IHttpContext::AllocateRequestMemory Method

Article
03/09/2018

Allocates a specified amount of memory.

Syntax

virtual VOID* AllocateRequestMemory(  
   IN DWORD cbAllocation  
) = 0;

Parameters

cbAllocation
[IN] The number of bytes to allocate.

Return Value

A pointer to VOID.

Remarks

The AllocateRequestMemory method allocates an amount of memory that is specified by the cbAllocation parameter and has the lifetime of the current request. The server will automatically reclaim this memory at the end of the request.

Example

The following code example demonstrates how to use the AllocateRequestMemory method to create an HTTP module that allocates a chunk of memory to retrieve the value of the HTTP User-Agent header.

#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 );

        // Create an HRESULT to receive return values from methods.
        HRESULT hr;
        
        // Buffers to store the returned header value.
        PCSTR pszUserAgent;
        
        // Length of the returned header value.
        USHORT cchUserAgent;
        
        // Retrieve a pointer to the request.
        IHttpRequest * pHttpRequest = pHttpContext->GetRequest();
        
        // Test for an error.
        if (pHttpRequest != NULL)
        {
            // Get the lengh of the "User-Agent" header.
            pszUserAgent = pHttpRequest->GetHeader("User-Agent",&cchUserAgent);
            
            // The header length will be 0 if the header was not found.
            if (cchUserAgent > 0)
            {
                // Allocate space to store the header.
                pszUserAgent = (PCSTR) pHttpContext->AllocateRequestMemory( cchUserAgent + 1 );
                
                // Test for an error.
                if (pszUserAgent==NULL)
                {
                    // Set the error status.
                    hr = HRESULT_FROM_WIN32(ERROR_NOT_ENOUGH_MEMORY);
                    pProvider->SetErrorStatus( hr );
                    // End additional processing.
                    return RQ_NOTIFICATION_FINISH_REQUEST;
                }
                // Retrieve the "User-Agent" header.
                pszUserAgent = pHttpRequest->GetHeader("User-Agent",&cchUserAgent);
            }
        }

        // Return processing to the pipeline.
        return RQ_NOTIFICATION_CONTINUE;
    }
};

// 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 the factory 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 );

    // Set the request notifications and exit.
    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 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

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