr *)&server_addr, sizeof(server_addr)) <
      0) {
    perror("bind error");
    exit(1);
  }
  printf("[SERVER] Bound to port %d\n", PORT);

  if (listen(server_sock, 5) < 0) {
    perror("listen error");
    exit(1);
  }
  printf("[SERVER] Listening...\n");

  while (1) {
    addr_size = sizeof(client_addr);
    client_sock =
        accept(server_sock, (struct sockaddr *)&client_addr, &addr_size);
    if (client_sock < 0) {
      perror("accept error");
      continue;
    }

    printf("[SERVER] Client connected\n");

    memset(buffer, 0, BUF_SIZE);
    n = recv(client_sock, buffer, BUF_SIZE - 1, 0);
    if (n > 0) {
      buffer[n] = '\0';
      printf("[SERVER] Received: %s\n", buffer);
    }

    strcpy(buffer, "HELLO FROM TCP SERVER");
    send(client_sock, buffer, strlen(buffer), 0);
    printf("[SERVER] Sent response\n");

    close(client_sock);
    printf("[SERVER] Client disconnected\n\n");
  }

  close(server_sock);
  return 0;
}