Modules are fairly low level and fire against every inbound request to the ASP.NET application. Http Handlers are more focused and operate on a specific request mapping, usually a page extension that is mapped to the handler.
Http Handler implementations are very basic in their requirements, but through access of the HttpContext object a lot of power is available. Http Handlers are implemented through a very simple IHttpHandler interface (or its asynchronous cousin, IHttpAsyncHandler) which consists of merely a single method – ProcessRequest() – and a single property IsReusable. The key is ProcessRequest() which gets passed an instance of the HttpContext object. This single method is responsible for handling a Web request start to finish.
Single, simple method? Must be too simple, right? Well, simple interface, but not simplistic in what’s possible! Remember that WebForms and WebServices are both implemented as Http Handlers, so there’s a lot of power wrapped up in this seemingly simplistic interface. The key is the fact that by the time an Http Handler is reached all of ASP.NET’s internal objects are set up and configured to start processing of requests. The key is the HttpContext object, which provides all of the relevant request functionality to retireve input and send output back to the Web Server.
For an HTTP Handler all action occurs through this single call to ProcessRequest(). This can be as simple as:
public void ProcessRequest(HttpContext context)
{
context.Response.Write("ASP.Net World");
}
to a full implementation like the WebForms Page engine that can render complex forms from HTML templates. The point is that it’s up to you to decide of what you want to do with this simple, but powerful interface!
Because the Context object is available to you, you get access to the Request, Response, Session and Cache objects, so you have all the key features of an ASP.NET request at your disposal to figure out what users submitted and return content you generate back to the client.
The key operation of the handler should be eventually write output into the Respone object or more specifically the Response object’s OutputStream. This output is what actually gets sent back to the client. Behind the scenes the ISAPIWorkerRequest manages sending the OutputStream back into the ISAPI ecb.WriteClient method that actually performs the IIS output generation.
So handlers are more efficient.
Http Handler implementations are very basic in their requirements, but through access of the HttpContext object a lot of power is available. Http Handlers are implemented through a very simple IHttpHandler interface (or its asynchronous cousin, IHttpAsyncHandler) which consists of merely a single method – ProcessRequest() – and a single property IsReusable. The key is ProcessRequest() which gets passed an instance of the HttpContext object. This single method is responsible for handling a Web request start to finish.
Single, simple method? Must be too simple, right? Well, simple interface, but not simplistic in what’s possible! Remember that WebForms and WebServices are both implemented as Http Handlers, so there’s a lot of power wrapped up in this seemingly simplistic interface. The key is the fact that by the time an Http Handler is reached all of ASP.NET’s internal objects are set up and configured to start processing of requests. The key is the HttpContext object, which provides all of the relevant request functionality to retireve input and send output back to the Web Server.
For an HTTP Handler all action occurs through this single call to ProcessRequest(). This can be as simple as:
public void ProcessRequest(HttpContext context)
{
context.Response.Write("ASP.Net World");
}
to a full implementation like the WebForms Page engine that can render complex forms from HTML templates. The point is that it’s up to you to decide of what you want to do with this simple, but powerful interface!
Because the Context object is available to you, you get access to the Request, Response, Session and Cache objects, so you have all the key features of an ASP.NET request at your disposal to figure out what users submitted and return content you generate back to the client.
The key operation of the handler should be eventually write output into the Respone object or more specifically the Response object’s OutputStream. This output is what actually gets sent back to the client. Behind the scenes the ISAPIWorkerRequest manages sending the OutputStream back into the ISAPI ecb.WriteClient method that actually performs the IIS output generation.
So handlers are more efficient.
The HttpApplication object is responsible for selecting the appropriate PageHandlerFactory for that requesting page; this creates an instance of the page class of the web page that has initiated the request. All handler factories implement the IHttphandler interface. How does the HttpApplication object know which is the handler for that page? It first determines the type of the incoming request and invokes the appropriate handler factory.
If the request is for a page, then it calls the PageHandlerFactory for that page.
It finds the handler for the page by searching the <httpHandlers> section of the machine.config file. The HttpModule is one that fits into the HttpPipeLine of objects and can filter or edit the requests or the responses that come its way. On the other hand, the HttpHandler is responsible for initiating rendering and is defined in the configuration files. Your web page class actually derives from the System.Web.UI.Page class and implements the IHttpHandler interface.
Each page handler implements the IHttpHandler interface that contains the ProcessRequest() method, which is actually responsible for processing the request. The response is complete and served to the client browser after the page is unloaded from the memory.
If the request is for a page, then it calls the PageHandlerFactory for that page.
It finds the handler for the page by searching the <httpHandlers> section of the machine.config file. The HttpModule is one that fits into the HttpPipeLine of objects and can filter or edit the requests or the responses that come its way. On the other hand, the HttpHandler is responsible for initiating rendering and is defined in the configuration files. Your web page class actually derives from the System.Web.UI.Page class and implements the IHttpHandler interface.
Each page handler implements the IHttpHandler interface that contains the ProcessRequest() method, which is actually responsible for processing the request. The response is complete and served to the client browser after the page is unloaded from the memory.
The following default httpHandlers element is configured in the root Web.config file in the .NET Framework 2.0.
<httpHandlers>
<add... />
<remove... />
<clear/>
</httpHandlers>
add : Optional element.Specifies verb/path mapping to a handler.
clear : Optional element.Removes all handler mappings that are currently configured or inherited.
remove : Optional element.Removes a verb/path mapping to a handler. The remove directive must exactly match the verb/path combination of a previous add directive. Wildcard characters are not supported.
The <httpHandlers> settings are inherited by the application subdirectories.
The <add> directives are processed in top-down, sequential order. If two or more <add> elements specify the same verb/path combination, the final <add> overrides all others.
<httpHandlers>
<add path="trace.axd" verb="*" type="System.Web.Handlers.TraceHandler" validate="True" />
<add path="WebResource.axd" verb="GET" type="System.Web.Handlers.AssemblyResourceLoader"
validate="True" />
<add path="*.axd" verb="*" type="System.Web.HttpNotFoundHandler" validate="True" />
<add path="*.aspx" verb="*" type="System.Web.UI.PageHandlerFactory" validate="True" />
<add path="*.ashx" verb="*" type="System.Web.UI.SimpleHandlerFactory" validate="True" />
<add path="*.asmx" verb="*" type="System.Web.Services.Protocols.WebServiceHandlerFactory,
System.Web.Services, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" validate="False" />
<add path="*.rem" verb="*" type="System.Runtime.Remoting.Channels.Http.HttpRemotingHandlerFactory,
System.Runtime.Remoting, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"
validate="False" />
<add path="*.soap" verb="*" type="System.Runtime.Remoting.Channels.Http.HttpRemotingHandlerFactory,
System.Runtime.Remoting, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"
validate="False" />
<add path="*.asax" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.ascx" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.master" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.skin" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.browser" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.sitemap" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.dll.config" verb="GET,HEAD" type="System.Web.StaticFileHandler" validate="True" />
<add path="*.exe.config" verb="GET,HEAD" type="System.Web.StaticFileHandler" validate="True" />
<add path="*.config" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.cs" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.csproj" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.vb" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.vbproj" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.webinfo" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.licx" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.resx" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.resources" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.mdb" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.vjsproj" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.java" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.jsl" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.ldb" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.dsdgm" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.ssdgm" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.lsad" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.ssmap" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.cd" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.dsprototype" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.lsaprototype" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.sdm" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.sdmDocument" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.mdf" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.ldf" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*" verb="GET,HEAD,POST" type="System.Web.DefaultHttpHandler" validate="True" />
<add path="*" verb="*" type="System.Web.HttpMethodNotAllowedHandler" validate="True" />
</httpHandlers>
Configurable locations:
<httpHandlers>
<add... />
<remove... />
<clear/>
</httpHandlers>
add : Optional element.Specifies verb/path mapping to a handler.
clear : Optional element.Removes all handler mappings that are currently configured or inherited.
remove : Optional element.Removes a verb/path mapping to a handler. The remove directive must exactly match the verb/path combination of a previous add directive. Wildcard characters are not supported.
The <httpHandlers> settings are inherited by the application subdirectories.
The <add> directives are processed in top-down, sequential order. If two or more <add> elements specify the same verb/path combination, the final <add> overrides all others.
<httpHandlers>
<add path="trace.axd" verb="*" type="System.Web.Handlers.TraceHandler" validate="True" />
<add path="WebResource.axd" verb="GET" type="System.Web.Handlers.AssemblyResourceLoader"
validate="True" />
<add path="*.axd" verb="*" type="System.Web.HttpNotFoundHandler" validate="True" />
<add path="*.aspx" verb="*" type="System.Web.UI.PageHandlerFactory" validate="True" />
<add path="*.ashx" verb="*" type="System.Web.UI.SimpleHandlerFactory" validate="True" />
<add path="*.asmx" verb="*" type="System.Web.Services.Protocols.WebServiceHandlerFactory,
System.Web.Services, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" validate="False" />
<add path="*.rem" verb="*" type="System.Runtime.Remoting.Channels.Http.HttpRemotingHandlerFactory,
System.Runtime.Remoting, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"
validate="False" />
<add path="*.soap" verb="*" type="System.Runtime.Remoting.Channels.Http.HttpRemotingHandlerFactory,
System.Runtime.Remoting, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"
validate="False" />
<add path="*.asax" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.ascx" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.master" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.skin" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.browser" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.sitemap" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.dll.config" verb="GET,HEAD" type="System.Web.StaticFileHandler" validate="True" />
<add path="*.exe.config" verb="GET,HEAD" type="System.Web.StaticFileHandler" validate="True" />
<add path="*.config" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.cs" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.csproj" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.vb" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.vbproj" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.webinfo" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.licx" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.resx" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.resources" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.mdb" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.vjsproj" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.java" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.jsl" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.ldb" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.dsdgm" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.ssdgm" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.lsad" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.ssmap" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.cd" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.dsprototype" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.lsaprototype" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.sdm" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.sdmDocument" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.mdf" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*.ldf" verb="*" type="System.Web.HttpForbiddenHandler" validate="True" />
<add path="*" verb="GET,HEAD,POST" type="System.Web.DefaultHttpHandler" validate="True" />
<add path="*" verb="*" type="System.Web.HttpMethodNotAllowedHandler" validate="True" />
</httpHandlers>
Configurable locations:
- Machine.config
- Root-level Web.config
- Application-level Web.config
- Virtual or physical directory–level Web.config