IHttpContext::GetParentContext Method

Article
05/24/2022

Retrieves a pointer to the parent context for the current context.

Syntax

virtual IHttpContext* GetParentContext(  
   VOID  
) const = 0;

Parameters

This method takes no parameters.

Return Value

A pointer to an IHttpContext interface.

Remarks

The GetParentContext method retrieves a pointer to the IHttpContext interface for the parent context of the current request. For example, if an HTTP module creates a child context by using the CloneContext method, the GetParentContext method can help determine whether the module is processing on the parent context or on the child context.

Note

When the current context does not have a parent context, the GetParentContext method will return NULL.

Example

The following code example demonstrates how to use the GetParentContext method to create an HTTP module that retrieves the parent context for the request. The module compares the parent context with NULL and the current request context to determine whether the parent context is different than the current context. The module then returns a message to the Web client and exits.

#define _WINSOCKAPI_
#include <windows.h>
#include <sal.h>
#include <httpserv.h>

// Create the module class.
class MyHttpModule : public CHttpModule
{
public:
    REQUEST_NOTIFICATION_STATUS
    OnBeginRequest(
        IN IHttpContext * pHttpContext,
        IN IHttpEventProvider * pProvider
    )
    {
        UNREFERENCED_PARAMETER( pProvider );

        // Clear the existing response.
        pHttpContext->GetResponse()->Clear();
        // Set the MIME type to plain text.
        pHttpContext->GetResponse()->SetHeader(
            HttpHeaderContentType,"text/plain",
            (USHORT)strlen("text/plain"),TRUE);

        // Retrieve a pointer to the parent context.
        IHttpContext * pParentContext = pHttpContext->GetParentContext();

        // Compare the parent context and return a message to the client.
        if (pParentContext == NULL) WriteResponseMessage(
            pHttpContext, "The parent context is null.");
        else if (pParentContext == pHttpContext) WriteResponseMessage(
            pHttpContext, "The current context equals the parent context.");
        else WriteResponseMessage(
            pHttpContext, "The parent context differs from the current context.");

        // End additional processing.
        return RQ_NOTIFICATION_FINISH_REQUEST;
    }
private:

    // Create a utility method that inserts a string value into the response.
    HRESULT WriteResponseMessage(
        IHttpContext * pHttpContext,
        PCSTR pszBuffer
    )
    {
        // Create an HRESULT to receive return values from methods.
        HRESULT hr;
        
        // Create a data chunk. (Defined in the Http.h file.)
        HTTP_DATA_CHUNK dataChunk;
        // Set the chunk to a chunk in memory.
        dataChunk.DataChunkType = HttpDataChunkFromMemory;
        // Buffer for bytes written of data chunk.
        DWORD cbSent;

        // Set the chunk to the buffer.
        dataChunk.FromMemory.pBuffer =
            (PVOID) pszBuffer;
        // Set the chunk size to the buffer size.
        dataChunk.FromMemory.BufferLength =
            (USHORT) strlen(pszBuffer);
        // Insert the data chunk into the response.
        hr = pHttpContext->GetResponse()->WriteEntityChunks(
            &dataChunk,1,FALSE,TRUE,&cbSent);
        // Test for an error.
        if (FAILED(hr))
        {
            // Return the error status.
            return hr;
        }

        // Return a success status.
        return S_OK;
    }
};

// Create the module's class factory.
class MyHttpModuleFactory : public IHttpModuleFactory
{
public:
    HRESULT
    GetHttpModule(
        OUT CHttpModule ** ppModule, 
        IN IModuleAllocator * pAllocator
    )
    {
        UNREFERENCED_PARAMETER( pAllocator );

        // Create a new instance.
        MyHttpModule * pModule = new MyHttpModule;

        // Test for an error.
        if (!pModule)
        {
            // Return an error if we cannot create the instance.
            return HRESULT_FROM_WIN32( ERROR_NOT_ENOUGH_MEMORY );
        }
        else
        {
            // Return a pointer to the module.
            *ppModule = pModule;
            pModule = NULL;
            // Return a success status.
            return S_OK;
        }            
    }

    void Terminate()
    {
        // Remove the class from memory.
        delete this;
    }
};

// Create the module's exported registration function.
HRESULT
__stdcall
RegisterModule(
    DWORD dwServerVersion,
    IHttpModuleRegistrationInfo * pModuleInfo,
    IHttpServer * pGlobalInfo
)
{
    UNREFERENCED_PARAMETER( dwServerVersion );
    UNREFERENCED_PARAMETER( pGlobalInfo );

    return pModuleInfo->SetRequestNotifications(
        new MyHttpModuleFactory,
        RQ_BEGIN_REQUEST,
        0
    );
}

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
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

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