IHttpRequest::ReadEntityBody Method

Article
06/14/2022

Returns the HTTP request entity body.

Syntax

virtual HRESULT ReadEntityBody(  
   OUT VOID* pvBuffer,  
   IN DWORD cbBuffer,  
   IN BOOL fAsync,  
   OUT DWORD* pcbBytesReceived,  
   OUT BOOL* pfCompletionPending = NULL  
) = 0;

Parameters

pvBuffer
[OUT] A pointer to a buffer that receives the request body.

cbBuffer
[IN] The size, in bytes, of the buffer pointed to by pvBuffer.

fAsync
[IN] true to complete the operation asynchronously; otherwise, false.

pcbBytesReceived
[OUT] A pointer to a DWORD buffer that receives the number of bytes actually read if the method call completes synchronously.

pfCompletionPending
[OUT] A pointer to a Boolean buffer that receives a value that specifies whether an asynchronous completion is pending.

Return Value

An HRESULT. Possible values include, but are not limited to, those in the following table.

Value	Description
S_OK	Indicates that the operation was successful.
ERROR_CONNECTION_INVALID	Indicates that the byte count for the current request is incorrect.
ERROR_HANDLE_EOF	Indicates that there is no remaining data to be read.
ERROR_INVALID_PARAMETER	Indicates that an invalid value was passed in one of the parameters.
ERROR_NOT_ENOUGH_MEMORY	Indicates that there is insufficient memory to perform the operation.

Remarks

The ReadEntityBody method supports both synchronous and asynchronous calls.

Note

If you are calling the ReadEntityBody method asynchronously, your module needs to return immediately after the call.

After the ReadEntityBody method is called, the pvBuffer buffer will contain the request body, and the pcbBytesReceived buffer will contain the size, in bytes, of the request body that was returned in the pvBuffer buffer if the method call completed synchronously.

In addition, the pfCompletionPending buffer will contain a Boolean value that specifies whether an asynchronous completion is pending.

Example

The following code example demonstrates how to use the ReadEntityBody method to create an HTTP module that retrieves a 1-KB buffer section from the current request.

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

// NOTE - Data needs to be passed to this module, e.g. a POST request, or it will not appear to return anything.

// 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;

        // Create a data chunk.
        HTTP_DATA_CHUNK dataChunk;
        // Set the chunk to a chunk in memory.
        dataChunk.DataChunkType = HttpDataChunkFromMemory;

        // 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);

        // Allocate a 1K buffer.
        DWORD cbBytesReceived = 1024;
        void * pvRequestBody = pHttpContext->AllocateRequestMemory(cbBytesReceived);
        
        // Test for an error.
        if (NULL == pvRequestBody)
        {
            // Set the error status.
            hr = HRESULT_FROM_WIN32(ERROR_NOT_ENOUGH_MEMORY);
            pProvider->SetErrorStatus( hr );
            // End additional processing.
            return RQ_NOTIFICATION_FINISH_REQUEST;
        }

        if (pHttpContext->GetRequest()->GetRemainingEntityBytes() > 0)
        {
            // Loop through the request entity.
            while (pHttpContext->GetRequest()->GetRemainingEntityBytes() != 0)
            {

                // Retrieve the request body.
                hr = pHttpContext->GetRequest()->ReadEntityBody(
                    pvRequestBody,cbBytesReceived,false,&cbBytesReceived,NULL);
                // Test for an error.
                if (FAILED(hr))
                {
                    // End of data is okay.
                    if (ERROR_HANDLE_EOF != (hr  & 0x0000FFFF))
                    {
                        // Set the error status.
                        pProvider->SetErrorStatus( hr );
                        // End additional processing.
                        return RQ_NOTIFICATION_FINISH_REQUEST;
                    }
                }
                dataChunk.FromMemory.pBuffer = pvRequestBody;
                dataChunk.FromMemory.BufferLength = cbBytesReceived;
                
                hr = pHttpContext->GetResponse()->WriteEntityChunks(
                    &dataChunk,1,FALSE,TRUE,NULL);
                if (FAILED(hr))
                {
                    // Set the error status.
                    pProvider->SetErrorStatus( hr );
                    // End additional processing.
                    return RQ_NOTIFICATION_FINISH_REQUEST;
                }
            }
            // End additional processing.
            return RQ_NOTIFICATION_FINISH_REQUEST;
        }

        // 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
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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