如何在C++中通过UDP发送任何文件(image，exe)

Question

我正在尝试在C++中通过UDP协议实现文件传输。我所拥有的是服务器，它可以发送客户端请求的文件，但它只适用于.txt文件。当我尝试对图像或可执行文件执行同样的操作时，传输会损坏，文件大小约为0 KB。

服务器：

#include <winsock2.h>
#include <stdio.h>
#include <iostream>
#include <sstream>
#pragma comment(lib, "ws2_32.lib")
#define cipherKey 'S'
int const bufferSize = 512;
char buffer[bufferSize];
void clearBuf(char* b)
{
int i;
for (i = 0; i < bufferSize; i++)
b[i] = '';
}
char* notFound = "File not found.";
char Cipher(char ch)
{
return ch ^ cipherKey;
}
int sendFile(FILE* file, char* buffer, int s)
{
int i, len;
if (file == NULL)
{
strcpy(buffer, notFound);
len = strlen(notFound);
buffer[len] = EOF;
return 1;
}
char ch, ch2;
for (i = 0; i < s; i++)
{
ch = fgetc(file);
ch2 = Cipher(ch);
buffer[i] = ch2;
if (ch == EOF)
return 1;
}
return 0;
}
int main()
{
WSADATA wsaData;
int wynik_winsock = WSAStartup(MAKEWORD(2,2), &wsaData);
if(wynik_winsock != 0)
{
exit(1);
}
SOCKET socketServer;
socketServer = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
if(socketServer == INVALID_SOCKET)
{
WSACleanup();
exit(1);
}
char* ipAdd = "127.0.0.1";
int port = 1234;
SOCKADDR_IN server;
server.sin_family = AF_INET;
server.sin_port = htons(port);
server.sin_addr.s_addr = inet_addr(ipAdd);
if(bind(socketServer, (SOCKADDR *)&server, sizeof(server)) == SOCKET_ERROR)
{
closesocket(socketServer);
WSACleanup();
exit(1);
}
std::cout << "Waiting." << std::endl;
SOCKADDR_IN client;
int len_client = sizeof(client);
FILE* file;
if(recvfrom(socketServer, buffer, bufferSize, 0, (SOCKADDR *)&client, &len_client) == SOCKET_ERROR) //Odbiór danych od clienta wraz z kontrolą błędów.
{
closesocket(socketServer);
WSACleanup();
exit(1);
}
else
{
file = fopen(buffer, "rb");
std::cout << "Filename: " << buffer << std::endl;
if(file == NULL)
{
std::cout << "Couldnt open a file." << std::endl;
}
else
{
while (true)
{
if(sendFile(file, buffer, bufferSize))
{
sendto(socketServer, buffer, bufferSize, 0, (SOCKADDR *)&client, len_client);
break;
}
sendto(socketServer, buffer, bufferSize, 0, (SOCKADDR *)&client, len_client);
clearBuf(buffer);
}
fclose(file);
}
}
closesocket(socketServer);
WSACleanup();
system("pause");
return 0;
}

客户：

#include <winsock2.h>
#include <stdio.h>
#include <iostream>
#include <sstream>
#include <string.h>
#pragma comment(lib, "ws2_32.lib")
#define cipherKey 'S'
int const bufferSize = 512;
char buffer[bufferSize];
void clearBuf(char* b)
{
int i;
for (i = 0; i < bufferSize; i++)
b[i] = '';
}
char Cipher(char ch)
{
return ch ^ cipherKey;
}
int recvFile(char* buffer, int s, FILE* file)
{
int i;
char ch;
for (i = 0; i < s; i++)
{
ch = buffer[i];
ch = Cipher(ch);
if (ch == EOF)
{
return 1;
}
else
{
fprintf(file, "%c", ch);
}
}
return 0;
}
int main()
{
WSADATA wsaData;
int wynik_winsock = WSAStartup(MAKEWORD(2,2), &wsaData);
if(wynik_winsock != 0)
{
exit(1);
}
SOCKET socketClient;
socketClient = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
if(socketClient == INVALID_SOCKET)
{
WSACleanup();
exit(1);
}
char* ipAdd = "127.0.0.1";
int port = 1234;
SOCKADDR_IN server;
server.sin_family = AF_INET;
server.sin_port = htons(port);
server.sin_addr.s_addr = inet_addr(ipAdd);
int serverSizeOf = sizeof(server);
std::cout << "Name of file to send: ";
std::cin >> buffer;
if(sendto(socketClient, buffer, bufferSize, 0, (SOCKADDR *)&server, serverSizeOf) == SOCKET_ERROR)
{
closesocket(socketClient);
WSACleanup();
exit(1);
}
FILE* file;
file = fopen(buffer, "ab");
while (true)
{
clearBuf(buffer);
if(recvfrom(socketClient, buffer, bufferSize, 0, (SOCKADDR *)&server, &serverSizeOf) == SOCKET_ERROR)
{
closesocket(socketClient);
WSACleanup();
exit(1);
}
if (recvFile(buffer, bufferSize, file))
{
break;
}
fclose(file);
}

closesocket(socketClient);
WSACleanup();
system("pause");
return 0;
}

为了完成上面所说的，我使用了教程：使用UDP(Linux(进行文件传输的C程序。如何调整代码以仅发送.txt以外的其他文件？提前谢谢。

Answer 1

正如上面的注释中所说，您需要一种数据类型，其中EOF的值与所有其他字符值不同，而char在这方面是不够的，尤其是在处理二进制数据时。

以下变化应该会改善

int sendFile(FILE* file, char* buffer, int s)
{
...
for (i = 0; i < s; i++)
{
int ch = fgetc(file);
if (ch == EOF)
return 1;
buffer[i] = Cipher(ch);
}
...

Answer 2

我决定更改我试图实现的原始解决方案中的几乎所有内容。最重要的更改是使用fread读取文件和使用fwrite写入文件。文件以512字节(或更少(的部分发送，这些部分在变量中计数。如果客户端请求的文件在服务器上不存在，则会发送特殊信息，并删除为保存数据而创建的文件。现在，即使对于可执行文件和SHA256这两个文件(原始文件和接收文件(，该程序也能正常工作。服务器：

//SERVER
#include <winsock2.h>
#include <stdio.h>
#include <iostream>
#include <sstream>
#include <algorithm>
#include <ctime>
#pragma comment(lib, "ws2_32.lib")
int main()
{
WSADATA wsaData;
int winsock_result = WSAStartup(MAKEWORD(2,2), &wsaData);
if(winsock_result != 0)
{
exit(1);
}
SOCKET server_socket;
server_socket = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
if(server_socket == INVALID_SOCKET)
{
WSACleanup();
exit(1);
}
char* ip_address = "127.0.0.1";
int port = 6666;
SOCKADDR_IN server;
server.sin_family = AF_INET;
server.sin_port = htons(port);
server.sin_addr.s_addr = inet_addr(ip_address);
if(bind(server_socket,(SOCKADDR *)&server, sizeof(server)) == SOCKET_ERROR)
{
closesocket(server_socket);
WSACleanup();
exit(1);
}
std::cout << "Waiting for data." << std::endl;
SOCKADDR_IN client;
int client_sizeof = sizeof(client);
int const buffer_size = 512;
char buffer[buffer_size];
if(recvfrom(server_socket, buffer, buffer_size, 0,(SOCKADDR *)&client, &client_sizeof) == SOCKET_ERROR)
{
closesocket(server_socket);
WSACleanup();
exit(1);
}
else
{
FILE* file;
file = fopen(buffer, "rb");
std::cout << "Filename: " << buffer << std::endl;
if(file == NULL)
{
std::cout << "Couldn't open the file." << std::endl;
strcpy(buffer, "NOFILE");
if(sendto(server_socket, buffer, buffer_size, 0,(SOCKADDR *)&client, client_sizeof) == SOCKET_ERROR)
{
fclose(file);
closesocket(server_socket);
WSACleanup();
exit(1);
}
}
fseek(file, 0, SEEK_END);
int file_size = ftell(file);
size_t reading_size;
int part = 0;
const clock_t begin_time = clock();
while((part * buffer_size) < file_size)
{
fseek(file, (part * buffer_size), SEEK_SET);
reading_size = fread(buffer, 1, buffer_size, file);
if(sendto(server_socket, buffer, reading_size, 0,(SOCKADDR *)&client, client_sizeof) == SOCKET_ERROR)
{
fclose(file);
closesocket(server_socket);
WSACleanup();
exit(1);
}
part++;
}
std::cout << "Sent " << part << " parts of " << buffer_size << " bytes." << std::endl;
std::cout << "Time of sending file: " << float( clock () - begin_time ) /  CLOCKS_PER_SEC << " seconds." << std::endl;
strcpy(buffer, "QUIT");
if(sendto(server_socket, buffer, buffer_size, 0,(SOCKADDR *)&client, client_sizeof) == SOCKET_ERROR)
{
fclose(file);
closesocket(server_socket);
WSACleanup();
exit(1);
}
fclose(file);
}
closesocket(server_socket);
WSACleanup();
system("pause");
return 0;
}

客户端：

//CLIENT
#include <winsock2.h>
#include <stdio.h>
#include <iostream>
#include <sstream>
#include <string.h>
#pragma comment(lib, "ws2_32.lib")
int main()
{
WSADATA wsaData;
int winsock_result = WSAStartup(MAKEWORD(2,2), &wsaData);
if(winsock_result != 0)
{
exit(1);
}
SOCKET client_socket;
client_socket = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
if(client_socket == INVALID_SOCKET)
{
WSACleanup();
exit(1);
}
char* ip_address = "127.0.0.1";
int port = 6666;
SOCKADDR_IN server;
server.sin_family = AF_INET;
server.sin_port = htons(port);
server.sin_addr.s_addr = inet_addr(ip_address);
int server_sizeof = sizeof(server);
int const buffer_size = 512;
char buffer[buffer_size];
std::cout << "Name of the requested file: ";
std::cin >> buffer;
char filename[buffer_size];
strcpy(filename, buffer);
if(sendto(client_socket, buffer, buffer_size, 0,(SOCKADDR *)&server, server_sizeof) == SOCKET_ERROR)
{
closesocket(client_socket);
WSACleanup();
exit(1);
}
FILE* file;
file = fopen(filename, "wb");
int received_size = 0;
while(true)
{
received_size = recvfrom(client_socket, buffer, buffer_size, 0,(SOCKADDR *)&server, &server_sizeof);
if(received_size == SOCKET_ERROR)
{
fclose(file);
closesocket(client_socket);
WSACleanup();
exit(1);
}
if(strcmp(buffer, "NOFILE") == 0)
{
std::cout << "The file does not exist on the server." << std::endl;
fclose(file);
remove(filename);
break;
}
else if(strcmp(buffer, "QUIT") == 0)
{
std::cout << "Transmission ended by the server." << std::endl;
break;
}
fwrite(buffer, sizeof(char), received_size, file);
}
fclose(file);
closesocket(client_socket);
WSACleanup();
system("pause");
return 0;
}