February 04, 2008

ASP.NET HttpHandler how to

HttpHandlers are class which extend HttpHandler and which IIS recognises as the classes to use to handle errors etc.
The HttpHandler class is usually stored inside a .ashx file.

You can create your on .ashx and place it in you web app root dir, it will be entered whenever a request comes in from the client.

If you do not want to show your HttpHandler file code in your web app then you can hide it in a dll see details below.

How to hide the .ashx with a HttpHandler

I'll describe here how to create a handler for a file with the extension .ashx, it's coincidental I require a HttpHandler in my web.config in order to alias my .ashx file which is too a HttpHandler.

Note: Before you can compile a HttpHandler into a dll you must remove the directive at the start of the .ashx file e.g. delete this line
<%@ WebHandler Language="C#" Class="MyWebHandler" %>
If you fail to do this your .ashx code will not appear in your dll and you will not be able to register the type MyWebHandler.

One way to hide .ashx files is by a creating a handler for .ashx files.
The Handler is a HttpHandler.
This Handler will handle any calls to to files with the extension .ashx, this could be any extesion (I think), whatever extension you want will be supplied in the Web Applications web.config
e.g. if you created a HttpHandler and you want it to cater for all .ashx files in your Web Application add something like this to your Web Application's web.config :

In IIS 6 Classic Pipeline:
<system.web>
<httpHandlers>
<add verb="*" path="*.ashx"
type="MyWebHandler.Service1,
WebServiceHandler, Version=1.0.0.0, Culture=neutral,
PublicKeyToken=9bae47114a98ed1a"/>
<add verb="*" path="Service5.asmx" type="Service4,
WebServiceHandler, Version=1.0.0.0,
Culture=neutral,
PublicKeyToken=9bae47114a98ed1a"/>

Or if you want to provide handler for a particular ashx file use something like this
<add verb="*" path="Service3.ashx"
type="MyWebServiceHandlerClass,
MyWebServiceHandlerDLL,
Version=1.0.0.0,
Culture=neutral,
PublicKeyToken=9bae47114a98ed1a"/>


in IIS 7 Integrated Pipeline, the section exists on the <system.webserver> and it has an additional Name attribute:

<system.webServer>
<httpHandlers>
<add name="MyHandler" verb="*" path="*.ashx"
type="MyWebHandler.Service1,
WebServiceHandler, Version=1.0.0.0, Culture=neutral,
PublicKeyToken=9bae47114a98ed1a"/>


<add name="Service4Handler" verb="*" path="Service5.asmx" type="Service4,
WebServiceHandler, Version=1.0.0.0,
Culture=neutral,
PublicKeyToken=9bae47114a98ed1a"/>

<system.webServer>

http://msdn.microsoft.com/en-us/library/46c5ddfy.aspx

Above the strong name is being used to locate the dll, this is because the dll is in the GAC, you do not have to put the dll in the GAC.

The second parameter in the 'type' list above is actually the name of the dll file, the Version, culture, PublicKeyToken, are all the fullname of the dll containing your HttpHandler code i.e. the strong name.

The Handler itself must include your code that was originally in your original file and also Implement the IHttpHandler Interface.
You can compile your HttpHandler into a seperate dll and add it to the GAC with the signature provided in the web.config of vice versa, just make sure that the Strong Name in the DLL is identical to the String name provided in the type in the Web Applications type.

If you choose to put your dll in the web apps bin directory then it can be registered as follows:
<add verb="*" path="Service3.ashx"
type="MyWebServiceHandlerClass,
MyWebServiceHandlerDLL"/>

Note: Only the dll name is required, no extension and no strong name it just needs to exist in the web apps bin directory.

Bug:
There's a small bug in ASP.NET 2.0, if you create a handler and you do not wish to use an assembly to store the HttpHandler code you can simple add the source file to the App_Code directory and just use the type in the web.config without and assembly, well this is how it's supposed to work but actually you have to do one more thing and that is you must create a codebehind file and place the code in there instead and add the details to the Http handlers directive
<%@ WebHandler Language="C#" Class="MyHandler" CodeBehind="MyHandler.ashx.cs" %>
web.config
<add verb="*" path="myfile.something"
type="MyHandler"/>

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