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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 <windows.h>
#include <wininet.h>
#include <string>
#include <iostream>
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;
}