counter.cpp

《Visual C++.NET MFC类库应用详解》程序实例

/////////////////////////////////////////////////////////////////////////////
// counter.cpp : Defines the initialization routines for the DLL.
//
// Written by Jeff Miller
// of Microsoft Product Support Services, Languages Developer Support
//
// This is a part of the Microsoft Foundation Classes C++ library.
// Copyright (c) Microsoft Corporation.  All rights reserved.
//
// This source code is only intended as a supplement to the
// Microsoft Foundation Classes Reference and related
// electronic documentation provided with the library.
// See these sources for detailed information regarding the
// Microsoft Foundation Classes product.

// This ISAPI DLL can be called in three ways:
// <IMG SRC="/scripts/counter.dll?clock">
// will return an x-bitmap image containing the current system time
// <IMG SRC="/scripts/counter.dll/mydir/mypage.htm">
// will return an x-bitmap image containing the accumulated
// count for the identifier /mydir/mypage.htm
// <IMG SRC="/scripts/counter.dll">
// will return an x-bitmap image containing the accumulated
// count for the page which called the DLL.

#include <afx.h>
#include <afxdb.h>
#include <afxisapi.h>
#include "resource.h"
#include "counter.h"

#include "charset.h"

// This program sends back xbitmap images rather than HTML.
static const TCHAR szContentType[] = _T("Content-Type: image/x-xbitmap\r\n");

// The following defines the location and filename for the log file.
// This should be placed in a location that can be read and written to.
static const TCHAR szLogFile[] = _T("C:\\counter.log");


// The following two headers will tell the client never to cache
// this information, as it is dynamic.
static const TCHAR szExpires[] = _T("Expires: Thu, 01 Jan 1995 01:00:00 GMT\r\n");
static const TCHAR szNoCache[] = _T("Pragma: no-cache\r\n");

///////////////////////////////////////////////////////////////////////
// command-parsing map

BEGIN_PARSE_MAP(CCounterExtension, CHttpServer)
	ON_PARSE_COMMAND(Clock, CCounterExtension, ITS_EMPTY)
	ON_PARSE_COMMAND(Default, CCounterExtension, ITS_EMPTY)
	DEFAULT_PARSE_COMMAND(Default, CCounterExtension)
END_PARSE_MAP(CCounterExtension)


///////////////////////////////////////////////////////////////////////
// The one and only CCounterExtension object

CCounterExtension theExtension;

///////////////////////////////////////////////////////////////////////
// CCounterExtension implementation

CCounterExtension::CCounterExtension()
{
}

CCounterExtension::~CCounterExtension()
{
}

BOOL CCounterExtension::GetExtensionVersion(HSE_VERSION_INFO* pVer)
{
	// Call default implementation for initialization
	CHttpServer::GetExtensionVersion(pVer);

	// Load description string
	TCHAR sz[HSE_MAX_EXT_DLL_NAME_LEN+1];
	ISAPIVERIFY(::LoadString(AfxGetResourceHandle(),
			IDS_SERVER, sz, HSE_MAX_EXT_DLL_NAME_LEN));
	_tcscpy(pVer->lpszExtensionDesc, sz);
	return TRUE;
}

///////////////////////////////////////////////////////////////////////
// CCounterExtension command handlers

void CCounterExtension::Default(CHttpServerContext* pCtxt)
{
	// We don't call StartContent() or WriteTitle() here due to the
	// fact that those will send back tags appropriate only to
	// HTML pages.  We will be sending back an image.

	// Don't allow these pages to be cached
	AddHeader(pCtxt, szExpires);
	AddHeader(pCtxt, szNoCache);

	TCHAR pstrBuffer[1024];

	// Check to see if a path was given after the DLL's name,
	// such as <IMG SRC="/scripts/counter.dll/mydir/mypage.htm">
	// If so, use the given path.  Otherwise, use the URL of
	// the page which called this DLL.

	if (_tcsclen(pCtxt->m_pECB->lpszPathInfo) != 0)
	{
		_tcscpy(pstrBuffer, pCtxt->m_pECB->lpszPathInfo);
	}
	else
	{
		// HTTP_REFERER contains the full URL of the page which
		// called this DLL.
		DWORD dwSize = 1024;
		pCtxt->GetServerVariable(_T("HTTP_REFERER"), pstrBuffer, &dwSize);
	}

	// Call member function to see how many times the requested
	// page has been accessed and update that count.
	// GetPageCount will return -1 if there was a problem reading the
	// counter log file.

	CString szPath(pstrBuffer);
	int nCount = GetPageCount(szPath);
	if (nCount != -1)
	{
		// call member function to output an xbitmap image
		// containing the digits
		CString szCount;
		szCount.Format(_T("%d"), nCount);
		OutputXBM(pCtxt, szCount);
	}

	// EndContent() is only appropriate for HTML files, so we
	// don't call it here.
}

void CCounterExtension::Clock(CHttpServerContext* pCtxt)
{
	// Clock
	// Called when DLL is accessed using the format
	// <IMG SRC="/scripts/counter.dll?Clock">

	// We don't call StartContent() or WriteTitle() here due to the
	// fact that those will send back tags appropriate only to
	// HTML pages.  We will be sending back an image.

	// Don't allow these pages to be cached
	AddHeader(pCtxt, szExpires);
	AddHeader(pCtxt, szNoCache);

	// Get the current system time, and put it into a form
	// which our function will accept.
	CTime time = CTime::GetCurrentTime();
	CString szTime = time.Format(_T("%H%%%M"));

	// call member function to output an xbitmap image
	// containing the digits
	OutputXBM(pCtxt, szTime);

	// EndContent() is only appropriate for HTML files, so we
	// don't call it here.
}

void CCounterExtension::OutputXBM(CHttpServerContext* pCtxt, CString& szDigits)
{
	// Function to take in a string containing the digits 0..9 and the character
	// ':' and output an xbitmap image of those digits to the stream

	// Start by writing the proper content type to the client
	AddHeader(pCtxt, szContentType);

	// NOTE: this code as is will only work properly with image data
	// that has a width = 8
	int nFinalWidth = char_width * szDigits.GetLength();
	int nFinalHeight = char_height;

	// write out the XBM header.  We cast to long int because there is
	// no CHttpServerContext << operator overload that accepts an
	// integer.
	*pCtxt << _T("#define counter_width ") << (long int)nFinalWidth << _T("\r\n");
	*pCtxt << _T("#define counter_height ") << (long int)nFinalHeight << _T("\r\n");
	*pCtxt << _T("static unsigned char counter_bits[] = {\r\n");

	// Now for each horizontal line of output, get the bitmap for each
	// character for that line and output it.
	for (int nLine=0; nLine<nFinalHeight; nLine++)
	{
		for (int nChar=0; nChar<szDigits.GetLength(); nChar++)
		{
			int nDigitOffset;
			if (szDigits[nChar] >= __TEXT('0') && szDigits[nChar] <= __TEXT('9'))
				nDigitOffset = szDigits[nChar] - __TEXT('0');
			else
				// colon is in index 10 in the bitmap array
				nDigitOffset = 10;

			CString szHex;
			szHex.Format(_T("0x%02X, "), char_bits[nDigitOffset][nLine]);
			*pCtxt << szHex;
		}
	}

	*pCtxt << _T("};\r\n");
}

int CCounterExtension::GetPageCount(CString& szPage)
{
	// Given a unique page identifier (szPage), check our "database"
	// to see how many times this page has been accessed, then
	// return that count.  If this function fails, -1 will be returned.

	CFile file;
	CFileException e;
	int nOpenAttempts = 0;

	// make sure only one thread operates on the log file at a time
	while (TRUE)
	{
		if (file.Open(szLogFile,
			CFile::modeRead | CFile::shareExclusive
			| CFile::modeCreate | CFile::modeNoTruncate, &e))
		{
			// we opened the file, so continue onwards
			break;
		}
		else
		{
			// we couldn't open the file...figure out why
			if (e.m_cause == CFileException::sharingViolation)
			{
				// sharing violation
				// another thread must have the file open, so wait and retry
				::Sleep(100);

				// increase the attempt counter
				nOpenAttempts++;
				if (nOpenAttempts == 30)
				{
					// too many retries. something's amiss
					CString szErrText;
					szErrText.LoadString(IDS_RETRYERR);
					TRACE0(szErrText);

					// return error code
					return -1;
				}
			}
			else
			{
				// not a sharing violation error
				// so it's probably serious
				TCHAR szCause[255];
				e.GetErrorMessage(szCause, 255);
				CString szErrText;
				szErrText.LoadString(IDS_OPENERR);
				TRACE1(szErrText, szCause);

				// return error code
				return -1;
			}
		}
	}

	// we've now successfully opened the log file so let's read it!

	CArchive archive(&file, CArchive::load);

	// Serialize in the data from the file
	try
	{
		m_Paths.Serialize(archive);
	}
	catch (CArchiveException* e)
	{
		// if we get endOfFile, it probably means that the counter
		// log file doesn't exist yet, so it's not a fatal error

		if (e->m_cause != CArchiveException::endOfFile)
		{
			TCHAR szCause[255];
			e->GetErrorMessage(szCause, 255);
			CString szErrText;
			szErrText.LoadString(IDS_SERIALIZEERR);
			TRACE1(szErrText, szCause);

			m_Paths.RemoveAll();

			archive.Close();
			file.Close();
			e->Delete();

			return -1;
		}

		e->Delete();
	}

	archive.Close();
	file.Close();

	// Try to find the page identifier in the log
	int nVal = 0;
	CString szCount;
	if (m_Paths.Lookup(szPage, szCount))
		nVal = atoi(szCount);

	// Increment the count.
	nVal++;

	// Set the new value.
	szCount.Format(_T("%d"), nVal);
	m_Paths.SetAt(szPage, szCount);

	// Write the updated log
	if ( !file.Open(szLogFile,
		CFile::modeWrite | CFile::shareExclusive
		| CFile::modeCreate, &e) )
	{
		TCHAR szCause[255];
		e.GetErrorMessage(szCause, 255);
		CString szErrText;
		szErrText.LoadString(IDS_OPENERR);
		TRACE1(szErrText, szCause);

		// return error code
		return -1;
	}

	CArchive archiveStore(&file, CArchive::store);

	try
	{
		m_Paths.Serialize(archiveStore);
	}
	catch (CArchiveException* e)
	{
		TCHAR szCause[255];
		e->GetErrorMessage(szCause, 255);
		CString szErrText;
		szErrText.LoadString(IDS_SERIALIZEERR);
		TRACE1(szErrText, szCause);

		archiveStore.Close();
		file.Close();
		e->Delete();

		// return error code
		return -1;
	}

	archiveStore.Close();
	file.Close();

	// Return the count we received
	return nVal;
}