使用WinINet实现HTTP下载

网上很难找到比较好的使用WinINet实现HTTP下载的代码,经过半天的研究MSDN(可以搜索关键字:MSDN HTTP sessions,链接:http://msdn.microsoft.com/en-us/library/aa384322(v=vs.85).aspx),还有在google的code搜索中找了一些例子(比如:这里),终于自己实现了一个简单的下载函数,记录到这里备忘。

函数特点:通过先发送一次HEAD请求,获得要下载资源的Header,可以对待下载的资源的类型和大小进行限制。另外,请求失败时自动尝试重新发送几次请求。

 

TODO: 如果要实现断点续传,可以在发送请求时,使用HttpAddRequestHeaders()添加Range头域,请求服务器文件的某个部分。(参见HTTP协议)

 

HTTP协议Range头域介绍:

  Range头域
  Range头域可以请求实体的一个或者多个子范围。例如,
  表示头500个字节:bytes=0-499
  表示第二个500字节:bytes=500-999
  表示最后500个字节:bytes=-500
  表示500字节以后的范围:bytes=500-
  第一个和最后一个字节:bytes=0-0,-1
  同时指定几个范围:bytes=500-600,601-999
  但是服务器可以忽略此请求头,如果无条件GET包含Range请求头,响应会以状态码206(PartialContent)返回而不是以200(OK)。

 

 

//code by MulinB, 2011-07-27

#include 
#include 

#include 
#include 
using namespace std;

#pragma comment(lib, "wininet.lib")

//下载
#define  DOWNHELPER_AGENTNAME         "MyAppByMulinB"
#define  LEN_OF_BUFFER_FOR_QUERYINFO  128
#define  DOWNLOAD_BUF_SIZE            (10*1024)  //10KB
#define  MAX_DOWNLOAD_REQUEST_TIME    10  
#define  MAX_DOWNLOAD_BYTESIZE        (1000*1024*1024) //1000MB


BOOL _TryHttpSendRequest(LPVOID hRequest, int nMaxTryTimes); //多次发送请求函数

//HTTP下载函数,通过先请求HEAD的方式然后GET,可以通过HEAD对下载的文件类型和大小做限制
BOOL DownloadUrl(std::string strUrl, std::string strFileName)
{
    BOOL bRet = FALSE;
    if (strUrl == "" || strFileName == "")
        return FALSE;

    //定义变量
    HINTERNET hInet = NULL; //打开internet连接handle
    HINTERNET hConnect = NULL; //HTTP连接
    HINTERNET hRequestHead = NULL; //HTTP Request
    HINTERNET hRequestGet = NULL; //HTTP Request
    HANDLE hFileWrite = NULL; //写文件的句柄
    char* pBuf = NULL; //缓冲区
    DWORD dwRequestTryTimes = MAX_DOWNLOAD_REQUEST_TIME; //尝试请求的次数
    DWORD dwDownBytes = 0; //每次下载的大小
    DWORD dwDownFileTotalBytes = 0; //下载的文件总大小
    DWORD dwWriteBytes = 0; //写入文件的大小
    char bufQueryInfo[LEN_OF_BUFFER_FOR_QUERYINFO] = {0}; //用来查询信息的buffer
    DWORD dwBufQueryInfoSize = sizeof(bufQueryInfo);
    DWORD dwStatusCode = 0;
    DWORD dwContentLen = 0;
    DWORD dwSizeDW = sizeof(DWORD);

    //分割URL
    CHAR pszHostName[INTERNET_MAX_HOST_NAME_LENGTH] = {0};
    CHAR pszUserName[INTERNET_MAX_USER_NAME_LENGTH] = {0};
    CHAR pszPassword[INTERNET_MAX_PASSWORD_LENGTH] = {0};
    CHAR pszURLPath[INTERNET_MAX_URL_LENGTH] = {0};
    CHAR szURL[INTERNET_MAX_URL_LENGTH] = {0};
    URL_COMPONENTSA urlComponents = {0};
    urlComponents.dwStructSize = sizeof(URL_COMPONENTSA);
    urlComponents.lpszHostName = pszHostName;
    urlComponents.dwHostNameLength = INTERNET_MAX_HOST_NAME_LENGTH;
    urlComponents.lpszUserName = pszUserName;
    urlComponents.dwUserNameLength = INTERNET_MAX_USER_NAME_LENGTH;
    urlComponents.lpszPassword = pszPassword;
    urlComponents.dwPasswordLength = INTERNET_MAX_PASSWORD_LENGTH;
    urlComponents.lpszUrlPath = pszURLPath;
    urlComponents.dwUrlPathLength = INTERNET_MAX_URL_LENGTH;

    bRet = InternetCrackUrlA(strUrl.c_str(), 0, NULL, &urlComponents);
    bRet = (bRet && urlComponents.nScheme == INTERNET_SERVICE_HTTP);
    if (!bRet)
    {
        goto _END_OF_DOWNLOADURL;
    }
    
    //打开一个internet连接
    hInet = InternetOpenA(DOWNHELPER_AGENTNAME, INTERNET_OPEN_TYPE_PRECONFIG, NULL, NULL, NULL);
    if (!hInet)
    {
        bRet = FALSE;
        goto _END_OF_DOWNLOADURL;
    }
    
    //打开HTTP连接
    hConnect = InternetConnectA(hInet, pszHostName, urlComponents.nPort, pszUserName, pszPassword, INTERNET_SERVICE_HTTP, 0, NULL);
    if (!hConnect)
    {
        bRet = FALSE;
        goto _END_OF_DOWNLOADURL;
    }
    
    //创建HTTP request句柄
    if (urlComponents.dwUrlPathLength !=  0)
        strcpy(szURL, urlComponents.lpszUrlPath);
    else
        strcpy(szURL, "/");
    
    //请求HEAD,通过HEAD获得文件大小及类型进行校验
    hRequestHead = HttpOpenRequestA(hConnect, "HEAD", szURL, "HTTP/1.1", "", NULL, INTERNET_FLAG_RELOAD, 0);
    bRet = _TryHttpSendRequest(hRequestHead, dwRequestTryTimes);
    if (!bRet)
    {
        goto _END_OF_DOWNLOADURL; //请求HEAD失败
    }
   
    //查询content-length大小
    dwContentLen = 0;
    dwSizeDW = sizeof(DWORD);
    bRet = HttpQueryInfo(hRequestHead, HTTP_QUERY_FLAG_NUMBER | HTTP_QUERY_CONTENT_LENGTH, &dwContentLen, &dwSizeDW, NULL);
    if (bRet)
    {
        //检查是否文件过大
        if (dwContentLen > MAX_DOWNLOAD_BYTESIZE)
        {
            bRet = FALSE;
            goto _END_OF_DOWNLOADURL;
        }
    }

    //校验完成后再请求GET,下载文件
    hRequestGet = HttpOpenRequestA(hConnect, "GET", szURL, "HTTP/1.1", "", NULL, INTERNET_FLAG_RELOAD, 0);
    bRet = _TryHttpSendRequest(hRequestGet, dwRequestTryTimes);
    if (!bRet)
    {
        goto _END_OF_DOWNLOADURL; //请求HEAD失败
    }

    //创建文件
    hFileWrite = CreateFileA(strFileName.c_str(), GENERIC_WRITE, FILE_SHARE_READ, NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
    if (INVALID_HANDLE_VALUE == hFileWrite)
    {
        bRet = FALSE;
        goto _END_OF_DOWNLOADURL;
    }

    //分配缓冲
    pBuf = new char[DOWNLOAD_BUF_SIZE]; //分配内存
    if (!pBuf)
    {
        bRet = FALSE;
        goto _END_OF_DOWNLOADURL;
    }

    //多次尝试下载文件
    dwDownFileTotalBytes = 0;
    while (1)
    {
        dwDownBytes = 0;
        memset(pBuf, 0, DOWNLOAD_BUF_SIZE*sizeof(char));
        bRet = InternetReadFile(hRequestGet, pBuf, DOWNLOAD_BUF_SIZE, &dwDownBytes);
        if (bRet)
        {
            if (dwDownBytes > 0)
            {
                dwDownFileTotalBytes += dwDownBytes;
                bRet = WriteFile(hFileWrite, pBuf, dwDownBytes, &dwWriteBytes, NULL); //写入文件
                if (!bRet)
                {
                    goto _END_OF_DOWNLOADURL;
                }
            }
            else if (0 == dwDownBytes)
            {
                bRet = TRUE;
                break; //下载成功完成
            }
        }
    }
    
    //清理
_END_OF_DOWNLOADURL:
    if (INVALID_HANDLE_VALUE != hFileWrite)
        CloseHandle(hFileWrite);
    if (pBuf)
        delete [] pBuf;
    if (hRequestGet)
        InternetCloseHandle(hRequestGet);
    if (hRequestHead)
        InternetCloseHandle(hRequestHead);
    if (hConnect)
        InternetCloseHandle(hConnect);
    if (hInet)
        InternetCloseHandle(hInet);
    
    return bRet;
}

//多次发送请求函数
BOOL _TryHttpSendRequest(LPVOID hRequest, int nMaxTryTimes)
{
    BOOL bRet = FALSE;
    DWORD dwStatusCode = 0;
    DWORD dwSizeDW = sizeof(DWORD);
    while (hRequest && (nMaxTryTimes-- > 0)) //多次尝试发送请求
    {
        //发送请求
        bRet = HttpSendRequestA(hRequest, NULL, 0, NULL, 0);
        if (!bRet)
        {
            continue;
        }
        else
        {
            //判断HTTP返回的状态码
            dwStatusCode = 0;
            dwSizeDW = sizeof(DWORD);
            bRet = HttpQueryInfo(hRequest, HTTP_QUERY_FLAG_NUMBER | HTTP_QUERY_STATUS_CODE, &dwStatusCode, &dwSizeDW, NULL);
            if (bRet)
            {
                //检查状态码
                if (HTTP_STATUS_OK == dwStatusCode) //200 OK
                {
                    break;
                }
                else
                {
                    bRet = FALSE;
                    continue;
                }
            }
        }
    }

    return bRet;
}


int main(int argc, char* argv[])
{
    cout << "正在下载...";
	BOOL bR = DownloadUrl("http://42.duote.com.cn/office2007.zip", "test.zip");
    if (bR)
        cout << "完成" << endl;
    else
        cout << "失败" << endl;
    return 0;
}


 

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