ข้อมูลสามารถถ่ายโอนระหว่างคอมพิวเตอร์ 2 เครื่องด้วย Socket programming ใน C
ในกรณีนี้ ไฟล์สามารถส่งได้ง่ายด้วย User Datagram Protocol (UDP) และ simple client/server
Security − จัดการโดย encryption
Protocol − UDP
Encryption − XOR encryption
Algorithm
Server เริ่มต้นและรอ filename
Client ส่ง filename
Server รับ filename ถ้าไฟล์มีอยู่ เริ่มอ่านไฟล์และส่ง buffer ที่เต็มไปด้วยเนื้อหาไฟล์ encrypted จนกว่าจะถึง file-end
End of File ถูก mark ด้วย EOF
ไฟล์ถูกรับเป็น buffers จนกว่าจะได้ EOF แล้ว decrypt
ถ้าไฟล์ไม่มี ส่งข้อความ "file not found"
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!"
// function for clearing buffer
void clearBuf(char* b1){
int i;
for (i = 0; i < Net_Buf_Size; i++)
b1[i] = '\0';
}
// function for encryption method
char Cipher(char ch1){
return ch1 ^ CipherKey;
}
// function for sending file
int sendFile(FILE* fp1, char* buf1, int s1){
int i, len;
if (fp1 == NULL) {
strcpy(buf1, NoFile);
len = strlen(NoFile);
buf1[len] = EOF;
for (i = 0; i <= len; i++)
buf1[i] = Cipher(buf1[i]);
return 1;
}
char ch1, ch2;
for (i = 0; i < s1; i++) {
ch1= fgetc(fp);
ch2 = Cipher(ch1);
buf1[i] = ch2;
if (ch1 == EOF)
return 1;
}
return 0;
}
// driver code
int main(){
int sockfd1, 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_buf1[Net_Buf_Size];
FILE* fp1;
// socket()
sockfd1 = socket(AF_INET, SOCK_DGRAM, IP_Protocol);
if (sockfd1 < 0)
printf("\nfile descriptor is not received!!\n");
else
printf("\nfile descriptor %d is received\n", sockfd1);
// bind()
if (bind(sockfd1, (struct sockaddr*)&addr_con, sizeof(addr_con)) == 0)
printf("\nSuccessfully is binded!\n");
else
printf("\nBinding is Failed!\n");
while (1) {
printf("\nWaiting for name of file...\n");
// receive name of file
clearBuf(net_buf1);
nBytes = recvfrom(sockfd1, net_buf1, Net_Buf_Size, SendRecvFlag, (struct sockaddr*)&addr_con, &addrlen);
fp1 = fopen(net_buf1, "r");
printf("\nFile Name is Received: %s\n", net_buf1);
if (fp1 == NULL)
printf("\nFile open is failed!\n");
else
printf("\nFile Successfully is opened!\n");
while (1) {
// process
if (sendFile(fp1, net_buf1, Net_Buf_Size)) {
sendto(sockfd1, net_buf1, Net_Buf_Size, SendRecvFlag, (struct sockaddr*)&addr_con, addrlen);
break;
}
// send
sendto(sockfd1, net_buf1, Net_Buf_Size, SendRecvFlag, (struct sockaddr*)&addr_con, addrlen);
clearBuf(net_buf1);
}
if (fp1 != NULL)
fclose(fp1);
}
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
// function for clearing buffer
void clearBuf(char* b1){
int i;
for (i = 0; i < Net_Buf_Size; i++)
b1[i] = '\0';
}
// function for decryption method
char Cipher(char ch1){
return ch1 ^ CipherKey;
}
// function for receiveing file
int recvFile(char* buf1, int s1) {
int i;
char ch1;
for (i = 0; i < s1; i++) {
ch1 = buf1[i];
ch1 = Cipher(ch1);
if (ch1 == EOF)
return 1;
else
printf("%c", ch1);
}
return 0;
}
// driver code
int main(){
int sockfd1, 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_buf1[Net_Buf_Size];
FILE* fp1;
// socket()
sockfd1 = socket(AF_INET, SOCK_DGRAM, IP_Protocol);
if (sockfd1 < 0)
printf("\nfile descriptor is not received!!\n");
else
printf("\nfile descriptor %d is received\n", sockfd1);
while (1) {
printf("\nPlease enter the name of file to receive:\n");
scanf("%s", net_buf1);
sendto(sockfd1, net_buf1, Net_Buf_Size, SendRecvFlag, (struct sockaddr*)&addr_con, addrlen);
printf("\n---------Data is Received---------\n");
while (1) {
// receive
clearBuf(net_buf1);
nBytes = recvfrom(sockfd1, net_buf1, Net_Buf_Size, SendRecvFlag, (struct sockaddr*)&addr_con, &addrlen);
// process
if (recvFile(net_buf1, Net_Buf_Size)) {
break;
}
}
printf("\n-------------------------------\n");
}
return 0;
}
