IHttpCacheKey::GetIsEqual Method

 

Returns a value that indicates whether two IHttpCacheKey pointers are equivalent.

Syntax

virtual bool GetIsEqual(  
   IHttpCacheKey* pCacheCompareKey  
) const = 0;  

Parameters

pCacheCompareKey
A non-NULL IHttpCacheKey pointer to compare with the current IHttpCacheKey.

Return Value

true if the current IHttpCacheKey is equivalent to the pCacheCompareKey parameter; otherwise, false.

Remarks

CGlobalModule derived classes that register for GL_CACHE_OPERATION events receive an ICacheProvider pointer as a parameter on the CGlobalModule::OnGlobalCacheOperationvirtual method. You can retrieve an IHttpCacheKey pointer by calling the ICacheProvider::GetCacheKey method on the ICacheProvider pointer. You can then compare two IHttpCacheKey pointers by calling the GetIsEqual method.

The pCacheCompareKey parameter must not be NULL; otherwise, GetIsEqual will throw an access violation. In addition, pCacheCompareKey must be the same extended interface type as the current IHttpCacheKey pointer. For example, if the current IHttpCacheKey pointer implements the IFileKey interface, the pCacheCompareKey parameter must implement IFileKey, as well.

The GetIsEqual return value depends on both interface and implementation. You should use the following information as a guideline, but it may not be correct in all scenarios:

• Classes that implement IFileKey return true only if the IFileKey::GetPath method returns equivalent values on both the current IHttpCacheKey and pCacheCompareKey pointers.

• Classes that implement the IHttpTokenKey interface return true only if the IHttpTokenKey::GetUserName and IHttpTokenKey::GetLogonMethod methods return equivalent values on both the current IHttpCacheKey and pCacheCompareKey pointers.

• Classes that implement the IUriKey interface return true only if the IUriKey::GetSiteId and IUriKey::GetUrl methods return equivalent values on both the current IHttpCacheKey and pCacheCompareKey pointers.

Example

The following code example demonstrates how to create a global module that listens for GL_CACHE_OPERATION and GL_CACHE_CLEANUP events and then writes the IHttpCacheKey and the GetIsEqual information to the Event Viewer. It also demonstrates that if the same IHttpCacheKey pointer is compared against itself, the GetIsEqual method will return true.

Warning

IIS 7 generates a large number of events in the Event Viewer. To avoid a log overflow error in a production environment, you should generally avoid writing cache information to the event log. For demonstration purposes, this code example writes an entry to the Event Viewer in debug mode only.

#pragma warning( disable : 4290 )
#pragma warning( disable : 4530 )

#define _WINSOCKAPI_
#include <windows.h>
#include <sal.h>
#include <tchar.h>
#include <initguid.h>
#include <httptrace.h>
#include <httpserv.h>
#include <httpcach.h>

#include <string>
using namespace std;

// The CConvert class mirrors the Convert class that is 
// defined in the .NET Framework. It converts primitives 
// and other data types to wstring types.
class CConvert
{
public:
    // The ToString method converts a BOOL to a wstring.
    // b: the BOOL value to convert to a wstring.
    // return: L"true" for true; otherwise, L"false" for false.
    static wstring ToString(BOOL b)
    {
        return (b) ? L"true" : L"false";
    }

    // The ToByteString converts a double-byte 
    // character string to a single-byte string.
    // str: the double-byte string to convert.
    // return: a single-byte string copied from str.
    static string ToByteString(const wstring& str)
    {
        // Get the length of the 
        // double-byte string.
        size_t length = str.length();

        // Create a temporary char pointer.
        char* byteChar = new char[length+1];
        byteChar[0] = '\0';
        // Copy the double-byte character string
        // into the single-byte string.        
        size_t charsReturned = 0;
        wcstombs_s(&charsReturned, byteChar, 
                   length+1, str.c_str(), length+1);
        // Create a string to return.
        string retString = byteChar;
        // Delete the temporary string and
        // set that string to NULL.
        delete[] byteChar;
        byteChar = NULL;

        // Return the single-byte string.
        return retString;
    }
};

// The CEventException class is 
// an exception that can be thrown 
// when writing an event fails.
class CEventException
{
public:
    // Creates the CEventException class.
    // str: the wstring that could 
    // not be written to a log.
    CEventException(const wstring& str)
        : m_string(str)
    {
        
    }

    // Creates the destructor for 
    // the CEventException class.
    virtual ~CEventException()
    {

    }

private:
    // Specify the wstring that could
    // not be written to an event viewer.
    wstring m_string;
};

// The CEventWriter class writes XML 
// documents and strings to the event log.
class CEventWriter
{
public:
    // Creates the CEventWriter class.
    // name: the name of the 
    // event log to open.
    CEventWriter(const wstring& name)
    {                
        #ifdef UNICODE
        m_eventLog = RegisterEventSource(NULL, name.c_str());
        #else
        string multiName = CConvert::ToByteString(name);
        m_eventLog = RegisterEventSource(NULL, multiName.c_str());
        #endif        
    }

    // Creates the destructor for the 
    // CEventWriter class. This destructor
    // closes the HANDLE to the event 
    // log if that HANDLE is open.
    virtual ~CEventWriter()
    {
        // If the HANDLE to the event 
        // log is open, close it.
        if (NULL != m_eventLog)
        {
            // Deregister the event log HANDLE.
            DeregisterEventSource(m_eventLog);
            // Set the HANDLE to NULL.
            m_eventLog = NULL;
        }
    }

    // The ReportInfo method writes 
    // a wstring to the event log.
    // info: the wstring to write.
    // return: true if the event log is written.
    BOOL ReportInfo(const wstring& info)
    {
        return ReportEvent(EVENTLOG_INFORMATION_TYPE, info);
    }
protected:
    // The ReportEvent method accepts an event type
    // and a wstring, and attempts to write that 
    // event to the event log.
    // type: the type of the event.
    // data: the wstring to write to the event log.
    // return: true if the event log is written;
    // otherwise, false.
    BOOL ReportEvent(WORD type, const wstring& data)
    {
        // If the m_eventLog HANDLE 
        // is NULL, return false.
        if (NULL == m_eventLog)
        {
            return FALSE;
        }

        #ifndef _DEBUG
        // If the current build is not debug,
        // return so the event log is not written.
        return TRUE;
        #endif

        #ifdef UNICODE
        // The unicode version of the ReportEvent
        // method requires double-byte strings.
        PCWSTR arr[1];
        arr[0] = data.c_str();
        return ::ReportEvent(m_eventLog,
                             type,
                             0, 0, NULL, 1, 
                             0, arr, (void*)arr);
        #else
        // The non-unicode version of the ReportEvent
        // method requires single-byte strings.
        string multiByte = 
            CConvert::ToByteString(data);
        LPCSTR arr[1];
        arr[0] = multiByte.c_str();
        return ::ReportEvent(m_eventLog,
                             type,
                             0, 0, NULL, 1,
                             0, arr, (void*)arr);
        #endif
    }
private:
    // Specify the HANDLE to the 
    // event log for writing.
    HANDLE m_eventLog;
};

// The CGlobalCacheModule class creates the CGlobalModule 
// class and registers for GL_CACHE_OPERATION and 
// GL_CACHE_CLEANUP events.
class CGlobalCacheModule : public CGlobalModule
{
public:
    // Creates the destructor for the 
    // CGlobalCacheModule class.
    virtual ~CGlobalCacheModule()
    {

    }

    // The RegisterGlobalModule method creates and registers 
    // a new CGlobalCacheModule for GL_CACHE_OPERATION and 
    // GL_CACHE_CLEANUP events.
    // dwServerVersion: the current server version.
    // pModuleInfo: the current IHttpModuleRegistrationInfo pointer.
    // pGlobalInfo: the current IHttpServer pointer.
    // return: ERROR_NOT_ENOUGH_MEMORY if the heap is out of 
    // memory; otherwise, the value from the call to the 
    // SetGlobalNotifications method on the pModuleInfo pointer.
    static HRESULT RegisterGlobalModule
    (
        DWORD dwServerVersion,
        IHttpModuleRegistrationInfo* pModuleInfo,
        IHttpServer* pGlobalInfo
    )
    {        
        // The pGlobalInfo parmeter must be non-NULL because
        // the constructor for the CGlobalCacheModule class
        // requires a non-NULL pointer to a valid IHttpServer 
        // pointer.
        if (NULL == pGlobalInfo)
        {
            return E_INVALIDARG;
        }

        // Create a new CGlobalCacheModule pointer.
        CGlobalCacheModule* traceModule = 
            new CGlobalCacheModule();

        // Return an out-of-memory error if the traceModule 
        // is NULL after the call to the new operator.
        if (NULL == traceModule)
        {            
            return HRESULT_FROM_WIN32(ERROR_NOT_ENOUGH_MEMORY);
        }        

        // Attempt to set global notification for both 
        // GL_CACHE_OPERATION and GL_CACHE_CLEANUP events 
        // by using the traceModule as a listener.
        HRESULT hr = pModuleInfo->SetGlobalNotifications
            (traceModule, GL_CACHE_OPERATION | GL_CACHE_CLEANUP);

        // If the SetGlobalNotifications method 
        // fails, return the HRESULT.
        if (FAILED(hr))
        {
            return hr;
        }

        // Set the priority to PRIORITY_ALIAS_FIRST, 
        // which will populate the data as much as possible.
        hr = pModuleInfo->SetPriorityForGlobalNotification(
            GL_CACHE_OPERATION, PRIORITY_ALIAS_FIRST);

        // Return the HRESULT from the call to 
        // the SetGlobalNotifications method.
        return hr;
    }
    // The OnGlobalCacheOperation method is called 
    // when GL_CACHE_OPERATION operations occur.
    // pProvider: the current ICacheProvider pointer.
    // return: GL_NOTIFICATION_CONTINUE if the event
    // log is written; otherwise, GL_NOTIFICATION_HANDLED.
    virtual GLOBAL_NOTIFICATION_STATUS OnGlobalCacheOperation
    (
        IN ICacheProvider* pProvider
    )
    {
        // The OnGlobalCacheOperation must return if the 
        // pProvider parameter is NULL because this pointer 
        // is needed for data to write to the event log.
        if (NULL == pProvider)
        {
            return GL_NOTIFICATION_CONTINUE;
        }

        try
        {
            // Get the IHttpCacheKey pointer 
            // from the ICacheProvider pointer.
            IHttpCacheKey* cacheKey = 
                pProvider->GetCacheKey();

            // Write the IHttpCacheKey pointer
            // information to the event log.
            Write(cacheKey);            
        }
        // A CEventException is thrown 
        // if any Write method cannot 
        // write to the event log.
        catch (CEventException)
        {
            return GL_NOTIFICATION_HANDLED;
        }

        // Return GL_NOTIFICATION_CONTINUE so that 
        // other listeners will receive the event.
        return GL_NOTIFICATION_CONTINUE;
    }

    // The OnGlobalCacheCleanup method is called 
    // when GL_CACHE_CLEANUP events occur.
    // return: GL_NOTIFICATION_CONTINUE.
    virtual GLOBAL_NOTIFICATION_STATUS OnGlobalCacheCleanup(VOID)
    {
        // Return GL_NOTIFICATION_CONTINUE so that 
        // other listeners will receive this event.
        return GL_NOTIFICATION_CONTINUE;
    }

    // PRE: none.
    // POST: the Terminate method calls delete on 
    // this, which releases the memory for the current 
    // CGlobalCacheModule pointer on the heap.
    virtual VOID Terminate(VOID)
    {
        delete this;
    }
protected:
    // Creates the constructor for 
    // the CGlobalCacheModule class.
    // The constructor initializes the 
    // private m_eventWriter to write 
    // to the IISADMIN event log.
    CGlobalCacheModule() : m_eventWriter(L"IISADMIN")
    {

    }

    // The ReportInfo method writes the 
    // formatted name and value of a method 
    // call to the event log.
    // name: the name of the method or property.
    // value: the value of the 
    // method or the property.
    // throws: a CEventException exception.
    void ReportInfo
    (
        const wstring& name,
        const wstring& value
    ) throw (CEventException)
    {
        // Create a formatted string to
        // write to the event log.
        wstring infoString =
            name + wstring(L":  ") + value;
        // Attempt to write the formatted 
        // string to the event log. If the 
        // ReportInfo method call fails,
        // throw a CEventException exception.
        if (!m_eventWriter.ReportInfo(infoString))
        {
            throw CEventException(infoString);
        }        
    }
    // The Write method writes IHttpCacheKey 
    // pointer information to the event log.
    // cacheKey: the IHttpCacheKey to write.
    // throws: a CEventException exception.
    void Write
    (
        IHttpCacheKey* cacheKey        
    ) throw (CEventException)
    {
        // If the cacheKey parameter is NULL, 
        // throw a CEventException exception.
        if (NULL == cacheKey)
        {            
            CEventException ce
                (L"NULL IHttpCacheKey pointer");
            throw ce;            
        }

        // Get IsEqual information from the 
        // IHttpCacheKey pointer by comparing 
        // the current pointer.
        BOOL isEqualBOOL = 
            cacheKey->GetIsEqual(cacheKey);

        // Convert the Boolean to a wstring.
        wstring isEqual = CConvert::ToString(isEqualBOOL);

        // Write the equivalence information
        // to the event log.
        ReportInfo(L"IHttpCacheKey::GetIsEqual", 
                   isEqual);
    }
private:
    // Specify the event writer.
    CEventWriter m_eventWriter;
};

// The RegisterModule method is the 
// main entry point for the DLL.
// dwServerVersion: the current server version.
// pModuleInfo: the current 
// IHttpModuleRegistrationInfo pointer.
// pGlobalInfo: the current IHttpServer pointer.
// return: the value returned by calling the
// CGlobalCacheModule::RegisterGlobalModule
// method.
HRESULT
__stdcall
RegisterModule(
    DWORD dwServerVersion,
    IHttpModuleRegistrationInfo* pModuleInfo,
    IHttpServer* pGlobalInfo
)
{        
    // Call the static method for initialization.
    return CGlobalCacheModule::RegisterGlobalModule            
        (dwServerVersion, 
         pModuleInfo, 
         pGlobalInfo);             
}

The above code writes a new event to the Event Viewer, where the Data box contains a string similar to the following.

IHttpCacheKey::GetIsEqual: true  

Your module must export the RegisterModule function. You can export this function by creating a module definition (.def) file for your project, or you can compile the module by using the /EXPORT:RegisterModule switch. For more information, see Walkthrough: Creating a Request-Level HTTP Module By Using Native Code.

You can optionally compile the code by using the __stdcall (/Gz) calling convention instead of explicitly declaring the calling convention for each function.

Requirements

Type	Description
Client	- IIS 7.0 on Windows Vista - IIS 7.5 on Windows 7 - IIS 8.0 on Windows 8 - IIS 10.0 on Windows 10
Server	- IIS 7.0 on Windows Server 2008 - IIS 7.5 on Windows Server 2008 R2 - IIS 8.0 on Windows Server 2012 - IIS 8.5 on Windows Server 2012 R2 - IIS 10.0 on Windows Server 2016 Technical Preview
Product	- IIS 7.0, IIS 7.5, IIS 8.0, IIS 8.5, IIS 10.0 - IIS Express 7.5, IIS Express 8.0, IIS Express 10.0
Header	Httpserv.h

See Also

IHttpCacheKey Interface