在服务中、一般程序中利用 Inet 相关函数下载数据

虽然可以使用 URLDownloadFileToXXX() 这个 API，但是，它在使用了代理的时候会遇到麻烦。
这点，Windows 自动更新发生过这样的问题：如果使用了 IE 代理，如果下载代码位于系统帐号
下，代理设置可能会失效。当然，也可以为系统帐号手动设置代理（其实就是 IE 的代理的设置
方法），不过，程序会受到很多的限制。

所以，可以考虑使用下属两个函数进行使用 - 服务程序亦可。^_^

//
// Download a file from the URL.
bool CHttpDownload::UrlDownloadToFile(TCHAR *ptszURL, TCHAR *ptszFilePath)
{
        
        HINTERNET                                hNet;
        HINTERNET                                hFile;
        std::string                                sProxyServer;

        DWORD                                        dwStatusCode;
        TCHAR                                        dwStatusCode1[32] = {0}; 
        DWORD                                        dwSize1 = sizeof(dwStatusCode1),        dwSize = sizeof(DWORD);
        
        int                                                nfilesize;                        // file size, 2GB limited. ;)

        m_sUrl = ptszURL;
        //OutputDebugString("/nCHttpDownload::UrlDownloadToFile() ++");

        // 
        if(m_ConnectionType == UseProxy)
        {
                //OutputDebugString("/n ==> Useproxy");
                hNet = InternetOpen(tszAgent, INTERNET_OPEN_TYPE_PROXY, m_sProxy.c_str(), NULL, 0);
        }
        else if(m_ConnectionType == DirectToInternet)        
        {
                //OutputDebugString("/n ==> DirectToInternet");
                hNet = InternetOpen(tszAgent, INTERNET_OPEN_TYPE_DIRECT, NULL, NULL, 0);
        }
        else if(m_ConnectionType == UsePreConfig)        
        {
                //OutputDebugString("/n ==> UsePreConfig");
                hNet = InternetOpen(tszAgent, INTERNET_OPEN_TYPE_PRECONFIG, NULL, NULL, 0);
        }

        if(hNet == NULL)
        {
                //OutputDebugString("/nCHttpDownload::UrlDownloadToFile() --.1");
                return false;
        }

        hFile = InternetOpenUrl(hNet, m_sUrl.c_str(), NULL, 0, 0, 0); 
        if(hFile == NULL)
        {
                InternetCloseHandle(hNet) ;
                //OutputDebugString(m_sUrl.c_str());
                //OutputDebugString(ptszURL);
                //OutputDebugString("/nCHttpDownload::UrlDownloadToFile() --.2");

                return false;
        }
        
        BOOL bRet = HttpQueryInfo(hFile, HTTP_QUERY_STATUS_CODE|HTTP_QUERY_FLAG_NUMBER,&dwStatusCode,&dwSize,NULL);
        if(200 != dwStatusCode)                // if URI is not exist, give up.
        {
                InternetCloseHandle(hNet) ;
                InternetCloseHandle(hFile) ;
                //OutputDebugString("/nCHttpDownload::UrlDownloadToFile() --.3");

                return false;
        }
        if(HttpQueryInfo(hFile,HTTP_QUERY_CONTENT_LENGTH, &dwStatusCode1,&dwSize1,NULL))
        {
                nfilesize = atoi(dwStatusCode1);                // file size.
        } 
        
        HANDLE hDownFile = CreateFile(ptszFilePath,
                                                                GENERIC_READ|GENERIC_WRITE,
                                                                FILE_SHARE_READ,
                                                                NULL,
                                                                CREATE_ALWAYS,
                                                                FILE_ATTRIBUTE_NORMAL,
                                                                NULL);

        if(INVALID_HANDLE_VALUE == hDownFile)
        {
                InternetCloseHandle(hNet) ;
                InternetCloseHandle(hFile) ;
                //OutputDebugString("/nCHttpDownload::UrlDownloadToFile() --.4");

                return false;
        }

        // O.K. save file
        DWORD dwWrite, dwBytesRead = 0;
        char  bufFile[MAX_BUFFER_SIZE] = {0};
        DWORD dwSurplus = nfilesize % sizeof(bufFile);        

        while(true)
        {
                // Read File Data From Net.
                BOOL bRead = InternetReadFile(hFile, bufFile, sizeof(bufFile), &dwBytesRead);
                if(dwBytesRead == 0)                // End of file.
                        break;

                // Write file data.
                WriteFile(hDownFile, bufFile, dwBytesRead, &dwWrite,NULL);
        }

        InternetCloseHandle(hFile) ;
        InternetCloseHandle(hNet) ;
        CloseHandle(hDownFile) ;

        //OutputDebugString("/nCHttpDownload::UrlDownloadToFile() --.");
        return true;
}

// Download URL contents to memory buffer.
// if pBuf == NULL, *pdwBufSize will contain the real size of remote size;
// *pdwBufSize alwayls contains the size of remote size.
bool CHttpDownload::UrlDownloadToBuffer(TCHAR *ptszURL, LPVOID pBuf, DWORD *pdwBufSize)
{
        
        HINTERNET                                hNet;
        HINTERNET                                hFile;
        std::string                                sProxyServer;
        
        DWORD                                        dwStatusCode;
        TCHAR                                        dwStatusCode1[32] = {0}; 
        DWORD                                        dwSize1 = sizeof(dwStatusCode1),        dwSize = sizeof(DWORD);
        
        int                                                nfilesize;                        // file size, 2GB limited. ;)
        
        m_sUrl                = ptszURL;
        
        //OutputDebugString("/nCHttpDownload::UrlDownloadToFile() ++");
        
        // 
        if(m_ConnectionType == UseProxy)
                hNet = InternetOpen(tszAgent, INTERNET_OPEN_TYPE_PROXY, m_sProxy.c_str(), NULL, 0);
        else if(m_ConnectionType == DirectToInternet)        
                hNet = InternetOpen(tszAgent, INTERNET_OPEN_TYPE_DIRECT, NULL, NULL, 0);
        else if(m_ConnectionType == UsePreConfig)        
                hNet = InternetOpen(tszAgent, INTERNET_OPEN_TYPE_PRECONFIG, NULL, NULL, 0);
        
        
        if(hNet == NULL)
        {
                //OutputDebugString("/nCHttpDownload::UrlDownloadToFile() --.1");
                return false;
        }
        
        hFile = InternetOpenUrl(hNet, m_sUrl.c_str(), NULL, 0, 0, 0); 
        if(hFile == NULL)
        {
                InternetCloseHandle(hNet) ;
                //OutputDebugString("/nCHttpDownload::UrlDownloadToFile() --.2");
                
                return false;
        }
        
        BOOL bRet = HttpQueryInfo(hFile, HTTP_QUERY_STATUS_CODE|HTTP_QUERY_FLAG_NUMBER,&dwStatusCode,&dwSize,NULL);
        if(200 != dwStatusCode)                // if URI is not exist, give up.
        {
                InternetCloseHandle(hNet) ;
                InternetCloseHandle(hFile) ;
                //OutputDebugString("/nCHttpDownload::UrlDownloadToFile() --.3");
                
                return false;
        }
        if(HttpQueryInfo(hFile,HTTP_QUERY_CONTENT_LENGTH, &dwStatusCode1,&dwSize1,NULL))
        {
                nfilesize = atoi(dwStatusCode1);                // file size.
                
        } 
        
        char                                szBuffer[MAX_BUFFER_SIZE+1] = {0};

        if(pBuf != NULL)        // We only copy the 1st MAX_BUFFER_SIZE data to user buffer!!!
        {
                 unsigned long nSize = 0;
                
                 
                BOOL bRet = InternetReadFile(hFile, szBuffer, MAX_BUFFER_SIZE, &nSize);

                 szBuffer[nSize] = '/0';

                // dump buffer.
                DWORD        dwtSize = (*pdwBufSize > nSize)? nSize: *pdwBufSize;
                memcpy(pBuf, szBuffer, dwtSize);
        }
        
        *pdwBufSize = nfilesize;

        InternetCloseHandle(hFile) ;
        InternetCloseHandle(hNet) ;

        
        return true;        
}

Using WinInet HTTP functions in Full Asynchronous Mode
http://www.codeproject.com/internet/asyncwininet.asp

Offline Browser using WinInet, URL Moniker and MSHTML APIs
http://www.codeproject.com/internet/OfflineBrowserWinInet.asp

Common HTTP and FTP WinInet APIs
http://www.dotnetheaven.com/UploadFile/mahesh/CommonHTTPandFTP05242005075834AM/CommonHTTPandFTP.aspx

http://topic.csdn.net/t/20050507/16/3987488.html

Discover WIN32. How to use a sync/async retrieve HTTP content in your ASP & VB projects.
http://www.codeproject.com/internet/retrievehttp.asp

HTTP Proxy download
http://www.vbforums.com/archive/index.php/t-225065.html

HTTP/FTP客户端开发库：libwww、libcurl、libfetch 以及更多
[url]http://blog.csdn.net/heiyeshuwu/archive/2007/07/15/1691904.aspx