IHttpServer::GetTraceContext Method

Article
03/09/2018

Retrieves an IHttpTraceContext interface.

Syntax

virtual IHttpTraceContext* GetTraceContext(  
   VOID  
) const = 0;

Parameters

This method takes no parameters.

Return Value

A pointer to an IHttpTraceContext interface.

Remarks

Use the IHttpServer::GetTraceContext method to retrieve an IHttpTraceContext interface when you need to raise an event that is not associated with an HTTP request. When you need to raise an event that is associated with an HTTP request, use either the IHttpServer::GetTraceContext or IHttpContext::GetTraceContext method to retrieve an IHttpTraceContext interface.

Example

The following code example demonstrates how to create an HTTP module that performs the following tasks:

Retrieves a pointer to an IHttpTraceContext interface by using the IHttpServer::GetTraceContext method.
Retrieves the trace activity GUID by using the IHttpTraceContext::GetTraceActivityId method.
Creates a string that contains the trace activity GUID and writes the string to the Event Viewer.

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

// Create a pointer for the global server interface.
IHttpServer * g_pHttpServer = NULL;

// Create the module's global class.
class MyGlobalModule : public CGlobalModule
{
public:
    GLOBAL_NOTIFICATION_STATUS
    OnGlobalPreBeginRequest(
        IN IPreBeginRequestProvider * pProvider
    )
    {
        UNREFERENCED_PARAMETER( pProvider );

        // Test for errors.
        if (NULL != g_pHttpServer)
        {
            // Retrieve the trace context.
            IHttpTraceContext * pTraceContext = g_pHttpServer->GetTraceContext();

            // Test for errors.
            if (NULL != pTraceContext)
            {
                // Retrieve the trace activity GUID.
                LPCGUID pTraceGuid = pTraceContext->GetTraceActivityId();

                // Test for errors.
                if (NULL != pTraceGuid)
                {
                    // Create a string buffer for the converted Unicode GUID.
                    WCHAR pwszGuid[256] = L"";
                    // Convert the GUID to a Unicode string.
                    int cbBytes = StringFromGUID2(*pTraceGuid, pwszGuid, 256);
                    // Allocate space for an ANSI string.
                    PSTR pszGuid =
                        (PSTR) pProvider->GetHttpContext()->AllocateRequestMemory(
                        (DWORD)cbBytes);
                    // Convert the Unicode string to an ANSI string.
                    wcstombs_s((size_t*)&cbBytes,pszGuid,cbBytes,pwszGuid,cbBytes);
                    // Test for errors.
                    if (cbBytes > 0)
                    {        
                        // Create an array of strings.
                        LPCSTR szBuffer[2] = {"Trace Activity ID",pszGuid};
                        // Write the strings to the Event Viewer.
                        WriteEventViewerLog(szBuffer,2);
                    }
                }
            }
        }

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

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

    MyGlobalModule()
    {
        // Open a handle to the Event Viewer.
        m_hEventLog = RegisterEventSource( NULL,"IISADMIN" );
    }

    ~MyGlobalModule()
    {
        // Test whether the handle for the Event Viewer is open.
        if (NULL != m_hEventLog)
        {
            // Close the handle to the Event Viewer.
            DeregisterEventSource( m_hEventLog );
            m_hEventLog = NULL;
        }
    }

private:

    // Create a handle for the event viewer.
    HANDLE m_hEventLog;

    // Define a method that writes to the Event Viewer.
    BOOL WriteEventViewerLog(LPCSTR szBuffer[], WORD wNumStrings)
    {
        // Test whether the handle for the Event Viewer is open.
        if (NULL != m_hEventLog)
        {
            // Write any strings to the Event Viewer and return.
            return ReportEvent(
                m_hEventLog,
                EVENTLOG_INFORMATION_TYPE,
                0, 0, NULL, wNumStrings,
                0, szBuffer, NULL );
        }
        return FALSE;
    }
};

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

    // Create an HRESULT to receive return values from methods.
    HRESULT hr;

    // Create an instance of the global module class.
    MyGlobalModule * pGlobalModule = new MyGlobalModule;
    // Test for an error.
    if (NULL == pGlobalModule)
    {
        return HRESULT_FROM_WIN32(ERROR_NOT_ENOUGH_MEMORY);
    }

    // Store the pointer for the global server interface.
    g_pHttpServer = pGlobalInfo;

    // Set the global notifications and exit.
    hr = pModuleInfo->SetGlobalNotifications(
        pGlobalModule, GL_PRE_BEGIN_REQUEST );

    // Test for an error and exit if necessary.
    if (FAILED(hr))
    {
        return hr;
    }

    // Set the global priority.
    hr = pModuleInfo->SetPriorityForGlobalNotification(
        GL_PRE_BEGIN_REQUEST,PRIORITY_ALIAS_HIGH);

    // Test for an error and exit if necessary.
    if (FAILED(hr))
    {
        return hr;
    }

    return S_OK;
}

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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