initializing a servlet in WEBRick

Xavier Noria · Xavier Noria

I am writing a web application where all the requests are served by the
same object, which needs initialization. This is being done this way:

<<initialize some stuff from the command line parameters>>
<<initialize the driver of the application from that stuff>>
server.mount_proc(path) { |req, res| driver.process(req, res) }

That seems to work fine, but I wonder if the driver could be a subclass
of HTTPServlet::AbstractServlet so that one would just say

server.mount(path, DriverServlet)

and have one instance serving all the pages and initialized as needed. I
have tried to figure it out from the sources but don't see how would it
work.

-- fxn

GOTOU Yuuzou · GOTOU Yuuzou

Hi,

In message <200309071203.04502.fxn@hashref.com>,
`Xavier Noria <fxn@hashref.com>' wrote:

> I am writing a web application where all the requests are served by the
> same object, which needs initialization. This is being done this way:
>
> <<initialize some stuff from the command line parameters>>
> <<initialize the driver of the application from that stuff>>
> server.mount_proc(path) { |req, res| driver.process(req, res) }
>
> That seems to work fine, but I wonder if the driver could be a subclass
> of HTTPServlet::AbstractServlet so that one would just say
>
> server.mount(path, DriverServlet)
>
> and have one instance serving all the pages and initialized as needed. I
> have tried to figure it out from the sources but don't see how would it
> work.

If it's explained simply, servelets are activated in the
following sequence:

<< accept connection and receive HTTP request >>
<< find a ServletClass associated with path of URL >>

# the third and more arguments of mount() will be passed to options.
servlet = ServletClass.get_instance(server, *options)
servlet.service(req, res)

<< send response >>

If it can respond to get_instance and service, any kind of
object can be mounted as a servelet.

AbstractServlet::get_instance just calls new() and instance
of servelet will be created for every request. Conversely
singleton servelet can be up by overriding of get_instance.

The following sample implements get_instance as a instance
method and initialize a servlet out of server before it's
started.

require 'webrick'

class AccessCounter < WEBrick::HTTPServlet::AbstractServlet
def initialize(server)
@mutex = Mutex.new # service should be MT-safe
@count = 0
end
def get_instance(server)
self # always returns same instance
end
def service(req, res)
@mutex.synchronize{ super }
end
def do_GET(req, res)
res.body = "<html><body>@count=<b>#{@count+=1}</b></body></html>"
res['content-type'] = "text/html"
end
end

svr = WEBrick::HTTPServer.new(:Port => 10080)
counter = AccessCounter.new(svr)
svr.mount("/", counter)
svr.start

--
gotoyuzo

Xavier Noria · Xavier Noria

On Sunday 07 September 2003 15:43, GOTOU Yuuzou wrote:

> If it's explained simply, servelets are activated in the
> following sequence:
>
> << accept connection and receive HTTP request >>
> << find a ServletClass associated with path of URL >>
>
> # the third and more arguments of mount() will be passed to
> options. servlet = ServletClass.get_instance(server, *options)
> servlet.service(req, res)
>
> << send response >>
>
> If it can respond to get_instance and service, any kind of
> object can be mounted as a servelet.

<< cut >>

That's very helpful, thank you very much GOTOU.

The code shouldn't depend on the implementation of WEBrick however, do
you think we can rely on the outlined sequence

* << accept connection and receive HTTP request >>
* << find a ServletClass associated with path of URL >>

* # the third and more arguments of mount() will be passed to options.
* servlet = ServletClass.get_instance(server, *options)
* servlet.service(req, res)

* << send response >>

?

-- fxn

PS: I am sorry for the typo in the subject.

GOTOU Yuuzou · GOTOU Yuuzou

In message <200309071717.08089.fxn@hashref.com>,
`Xavier Noria <fxn@hashref.com>' wrote:

> On Sunday 07 September 2003 15:43, GOTOU Yuuzou wrote:

> > If it can respond to get_instance and service, any kind of
> > object can be mounted as a servelet.

>
> << cut >>
>
> That's very helpful, thank you very much GOTOU.
>
> The code shouldn't depend on the implementation of WEBrick however, do
> you think we can rely on the outlined sequence
>
> * << accept connection and receive HTTP request >>
> * << find a ServletClass associated with path of URL >>
>
> * # the third and more arguments of mount() will be passed to options.
> * servlet = ServletClass.get_instance(server, *options)
> * servlet.service(req, res)
>
> * << send response >>

Yes, requirement of get_instance and service is the spec
of WEBrick::HTTPServer. I guess it will not be changed.
# at least in Ruby-1.8..

By the way, the code of servlet activation is described in
HTTPServer#service. We can rewrite it to build specific
purpose server or realize another idea about uri-to-service
mapping.

require "webrick"
class NotFoundServer < WEBrick::HTTPServer
def service(req, res)
# returns 404 against every request.
raise WEBrick::HTTPStatus::NotFound
end
end
NotFoundServer.new(:Port=>10080).start

--
gotoyuzo

initializing a servlet in WEBRick

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