C TCP Sliding Window Client Example with Timeout

C TCP Sliding Window Client Example

Source code with timeout and acknowledgment handling

Note: This example demonstrates socket programming in C using a sliding window and a receive timeout. It sends numbered frames, waits for acknowledgments, and resends frames on timeout.

Key points

• Uses setsockopt to set a receive timeout (SO_RCVTIMEO)
• Sends sequential frames and handles acknowledgments
• Resends a window of frames when acknowledgments are not received

#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <time.h>
#include <sys/time.h>
#include <unistd.h>
#include <arpa/inet.h>
#define MAX 80
#define PORT 8080
#define SA struct sockaddr

struct timeval timeout;

void func(int sockfd, int nf, int ws)
{
    char buff[MAX];
    int ack, i = 0, n, k, w1 = 0, w2 = ws - 1, j, flag = 0;
    if (setsockopt(sockfd, SOL_SOCKET, SO_RCVTIMEO, (const char *)&timeout,
                   sizeof(timeout)) < 0)
        perror("setsockopt(SO_RCVTIMEO) failed");
    for (i = 0; i < nf && i <= w2; i++) {
        bzero(buff, sizeof(buff));
        snprintf(buff, sizeof(buff), "%d", i);
        k = send(sockfd, buff, sizeof(buff), 0);
        printf("Frame %d sent\n", i);
    }
    while (1) {
        if (w2 - w1 != ws - 1 && flag == 0 && i != nf) {
            bzero(buff, sizeof(buff));
            snprintf(buff, sizeof(buff), "%d", i);
            k = send(sockfd, buff, sizeof(buff), 0);
            printf("Frame %d sent\n", i);
            w2++;
            i++;
        }
        flag = 0;
        bzero(buff, sizeof(buff));
        n = recv(sockfd, buff, MAX, 0);
        ack = atoi(buff);
        if (n > 0) {
            if (ack + 1 == nf) {
                printf("acknowledgment received: %d\nExit\n", ack);
                bzero(buff, sizeof(buff));
                strcpy(buff, "Exit");
                k = send(sockfd, buff, sizeof(buff), 0);
                break;
            }
            if (ack == w1) {
                w1++;
                printf("acknowledgment received: %d\n", ack);
            }
        } else {
            printf("Acknowledgment not received for %d\nResending frames\n", w1);
            for (j = w1; j < nf && j < w1 + ws; j++) {
                bzero(buff, sizeof(buff));
                snprintf(buff, sizeof(buff), "%d", j);
                k = send(sockfd, buff, sizeof(buff), 0);
                printf("Frame %d sent\n", j);
            }
            flag = 1;
        }
    }
}

void main() {
    int sockfd, connfd, f, w;
    struct sockaddr_in servaddr, cli;
    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd == -1) {
        printf("Socket creation failed\n");
        exit(0);
    } else
        printf("Socket successfully created\n");
    bzero(&servaddr, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_addr.s_addr = inet_addr("127.0.0.1");
    servaddr.sin_port = htons(PORT);
    timeout.tv_sec = 3;
    timeout.tv_usec = 0;
    if (connect(sockfd, (SA *)&servaddr, sizeof(servaddr)) != 0) {
        printf("Connection to the server failed\n");
        exit(0);
    } else
        printf("Connected to the server\n");
    printf("Enter the number of frames: ");
    scanf("%d", &f);
    printf("Enter the window size: ");
    scanf("%d", &w);
    func(sockfd, f, w);
    close(sockfd);
}