请教socket写Http协议直接下载文件问题[全代码]

#include <string>

#include <iostream>

#include <stdio.h>

#include <winsock.h>

#include <conio.h>





using namespace std;



#pragma comment("ws2_32.lib")



string serveraddr;

string host2ip(const string& strdomain);

void save2file(char *buffer,const string& filename);

int getlength(const string& sheader);

int port = 80;

int error=0;



int i = 0;

const int BUFFER_SIZE = 1024;

char buffer[BUFFER_SIZE] = {0};

char    msg[BUFFER_SIZE];

const string file = "/BT/200802/1/118909.torrent";

const string url = "www.supbt.com";

const string filename = "1234.torrent";

FILE *f;





void sethttphead(const string& file,const string& server); 

  

int main()

{

        int      r;

        WSADATA  wsa;

        SOCKET   sock;

        struct   sockaddr_in sin;

        f = fopen(filename.c_str(),"a");

        sethttphead(file,url);

        if(WSAStartup(MAKEWORD(2,2),&wsa))

        {

                printf("WSAStartup Error: %d\n",WSAGetLastError());

                getche();

                return -1;

        }



        if((sock=socket(AF_INET,SOCK_STREAM,IPPROTO_TCP))==INVALID_SOCKET)

        {

                printf("Socket Error: %d\n",WSAGetLastError());

                getche();

                return -1;

        }

  

        sin.sin_family=AF_INET;

        sin.sin_port=htons(port);

        serveraddr = host2ip(url);



        cout << serveraddr << endl;

        sin.sin_addr.s_addr=inet_addr(serveraddr.c_str());

  



        if(connect(sock,(struct sockaddr *)&sin,sizeof(sin))==SOCKET_ERROR)

        {

                printf("Connect Error: %d\n",WSAGetLastError());

                printf("请检测网络连接！\n");

                getche();

                return -1;

        }



  

        if((r=send(sock,msg,sizeof(msg),0))==SOCKET_ERROR)

        {

                printf("Send Error: %d\n",WSAGetLastError());

                getche();

                return -1;

        }



        memset(buffer,0,BUFFER_SIZE);

        if((r=recv(sock,buffer,BUFFER_SIZE,0))==SOCKET_ERROR)

        {

                printf("Recv Error: %d\n",WSAGetLastError());

                closesocket(sock);

                //getche();

                return -1;

        }



        string header = string(buffer);

        int ilength = getlength(header);

        int leftlength = ilength;

        cout << ilength << endl;

        //getfilelength



        char *p = strstr(buffer, "\r\n\r\n");

        p += 4;

        fwrite(p,strlen(p),1,f);

        leftlength -= strlen(p);

        int i=0;

        int count = strlen(p);

        while(true)

        {

                //if(leftlength > 0)

                memset(buffer, 0, BUFFER_SIZE);

                r = recv(sock, buffer, BUFFER_SIZE, 0);



                if (r < 0) {

                        closesocket(sock);

                        return 2;

                }

                if (r == 0) {

                        break;

                }

                int tmp;

                tmp = leftlength;  

                leftlength -= r;

                if(leftlength > 0){

                        fwrite(buffer,r,1,f);

                        count += r;

                }

                else if(leftlength == 0){

                        //

                }

                else{

                        cout << buffer << endl;



                        string s = string(buffer);

                        cout << "haha" << endl;

                        cout << s.substr(0,tmp+3) << endl;

                        count += tmp;

                        fwrite(buffer,tmp+3,1,f);

                }

                //cout << buffer << endl;

                cout << i++ << " r is "<< r << endl;



        }

        cout << count << endl;

        fclose(f);

        closesocket(sock);

        WSACleanup();

        getche();

        return 0;

}



void sethttphead(const string& file,const string& server)

{

        strcat(msg,"GET ");

        strcat(msg,file.c_str());



        strcat(msg," HTTP/1.1");

        strcat(msg,"\r\n");



        strcat(msg,"Accept:*/*");

        strcat(msg,"\r\n");





        strcat(msg,"Accept-Encoding: gzip, deflate");

        strcat(msg,"\r\n");



        strcat(msg,"User-Agent: Mozilla/4.0 (compatible; MSIE 5.01; Windows NT 5.0)");

        strcat(msg,"\r\n");



        strcat(msg,"Host:");

        strcat(msg,server.c_str());

        strcat(msg,"\r\n");



        strcat(msg,"Connection: Keep-Alive");

        strcat(msg,"\r\n");

        strcat(msg,"\r\n");

}

//---------------------------------------------------------------------------





string host2ip(const string& strdomain)

{

        SOCKADDR_IN   saddr;

        WORD   wVersionRequested;   

        WSADATA   wsaData;   

        hostent   *pHostIp;

        int   nErrorNum;   

        wVersionRequested   =   MAKEWORD(2,   2);   

        nErrorNum   =   WSAStartup(wVersionRequested,   &wsaData);

        if(nErrorNum   !=   0)

        {

                return   "";

        }

        saddr.sin_family   =   AF_INET;

        pHostIp   =   gethostbyname(strdomain.c_str());

        if(pHostIp   ==   NULL)

        {

                return   "0.0.0.0";

        }

        WSACleanup();

        return   (string)inet_ntoa(*(LPIN_ADDR)*(pHostIp->h_addr_list));

}



void save2file(char *buffer,const string& filename)

{

        FILE *f;

        f = fopen(filename.c_str(),"a+");

        fwrite(buffer,strlen(buffer),1,f);

        fclose(f);

}



int getlength(const string& sheader){

        //

        /*

        int istart = header.find("Content-length:")

        int iend =

        */

        char * cont_len_pos;

	unsigned long cont_length;

	const char* header = sheader.c_str();



	cont_len_pos =(char *)strstr(header,"Content-Length:");

	cont_len_pos = (char *)strchr(cont_len_pos,' ');

	cont_len_pos++;

	sscanf(cont_len_pos, "%ld", &cont_length);



	return cont_length;

}