Implementation of File Transfer Protocol

Algorithms

Server

Step 1: Initialize networking

• Create a TCP socket descriptor.
• Fill a server address structure with AF_INET, INADDR_ANY, and port 5555.
• Bind the socket to that address so the OS reserves the port.

Step 2: Prepare to accept clients

• Put the socket into listening mode with a reasonable backlog.
• Block on accept until a client connects; obtain a dedicated client socket.

Step 3: Receive the file

• Open/create received_file.txt for binary writing.
• Repeat until recv returns zero or negative:
  • Read the next chunk of bytes from the client socket.
  • Immediately write that chunk to the open file.
• Close the file and the client socket.

Step 4: Clean up

• Close the original listening socket and terminate.

Client

Step 1: Initialize networking

• Create a TCP socket descriptor.
• Fill a server address structure with AF_INET, IP 127.0.0.1, and port 5555.
• Initiate a connect call to establish the TCP session with the server.

Step 2: Send the file

• Open send.txt for binary reading.
• Repeat until the file reaches EOF:
  • Read the next block (up to 1024 bytes) into a buffer.
  • Transmit that block over the established socket.
• Close the file once all data is sent.

Step 3: Clean up

• Close the socket connection and exit.

---

Programs

Server

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

#define PORT 5555
#define BUFFER_SIZE 1024

void receive_file(int sock, char *filename) {
    char buffer[BUFFER_SIZE];
    FILE *fp = fopen(filename, "wb");
    int n;

    if (fp == NULL) {
        printf("Error creating file\n");
        return;
    }

    while ((n = recv(sock, buffer, BUFFER_SIZE, 0)) > 0) {
        fwrite(buffer, 1, n, fp);
    }

    fclose(fp);
    printf("File received: %s\n", filename);
}

int main() {
    int server_fd, client_fd;
    struct sockaddr_in server_addr, client_addr;
    socklen_t addr_len;

    server_fd = socket(AF_INET, SOCK_STREAM, 0);
    if (server_fd < 0) {
        printf("Socket creation failed\n");
        exit(1);
    }

    server_addr.sin_family = AF_INET;
    server_addr.sin_addr.s_addr = INADDR_ANY;
    server_addr.sin_port = htons(PORT);

    if (bind(server_fd, (struct sockaddr*)&server_addr, sizeof(server_addr)) < 0) {
        printf("Bind failed\n");
        exit(1);
    }

    listen(server_fd, 5);
    printf("Server listening on port %d...\n", PORT);

    addr_len = sizeof(client_addr);
    client_fd = accept(server_fd, (struct sockaddr*)&client_addr, &addr_len);
    if (client_fd < 0) {
        printf("Accept failed\n");
        exit(1);
    }

    printf("Client connected.\n");
    receive_file(client_fd, "received_file.txt");

    close(client_fd);
    close(server_fd);
    return 0;
}

Client

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

#define PORT 5555
#define BUFFER_SIZE 1024

void send_file(int sock, char *filename) {
    char buffer[BUFFER_SIZE];
    FILE *fp = fopen(filename, "rb");
    int n;

    if (fp == NULL) {
        printf("File not found: %s\n", filename);
        return;
    }

    while ((n = fread(buffer, 1, BUFFER_SIZE, fp)) > 0) {
        send(sock, buffer, n, 0);
    }

    fclose(fp);
    printf("File sent: %s\n", filename);
}

int main() {
    int sock;
    struct sockaddr_in server_addr;

    sock = socket(AF_INET, SOCK_STREAM, 0);
    if (sock < 0) {
        printf("Socket creation failed\n");
        exit(1);
    }

    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) {
        printf("Connection failed\n");
        exit(1);
    }

    printf("Connected to server.\n");
    send_file(sock, "send.txt");

    close(sock);
    return 0;
}