sourceafBedSheet::Middleware.fan

** Implement to define BedSheet middleware. 
** 
** HTTP requests are funnelled through a stack of middleware instances until either one of them 
** returns 'true', or they reach a terminator. The default BedSheet terminator returns a 404 error.
**  
** Middleware may perform processing before and / or after passing the request down the pipeline to 
** other middleware instances. Use middleware to address cross cutting concerns such as 
** authentication and authorisation. See the FantomFactory article 
** [Basic HTTP Authentication With BedSheet]`http://www.fantomfactory.org/articles/basic-http-authentication-with-bedSheet#.U2I2MyhfyJA` for examples.
** 
** Because middleware effectively wrap other middleware instances and each can terminate the 
** pipeline prematurely, the ordering of middleware is extremely important. 
** 
** 'Route' instances are processed in the 'Routes' middleware. So generally you would explicitly 
** contribute your own middleware to be *before* or *after* this.
** 
** IOC Configuration
** =================
** Instances of 'Middleware' should be contributed to the 'MiddlewarePipeline' service.
** 
** For example, in your 'AppModule' class:
** 
** pre>
**   @Contribute { serviceType=MiddlewarePipeline# }
**   static Void contributeMiddleware(Configuration conf) {
**       conf.set("AuthMiddleware", conf.autobuild(AuthMiddleware#), ["before: Routes"])
**   }
** <pre
// Used by Duvet
const mixin Middleware {

    ** Return 'true' if you handled the request and no further request processing should be performed. 
    ** Otherwise the request should be sent down the pipeline.
    abstract Void service(MiddlewarePipeline pipeline) 

}