Client and Server Interaction with TCP

TCP (Transmission Control Protocol)

1. TCP is a connection-oriented protocol.
2. The connection is established and maintained until the application programs at each end have finished exchanging messages.
3. TCP is a transport layer protocol used by applications that require guaranteed delivery.
4. It is a sliding window protocol that provides handling for both timeouts and retransmissions.
5. TCP establishes a full duplex virtual connection between two endpoints.
6. Each endpoint is defined by an IP address and a TCP port number.

Example TCP Server program:

// Server side C/C++ program to demonstrate Socket programming
#include <stdio.h>
#include <sys/socket.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <string.h>
#define PORT 8080

#include <pthread.h>
#include <errno.h>

void *thread_receiver(void *new_socket)
{
    int valread = 0;
    char buffer[1024];

    while(1) {
        memset(buffer,0, sizeof(buffer));
        if((valread = read( (*(int *)new_socket), buffer, 1024)) < 0) {
            perror("Error in receiving : ");
        }

        // zero indicates end of file
        if(valread == 0) {
            printf("\n\n The client process is terminated so closing the connection \n");
            exit(0);
        }

        printf("\nVel Server received no of bytes = (%d) Data = (%s) errno = %d\n", valread, buffer, errno);
    }

    return NULL;
}

int main(int argc, char const *argv[])
{
    int server_fd, new_socket, valread;
    struct sockaddr_in address;
    int opt = 1;
    int addrlen = sizeof(address);
    char buffer[1024] = {0};
    char *hello = "Hello from server";
    pthread_t thread_id;

    if(argc < 2)
    {
        printf("\nUsage: %s <port>\n", argv[0]);
        printf("Port is the server listining port number\n");
        exit(1);
    }

    // Creating socket file descriptor
    if ((server_fd = socket(AF_INET, SOCK_STREAM, 0)) == 0)
    {
        perror("socket failed");
        exit(EXIT_FAILURE);
    }

    // Forcefully attaching socket to the port 8080
    if (setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR | SO_REUSEPORT,
                &opt, sizeof(opt)))
    {
        perror("setsockopt");
        exit(EXIT_FAILURE);
    }
    address.sin_family = AF_INET;
    address.sin_addr.s_addr = INADDR_ANY;
    address.sin_port = htons( atoi(argv[1]));

    // Forcefully attaching socket to the port 8080
    if (bind(server_fd, (struct sockaddr *)&address,
                sizeof(address))<0)
    {
        perror("bind failed");
        exit(EXIT_FAILURE);
    }
    if (listen(server_fd, 3) < 0)
    {
        perror("listen");
        exit(EXIT_FAILURE);
    }
    printf("Vel: Waiting for Client to connect:\n");
    if ((new_socket = accept(server_fd, (struct sockaddr *)&address,
                    (socklen_t*)&addrlen))<0)
    {
        perror("accept");
        exit(EXIT_FAILURE);
    }
    printf("Vel: Got the request from Client & connected to the client:  \n");

    pthread_create(&thread_id, NULL, thread_receiver, (void *)&new_socket);

    while(1) {
        memset(buffer,0,sizeof(buffer));

        printf("Enter the string to send to Client:");
        scanf("%s",buffer);
        if(send(new_socket , buffer, strlen(buffer) , 0 )<0) {
            perror("Error in sending : \n");
        }
    }

    return 0;
}

Example TCP Client program:

/ Client side C/C++ program to demonstrate Socket programming
#include <stdio.h>
#include <sys/socket.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <string.h>
#define PORT 8080

#include <pthread.h>
#include <errno.h>

void *thread_receiver(void *sock)
{
    int valread = 0;
    char buffer[1024];

    while(1) {
        memset(buffer,0, sizeof(buffer));
        if((valread = read( (*(int *)sock), buffer, 1024)) < 0 ) {
            perror("Error in receiving : ");
        }
        // zero indicates end of file
        if(valread == 0) {
            printf("\n\n The server process is terminated so closing the connection \n");
            exit(0);
        }

        printf("\nVel Client Received no of byte = (%d) data = (%s) err= %d\n", valread, buffer, errno );

    }

    return NULL;
}

int main(int argc, char const *argv[])
{
    struct sockaddr_in address;
    int sock = 0, valread;
    struct sockaddr_in serv_addr;
    char *hello = "Hello from client";
    char buffer[1024] = {0};
    pthread_t thread_id;

    if(argc < 3)
    {
        printf("\nUsage: %s <dstaddress> <port>\n", argv[0]);
        printf("- dstaddress is the target tcp server IP\n");
        printf("- port is the server listining port number\n");
        exit(1);
    }

    // Creating socket file descriptor
    if ((sock = socket(AF_INET, SOCK_STREAM, 0)) < 0)
    {
        printf("\n Socket creation error \n");
        return -1;
    }

    memset(&serv_addr, '0', sizeof(serv_addr));

    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(atoi(argv[2]));

    // Convert IPv4 and IPv6 addresses from text to binary form
    if(inet_pton(AF_INET, argv[1], &serv_addr.sin_addr)<=0)
    {
        printf("\nInvalid address/ Address not supported \n");
        return -1;
    }

    if (connect(sock, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0)
    {
        printf("\nConnection Failed \n");
        return -1;
    }

    pthread_create(&thread_id, NULL, thread_receiver, (void *)&sock);
    while(1) {
        printf("Enter the string to send to Server:");
        scanf("%s",buffer);
        send(sock, buffer, strlen(buffer) , 0 );
    }

    return 0;
}