Develop a Native C\C++ Module for IIS 7.0

By Mike Volodarsky

November 24, 2007

Introduction

IIS 7.0 and above allows for extending the server by modules which are developed in two ways:

  • Using managed code, and the ASP.NET server extensibility APIs
  • Using native code, and the IIS native server extensibility APIs

Unlike the previous versions of IIS, the majority of server extensibility scenarios does not require native (C++) code development, and can be accommodated using managed code and the ASP.NET APIs. Using ASP.NET to extend the server allows you to reduce dramatically development time, and to take advantage of the rich functionality of ASP.NET and the .NET Framework. To learn more about extending IIS with ASP.NET, see Developing an IIS Module with .NET.

IIS also provides a (C++) native core server API, which replaces ISAPI filter and extension API from previous IIS releases. If you have specific requirements that demand native code development, or would like to convert your existing native ISAPI components, take advantage of this API to build server components. The new native server API features object-oriented development with an intuitive object model, provides more control over request processing, and uses simpler design patterns to help you write robust code.

This walkthrough examines the following tasks:

  • Developing a native module using the native (C++) server API
  • Deploying a native module on the server

In order to compile the module, you must install the Platform SDK that contains the IIS header files. The latest Windows Vista Platform SDK is available here.

In order to use the Platform SDK with Visual Studio 2005, you must register the SDK. After you have installed the SDK, do this via Start > Programs > Microsoft Windows SDK > Visual Studio Registration > Register Windows SDK Directories with Visual Studio.

The source code for this module is available in the Visual Studio IIS7 Native Module Sample.

Develop a Native Module

In this task, we examine the development of a native module using the new native (C++) server API. A native module is a Windows DLL that contains the following:

  • RegisterModule exported function. This function is responsible for creating a module factory, and registering the module for one or more server events.
  • Implementation of the module class inheriting from the CHttpModule base class. This class provides the main functionality of your module.
  • Implementation of the module factory class implementing the IHttpModuleFactory interface. The class is responsible for creating instances of your module.

Note: In some cases, you can also implement the IGlobalModule interface, in order to extend some of the server functionality that is not related to request processing. This is an advanced topic and is not covered in this walkthrough.

Your native module has the following life cycle:

1. When the server worker process starts, it will load the DLL containing your module, and invoke its exported RegisterModule function. In this function, you:

a. Create the module factory.
b. Register the module factory for the request pipeline events your module implements.

2. When a request arrives, the server:

a. Creates an instance of your module class using the factory you provided.
b. Calls the appropriate event handler method on the module instance for each of the request events you registered for.
c. Disposes the instance of the module at the end of request processing.

Now, to build it.

The full source code for the module is available in the Visual Studio IIS7 Native Module Sample. The steps below are the most important for developing the module, and do not include supporting code and error handling.

Implement the RegisterModule function that the server invokes when the module DLL is loaded. Its signature and the rest of the native API is defined in the httpserv.h header file, which is part of the Platform SDK (if you do not have the Platform SDK, please see the Introduction for information on obtaining it):

main.cpp:

HRESULT
__stdcall
RegisterModule(
DWORD dwServerVersion,
IHttpModuleRegistrationInfo * pModuleInfo,
IHttpServer * pHttpServer
)
{
// step 1: save the IHttpServer and the module context id for future use
g_pModuleContext = pModuleInfo->GetId();
g_pHttpServer = pHttpServer;

// step 2: create the module factory
pFactory = new CMyHttpModuleFactory();


// step 3: register for server events
hr = pModuleInfo->SetRequestNotifications( pFactory,
RQ_ACQUIRE_REQUEST_STATE,
0 );
}

The RegisterModule

There are three basic tasks we need to accomplish inside RegisterModule:

Save the Global State

We will store the global server instance, and the module context id for later use in global variables. While this example does not use this information, many modules find it useful to save and use later during request processing. The IHttpServer interface provides access to many server functions, such as opening files, and accessing the cache. The module context id is used to associate the custom module state with several server objects, such as request and application.

Create Module Factory

We will implement our factory class, CMyHttpModuleFactory, later in this walkthrough. This factory is responsible for manufacturing instances of our module for each request.

Register the Module Factory for the Desired Request Processing Events

The registration is done through the SetRequestNotificatons method, which instructs the server: to create our module instance for each request using the specified factory; and, to invoke the appropriate event handlers on it for each of the specified request processing stages.

In this case, we are only interested in the RQ_ACQUIRE_REQUEST_STATE stage. The complete list of the stages that comprise the request processing pipeline is defined in httpserv.h:

#define RQ_BEGIN_REQUEST 0x00000001 // request is beginning
#define RQ_AUTHENTICATE_REQUEST 0x00000002 // request is being authenticated
#define RQ_AUTHORIZE_REQUEST 0x00000004 // request is being authorized
#define RQ_RESOLVE_REQUEST_CACHE 0x00000008 // satisfy request from cache
#define RQ_MAP_REQUEST_HANDLER 0x00000010 // map handler for request
#define RQ_ACQUIRE_REQUEST_STATE 0x00000020 // acquire request state
#define RQ_PRE_EXECUTE_REQUEST_HANDLER 0x00000040 // pre-execute handler
#define RQ_EXECUTE_REQUEST_HANDLER 0x00000080 // execute handler
#define RQ_RELEASE_REQUEST_STATE 0x00000100 // release request state
#define RQ_UPDATE_REQUEST_CACHE 0x00000200 // update cache
#define RQ_LOG_REQUEST 0x00000400 // log request
#define RQ_END_REQUEST 0x00000800 // end request

In addition, you can subscribe to several non-deterministic events that may occur during request processing due to actions that other modules take, such as flushing the response to client:

#define RQ_CUSTOM_NOTIFICATION 0x10000000 // custom notification
#define RQ_SEND_RESPONSE 0x20000000 // send response
#define RQ_READ_ENTITY 0x40000000 // read entity
#define RQ_MAP_PATH 0x80000000 // map a url to a physical path

In order for our RegisterModule implementation to be accessible to the server, we must export it. Use a .DEF file that contains the EXPORTS keyword to export our RegisterModule function.

Next, implement the module factory class:

mymodulefactory.h:

class CMyHttpModuleFactory : public IHttpModuleFactory
{
public:
virtual HRESULT GetHttpModule(
OUT CHttpModule **ppModule,
IN IModuleAllocator *
)

{
}

virtual void Terminate()
{
}

};

The module factory implements the IHttpModuleFactory interface, and serves to create instances of the module on each request.

The server calls the GetHttpModule method at the beginning of every request to obtain the instance of the module to use for this request. The implementation simply returns a new instance of our module class, CMyHttpModule, which we implement next. As we see shortly, this enables us to store request state easily without worrying about thread safety, because the server always create and uses a new instance of the module for each request.

More advanced factory implementations may decide to use a singleton pattern instead of creating a new instance each time, or use the provided IModuleAllocator interface to allocate module memory in the request pool. These advanced patterns are not discussed in this walkthrough.

The Terminate method is called by the server when the worker process shuts down to perform final cleanup of the module. If you initialize any global state in RegisterModule, implement its cleanup in this method.

Implementing the Module Class

This class is responsible for providing the main functionality of the module during one or more server events:

myhttpmodule.h:

class CMyHttpModule : public CHttpModule
{
public:
REQUEST_NOTIFICATION_STATUS
OnAcquireRequestState(
IN IHttpContext * pHttpContext,
IN OUT IHttpEventProvider * pProvider
);
};

The module class inherits from the CHttpModule base class, which defines an event handler method for each of the server events discussed earlier. When the request processing pipeline executes each event, it invokes the associated event handler method on each of the module instances that have registered for that event.

Each event handler method has the following signature:

REQUEST_NOTIFICATION_STATUS
OnEvent(
IN IHttpContext * pHttpContext,
IN OUT IHttpEventProvider * pProvider
);

The IHttpContext interface provides access to the request context object, which can be used to perform request processing tasks such as inspecting the request, and manipulating the response.

The IHttpEventProvider interface is replaced with a more specific interface for each of the events that provide specific functionality to the module. For example, the OnAuthenticateRequest event handler receives the IAuthenticationProvider interface that allows the module to set the authenticated user.

The return of each event handler method is one of the values of the REQUEST_NOTIFICATION_STATUS enumeration. You must return RQ_NOTIFICATION_CONTINUE if the module successfully performed the task; the pipeline should continue execution.

If a failure occurred and you want to abort request processing with an error, you must set the error status and return RQ_NOTIFICATION_FINISH_REQUEST. The RQ_NOTIFICATION_PENDING return allows you to perform work asynchronously, and to let go of the thread processing the request so it can be reused for another request. Asynchronous execution is not discussed in this article.

Our module class overrides the OnAcquireRequestState event handler method. In order to provide functionality in any of the pipeline stages, the module class must override the respective event handler method. If you register for an event in RegisterModule, but do not override the appropriate event handler method on your module class, your module will fail at runtime (and trigger a debug-time assertion if compiled in the debug mode). Be careful and make sure that the method signature of the overriding method is exactly equivalent to the base class method of the CHttpModule class you are overriding.

Compiling the Module

Remember, you require the Platform SDK in order to compile. See the Introduction for more information about obtaining it and enabling Visual Studio to reference it.

Deploying a Native Module

After you have compiled your module, you must deploy it on the server. Compile the module, and then copy IIS7NativeModule.dll (and the IIS7NativeModule.pdb debugging symbols file if desired) to any location on the machine running IIS.

Native modules, unlike managed modules that can be added directly to the application, need to first be installed on the server. This requires Administrative privileges.

In order to install a native module, you have several options:

  • Use APPCMD.EXE command line tool
    APPCMD makes module installation simple. Go to Start>Programs>Accessories, Right click on the Command Line Prompt, and choose Run As Administrator. €In the command line window, execute the following:
    %systemroot%\system32\inetsrv\appcmd.exe install module /name:MyModule /image:[FULL_PATH_TO_DLL]
    Where [FULL_PATH_TO_DLL] is the full path to the compiled DLL containing module you just built.
  • Use the IIS Administration Tool
    This enables you to add a module by using a GUI. Go to Start>Run, type in inetmgr, and press Enter. Connect to localhost, locate the Modules task, and double-click to open it. Then, click the œAdd a Native Module task on the right pane.
  • Install the module manually
    Install the module manually by adding it to the <system.webServer>/<globalModules> configuration section in applicationHost.config configuration file, and add a reference to it in the <system.webServer>/<modules> configuration section in the same file in order to enable it. We recommend that you use one of the previous two options to install the module instead of editing the configuration directly.

The task is complete--we have finished configuring the new native module.

Summary

In this walkthrough, you learned how to develop and deploy a custom native module using the new native (C++) extensibility APIs. Please consult the IIS 7.0 SDK documentation to learn more about the native (C++) server APIs.

To learn about extending IIS using managed code and the .NET framework, see Developing an IIS module With .NET. To learn more about managing IIS modules, see the module overview white paper.



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