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Posted 1 Jun 2004

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Browser Detection using ASP.NET

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6 May 2009CPOL5 min read
Using and updating your machine.config file to better detect browser type in ASP.NET

The old method: Determining browser type in ASP

In web development it is often important to know which browser is viewing the page you are serving. Traditional ASP applications used the Browser Capabilities object that resides in the \system32\inetsrv\browscap.dll DLL. This object takes the User Agent string that a browser sends to a website and compares it to a list of simple wildcard expressions in the browscap.ini file to determine the type of browser currently requesting a page.

The browsercap.ini file has the following form:

[IE 6.0]
browser=IE
version=6
majorver=6
minorver=0
css=2
frames=True
iframes=True
tables=True
cookies=True
backgroundsounds=True
vbscript=True
javascript=True
javaapplets=True
activexcontrols=True
cdf=True
aol=False
beta=False
win16=False
crawler=False
stripper=False
wap=False
netclr=False
AK=False
SK=False

[Mozilla/4.0 (compatible; MSIE 6.0*;*Windows NT 5.1*)*]
parent=IE 6.0
platform=WinXP

If the expression Mozilla/4.0 (compatible; MSIE 6.0*;*Windows NT 5.1*)* matches the user agent string that the browser has sent, then the browser will be identified as IE 6.0 on the WinXP platform, with the properties defined by the [IE 6.0] section. The file is extensible in the sense that you can add your own properties (such as 'crawler', 'stripper' etc) and add your own browser-sniffing filters for newer browsers such as Firebird and Firefox.

To access this information within an ASP page you would do something like the following:

VBScript
Dim BT
Set BT = Server.CreateObject("MSWC.BrowserType")

Dim BrowserName    : BrowserName    = BT.Browser
Dim BrowserVersion : BrowserVersion = BT.Version

Set BT = nothing

The main problem with this method is that a new version of a new browser needs a new entry. When IE 7 comes out you will have to update your browscaps.ini file. If you don't then you could be rendering your pages incorrectly to your readers or disabling functionality based on incorrect assumptions.

The new method: Determining browser type in ASP.NET

ASP.NET solves this problem by introducing a more powerful regular expression-based method of determining the browser. Instead of relying on simple wildcard searches, the ASP.NET browser detection uses regular expressions to allow more complex testing and data extraction. An example of the format of the browser-sniffing expressions is given below

XML
<browserCaps>
    <use var="HTTP_USER_AGENT" />
    <filter>
        <!-- Opera -->
        <case match="Opera[ /](?'version'(?'major'\d+)(?'minor'\.\d+)(?'letters'\w*))">
            browser=Opera
            version=${version}
            majorversion=${major}
            minorversion=${minor}
            frames=true    
            tables=true
            cookies=true
            javascript=true
            ecmascriptversion=1.1
            isMobileDevice="true"

            <filter match="[4-9]" with="${major}">
                ecmascriptversion=1.3
                css1=true
                css2=true
                xml=true

                <filter match="[5-9]" with="${major}">
                    w3cdomversion=1.0    
                </filter>
            </filter>
            <filter match="^b" with="${letters}">
                beta=true
            </filter>
        </case>

This branch specifies that the HTTP_USER_AGENT header sent from the browser should be matched against the <filter> expressions that follow. You will notice the expression differs from the traditional ASP method in that it's possible to extract information from the match and assign the extracted values to browser properties. For example, when the user agent string

Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.2) Opera 7.23 [en]

is matched against the expression

Opera[ /](?'version'(?'major'\d+)(?'minor'\.\d+)(?'letters'\w*))

the values 'version', 'major' and 'minor' will be set as '7.23', '7' and '.23' respectively.

To access this information you would do something like the following:

ASP.NET
<% 
    Response.Write(Request.Browser.Browser.ToString());
    Response.Write(Request.Browser.Version.ToString());
%>

Updating browser and platform types

The browser matching regular expressions are contained in the configuration/system.web/browsercaps section of the machine.config file in your \WINDOWS\Microsoft.NET\Framework\v1.1.4322\CONFIG\ directory.

If you wish to add a new platform (eg Windows 2003 or Longhorn) then you can add a new filter under the browsercaps branch below the <use var="HTTP_USER_AGENT" /> directive:

XML
<filter>
    <case match="Windows NT 5.2|Windows 2003">
        platform=Win2003
    </case>
</filter>

To add a new expression to detect Gecko-based browsers you would add

XML
<case match="^Mozilla/5\.0 \([^)]*\) (Gecko/[-\d]+)? (?'type'[^/\d]*)([\d]*)
/(?'version'(?'major'\d+)(?'minor'\.\d+)(?'letters'\w*)).*">
    browser=Gecko
    type=${type}
    frames=true
    tables=true
    cookies=true
    javascript=true
    javaapplets=true
    ecmascriptversion=1.5
    w3cdomversion=1.0
    css1=true
    css2=true
    xml=true
    tagwriter=System.Web.UI.HtmlTextWriter
    <case match="rv:(?'version'(?'major'\d+)(?'minor'\.\d+)(?'letters'\w*))">
        version=${version}
        majorversion=${major}
        minorversion=${minor}
        <case match="^b" with="${letters}">
            beta=true
        </case>
    </case>
</case>

The point here is that future versions of the browser will automatically be detected. As long as your browser-dependant code is of the form if BrowserVersion >= X then ... (and assuming that forward compatibility is maintained for that particular browser) you will be fine.

The Problem, and How You Can Help

With new browsers are constantly being released, and new spiders, crawlers and site-strippers being written it's a difficult job to ensure your config file is up to date. Microsoft has not committed to keeping the machine.config file updated, instead preferring to let cyScape, Inc. do the work. The problem with this is that it isn't being updated, and in fact now seems to have been removed altogether.

Rob Eberhardt at http://slingfive.com/pages/code/browserCaps/ has provided an update for the machine.config file that includes Gecko, Safari and Konqueror browsers, and I've made a small update to demonstrate how to include detection for Windows 2003. There is an excellent browsercap.ini file maintained by Gary Keith at http://www.garykeith.com/browsers/ that lists not only browsers, but all crawlers, spiders and strippers that have been detected. Gary has done an outstanding job.

Rob Eberhardt and I would like to use the combined resources of the CodeProject community, along with the amassed information provided by Gary to start our own CodeProject maintained browsercaps compilation for ASP.NET machine.config files. With your help we can ensure that our browser detection is up to date.

A test page has been provided here. If you have a browser that is mis-reported or not detected then please either let us know or better yet, take the time to determine the expression matches needed and send them in so we can merge them. Better yet, if someone has the time and patience to develop a database driven config file generator then that would automate the process and speed up updates.

For the moment we will do our best to ensure the current file is updated as often as possible. It's over to you.

Resources

History

  • 2 Jun 2004 - first posted
  • 9 Dec 2004 - Rob Eberhardt updated the XML file to pick up plain (non-Firefox) Mozilla correctly, missed some Safari and Konqueror variations, and added an Opera section
  • 4 Jul 2005 - Updated XML file, NUnit test library and simple command line tool to test useragents provided by Owen Brady
  • 10 Oct 2005 - Updated XML file with updates for Opera/Gecko/AppleWebKit based browsers. Mainly to properly detect version and other settings according to there websites information. Update provided by Owen Brady
  • 18 May 2006 - Updated XML file using JWhite's suggestions.
  • 25 July 2006 - More updates from Owen Wilson for Opera/Gecko/AppleWebKit browsers
  • 6 May 2009 - updated the resource section

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


Written By
Founder CodeProject
Canada Canada
Current passion project: CodeProject.AI Server. Please join in!

Chris is the Co-founder of the popular code-sharing site CodeProject.com, the digital advertising agency DeveloperMedia.com and the content marketing agency ContentLab.IO.

He's been programming way too long and has been, in various guides, an astrophysicist, mechanic, mathematician, physicist, breeder of carnivorous plants, hydrologist, geomorphologist, defence intelligence researcher and then, when all that got a bit rough on the nerves, a serial entrepreneur.

Chris has programmed everything from FORTRAN on a CRAY to Python on a Pi, but generally leans on TypeScript, C#, and SQL for the front, middle and back bits of his applications. His current focus is on ensuring developers know enough about Artificial Intelligence to be dangerous.

Comments and Discussions

 
GeneralClient Computer Name Pin
Majid Shahabfar5-Jun-04 0:57
Majid Shahabfar5-Jun-04 0:57 
GeneralRe: Client Computer Name Pin
Comatoast 709-Jun-04 6:42
sussComatoast 709-Jun-04 6:42 
QuestionWhy detect the browser type? Pin
waveangle3-Jun-04 7:07
waveangle3-Jun-04 7:07 
AnswerRe: Why detect the browser type? Pin
Chris Maunder3-Jun-04 9:39
cofounderChris Maunder3-Jun-04 9:39 
GeneralRe: Why detect the browser type? Pin
Anonymous3-Jun-04 19:12
Anonymous3-Jun-04 19:12 
GeneralRe: Why detect the browser type? Pin
Chris Maunder4-Jun-04 6:31
cofounderChris Maunder4-Jun-04 6:31 
GeneralRe: Why detect the browser type? Pin
Dave Bacher11-Nov-04 12:33
Dave Bacher11-Nov-04 12:33 
AnswerRe: Why detect the browser type? Pin
nmg1968-Nov-05 6:38
nmg1968-Nov-05 6:38 
> If you code and design to web standards, you can save a lot of extra work.

Except there are no browsers that have yet been released which properly support all the standards (no, not even Firefox does).

> code for the standard, ignore the browser.

That's OK for mypersonalwebsite.com, but a totally useless recommendation for professional web developers with a job to hold down. IE 6 is not standards compliant and you'd be pretty stupid if you choose not to support it since it's the main web browser in use by 85%-95% of web users (depending on the type of site).

> I just try to remember to use a couple of javascript tricks or css hacks where important

You call CSS hacks coding for the standards?! All the CSS hacks I've seen involve exploiting parser bugs, rendering bugs or purposely using features IE doesn't support in order to get a different appearance. That means when IE does support those features - all your sites will break. Great hack. Most pros make a point of never using CSS hacks.
GeneralGood to know... Pin
Heath Stewart2-Jun-04 14:34
protectorHeath Stewart2-Jun-04 14:34 

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