我正在尝试为多线程服务器编写 TCP FTP 服务。我发现这个教程http://www.mario-konrad.ch/wiki/doku.php?id=programming:multithreading:tutorial-04 对理解 TCP 协议客户端的多线程非常有帮助。事实上，这段代码创建了一个可以同时接受来自不同客户端的多个连接的服务器。
但是，我正在努力寻找如何在其上应用 ftp 服务。确切地说，如何在 FTP 服务器上放置和获取文件。
有什么帮助吗？
【问题讨论】：
下面的代码是我去年为一篇网络论文所做的作业。希望对您有所帮助。
#include <windows.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <winsock.h>
#include <winsock2.h>
#define BUFFERSIZE 800
#define WSVERS MAKEWORD(2,0)
WSADATA wsadata;
void wy_fileName_collector(char *_buffer, char *_nameBuffer);
int main(int argc, char *argv[])
{
//INITIALIZATION
struct sockaddr_in localaddr,remoteaddr;
struct sockaddr_in remoteaddr_act;
SOCKET s,ns;
SOCKET s_data_act=0;
char send_buffer[BUFFERSIZE],receive_buffer[BUFFERSIZE];
char fileName[40];
int n,bytes,addrlen;
memset(&localaddr,0,sizeof(localaddr));//clean up the structure
memset(&localaddr,0,sizeof(remoteaddr));//clean up the structure
//WSASTARTUP
if (WSAStartup(WSVERS, &wsadata) != 0)
{
WSACleanup();
printf("WSAStartup failed\n");
exit(1);
}
//SOCKET
s = socket(PF_INET, SOCK_STREAM, 0);
if (s <0)
{
printf("socket failed\n");
}
localaddr.sin_family = AF_INET;
if (argc == 2) localaddr.sin_port = htons((u_short)atoi(argv[1]));
else localaddr.sin_port = htons(1234);//default listening port
localaddr.sin_addr.s_addr = INADDR_ANY;//server address should be local
//BIND
if (bind(s,(struct sockaddr *)(&localaddr),sizeof(localaddr)) != 0)
{
printf("Bind failed!\n");
exit(0);
}
//LISTEN
listen(s,5);
while (1)
{
addrlen = sizeof(remoteaddr);
//NEW SOCKET newsocket = accept
ns = accept(s,(struct sockaddr *)(&remoteaddr),&addrlen);
if (ns <0 ) break;
printf("accepted a connection from client IP %s port %d \n",inet_ntoa(remoteaddr.sin_addr),ntohs(localaddr.sin_port));
//Respond with welcome message
sprintf(send_buffer,"\n==220 Welcome to Alan's FTP site== \r\n\n");
bytes = send(ns, send_buffer, strlen(send_buffer), 0);
while (1)
{
n = 0;
while (1)
{
//RECEIVE
bytes = recv(ns, &receive_buffer[n], 1, 0);//receive byte by byte...
//PROCESS REQUEST
if ( bytes <= 0 ) break;
if (receive_buffer[n] == '\n')
{ /*end on a LF*/
receive_buffer[n] = '\0';
break;
}
if (receive_buffer[n] != '\r') n++; /*ignore CRs*/
}
if ( bytes <= 0 ) break;
printf("-->DEBUG: the message from client reads: '%s' \r\n", receive_buffer);
/**
* @brief Exception handling
*/
if(strncmp(receive_buffer,"USER",4) && strncmp(receive_buffer,"PASS",4) && strncmp(receive_buffer,"SYST",4)
&&strncmp(receive_buffer,"PORT",4) && strncmp(receive_buffer,"STOR",4) && strncmp(receive_buffer,"RETR",4)
&&strncmp(receive_buffer,"LIST",4) && strncmp(receive_buffer,"NLST",4) && strncmp(receive_buffer,"QUIT",4))
{
sprintf(send_buffer,"202 Command not implemented, superfluous at this site. \r\n");
bytes = send(ns, send_buffer, strlen(send_buffer), 0);
}
if (strncmp(receive_buffer,"USER",4)==0)
{
printf("Logging in \n");
sprintf(send_buffer,"331 Password required \r\n");
bytes = send(ns, send_buffer, strlen(send_buffer), 0);
if (bytes < 0) break;
}
if (strncmp(receive_buffer,"PASS",4)==0)
{
printf("Typing password (anything will do... \n");
sprintf(send_buffer,"230 Public login sucessful \r\n");
bytes = send(ns, send_buffer, strlen(send_buffer), 0);
if (bytes < 0) break;
}
if (strncmp(receive_buffer,"SYST",4)==0)
{
system("ver > tmp.txt");
FILE *fin=fopen("tmp.txt","r");//open tmp.txt file
sprintf(send_buffer,"150 Transfering... \r\n");
bytes = send(ns, send_buffer, strlen(send_buffer), 0);
char temp_buffer[80];
while (!feof(fin))
{
fgets(temp_buffer,78,fin);
sprintf(send_buffer,"%s",temp_buffer);
send(s_data_act, send_buffer, strlen(send_buffer), 0);
}
fclose(fin);
sprintf(send_buffer,"226 File transfer completed... \r\n");
bytes = send(ns, send_buffer, strlen(send_buffer), 0);
if (bytes < 0) break;
}
//PORT
if(strncmp(receive_buffer,"PORT",4)==0)
{
s_data_act = socket(AF_INET, SOCK_STREAM, 0);
//local variables
unsigned char act_port[2];
int act_ip[4], port_dec;
char ip_decimal[40];
sscanf(receive_buffer, "PORT %d,%d,%d,%d,%d,%d",&act_ip[0],&act_ip[1],&act_ip[2],&act_ip[3],(int*)&act_port[0],(int*)&act_port[1]);
remoteaddr_act.sin_family=AF_INET;//local_data_addr_act
sprintf(ip_decimal, "%d.%d.%d.%d", act_ip[0], act_ip[1], act_ip[2],act_ip[3]);
printf("IP is %s\n",ip_decimal);
remoteaddr_act.sin_addr.s_addr=inet_addr(ip_decimal);
port_dec=act_port[0]*256+act_port[1];
printf("port %d\n",port_dec);
remoteaddr_act.sin_port=htons(port_dec);
if (connect(s_data_act, (struct sockaddr *)&remoteaddr_act, (int) sizeof(struct sockaddr)) != 0)
{
printf("trying connection in %s %d\n",inet_ntoa(remoteaddr_act.sin_addr),ntohs(remoteaddr_act.sin_port));
sprintf(send_buffer, "425 Something is wrong, can't start the active connection... \r\n");
bytes = send(ns, send_buffer, strlen(send_buffer), 0);
closesocket(s_data_act);
}
else
{
sprintf(send_buffer, "200 Ok\r\n");
bytes = send(ns, send_buffer, strlen(send_buffer), 0);
printf("Data connection to client created (active connection) \n");
}
}
/**
* @brief STOR
*/
if((strncmp(receive_buffer,"STOR",4)==0))
{
memset(&fileName, 0, strlen(fileName));
wy_fileName_collector(receive_buffer, fileName);
if(fopen(fileName,"w") == NULL)
{
printf("@alan:line1\n");
sprintf(send_buffer,"450 Requested file action not taken. \r\n");
bytes = send(ns, send_buffer, strlen(send_buffer), 0);
}
else
{
FILE *fout=fopen(fileName,"w");
sprintf(send_buffer,"150 File status okay; about to open data connection. \r\n");
bytes = send(ns, send_buffer, strlen(send_buffer), 0);
while(1)
{
n = 0;
while(1)
{
//RECEIVE
bytes = recv(s_data_act, &receive_buffer[n], 1, 0);//receive byte by byte...
//PROCESS REQUEST
if ( bytes <= 0 ) break;
if (receive_buffer[n] == '\n')
{ /*end on a LF*/
receive_buffer[n] = '\0';
break;
}
if (receive_buffer[n] != '\r') n++; /*ignore CRs*/
}
if ( bytes <= 0 ) break;
fprintf(fout,"%s\n",receive_buffer);
}
sprintf(send_buffer,"226 File transfer completed... \r\n");
bytes = send(ns, send_buffer, strlen(send_buffer), 0);
fclose(fout);
closesocket(s_data_act);
}
}
/**
* @brief RETR
*/
if((strncmp(receive_buffer,"RETR",4)==0))
{
memset(&fileName, 0, strlen(fileName));
wy_fileName_collector(receive_buffer, fileName);
if(fopen(fileName,"r")==NULL)
{
sprintf(send_buffer,"450 Requested file action not taken. \r\n");
bytes = send(ns, send_buffer, strlen(send_buffer), 0);
}
else
{
FILE *fin=fopen(fileName,"r");//open tmp.txt file
sprintf(send_buffer,"150 Transfering... \r\n");
bytes = send(ns, send_buffer, strlen(send_buffer), 0);
char temp_buffer[80];
while (!feof(fin))
{
fgets(temp_buffer,78,fin);
sprintf(send_buffer,"%s",temp_buffer);
send(s_data_act, send_buffer, strlen(send_buffer), 0);
}
fclose(fin);
sprintf(send_buffer,"226 File transfer completed... \r\n");
bytes = send(ns, send_buffer, strlen(send_buffer), 0);
}
closesocket(s_data_act);
}
//LIST or NLST
if ( (strncmp(receive_buffer,"LIST",4)==0) || (strncmp(receive_buffer,"NLST",4)==0))
{
system("dir > tmp.txt");
FILE *fin=fopen("tmp.txt","r");//open tmp.txt file
sprintf(send_buffer,"150 Transfering... \r\n");
bytes = send(ns, send_buffer, strlen(send_buffer), 0);
char temp_buffer[80];
while (!feof(fin))
{
fgets(temp_buffer,78,fin);
sprintf(send_buffer,"%s",temp_buffer);
send(s_data_act, send_buffer, strlen(send_buffer), 0);
}
fclose(fin);
sprintf(send_buffer,"226 File transfer completed... \r\n");
bytes = send(ns, send_buffer, strlen(send_buffer), 0);
closesocket(s_data_act);
}
//QUIT
if (strncmp(receive_buffer,"QUIT",4)==0)
{
printf("Quit \n");
sprintf(send_buffer,"221 Connection closed by the FTP client\r\n");
bytes = send(ns, send_buffer, strlen(send_buffer), 0);
if (bytes < 0) break;
closesocket(ns);
}
}
//CLOSE SOCKET
closesocket(ns);
printf("disconnected from %s\n",inet_ntoa(remoteaddr.sin_addr));
}
closesocket(s);//it actually never gets to this point....use CTRL_C
}
/**
* @brief Return file name from the string passed in.
*/
void wy_fileName_collector(char *_buffer, char *_nameBuffer)
{
char bf[BUFFERSIZE];
char sep[2] = " "; //separation is space
char *word;
int wcount=0;
strcpy(bf, _buffer);
for (word = strtok(bf, sep);word;word = strtok(NULL, sep))
{
wcount++;
if(wcount == 2) // jump the first space"_".
{
strcpy(_nameBuffer, word);
}
}
}
【讨论】：
gcc ftp.c -lwsock32 -lws2_32 -o ftp.exe)。它通过 windows ftp 命令工作，但 Total Commander ftp 客户端挂起欢迎消息。有没有办法让它在 totalcmd 中工作？
sprintf(send_buffer,"\n220 Welcome to Alan's FTP site \r\n\n");。
FTP 使用两个 TCP 连接来传输文件：一个控制连接和一个数据连接。
Establish a control connection 到 FTP 服务器，log in。
接下来，establish the data connection。如果您从路由器后面连接，则发送PASV 命令以要求服务器侦听新的数据套接字并将 IP/端口发回给您。如果您不在路由器后面，则需要监听新的数据套接字并使用PORT 命令将 IP/端口发送到服务器。
建立数据连接后，send the STOR (upload) or RETR (download) command over the control connection 开始传输。
通过控制套接字的数据看起来像这样：
(Open Control Connection)
SERVER: 220 System Ready
CLIENT: USER MyUserName
SERVER: 331 Please specify the password.
CLIENT: PASS MyPassword
SERVER: 230 Login successful.
CLIENT: TYPE I
SERVER: 200 Switching to Binary mode.
CLIENT: PASV
SERVER: 227 Entering Passive Mode (173,254,254,254,211,37)
(Client connects data connection to the specified address)
CLIENT: RETR example.html
SERVER: 150 Opening BINARY mode data connection for example.html (10403 bytes).
SERVER: 226 File send OK.
(Both close the data connection)
CLIENT: QUIT
SERVER: 221 Goodbye
(Both close control connection)
【讨论】：