Professional ASP.NET 3.5 in C# and Visual Basic Part 116 pot

Figure 24-6Page output of tracing shows only the data collected for the current page request.. When set totrue, it shows the most recent requests that are stored in the trace log up to t

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Section Description

Request Details Includes the ASP.NET Session ID, the character encoding of the request

and response, and the HTTP conversation’s returned status code Be aware

of the request and response encoding, especially if you’re using any non-Latin character sets If you’re returning languages other than English, you’ll want your encoding to be UTF-8 Fortunately that is the default

Trace Information Includes all theTrace.Writemethods called during the lifetime of the

HTTP request and a great deal of information about timing This is probably the most useful section for debugging The timing information located here is valuable when profiling and searching for methods in your application that take too long to execute

Control Tree Presents an HTML representation of the ASP.NET Control Tree Shows

each control’s unique ID, runtime type, the number of bytes it took to be rendered, and the bytes it requires in ViewState and ControlState Don’t undervalue the usefulness of these two sections, particularly of the three columns showing the weight of each control The weight of the control indicates the number of bytes occupied in ViewState and/or ControlState

by that particular Control Be aware of the number of bytes that each of your controls uses, especially if you write your own custom controls, as you want your controls to return as few bytes as possible to keep overall page weight down

Session State Lists all the keys for a particular user’s session, their types, and their

values Shows only the current user’s Session State

Application State Lists all the keys in the current application’s Application object and their

types and values

Request Cookies Lists all the cookies passed in during the page’s request

Response Cookies Lists all the cookies that were passed back during the page’s response

Headers Collection Shows all the headers that might be passed in during the request from the

browser, including Accept-Encoding, indicating whether the browser supports compressed HTTP responses; Accept-Languages, a list of ISO language codes that indicate the order of the user’s language preferences;

and User-Agent, the identifying string for the user’s browser The string also contains information about the user’s operating system and the version or versions of the NET Framework he is running (on IE)

Form Collection Displays a complete dump of the Form collection and all its keys and

values

Querystring Collection Displays a dump of the Querystring collection and all its contained keys

and values

Server Variables A complete dump of name-value pairs of everything that the Web server

knows about the application and the requesting browser

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Figure 24-6

Page output of tracing shows only the data collected for the current page request However, when visiting

http://localhost/yoursite/trace.axdyou’ll see detailed data collected for all requests to the site thus far If you’re using the built-in ASP.NET Development Server, remove the current page from the URL

and replace it withtrace.axd Don’t change the automatically selected port or path

Again,trace.axdis an internal handler, not a real page When it’s requested from a local browser, as

shown in Figure 24-7, it displays all tracing information for all requests up to a preset limit

Figure 24-7 shows that nine requests have been made to this application and the right side of the header indicates ‘‘Remaining: 1’’ That means that there is one more request remaining before tracing stops for

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this application After that final request, tracing data is not saved until an application recycle or until you

click ‘‘Clear current trace’’ from thetrace.axdpage The request limit can be raised inweb.configat the

expense of memory:

Figure 24-7

The maximum request limit value is 10000 If you try to use any greater value, ASP.NET uses 10000

anyway and gives you no error However, a new property calledmostRecentwas added to the trace

section in ASP.NET 2.0 When set totrue, it shows the most recent requests that are stored in the trace

log up to the request limit — instead of showing tracing in the order it occurs (the default) — without

using up a lot of memory SettingmostRecentto true causes memory to be used only for the trace

infor-mation it stores and automatically throws away tracing inforinfor-mation over therequestLimit

Clicking View Details fromTrace.axdon any of these requests takes you to a request-specific page with

the same details shown in Figure 24-6

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Tracing from Components

The tracing facilities of ASP.NET are very powerful and can stand alone However, previously we

mentionedSystem.Diagnostics.Trace, the tracing framework in the Base Class Library that is not

Web-specific and that receives consistent and complete tracing information when an ASP.NET applica-tion calls a non–Web-aware component This can be confusing Which should you use?

System.Diagnostics.Traceis the core NET Framework tracing library Along with System

Diagnostics.Debug, this class provides flexible, non-invasive tracing and debug output for any

appli-cation But, as mentioned earlier, there is rich tracing built into theSystem.Webnamespace As a Web

developer, you’ll find yourself using ASP.NET’s tracing facilities You may need to have

ASP.NET-specific tracing forwarded to the base framework’sSystem.Diagnostics.Trace, or more likely, you’ll

want to have your non–Web-aware components output their trace calls to ASP.NET so you can take

advantage oftrace.axdand other ASP.NET specific features

Additionally, some confusion surroundsTrace.WriteandDebug.Writefunctions Look at the source

code forDebug.Write, and you see something like this:

[Conditional("DEBUG")]

public static void Write(string message)

{

TraceInternal.Write(message);

}

Notice thatDebug.Writecalls a function namedTraceInternal.Write, which has a conditional attribute indicating thatDebug.Writeis compiled only if the debug preprocessor directive was set In other words, you can put as many calls toDebug.Writeas you want in your application without affecting your perfor-mance when you compile in Release mode This enables you to be as verbose as you want to be during the debugging phase of development

TraceInternalcycles through all attached trace listeners, meaning all classes that derive from

theTraceListenerbase class and are configured in that application’s configuration file The default

TraceListenerlives in the aptly namedDefaultTraceListenerclass and calls the Win32 API

OutputDebugString.OutputDebugStringsends your string into the abyss and, if a debugger is

listen-ing, it is displayed If no debugger is listenlisten-ing,OutputDebugStringdoes nothing Everyone knows the

debugger listens for output fromOutputDebugStringso this can be a very effective way to listen in on

debug versions of your application

For quick and dirty no-touch debugging, try using DbgView from SysInternals at

www.sysinternals.com/ntw2k/freeware/debugview.shtml DbgView requires no

installation, works great with all your calls to Debug.Writer, and has lots of cool

features such as highlighting and logging to a file.

Now, if you look at the source code forTrace.Write(that’sTRACEnotDEBUG), you see something like this:

[Conditional("TRACE")]

public static void Write(string message)

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TraceInternal.Write(message);

}

The only difference betweenDebug.WriteandTrace.Writegiven these two source snippets is the

conditional attribute indicating the preprocessor directiveTRACE You can conditionally compile your

assemblies to include tracing statements, debug statements, both, or neither Most people keepTRACE

defined even for release builds and use the configuration file to turn tracing on and off More than likely,

the benefits you gain from making tracing available to your users far outweigh any performance issues

that might arise

BecauseTrace.Writecalls theDefaultTraceListenerjust likeDebug.Write, you can use any debugger

to tap into tracing information So, what’s the difference?

When designing your application, think about your deployment model Are you going to ship debug

builds or release builds? Do you want a way for end users or systems engineers to debug your application

using log files or the event viewer? Are there things you want only the developer to see?

Typically, you want to use tracing andTrace.Writefor any formal information that could be useful

in debugging your application in a production environment.Trace.Writegives you everything that

Debug.Writedoes, except it uses theTRACEpreprocessor directive and is not affected by debug or release

builds

This means you have four possibilities for builds: Debug On, Trace On, Both On, or Neither On You

choose what’s right for you Typically, use Both On for debug builds and Trace On for production builds

You can specify these conditional attributes in the property pages or the command line of the compiler,

as well as with the C##definekeyword or#CONSTkeyword for Visual Basic

Trace Forwarding

You often find existing ASP.NET applications that have been highly instrumented and make

exten-sive use of the ASP.NETTraceContextclass ASP.NET version 2.0 introduces a new attribute to the

web.config<trace>element that allows you to route messages emitted by ASP.NET tracing to

System.Diagnostics.Trace:writeToDiagnosticsTrace

When you setwriteToDiagnosticsTracetotrue, all calls toSystem.Web.UI.Page.Trace.Write(the

ASP.NET TraceContext) also go toSystem.Diagnostics.Trace.Write, enabling you to use all the

stan-dard TraceListeners and tracing options that are covered later in this chapter The simple

writeToDiagnoticsTracesetting connects the ASP.NET tracing functionality with the rest of the base

class library I use this feature when I’m deep in debugging my pages, and it’s easily turned off using this

configuration switch I believe that more information is better than less, but you may find the exact page

event information too verbose Try it and form your own opinion

TraceListeners

Output fromSystem.Diagnostics.Tracemethods is routable by a TraceListener to a text file, to

ASP.NET, to an external monitoring system, even to a database This powerful facility is a woefully

underused tool in many ASP.NET developers’ tool belts In ASP.NET 1.1, some component

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develop-toSystem.Weband callHttpContext.Current.Trace They did this so that their tracing information

would appear in the developer-friendly ASP.NET format All components called within the context of an

HttpRequestautomatically receive access to that request’s current context, enabling the components to talk directly to the request and retrieve cookies or collect information about the user

However, assuming anHttpContextwill always be available is dangerous for a number of reasons First, you are making a big assumption when you declare that your component can be used only within the

context of an HttpRequest Notice that this is said within the context of a request, not within the context of

an application If you accessHttpContext.Currenteven from within theApplication_Start, you will be surprised to find thatHttpContext.Currentis null Second, marrying your component’s functionality to

HttpContextmakes it tricky if not impossible to use your application in any non-Web context, and unit testing becomes particularly difficult

If you have a component that is being used by a Web page, but it also needs to be unit tested outside of Web context or must be called from any other context, don’t callHttpContext.Current.Trace Instead, use the standardSystem.Diagnostics.Traceand redirect output to the ASP.NET tracing facilities using the new WebPageTraceListener described in the next section Using the standard trace mechanism means your component can be used in any context, Web or otherwise You’ll still be able to view the

compo-nent’s trace output with a TraceListener

The framework comes with a number of very useful TraceListeners; you can add them programmatically

or via a.configfile For example, you can programmatically add a TraceListener log to a file, as shown

in Listing 24-2 These snippets required theSystem.DiagnosticsandSystem.IOnamespaces

Listing 24-2: Configuring TraceListeners

VB

Dim myTextListener As New TextWriterTraceListener(File.Create("c:\myListener.log"))

Trace.Listeners.Add(myTextListener)

C#

TextWriterTraceListener myTextListener = new

TextWriterTraceListener(File.Create(@"c:\myListener.log"));

Trace.Listeners.Add(myTextListener);

You can do the same thing declaratively inweb.configvia anaddelement that passes in the type of

TraceListener to use, along with any initializing data it might need TraceListeners already configured

inmachine.configor a parentweb.configcan also be removed using theremovetag, along with their name:

<system.diagnostics>

<add name="myListener"

type="System.Diagnostics.TextWriterTraceListener"

initializeData="c:\myListener.log" />

</listeners>

</trace>

</system.diagnostics>

</configuration>

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TraceListeners, such asTextWriterTraceListener, that access a resource (such as a file, event log, or

database) require that the ASP.NET worker process be run as a user who has sufficient access In order

to write toc:\foo\example.log, for example, the ASP.NET worker process requires explicit write access

in the Access Control List (ACL) of that file

Notice the preceding example also optionally removes the default TraceListener If you write your own

TraceListener, you must provide a fully qualified assembly name in thetypeattribute

The New ASP.NET WebPageTraceListener

The new ASP.NETWebPageTraceListenerderives fromSystem.Diagnostics.TraceListenerand

auto-matically forwards tracing information from any component calls toSystem.Diagnostics.Trace.Write

This enables you to write your components using the most generic trace provider and to see its tracing

output in the context of your ASP.NET application

TheWebPageTraceListeneris added to theweb.configas shown in the following example Note that

we use the fully qualified assembly name for System.Web:

<add name="webListener"

type="System.Web.WebPageTraceListener, System.Web, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a"/>

</listeners>

</trace>

<system.web>

</system.web>

</configuration>

Figure 24-8 shows output from a call toSystem.Diagnostics.Trace.Writefrom a referenced library It

appears within ASP.NET’s page tracing The line generated from the referenced library is circled in this

figure

EventLogTraceListener

Tracing information can also be sent to the event log using the EventLogTraceListener This can be a little

tricky because ASP.NET requires explicit write access to the event log:

<add name="EventLogTraceListener"

type="System.Diagnostics.EventLogTraceListener"

initializeData="Wrox"/>

</listeners>

</trace>

</configuration>

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Figure 24-8

Notice that"Wrox"is passed in as a string to theinitializeDataattribute as the TraceListener is added The string"Wrox"appears as the application or source for this event This works fine when debugging

your application; most likely, the debugging user has the appropriate access However, when your appli-cation is deployed, it will probably run under a less privileged account, so you must give explicit write access to a registry key such asHKLM\System\CurrentControlSet\Services\EventLog\Application\

Wrox, where"Wrox"is the same string passed in toinitializeData Remember that registry keys

have ACLs (Access Control Lists) just as files do UseRegEdit.exeto change the permissions on a

registry key by right-clicking the key and selecting Properties, and setting the ACL just like you would for

a file

Be careful when using the EventLogTraceListener because your event log can fill up fairly quickly if you have a particularly chatty application Figure 24-9 shows the same tracing output used in Figure 24-8,

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this time in the event log The Event Viewer has changed in Windows Vista and you’ll need to create a

simple Custom View that shows only ‘‘Wrox’’ events

Figure 24-9

Other Useful Listeners

The NET 2.0 Framework added two TraceListeners in addition to the WebPageTraceListener:

❑ XmlWriterTraceListener:Derives fromTextWriterTraceListenerand writes out a strongly

typed XML file

❑ DelimitedListTraceListener:Also derives fromTextWriterTraceListener; writes out

comma-separated values (CSV) files

One of the interesting things to note about the XML created by the XmlWriterTraceListener — it’s not

well-formed XML! Specifically, it doesn’t have a root node; it’s just a collection of peer nodes, as shown

in the following code This may seem like it goes against many of the ideas you’ve been told about XML,

but think of each event as a document Each stands alone and can be consumed alone They just happen

to be next to each other in one file Certainly, the absence of an ultimate closing tag cleverly dodges the

issue of wellformedness and allows easy appending to a file

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<Computer>SCOTTPC</Computer>

</System>

</E2ETraceEvent>

the XML continues

The ‘‘E2E’’ inE2ETraceEventstands for end-to-end Notice that it includes information such as your

computer name and a ‘‘correlation id.’’ Microsoft will include TraceViewer tools with coming products,

such as the product codenamed Indigo and the managed WinFX API that will consume this XML Schema

and help you diagnose problems with operations that span multiple machines in a Web farm If your

ASP.NET application makes calls to an Indigo service, you may want your app to supply its tracing

information in this format to make aggregated analysis easier

The NET 3.5 Framework added one additional TraceListeners, the IisTraceListener This new TraceLis-tener has been added to the System.Web Assembly in the NET 3.5 but that assembly is still versioned

as 2.0 Consequently, this class is available only on systems that have the NET Framework 3.5 installed Remember that the NET Framework 3.5 includes fixes for the 2.0 Framework as well as some new func-tionality, like theIisTraceListener

Much like theWebPageTraceListenerbridges Diagnostics Tracing with ASP.NET tracing, the

IisTraceListenerbridges the tracing mechanism of ASP.NET with IIS 7.0 This listener lets us raise

events to the IIS 7.0 infrastructure See Chapter 11 on IIS7 for more details on this new class and its use

Diagnostic Switches

It’s often not convenient to recompile your application just because you want to change tracing character-istics Sometimes you may want to change your configuration file to add and remove TraceListeners At other times, you may want to change a configuration parameter or ‘‘flip a switch’’ to adjust the amount of detail the tracing produces That’s whereSwitchcomes in.Switchis an abstract base class that supports

a series of diagnostic switches that you can control by using the application’s configuration file

BooleanSwitch

To use aBooleanSwitch, create an instance and pass in the switch name that appears in the application’s

configfile (see Listing 24-3)

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