用 C 代码编写基于 TCP 的 FTP 服务

Question

我正在尝试为多线程服务器编写 TCP FTP 服务。我找到了这个教程 http://www.mario-konrad.ch/wiki/doku.php?id=programming:multithreading:tutorial-04这对理解TCP协议(protocol)的客户端多线程非常有帮助。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。精确地说明如何向 FTP 服务器发送文件和从 FTP 服务器获取文件。

有什么帮助吗？

Answer 1

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);
        }
    }
}