C-Programm zur Dateiübertragung per UDP

数据可以在两台使用 C 语言实现 Socket 编程的计算机之间传输。

在同样的情况下，可以轻松地通过实现用户数据报协议 (UDP) 和 简单的客户端/服务器。

安全性 - 通过加密处理。

协议 - UDP

加密 - 异或加密

算法

• 服务器启动并等待文件名。

• 客户端发送文件名。

• 该文件名由服务器接收。如果文件存在，服务器开始读取文件，并继续发送一个填充有加密文件内容的缓冲区，直到到达文件末尾。

• 文件结尾标记为EOF。

• 文件将作为缓冲区接收，直到且除非收到 EOF。之后对其进行加密。

• 如果文件不存在，则会发送一条消息“找不到文件”。

服务器

// 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 &#39;S&#39;
#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] = &#39;\0&#39;;
}
// 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("</p><p>file descriptor is not received!!</p><p>");
   else
      printf("</p><p>file descriptor %d is received</p><p>", sockfd1);
   // bind()
   if (bind(sockfd1, (struct sockaddr*)&addr_con,
      sizeof(addr_con)) == 0)
      printf("</p><p>Successfully is binded!</p><p>");
   else
      printf("</p><p>Binding is Failed!</p><p>");
   while (1) {
      printf("</p><p>Waiting for name of file...</p><p>");
      // 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("</p><p>File Name is Received: %s</p><p>", net_buf1);
      if (fp1 == NULL)
      printf("</p><p>File open is failed!</p><p>");
      else
      printf("</p><p>File Successfully is opened!</p><p>");
      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;
}

客户端

// 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 &#39;S&#39;
#define SendRecvFlag 0
// function for clearing buffer
void clearBuf(char* b1){
   int i;
   for (i = 0; i < Net_Buf_Size; i++)
   b1[i] = &#39;\0&#39;;
}
// 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("</p><p>file descriptor is not received!!</p><p>");
   else
   printf("</p><p>file descriptor %d is received</p><p>", sockfd1);
   while (1) {
      printf("</p><p>Please enter the name of file to receive:</p><p>");
      scanf("%s", net_buf1);
      sendto(sockfd1, net_buf1, Net_Buf_Size,
      SendRecvFlag, (struct sockaddr*)&addr_con,
      addrlen);
      printf("</p><p>---------Data is Received---------</p><p>");
      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("</p><p>-------------------------------</p><p>");
   }
   return 0;
}

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