C program for file Transfer using UDP

Data can be transferred between two computers using Socket programming in C.

Similarly, files can easily be sent using UDP protocol and a simple client/server.

Security : Handled by encryption.

Protocol : UDP
Encryption: XOR encryption

Algorithm :

1. The server starts and waits for filename.
2. The client sends a filename.
3. The server receives filename.
   If file is present,
   server starts reading file 
   and continues to send a buffer filled with
   file contents encrypted until file-end is reached.
4. End is marked by EOF.
5. File is received as buffers until EOF is 
received. Then it is decrypted.
6. If Not present, a file not found is sent.

The Server :

// server code for UDP socket programming 
#include <arpa/inet.h> 
#include <netinet/in.h> 
#include <stdio.h> 
#include <stdlib.h> 
#include <string.h> 
#include <sys/socket.h> 
#include <sys/types.h> 
#include <unistd.h> 
  
#define IP_PROTOCOL 0 
#define PORT_NO 15050 
#define NET_BUF_SIZE 32 
#define cipherKey 'S' 
#define sendrecvflag 0 
#define nofile "File Not Found!" 
  
// funtion to clear buffer 
void clearBuf(char* b) 
{ 
    int i; 
    for (i = 0; i < NET_BUF_SIZE; i++) 
        b[i] = ''; 
} 
  
// funtion to encrypt 
char Cipher(char ch) 
{ 
    return ch ^ cipherKey; 
} 
  
// funtion sending file 
int sendFile(FILE* fp, char* buf, int s) 
{ 
    int i, len; 
    if (fp == NULL) { 
        strcpy(buf, nofile); 
        len = strlen(nofile); 
        buf[len] = EOF; 
        for (i = 0; i <= len; i++) 
            buf[i] = Cipher(buf[i]); 
        return 1; 
    } 
  
    char ch, ch2; 
    for (i = 0; i < s; i++) { 
        ch = fgetc(fp); 
        ch2 = Cipher(ch); 
        buf[i] = ch2; 
        if (ch == EOF) 
            return 1; 
    } 
    return 0; 
} 
  
// driver code 
int main() 
{ 
    int sockfd, nBytes; 
    struct sockaddr_in addr_con; 
    int addrlen = sizeof(addr_con); 
    addr_con.sin_family = AF_INET; 
    addr_con.sin_port = htons(PORT_NO); 
    addr_con.sin_addr.s_addr = INADDR_ANY; 
    char net_buf[NET_BUF_SIZE]; 
    FILE* fp; 
  
    // socket() 
    sockfd = socket(AF_INET, SOCK_DGRAM, IP_PROTOCOL); 
  
    if (sockfd < 0) 
        printf("
file descriptor not received!!
"); 
    else
        printf("
file descriptor %d received
", sockfd); 
  
    // bind() 
    if (bind(sockfd, (struct sockaddr*)&addr_con, sizeof(addr_con)) == 0) 
        printf("
Successfully binded!
"); 
    else
        printf("
Binding Failed!
"); 
  
    while (1) { 
        printf("
Waiting for file name...
"); 
  
        // receive file name 
        clearBuf(net_buf); 
  
        nBytes = recvfrom(sockfd, net_buf, 
                          NET_BUF_SIZE, sendrecvflag, 
                          (struct sockaddr*)&addr_con, &addrlen); 
  
        fp = fopen(net_buf, "r"); 
        printf("
File Name Received: %s
", net_buf); 
        if (fp == NULL) 
            printf("
File open failed!
"); 
        else
            printf("
File Successfully opened!
"); 
  
        while (1) { 
  
            // process 
            if (sendFile(fp, net_buf, NET_BUF_SIZE)) { 
                sendto(sockfd, net_buf, NET_BUF_SIZE, 
                       sendrecvflag,  
                    (struct sockaddr*)&addr_con, addrlen); 
                break; 
            } 
  
            // send 
            sendto(sockfd, net_buf, NET_BUF_SIZE, 
                   sendrecvflag, 
                (struct sockaddr*)&addr_con, addrlen); 
            clearBuf(net_buf); 
        } 
        if (fp != NULL) 
            fclose(fp); 
    } 
    return 0; 
} 

The Client:

// client code for UDP socket programming 
#include <arpa/inet.h> 
#include <netinet/in.h> 
#include <stdio.h> 
#include <stdlib.h> 
#include <string.h> 
#include <sys/socket.h> 
#include <sys/types.h> 
#include <unistd.h> 
  
#define IP_PROTOCOL 0 
#define IP_ADDRESS "127.0.0.1" // localhost 
#define PORT_NO 15050 
#define NET_BUF_SIZE 32 
#define cipherKey 'S' 
#define sendrecvflag 0 
  
// funtion to clear buffer 
void clearBuf(char* b) 
{ 
    int i; 
    for (i = 0; i < NET_BUF_SIZE; i++) 
        b[i] = ''; 
} 
  
// function for decryption 
char Cipher(char ch) 
{ 
    return ch ^ cipherKey; 
} 
  
// function to receive file 
int recvFile(char* buf, int s) 
{ 
    int i; 
    char ch; 
    for (i = 0; i < s; i++) { 
        ch = buf[i]; 
        ch = Cipher(ch); 
        if (ch == EOF) 
            return 1; 
        else
            printf("%c", ch); 
    } 
    return 0; 
} 
  
// driver code 
int main() 
{ 
    int sockfd, nBytes; 
    struct sockaddr_in addr_con; 
    int addrlen = sizeof(addr_con); 
    addr_con.sin_family = AF_INET; 
    addr_con.sin_port = htons(PORT_NO); 
    addr_con.sin_addr.s_addr = inet_addr(IP_ADDRESS); 
    char net_buf[NET_BUF_SIZE]; 
    FILE* fp; 
  
    // socket() 
    sockfd = socket(AF_INET, SOCK_DGRAM, 
                    IP_PROTOCOL); 
  
    if (sockfd < 0) 
        printf("
file descriptor not received!!
"); 
    else
        printf("
file descriptor %d received
", sockfd); 
  
    while (1) { 
        printf("
Please enter file name to receive:
"); 
        scanf("%s", net_buf); 
        sendto(sockfd, net_buf, NET_BUF_SIZE, 
               sendrecvflag, (struct sockaddr*)&addr_con, 
               addrlen); 
  
        printf("
---------Data Received---------
"); 
  
        while (1) { 
            // receive 
            clearBuf(net_buf); 
            nBytes = recvfrom(sockfd, net_buf, NET_BUF_SIZE, 
                              sendrecvflag, (struct sockaddr*)&addr_con, 
                              &addrlen); 
  
            // process 
            if (recvFile(net_buf, NET_BUF_SIZE)) { 
                break; 
            } 
        } 
        printf("
-------------------------------
"); 
    } 
    return 0; 
} 

Output :
Server :
server
Client :
client

C program for file Transfer using UDP

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