The Web Request Broker (WRB)

Whenever the Web Listener receives a URL that calls for the WRB, it passes execution of the request to the WRB Dispatcher or simply Dispatcher. The Dispatcher maintains communication with a pool of processes called WRB Executable Engines (WRBXs).The Dispatcher finds a free WRBX that is configured to run the desired WRB Service and passes execution to it. The result is that the Listener can receive and validate URLs coming in, while each request is handed off to a process that executes it in the background. Each WRBX uses the WRB API to interface to a WRB cartridge. WRB cartridges can be of the following types:

• The PL/SQL Agent. This cartridge executes PL/SQL commands stored in the database. It is better optimized for database access than the Java cartridge, but doesn't have all of Java's functionality.
• The Java™ Interpreter. This cartridge lets you execute Java on the server to generate dynamic Web pages. You can also execute PL/SQL from within Java using this cartridge.
• The LiveHTML Interpreter. This cartridge is Oracle's implementation and extension of the industry-standard Server Side Includes functionality. LiveHTML enables you to include in your Web pages the output of any program that your Operating System can execute.

WRB Services

The Dispatcher determines which WRB Service to send a given request to on the basis of the path and the file extension (MIME type) specified in the URL. You configure the WRB in the WebServer Manager to determine which combinations of path and extension correspond to which Services.

The WRB API is designed so that third parties can write their own extensions to the WebServer. The three cartridges listed above come with the WebServer, but you can obtain additional cartridges from third parties or write your own.

The WRB Services can also augment the access control specified by the Listener with Service-specific control. The Services included with the WebServer do not do this, but the WRB API provides a callback routine that enables you to put this functionality in cartridges that you write. This routine enables your cartridge to do any of the following:

• Prompt for a username and password, using either a Basic or a Digest scheme. The difference between Basic and Digest is that a Digest scheme encrypts the password (for more information on these terms, see the discussion of the Listener earlier in this section).
• Specify by name some restriction scheme to be applied to this request. Such restriction schemes are defined in the Listener and limit access by IP address or Domain Name.

WRB Executable Engines

• The URL triggering the request. This can include a file extension indicating the desired MIME type of the result.
• The desired language of the result.
• The desired character set of the result (how the language is encoded, for example, ISO or Unicode).
• CGI environment variables, which allow WRB cartridges to be run by applications written for CGI.
• If the request involves the use of the PL/SQL Agent, which of the Database Connection Descriptors (DCDs) to use.

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