2.14 Serving Servlets

procedure
( make-cached-url->servlet url->path
path->serlvet)

→
(->* ()((or/c false/c (listof url? ))(-> servlet? void? ))void? )
url->servlet/c
url->path:url->path/c
path->serlvet:path->servlet/c

The first return value is a procedure that flushes the cache. If its first optional argument is #f (the default), all servlet caches are flushed. Otherwise, only those servlet caches to which url->path maps the given URLs are flushed. The second optional argument is a procedure which is invoked on each cached value before it is flushed, which can be used to finalize servlet resources. Beware that the default value void performs no finalization. In particular, it does not shut down the servlet’s custodian, instead allowing the servlet’s custodian-managed resources (such as threads) to persist.

The second return value is a procedure that uses url->path to resolve the URL to a path, then uses path->servlet to resolve that path to a servlet, caching the results in an internal table.

Changed in version 1.3 of package web-server-lib: Added optional argument to first return value for list of URLs.
Changed in version 1.3: Added optional argument to first return value for servlet finalizer procedure.

procedure
( make url->servlet
[ #:responders-servlet-loadingresponders-servlet-loading
#:responders-servletresponders-servlet])
→dispatcher/c
url->servlet:url->servlet/c

responders-servlet-loading : (url? exn? . -> .can-be-response?)
= servlet-loading-responder

responders-servlet : (url? exn? . -> .can-be-response?)
= servlet-error-responder

This dispatcher runs racket servlets, using url->servlet to resolve URLs to the underlying servlets. If servlets have errors loading, then responders-servlet-loading is used. Other errors are handled with responders-servlet. If a servlet raises calls next-dispatcher, then the signal is propagated by this dispatcher.

2.14.1Setting Up Servlets🔗 i

(require web-server/servlet/setup ) package: web-server-lib

This module is used internally to build and load servlets. It may be useful to those who are trying to extend the server.

procedure
( make-v1.servlet directorytimeoutstart)→servlet?
directory:path-string?
timeout:integer?
start:(request? . -> .can-be-response?)

Creates a version 1 servlet that uses directory as its current directory, a timeout manager with a timeout timeout, and start as the request handler.

procedure
( make-v2.servlet directorymanagerstart)→servlet?
directory:path-string?
manager:manager?
start:(request? . -> .can-be-response?)

Creates a version 2 servlet that uses directory as its current directory, a manager as the continuation manager, and start as the request handler.

procedure
( make-stateless.servlet directory
stuffer
manager
start) → servlet?
directory:path-string?
stuffer:(stuffer/c serializable? bytes? )
manager:manager?
start:(request? . -> .can-be-response?)

Creates a stateless web-server servlet that uses directory as its current directory, stuffer as its stuffer, and manager as the continuation manager, and start as the request handler.

value
default-module-specs :(listof module-path? )

The modules that the Web Server needs to share with all servlets.

value
path->servlet/c :contract?

Equivalent to (-> path? servlet? ).

procedure
( make-default-path->servlet
[ #:make-servlet-namespacemake-servlet-namespace
#:timeouts-default-servlettimeouts-default-servlet])
→path->servlet/c

make-servlet-namespace : make-servlet-namespace/c
= (make-make-servlet-namespace )
timeouts-default-servlet:integer? =30

Constructs a procedure that loads a servlet from the path in a namespace created with make-servlet-namespace, using a timeout manager with timeouts-default-servlet as the default timeout (if no manager is given.)

2.14.2Servlet Namespaces🔗 i

(require web-server/configuration/namespace )

package: web-server-lib

This module provides a function to help create the make-servlet-namespace procedure needed by the make function of web-server/dispatchers/dispatch-servlets.

value
make-servlet-namespace/c :contract?

Equivalent to

(->* ()
(#:additional-specs(listof module-path? ))
namespace? )

procedure
( make-make-servlet-namespace #:to-be-copied-module-specsto-be-copied-module-specs)
→make-servlet-namespace/c
to-be-copied-module-specs:(listof module-path? )

This function creates a function that when called will construct a new namespace that has all the modules from to-be-copied-module-specs and additional-specs, as well as racket and mred, provided they are already attached to the (current-namespace ) of the call-site.

Example:

(make-make-servlet-namespace
#:to-be-copied-module-specs`((lib"database.rkt""my-module")))

2.14.2.1Why this is useful🔗 i

A different namespace is needed for each servlet, so that if servlet A and servlet B both use a stateful module C, they will be isolated from one another. We see the Web Server as an operating system for servlets, so we inherit the isolation requirement on operating systems.

However, there are some modules which must be shared. If they were not, then structures cannot be passed from the Web Server to the servlets, because Racket’s structures are generative.

Since, on occasion, a user will actually wanted servlets A and B to interact through module C. A custom make-servlet-namespace can be created, through this procedure, that attaches module C to all servlet namespaces. Through other means (see Dispatchers) different sets of servlets can share different sets of modules.

2.14.3Internal Servlet Representation🔗 i

(require web-server/private/servlet )

package: web-server-lib

struct
(struct servlet (custodiannamespacemanagerdirectoryhandler)
#:extra-constructor-namemake-servlet
#:mutable)
custodian:custodian?
namespace:namespace?
manager:manager?
directory:path-string?
handler:(request? . -> .can-be-response?)

Instances of this structure hold the necessary parts of a servlet: the custodian responsible for the servlet’s resources, the namespace the servlet is executed within, the manager responsible for the servlet’s continuations, the current directory of the servlet, and the handler for all requests to the servlet.

top ← prev up next →