2.12 Serving Servlets
The first return value flushes the cache.
The second 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.
| (make | | url->servlet | | | | [ | #:responders-servlet-loading responders-servlet-loading | | | | | #:responders-servlet responders-servlet]) | |
|
| → dispatcher/c |
| url->servlet : url->servlet/c |
|
|
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.
2.12.1 Setting Up Servlets
This module is used internally to build and load servlets. It may be useful to those who are trying to extend the server.
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.
Creates a version 2 servlet that uses directory as its current directory, a manager as the continuation manager, and start as the request handler.
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.
The modules that the Web Server needs to share with all servlets.
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.)
2.12.2 Servlet Namespaces
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.
2.12.2.1 Why this is useful
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.
2.12.3 Internal Servlet Representation
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.