从HTTP服务器上下载一个文件有很多方法，“热心”的微软提供了 WinInet 类，用起来也很方便。当然，我们也可以自己实现这些功能，通过格式化请求头很容易就能实现断点续传和检查更新等等功能 。
1. 连接主机
2. 格式化请求头
3. 设置接收,发送超时
要想从服务器下载文件，首先要向服务器发送一个请求。HTTP 请求头由若干行字符串组成。下面结合实例说说 HTTP 请求头的格式。假设要下载
http://www.sina.com.cn/index.html 这个网页 ，那么请求头的写法如下：
第1行：方法，请求的内容，HTTP协议的版本
下载一般可以用GET方法，请求的内容是“/index.html”，HTTP协议的版本是指浏览器支持的版本，对于下载软件来说无所谓，所以用1.1版 “HTTP/1.1”；
“GET /index.html HTTP/1.1”
第2行：主机名，格式为“Host:主机”
在这个例子中是：“Host:www.sina.com.cn”
第3行：接受的数据类型，下载软件当然要接收所有的数据类型，所以：
“Accept:*/*”
第4行：指定浏览器的类型
有些服务器会根据客户服务器种类的不同会增加或减少一些内容，在这个例子中可以这样写：
“User-Agent:Mozilla/4.0 (compatible; MSIE 5.00; Windows 98)”
第5行：连接设置
设定为一直保持连接：“Connection:Keep-Alive”
第6行：若要实现断点续传则要指定从什么位置起接收数据，格式如下：
“Range: bytes=起始位置 - 终止位置”
比如要读前500个字节可以这样写：“Range: bytes=0 - 499”；从第 1000 个字节起开始下载：
“Range: bytes=999 -”
最后，别忘了加上一行空行，表示请求头结束。整个请求头如下：
GET /index.html HTTP/1.1
Host:www.sina.com.cn
Accept:*/*
User-Agent:Mozilla/4.0 (compatible; MSIE 5.00; Windows 98)
Connection:Keep-Alive
下面用例子看看如何进行断点的下载吧
// DownloadFile.h: interface for the CDownloadFile class.
//
/**///////////////////////////////////////////////////////////////////////
#if !defined(AFX_DOWNLOADFILE_H__E9A59779_BEF9_4A78_8D0E_ED8C9498E07C__INCLUDED_)
#define AFX_DOWNLOADFILE_H__E9A59779_BEF9_4A78_8D0E_ED8C9498E07C__INCLUDED_
#if _MSC_VER > 1000
#pragma once
#endif // _MSC_VER > 1000
#define NOTIFY_MSG_WPARAM_GENDOWNFILEID 0x01
#define NOTIFY_MSG_LOW_WPARAM_FULLSIZE 0x10
#define NOTIFY_MSG_LOW_WPARAM_CURRENTSIZE 0x20
#define NOTIFY_MSG_LOW_WPARAM_DOWNSIZE 0x30
#define NOTIFY_MSG_LOW_WPARAM_DOWNSPEED 0x40
class CDownloadFile
{
public:
BOOL OpenRedirectHttpURL(CString &strOldLocation,CInternetSession &cSession);
BOOL DownLoadFile(LPCTSTR lpFileURL,LPCTSTR lpSaveFile);
CDownloadFile();
virtual ~CDownloadFile();
LPCTSTR GetSavedFileName() { return m_strSaveToFile;}
LPCTSTR GetDownURL() { return m_strFileURL;}
public:
WORD GenFileID();
void RegisterNotifyWindow(DWORD dwThreadID,HWND hWnd,DWORD dwMsg);
BOOL GetUNCFile();
bool m_bForceReload;
DWORD m_TimeOut;
WORD m_wFileID;
protected:
DWORD m_dwThreadID;
void PostNotifyMessage(WPARAM wParam, LPARAM lParam);
DWORD m_dwMsgID;
HWND m_hNotify;
BOOL GetFtpFile(CInternetSession &cSession);
BOOL GetHttpFile(CInternetSession &cSession);
CString m_strTmpFileName;
CString m_strFileURL;
CString m_strSaveToFile;
CString m_rawHeaders;
float m_transferRate;
DWORD m_infoStatusCode;
};
#endif // !defined(AFX_DOWNLOADFILE_H__E9A59779_BEF9_4A78_8D0E_ED8C9498E07C__INCLUDED_)
// DownloadFile.cpp: implementation of the CDownloadFile class.
//
/**///////////////////////////////////////////////////////////////////////
#include "stdafx.h"
#include "DownloadFile.h"
#pragma comment( lib,"Wininet.lib" )
#include "shlwapi.h"
#pragma comment( lib,"shlwapi.lib" )
#ifdef _DEBUG
#undef THIS_FILE
static char THIS_FILE[]=__FILE__;
#define new DEBUG_NEW
#endif
#define BUFFER_SIZE 4095
const TCHAR szHeaders[] = _T("Accept: */*\r\nUser-Agent: Mozilla/4.0 (compatible; MSIE 5.00; Windows 98)\r\n");
/**///////////////////////////////////////////////////////////////////////// Construction/Destruction
/**///////////////////////////////////////////////////////////////////////
CDownloadFile::CDownloadFile()
{
m_TimeOut = 0;
m_bForceReload = true;
m_dwThreadID = 0;
m_hNotify = NULL;
m_dwMsgID = 0;
m_wFileID = 0;
}
CDownloadFile::~CDownloadFile()
{
}
BOOL CDownloadFile::DownLoadFile(LPCTSTR lpFileURL, LPCTSTR lpSaveFile)
{
BOOL bRet = FALSE;
if ( !::PathIsURL(lpFileURL) )
{
return bRet;
}
m_strSaveToFile = lpSaveFile;
m_strFileURL = lpFileURL;
m_strTmpFileName = lpSaveFile;
m_strTmpFileName += _T(".df!");
CString strServer,strObject;INTERNET_PORT nPort;
CString strAgentCaption = _T("Update Download ") ;
strAgentCaption += ::PathFindFileName(lpSaveFile);
DWORD dwFlags = 0;
InternetGetConnectedState(&dwFlags, 0);
CInternetSession session (strAgentCaption, 1,
(dwFlags & INTERNET_CONNECTION_PROXY) == INTERNET_CONNECTION_PROXY ? INTERNET_OPEN_TYPE_PRECONFIG : INTERNET_OPEN_TYPE_PRECONFIG_WITH_NO_AUTOPROXY,
NULL, NULL, 0);
AfxParseURL(m_strFileURL,dwFlags,strServer,strObject,nPort);
if (m_TimeOut != 0)
session.SetOption(INTERNET_OPTION_DATA_RECEIVE_TIMEOUT, m_TimeOut);
if( !m_wFileID )
m_wFileID = GenFileID();
PostNotifyMessage(NOTIFY_MSG_WPARAM_GENDOWNFILEID,m_wFileID);
try
{
if ( dwFlags== AFX_INET_SERVICE_HTTP )
{
bRet = GetHttpFile(session);
}
else if( dwFlags== AFX_INET_SERVICE_FTP )
{
bRet = GetFtpFile(session);
}
else if( dwFlags== AFX_INET_SERVICE_FILE )
{
if( UrlIsFileUrl(m_strFileURL) )
bRet = GetUNCFile();
}
else
{
;
}
}
catch (CException* pEx)
{
TCHAR szErrorMsg[MAX_PATH] = {0};
pEx->GetErrorMessage(szErrorMsg, MAX_PATH);
TRACE( _T("Exception: %s\n") , szErrorMsg);
pEx->Delete();
}
session.Close();
m_wFileID = 0;
if (bRet)
{
if (!::MoveFileEx(m_strTmpFileName,m_strSaveToFile,MOVEFILE_REPLACE_EXISTING) )
{
Sleep(1000);
::MoveFileEx(m_strTmpFileName,m_strSaveToFile,MOVEFILE_REPLACE_EXISTING);
}
}
return bRet;
}
BOOL CDownloadFile::GetHttpFile(CInternetSession &cSession)
{
BOOL bRet = FALSE;
CFile m_TmpFile;
CFileException fileException;
if ( !m_TmpFile.Open (m_strTmpFileName,
CFile::modeCreate | CFile::modeNoTruncate | CFile::modeReadWrite
| CFile::shareDenyWrite | CFile::typeBinary,
&fileException ) )
{
TRACE( _T("Open File failed: %d\n"), fileException.m_cause );
return bRet;
}
CString strRangeQuest;
if (m_TmpFile.GetLength()>0)
{
PostNotifyMessage(MAKEWPARAM(NOTIFY_MSG_LOW_WPARAM_CURRENTSIZE,m_wFileID),m_TmpFile.GetLength());
m_TmpFile.SeekToEnd();
strRangeQuest.Format( _T("%sRange: bytes=%d-\r\n"), szHeaders,m_TmpFile.GetLength());
}
else
strRangeQuest = szHeaders;
DWORD dwCount = 0;
CHttpFile* pFile = NULL;
CString strTmpURL = m_strFileURL;
try
{
DWORD dwFlags = INTERNET_FLAG_TRANSFER_BINARY
|INTERNET_FLAG_DONT_CACHE
|INTERNET_FLAG_PRAGMA_NOCACHE
;
if (m_bForceReload) {
dwFlags |= INTERNET_FLAG_RELOAD;
}
//Here Find URLFile Redirect.
// OpenRedirectHttpURL(strTmpURL,cSession);
pFile = (CHttpFile*) cSession.OpenURL(strTmpURL, 1, dwFlags,strRangeQuest, -1);
}
catch (CInternetException* e)
{
TCHAR szCause[MAX_PATH] = {0};
e->GetErrorMessage(szCause, MAX_PATH);
e->Delete();
delete pFile;
pFile = NULL;
return bRet;
}
COleDateTime startTime = COleDateTime::GetCurrentTime();
DWORD dwHttpFileSize = 0;
if (pFile)
{
BYTE buffer[BUFFER_SIZE+1] = {0};
try {
UINT nRead = 0;
pFile->QueryInfo(HTTP_QUERY_CONTENT_LENGTH | HTTP_QUERY_FLAG_NUMBER,dwHttpFileSize);
PostNotifyMessage(MAKEWPARAM(NOTIFY_MSG_LOW_WPARAM_FULLSIZE,m_wFileID),dwHttpFileSize);
TRACE( _T("Totoal Length is %d\n"), dwHttpFileSize );
dwCount = 0;
do
{
nRead = pFile->Read(buffer, BUFFER_SIZE);
if (nRead > 0)
{
buffer[nRead] = 0;
m_TmpFile.Write(buffer,nRead);
COleDateTimeSpan elapsed = COleDateTime::GetCurrentTime() - startTime;
double dSecs = elapsed.GetTotalSeconds();
PostNotifyMessage(MAKEWPARAM(NOTIFY_MSG_LOW_WPARAM_DOWNSIZE,m_wFileID),dwCount);
if (dSecs > 0.0)
{
dwCount += nRead;
m_transferRate = (float) ( dwCount / 1024.0 / dSecs );
TRACE("Read %d bytes (%0.1f Kb/s)\n", dwCount, m_transferRate );
}
else
{
TRACE("Read %d bytes\n", dwCount);
m_transferRate = (float) ( dwCount / 1024.0 );
}
PostNotifyMessage(MAKEWPARAM(NOTIFY_MSG_LOW_WPARAM_DOWNSPEED,m_wFileID),(LPARAM)m_transferRate);
}
}
while (nRead > 0);
bRet = TRUE;
}
catch (CFileException *e)
{
TCHAR szCause[MAX_PATH] = {0};
e->GetErrorMessage(szCause, MAX_PATH);
TRACE("ErrorMsg : %s\n", szCause);
e->Delete();
delete pFile;
m_TmpFile.Close();
return FALSE;
}
pFile->QueryInfoStatusCode(m_infoStatusCode);
pFile->QueryInfo(HTTP_QUERY_RAW_HEADERS ,m_rawHeaders);
pFile->Close();
m_TmpFile.Close();
delete pFile;
}
return bRet;
}
BOOL CDownloadFile::OpenRedirectHttpURL(CString &strOldLocation,CInternetSession &cSession)
{
BOOL bRet = FALSE;
CHttpFile *pFile = NULL;
CHttpConnection* pServer = NULL;
CString strServerName,strObject;
INTERNET_PORT nPort = 0;
DWORD dwServiceType = 0;
if (!AfxParseURL(strOldLocation, dwServiceType, strServerName, strObject, nPort) ||
dwServiceType != INTERNET_SERVICE_HTTP)
{
TRACE( _T("Not A Http Quest!\n") );
return bRet;
}
pServer = cSession.GetHttpConnection(strServerName, nPort);
pFile = pServer->OpenRequest(CHttpConnection::HTTP_VERB_GET,
strObject, NULL, 1, NULL, NULL,
INTERNET_FLAG_EXISTING_CONNECT | INTERNET_FLAG_NO_AUTO_REDIRECT);
pFile->AddRequestHeaders(szHeaders);
pFile->SendRequest();
DWORD dwRet;
pFile->QueryInfoStatusCode(dwRet);
// if access was denied, prompt the user for the password
if (dwRet == HTTP_STATUS_DENIED)
{
DWORD dwPrompt;
dwPrompt = pFile->ErrorDlg(NULL, ERROR_INTERNET_INCORRECT_PASSWORD,
FLAGS_ERROR_UI_FLAGS_GENERATE_DATA | FLAGS_ERROR_UI_FLAGS_CHANGE_OPTIONS, NULL);
// if the user cancelled the dialog, bail out
if (dwPrompt != ERROR_INTERNET_FORCE_RETRY)
{
TRACE( _T("Access denied: Invalid password\n") );
// close up the redirected site
pFile->Close();
delete pFile;
pServer->Close();
delete pServer;
return bRet;
}
pFile->SendRequest();
pFile->QueryInfoStatusCode(dwRet);
}
// were we redirected?
// these response status codes come from WININET.H
if (dwRet == HTTP_STATUS_MOVED ||
dwRet == HTTP_STATUS_REDIRECT ||
dwRet == HTTP_STATUS_REDIRECT_METHOD)
{
CString strNewLocation;
pFile->QueryInfo(HTTP_QUERY_RAW_HEADERS_CRLF, strNewLocation);
int nPlace = strNewLocation.Find(_T("Location: "));
if (nPlace == -1)
{
TRACE( _T("Error: Site redirects with no new location\n") );
// close up the redirected site
pFile->Close();
delete pFile;
pServer->Close();
delete pServer;
return bRet;
}
strNewLocation = strNewLocation.Mid(nPlace + 10);
nPlace = strNewLocation.Find('\n');
if (nPlace > 0)
strNewLocation = strNewLocation.Left(nPlace);
strOldLocation = strNewLocation;
}
if ( dwRet == HTTP_STATUS_OK )
{
bRet = TRUE;
}
// close up the redirected site
pFile->Close();
delete pFile;
pServer->Close();
delete pServer;
return bRet;
}
BOOL CDownloadFile::GetFtpFile(CInternetSession &cSession)
{
BOOL bRet = FALSE;
CFile m_TmpFile;
CFileException fileException;
if ( !m_TmpFile.Open (m_strTmpFileName,
CFile::modeCreate | CFile::modeNoTruncate | CFile::modeReadWrite
| CFile::shareDenyWrite | CFile::typeBinary,
&fileException ) )
{
TRACE( _T("Open File failed: %d\n"), fileException.m_cause );
return bRet;
}
DWORD dwCount = 0;
CFtpConnection *pFtpConn = NULL;
CInternetFile *pFile = NULL;
try
{
CString strServerName,strObject,strUserName,strPassword;
INTERNET_PORT nPort = 0;
DWORD dwServiceType = 0;
CString strRestPointCommand;
if (!AfxParseURLEx(m_strFileURL, dwServiceType, strServerName, strObject, nPort,
strUserName, strPassword) ||
dwServiceType != INTERNET_SERVICE_FTP)
{
TRACE( _T("Not A Ftp Quest!\n") );
}
// CFtpConnection ERROR_INTERNET_NO_DIRECT_ACCESS CInternetSession
if (strUserName.IsEmpty())
pFtpConn = cSession.GetFtpConnection(strServerName,NULL,NULL,nPort,m_bForceReload);
else
pFtpConn = cSession.GetFtpConnection(strServerName,strUserName,strPassword,nPort,m_bForceReload);
if (m_TmpFile.GetLength())
{
PostNotifyMessage(MAKEWPARAM(NOTIFY_MSG_LOW_WPARAM_CURRENTSIZE,m_wFileID),m_TmpFile.GetLength());
m_TmpFile.SeekToEnd();
strRestPointCommand.Format( _T("REST %d"), m_TmpFile.GetLength());
//strRestPointCommand.Format( _T("ls") );
if ( !FtpCommand((*pFtpConn), FALSE, FTP_TRANSFER_TYPE_ASCII,
strRestPointCommand, 0, 0) )
{
TRACE( _T("FtpCommand failed, error: %d\n"), GetLastError());
m_TmpFile.SeekToBegin();
}
}
if (pFtpConn)
{
pFile = pFtpConn->OpenFile(strObject);
}
}
catch (CInternetException* e)
{
TCHAR szCause[MAX_PATH] = {0};
e->GetErrorMessage(szCause, MAX_PATH);
e->Delete();
delete pFile;
delete pFtpConn;
return bRet;
}
COleDateTime startTime = COleDateTime::GetCurrentTime();
DWORD dwFtpFileSize = 0;
if (pFile)
{
BYTE buffer[BUFFER_SIZE+1] = {0};
try {
UINT nRead = 0;
dwFtpFileSize = FtpGetFileSize( (*pFile),0);
PostNotifyMessage(MAKEWPARAM(NOTIFY_MSG_LOW_WPARAM_FULLSIZE,m_wFileID),dwFtpFileSize);
TRACE( _T("Totoal Length is %d\n"), dwFtpFileSize );
dwCount = 0;
do
{
nRead = pFile->Read(buffer, BUFFER_SIZE);
if (nRead > 0)
{
buffer[nRead] = 0;
m_TmpFile.Write(buffer,nRead);
COleDateTimeSpan elapsed = COleDateTime::GetCurrentTime() - startTime;
double dSecs = elapsed.GetTotalSeconds();
PostNotifyMessage(MAKEWPARAM(NOTIFY_MSG_LOW_WPARAM_DOWNSIZE,m_wFileID),dwCount);
if (dSecs > 0.0)
{
dwCount += nRead;
m_transferRate = (float)(dwCount / 1024.0 / dSecs);
TRACE("Read %d bytes (%0.1f Kb/s)\n", dwCount, m_transferRate );
}
else
{
TRACE("Read %d bytes\n", dwCount);
m_transferRate = (float)(dwCount / 1024.0);
}
PostNotifyMessage(MAKEWPARAM(NOTIFY_MSG_LOW_WPARAM_DOWNSPEED,m_wFileID),(LPARAM)m_transferRate);
}
}
while (nRead > 0);
bRet = TRUE;
}
catch (CFileException *e)
{
TCHAR szCause[MAX_PATH] = {0};
e->GetErrorMessage(szCause, MAX_PATH);
TRACE("ErrorMsg : %s\n", szCause);
e->Delete();
delete pFile;
pFtpConn->Close();
delete pFtpConn;
m_TmpFile.Close();
return FALSE;
}
pFile->Close();
delete pFile;
m_TmpFile.Close();
pFtpConn->Close();
delete pFtpConn;
}
return bRet;
}
BOOL CDownloadFile::GetUNCFile()
{
BOOL bRet = FALSE;
CFile m_TmpFile,m_SrcFile;
CFileException fileException;
CString strOldLocation = m_strFileURL;
if ( !m_TmpFile.Open (m_strTmpFileName,
CFile::modeCreate | CFile::modeNoTruncate | CFile::modeReadWrite
| CFile::shareDenyWrite | CFile::typeBinary,
&fileException ) )
{
TRACE( _T("Open File failed: %d\n"), fileException.m_cause );
return bRet;
}
strOldLocation.TrimLeft();
strOldLocation.TrimRight();
if( StrCmpNI(strOldLocation, _T("file:/"),6) == 0 )
{
strOldLocation = strOldLocation.Mid(8);
strOldLocation.Replace( _T('/'), _T('\\'));
}
if ( !m_SrcFile.Open ( strOldLocation,
CFile::modeRead | CFile::shareDenyWrite | CFile::typeBinary,
&fileException ) )
{
TRACE( _T("Open File failed: %d\n"), fileException.m_cause );
return bRet;
}
COleDateTime startTime = COleDateTime::GetCurrentTime();
DWORD dwCount = 0;
try {
if (m_TmpFile.GetLength())
{
PostNotifyMessage(MAKEWPARAM(NOTIFY_MSG_LOW_WPARAM_CURRENTSIZE,m_wFileID),m_TmpFile.GetLength());
m_TmpFile.SeekToEnd();
m_SrcFile.Seek(m_TmpFile.GetLength(), CFile::begin);
}
BYTE buffer[BUFFER_SIZE+1] = {0};
UINT nRead = 0;
PostNotifyMessage(MAKEWPARAM(NOTIFY_MSG_LOW_WPARAM_FULLSIZE,m_wFileID),m_SrcFile.GetLength());
TRACE( _T("Totoal Length is %d,left is %d\n"), m_SrcFile.GetLength() ,m_SrcFile.GetLength() - m_TmpFile.GetLength());
dwCount = 0;
do
{
nRead = m_SrcFile.Read(buffer, BUFFER_SIZE);
if (nRead > 0)
{
buffer[nRead] = 0;
m_TmpFile.Write(buffer,nRead);
COleDateTimeSpan elapsed = COleDateTime::GetCurrentTime() - startTime;
double dSecs = elapsed.GetTotalSeconds();
PostNotifyMessage(MAKEWPARAM(NOTIFY_MSG_LOW_WPARAM_DOWNSIZE,m_wFileID),dwCount);
if (dSecs > 0.0)
{
dwCount += nRead;
m_transferRate = (float)(dwCount / 1024.0 / dSecs);
TRACE("Read %d bytes (%0.1f Kb/s)\n", dwCount, m_transferRate );
}
else
{
TRACE("Read %d bytes\n", dwCount);
m_transferRate = (float)(dwCount / 1024.0);
}
PostNotifyMessage(MAKEWPARAM(NOTIFY_MSG_LOW_WPARAM_DOWNSPEED,m_wFileID),(LPARAM)m_transferRate);
}
}
while (nRead > 0);
bRet = TRUE;
}
catch (CFileException *e)
{
TCHAR szCause[MAX_PATH] = {0};
e->GetErrorMessage(szCause, MAX_PATH);
TRACE("ErrorMsg : %s\n", szCause);
e->Delete();
m_TmpFile.Close();
return FALSE;
}
m_TmpFile.Close();
return bRet;
}
void CDownloadFile::RegisterNotifyWindow(DWORD dwThreadID,HWND hWnd, DWORD dwMsg)
{
m_dwThreadID = dwThreadID;
m_hNotify = hWnd;
m_dwMsgID = dwMsg;
}
void CDownloadFile::PostNotifyMessage(WPARAM wParam, LPARAM lParam)
{
if (m_hNotify)
{
::PostMessage(m_hNotify, m_dwMsgID, wParam, lParam);
}
if ( m_dwThreadID )
{
::PostThreadMessage(m_dwThreadID,m_dwMsgID, wParam, lParam);
}
}
WORD CDownloadFile::GenFileID()
{
srand(GetTickCount());
return rand() & 0xFFFF;
}
UINT ThreadDownSingleFile( LPVOID pParam )
{
CDownloadFile m_DownFile;
UINT uRet = 0;
if (lpDownParam)
{
m_DownFile.m_wFileID = m_DownFile.GenFileID();
//这里注册通知窗口和消息
//m_DownFile.RegisterNotifyWindow
if ( m_DownFile.DownLoadFile(m_Msg.lpFileSrc, m_Msg.lpFileDst) )
{
uRet = 1;
}
}
return uRet;
}