Understanding ASP.NET Under The Cover - Miguel A. Castro

UNDERSTANDING ASP.NETUNDER THE COVERS

Miguel A. Castro

[email protected]

Agenda

Defining ASP.NET

Terms & Buzzwords

A Request-to-Response Walkthrough

Additional Technologies

Summary

Miguel A. Castro

ineta

.NET Architect, Developer, & Trainer Microsoft MVP ASP Insider Member of the INETA Speakers Bureau Conference Speaker Creator of CodeBreeze In IT business since 1986

Your Speaker

Miguel A. Castro

ineta

.NET Architect, Developer, & Trainer Microsoft MVP ASP Insider Member of the INETA Speakers Bureau Conference Speaker Creator of CodeBreeze In IT business since 1986

Agenda

Defining ASP.NET

Terms & Buzzwords



Summary

Classic ASP

• Interpreted language• Included embedded scripting code mixed

into HTML• Limited to VBScript• Ran in the same process as IIS• Inherently not scalable (needed MTS)

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Walking Upright

• Designed by Scott Guthrie & Mark Anders• Early iteration of ASP.NET• Originally known as XSP

– Not .NET-related – Java based !

• Became ASP+ with the design of the CLR– Rewritten in C#

• Renamed when .NET branding introduced

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What is ASP.NET

• A framework for developing and delivering information & applications on the web.

• Known primarily as a page framework.• A complete Request/Response

management system.• Can handle and respond to all sorts of

requests on the Internet (or an Intranet).

Not a language !

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Characteristics of ASP.NET

• Runs under its own worker process.• No longer tied to IIS.• Code execution managed by CLR.• Code-Behind model allows code

separation.• Includes state handling facilities.• Provides caching functionality.

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Agenda

Terms & Buzzwords

Defining ASP.NET



Summary

Commonly Used Terms

• Request– An HTTP query initiated by a client to a server for

the purpose of performing some action.

• Response– A stream of information sent back to a client from

the HTTP server that processed the client’s request.

• ASP.NET Pipeline– A series of extensible functionality points which

continue the process of a request in order to eventually obtain a response.

End of line

Commonly Used Terms

• Page Lifecycle– Another series of functionality points that form

the process of converting an ASPX page to HTML output.

– The entire page lifecycle occurs between two pipeline points.

• Control Model– The heart of how ASP.NET builds HTML from

compiled classes that represent visual components.

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Agenda


Defining ASP.NET

Terms & Buzzwords


Summary

What Everyone SeesDesktop Browser

http://www.microsoft.com/default.aspx

Web Server (IIS)

Convert ASPX to HTML

Rendered HTML

Now the long version…

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Web Server (IIS)

Convert ASPX to HTML

Getting it to .NET (the low level stuff)

Web Server (IIS)

http.sys

Worker Process(w3wp.exe) – (one per app pool)

aspnet_isapi.dll

Kernel Mode Driver:Http API used by IIS

Worker Process started (one per pool)

and if needed, AppDomain is created.

AppDomain(one per site/VD)

Attached to the extension of the request.

Unmanaged DLL that loads the CLR and routes requests to the managed runtime classes via COM-compliant interfaces.

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ISAPIRuntime(ProcessRequest method)

HttpRuntime.ProcessRequest

Request sent to the ASP.NET runtime for processing.

ASP.NET Takes Over

HttpRuntime.ProcessRequest

HttpContext created.This serves as an entry point into the request, response, and other

accessible variables.

Accessible from now until the end of the request processing.

Accessible through HttpContext.Current

An HttpApplication instance is created.

HttpApplication

Init method starts pipeline processing.

This is where it starts to mean something to you,

the developer.

Each AppDomain manages multiple instances so they do not conflict with each other

(different users or same user with more than one request).

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Entering the Pipeline

Pipeline kicked off in the Init method. HttpApplication

Performs event processing.

Checks hooks from Global.asax class.

Checks hooks from external HTTP Modules.

BeginRequest

AuthenticateRequest / Post

AuthorizeRequest / Post

ResolveRequestCache / Post

MapRequestHandler / Post

AcquireRequestState / Post

PreRequestHandlerExecute / Post

ReleaseRequestState / Post

UpdateRequestCache / Post

LogRequest / Post

EndRequest

PreSendRequestHeaders

PreSendRequestContent

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Entering the Pipeline

HttpApplication

BeginRequest









LogRequest / Post

EndRequest



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Pipeline Events of Interest

HttpApplication

BeginRequest









LogRequest / Post

EndRequest



Determine whether to use cached response.

Provide URL-Rewriting functionality.

Repopulate HttpContext.Current.User with

stored principal.

Page authentication occurs here.

End of line

Any event can be hooked in

Global.asax or in an HTTP Module.

HTTP Modules

• Classes that implement IHttpModule.MyModule : IHttpModule

Delegate-based Properties in HttpApplication instance

can be wired up.

Method functionality equivalent to hooking event

in Global.asax

Event hooks in modules checked

during pipeline processing.

End of line

• WindowsAuthenticationModule• FormsAuthenticationModule• UrlAuthenticationModule• FileAuthorizationModule• ServiceModel• SessionStateModule• OutputCacheModule

AuthenticateRequest

AuthenticateRequest

EndRequest

AuthorizeRequest

AuthorizeRequest

PostAuthenticateRequest

AcquireRequestState

ReleaseRequestState

EndRequest

AcquireRequestState

ASP.NET HTTP Modules of Interest

End of line

Module Installation

Any level in the Config chain

You do know what the Config chain is, right?

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The Process Continues

HttpApplication

BeginRequest









LogRequest / Post

EndRequest



Just before this event:Proper HTTP Handler located based on request’s extension.

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Handlers provide necessary processing in order to create a response.

HTTP Handlers

• Classes that implement IHttpHandler.

MyHandler : IHttpHandler Determines if the handler instance can be reused by

another request.

Functionality assigned to this particular handler.

Remember the HttpContext contains

all accessible variables, including

Response.

End of line

HTTP Handler Factories

• Can also implement IHttpHandlerFactory.

MyHandlerFactory : IHttpHandlerFactory Allows the instantiation of any handler based on specific

conditioning scenarios.

End of line

Characteristics of an HTTP Handler

• Access to current HttpContext.– Request is in there (as is the Response) !

• Handlers are wired to extensions (aspx, etc.).

• Every handler is responsible for what the response is going to be for a request.– ASPX requests expect an HTML response.– Config requests expect a “forbidden”

response.

End of line

Handler Execution

HttpApplication

BeginRequest









LogRequest / Post

EndRequest



The determined handler is processed between the

PreRequestHandlerExecute and

PostRequestHandlerExecute.

End of line

Handler Installation

Any level in the Config chain

End of line

Handler factory that returns and executes the handler that will

convert an ASPX page to HTML output.

The PageHandlerFactory Class

• Implements IHttpHandlerFactory.– GetHandler method returns an IHttpHandler in the

form of System.Web.UI.Page-derived class hierarchy.

• Page class implements IHttpHandler.• Page class inherits from Control.• Control contains events/methods for the “Page

Event Lifecycle”.• PageHandlerFactory creates a class structure

out of your request.

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Page Class StructureCreated by the PageHandlerFactory class

Virtual class created from ASPX page.

Partial class with control declarations (class name same as code-behind).

Code-behind class is other side of partial class.

System.Web.UI.Page

System.Web.UI.Control IHttpHandler

inherits

partials with

inherits

inherits implements

Follows the structure of an ASP.NET Server Control.Referred to as Page-Gen

Class.

Controls created based on ASPX

content.

This is why you can tap into

events from your code-behind. ProcessRequest

method calls lifecycle events in

Control.

End of line





System.Web.UI.Page


inherits

partials with

inherits

inherits implements

End of line

Virtual ClassCreated from ASPX content

Determines language to be

used to generate page-gen class.

Specifies the partial class to serve as the code-behind.

Optional:Name of the code-file for

Visual Studio.

End of line


LiteralControl

End of line

LiteralControl

LiteralControl

LiteralControl

LiteralControl

LiteralControl

Converted to instances of System.Web.UI.LiteralControl

that are added to the control tree of this class.Remember, this class will ultimately inherit from

System.Web.UI.Control


LiteralControl

End of line

LiteralControl

LiteralControl

LiteralControl

LiteralControl

LiteralControl

LiteralControl

Program code directly added to virtual class.


LiteralControl

End of line

LiteralControl

LiteralControl

LiteralControl

LiteralControl

LiteralControl

LiteralControl

Converted to instances of the corresponding server control class for each of these control tags, that will be added to the control tree of this class. The Form control instance is placed

directly in the control tree of the class being created; while the TextBox and

Label controls are added to the control tree of the Form control.


LiteralControl

End of line

LiteralControl

LiteralControl

LiteralControl

LiteralControl

LiteralControl

LiteralControl

“asp” tag-prefix located in config file or Register directive.

Class with tag name located in appropriate namespace and assembly.


LiteralControl

LiteralControl

End of line

LiteralControl

LiteralControl

LiteralControl

LiteralControl

LiteralControl

__PAGE System.Web.UI.Page

ctrl0 System.Web.UI.LiteralControl

Function Code


form1 System.Web.UI.HtmlControls.HtmlForm


TextBox1 System.Web.UI.WebControls.TextBox


Label1 System.Web.UI.WebControls.Label



Remember: this class “ultimately” inherits from System.Web.UI.Page

Control IDs


LiteralControl

LiteralControl

End of line

LiteralControl

LiteralControl

LiteralControl

LiteralControl

LiteralControl

This is the next class you’ll see now.





System.Web.UI.Page


inherits

partials with

inherits

inherits implements

End of line

Partial ClassBase for virtual class and partial to code-behind

Notice the name is the same as the page’s code-behind class.

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System.Web.UI.Page


inherits

partials with

inherits

inherits implements

End of line

Code-Behind ClassOther side of the Control Declarations class

Inheriting from Page gives you access to a control’s event lifecycle.

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System.Web.UI.Page


inherits

partials with

inherits

inherits implements

End of line

Events for the lifecycle come

from here.

ProcessRequest comes from here.

It is from there that the lifecycle

events are called.

Remember, this entire class hierarchy is the handler returned by

the PageHandlerFactory class.

It is the HttpApplication pipeline that calls ProcessRequest, kicking

off the Page Lifecycle.

Page (Control) Lifecycle• PreInit• Init• InitComplete• CreateChildControls (IsPostBack)• LoadViewState/LoadControlState• IPostBackDataHandler.LoadPostData• PreLoad• Load• IPostBackDataHandler.RaisePostBackChangedEvent• IPostBackEventHandler.RaisePostBackEvent• LoadComplete• CreateChildControls (!IsPostBack)• PreRender• DataBind• PreRenderComplete• SaveViewState/SaveControlState• Render• Unload

Complete List

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Most Commonly Known Points

Postback only

Begin tracking ViewState: TrackViewState methodBegin tracking ViewState: TrackViewState method

Load: OnLoad method and Load eventLoad: OnLoad method and Load event

PreRender: OnPreRender method and PreRender eventPreRender: OnPreRender method and PreRender event

Save View State: SaveViewState methodSave View State: SaveViewState method

Render: Render methodRender: Render method

Unload: OnUnload method and Unload eventUnload: OnUnload method and Unload event

Raise Postback Event: IPostBackEventHandler.RaisePostBackEvent methodRaise Postback Event: IPostBackEventHandler.RaisePostBackEvent method

Raise Changed Events: IPostBackDataHandler.RaisePostBackChangedEvent methodRaise Changed Events: IPostBackDataHandler.RaisePostBackChangedEvent method

Load Postback Data: IPostBackDataHandler.LoadPostdata methodLoad Postback Data: IPostBackDataHandler.LoadPostdata method

Load View State: LoadViewState methodLoad View State: LoadViewState method

Initialize: OnInit method and Init eventInitialize: OnInit method and Init event

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Control Rendering

• Activated through the Control class’ Render method.

• Each control is designed to output something to the response buffer.

• Most controls output HTML.• Some controls contain others in their tree.• Control rendering involves recursively rendering

child controls.• Controls don’t need to output anything

– ScriptManager

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Getting a Response

• “Rendering” uses an HtmlTextWriter stored in the Response object.

• Response object is part of HttpContext.• Writer sent into Render method.• After pipeline complete, contents returned

up the chain to aspnet_isapi.dll then http.sys.

• Results viewed on browser.

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Agenda


Defining ASP.NET

Terms & Buzzwords


Summary

Postbacks

• Invoked by controls on form that trigger the form to “post”.– Another HTTP Request, but of a post-type.

• Certain lifecycle methods only invoked on postback only.

• In a postback, the Request object’s Form property contains posted data from HTML elements (using their client IDs).

Postbacks

Postback only

Begin tracking ViewState: TrackViewState methodBegin tracking ViewState: TrackViewState method

Load: OnLoad method and Load eventLoad: OnLoad method and Load event

PreRender: OnPreRender method and PreRender eventPreRender: OnPreRender method and PreRender event

Save View State: SaveViewState methodSave View State: SaveViewState method

Render: Render methodRender: Render method

Unload: OnUnload method and Unload eventUnload: OnUnload method and Unload event

Raise Postback Event: IPostBackEventHandler.RaisePostBackEvent methodRaise Postback Event: IPostBackEventHandler.RaisePostBackEvent method

Raise Changed Events: IPostBackDataHandler.RaisePostBackChangedEvent methodRaise Changed Events: IPostBackDataHandler.RaisePostBackChangedEvent method

Load Postback Data: IPostBackDataHandler.LoadPostdata methodLoad Postback Data: IPostBackDataHandler.LoadPostdata method

Load View State: LoadViewState methodLoad View State: LoadViewState method

Initialize: OnInit method and Init eventInitialize: OnInit method and Init event

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ASCX User Controls

Register directive defines tag prefix and name for user control.

src points to an ascx file in the current web application.

Usage in an ASPX page (or another ASCX control) is just

like a server control.

During parsing, virtual class is built just like a page, except the base is called UserControl.

Also, added to Page’s Controls collection.

UserControl also inherits from Control but does NOT implement IHttpHandler.

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Master Pages

End of line

Master directive similar to a Page directive.

Code-Behind class inherits from MasterPage, which inherits from

UserControl.

ASPX page points to a master page file.

Master Pages

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Control that specifies content to be defined in

an ASPX page.

Control that wraps content. Each Content control

corresponds to a ContentPlaceHolder control.

Master PagesWeb Server (IIS)Desktop Browser

Browse to Default.aspx

PageHandlerFactory commences building of virtual class.

MasterPageFile attribute encountered.

Parsing shifts to master page file and code-behind.

Control tree build and added to virtual class.

Parsing returns to ASPX page and Content controls turned to code.

Each Content control added to the Controls collection of corresponding ContentPlaceHolder control.

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Direct Browsing

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Note: you cannot browse directly to an ASCX control or a Master page.

ASHX Handlers

End of line

SimpleHandlerFactory in charge of returning HTTP Handler.

ASHX Handlers

PageHandlerFactory:Parses ASPX file, building virtual class as an HTTP Handler, with ProcessRequest kicking off page lifecycle.

SimpleHandlerFactory:Takes this handler code and returns is as HTTP Handler.

End of line

ProcessRequest called in the pipeline as always.

Themes & Skins

• Contain server control declarations (without IDs) whose properties overwrite those declared on the ASPX page.

• Control “registration” applies.– Either in skin file or in config file.

• Applied just before Init lifecycle event.– Programmatic application MUST be made in PreInit

event.– Application using Theme attribute occurs last.– Application using StyleSheetTheme attribute occurs

first.

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ASP.NET Ajax

• More interactive model.• Uses JavaScript to invoke Ajax requests.• Web Service (WCF) technology can be used to

handle response.• Ships with controls and components that

encapsulate functionality.• Ajax Control Toolkit – ships separately

– Community driven and supported– Undergoes Microsoft Scrutiny

• Better user experience.

End of line

ASP.NET MVC• Process nearly identical to conventional ASP.NET.

– It’s still ASP.NET

• Uses a URL routing engine to parse URLs and invoke appropriate classes.– http://site/controller/action/id

• Pipeline is intercepted by a module tapping into PostResolveRequestCache event.

• Request is picked up by another handler for processing.

• Controller classes are sought out and processed (similar to code-behind classes).

• Appropriate Views parsed and rendered.

End of line

Why Custom Modules

• Background processes• URL rewriting or routing• Identity persistence for custom providers

(or any other kind of persistence)• Benchmarking

Why Custom Handlers

• Image watermarking• Dynamic image generation• RSS output generation• File denial or protection

Tips & Tricks

• Use your own base page to house common functionality.– If overriding On{event} methods, remember that the

event-wire-up methods in code-behind fire when you call base On{event}.

• Example: override OnLoad in a base class, Page_Load in code-behind gets called when you call base.OnLoad.

– Use <page pageBaseType= demo

• Register your server controls in your Web.Config file.– Eliminates repeat registrations in ASPX & ASCX files.– Eliminates registrations in Skin files.

End of line

Tips & Tricks

• Remove HTTP Modules that you don’t need

• If file protection necessary, add file extension (ZIP) to registered extensions in IIS.– Bring them into the pipeline for protection and

controlled exposure.– Presentation available on my site.

End of line

Tips & Tricks

• Turn ViewState off in controls that don’t need them – especially grids.– In 4.0 the model can be reversed.– More compact in 4.0.

• Override LoadPageStateFromPersistenceMedium & SavePageStateToPersistenceMedium to alter where and how ViewState is saved.

Tips & Tricks

• Deployment Mode– In <system.web>– <deployment retail=“true” />– Turns debugging, tracing, and detailed errors

OFF– Machine.Config ONLY

• Way Advanced– PageParserFilter abstract base class– Lets you govern the behavior of the ASP.NET

Page Parser

Agenda

Summary

Defining ASP.NET

Terms & Buzzwords



What To Take Away From This

• ASP.NET does much more than serve pages.• Decoupled architecture allows flexible hosting.• Pipeline and Event cycle – two different things.• Extensible architecture allows opportunities for

interception and alteration.• Module and Handler model enforce

encapsulation and reusability.• Be mindful of how much is happenning behind

the scenes.

End of line

References

• Great Wikipedia entry– http://en.wikipedia.org/wiki/ASP+

• Article: How ASP.NET Works– http://www.west-wind.com/presentations/

howaspnetworks/howaspnetworks.asp– Code Magazine – Nov/Dec 2005– Rick Strahl

References

• Article: Truly Understanding ViewState– http://weblogs.asp.net/infinitiesloop/archive/

2006/08/03/truly-understanding-viewstate.aspx

– Dave Reed

• Understanding ASP.NET Internals– http://grokable.com/teched-2007-

presentation-slides-and-demos/– Rob Howard

References

www.dotnetdude.comwww.steelbluesolutions.com

• Essential ASP.NET 2.0• Addison-Wesley• Fritz Onion & Keith Brown

• My Site & Email:• www.dotnetdude.com • [email protected]

Understanding ASP.NET Under The Cover - Miguel A. Castro

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