Service Detection

From GridSiteWiki

Traditional web services require that the client is either configured for one particular instance of the service, with a hard-coded location (as is the case with the command line client for the GridSite Delegation protocol , once compiled), or that the user of the client provides the URL of the service they wish to use. This can cause problems if locations of services change or users wish to locate alternative services providing the same functionality.

A system was developed to allow a browser (and in turn the GridSite Toolbar) to be notified of an available delegation service by a web site. The URL of the service is provided either in HTTP headers or in a META element in the HTML source of the page being viewed. The META element method is similar to the method employed by sites and browsers to enable automatic location of RSS feeds, which uses a LINK element.

The header used for the notification is "Proxy-Delegation-Service", the value of which should be the URL of the delegation service. The insertion of this header can be easily achieved with GridSite Apache module and setting the GridSiteDelegationURI directive in the web server's configuration file. To deliver the same information without using HTTP headers, a META element containing the http-equiv attribute can be inserted into the HEAD element of a web page. The META element would have the following format:

<META http-equiv = "Proxy-Delegation-Service" content = "">

The combination of the two methods above provides great flexibility for different groups of people to alert users to a delegation service. The HTTP header method allows a web server administrator to inform all visitors of a related delegation service and META element method allows an individual page (a personal home page, for example) to do the same. The latter may be useful in an environment where enabling server-wide options are not possible (e.g. pages located on unrelated servers) or on a server not using the GridSite software.