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+Lately I've been toying a lot with [[http://plackperl.org/][Plack]] and
+two Perl web framework:
+[[http://search.cpan.org/perldoc?Tatsumaki][Tatsumaki]] and
+[[http://search.cpan.org/perldoc?Dancer][Dancer]]. I use both of them
+for different purposes, as their features complete each other.
+
+** Plack
+
+If you don't already know what Plack is, you would want to take a look
+at the following Plack resources:
+
+-  [[http://plackperl.org][Plack (redesigned) website]]
+-  [[http://search.cpan.org/perldoc?Plack][Plack documentation]]
+-  [[http://bulknews.typepad.com/blog/2009/11/plack-and-psgi-screencast-and-feedbacks.html][Miyagawa's
+   screencast]]
+-  [[http://advent.plackperl.org/][Plack advent calendar]]
+
+#+BEGIN_QUOTE
+  As [[http://www.sukria.net/][sukria]] is planning to talk about
+  [[http://perldancer.org][Dancer]] during the
+  [[http://journeesperl.fr/fpw2010/index.html][FPW 2010]], I will
+  probably do a talk about Plack.
+#+END_QUOTE
+
+After reading some code, I've started to write two middleware: the first
+one add ETag header to the HTTP response, and the second one provides a
+way to limit access to your application.
+
+*** Plack::Middleware::ETag
+
+This middleware is really simple: for each request, an
+[[http://en.wikipedia.org/wiki/HTTP_ETag][ETag]] header is added to the
+response. The ETag value is a sha1 of the response's content. In case
+the content is a file, it works like apache, using various information
+from the file: inode, modified time and size. This middleware can be
+used with
+[[http://search.cpan.org/perldoc?Plack::Middleware::ConditionalGET][Plack::Middleware::ConditionalGET]],
+so the client will have the ETag information for the page, and when he
+will do a request next time, it will send an "if-modified" header. If
+the ETag is the same, a 304 response will be send, meaning the content
+have not been modified. This module is
+[[http://search.cpan.org/perldoc?Plack::Middleware::ETag][available on
+CPAN]].
+
+Let's see how it works. First, we create a really simple application (we
+call it app.psgi):
+
+#+BEGIN_SRC perl
+    #!/usr/bin/env perl
+    use strict;
+    use warnings;
+    use Plack::Builder;
+
+    builder {
+        enable "Plack::Middleware::ConditionalGET";
+        enable "Plack::Middleware::ETag";
+        sub {
+            ['200', ['Content-Type' => 'text/html'], ['Hello world']];
+        };
+    };
+#+END_SRC
+
+Now we can test it:
+
+#+BEGIN_EXAMPLE
+    % plackup app.psgi&
+    % curl -D - http://localhost:5000
+    HTTP/1.0 200 OK
+    Date: Sat, 03 Apr 2010 09:31:43 GMT
+    Server: HTTP::Server::PSGI
+    Content-Type: text/html
+    ETag: 7b502c3a1f48c8609ae212cdfb639dee39673f5e
+    Content-Length: 11
+
+    % curl -H "If-None-Match: 7b502c3a1f48c8609ae212cdfb639dee39673f5e" -D - http://localhost:5000
+    HTTP/1.0 304 Not Modified
+    Date: Sat, 03 Apr 2010 09:31:45 GMT
+    Server: HTTP::Server::PSGI
+    ETag: 7b502c3a1f48c8609ae212cdfb639dee39673f5e
+#+END_EXAMPLE
+
+*** Plack::Middleware::Throttle
+
+[[http://git.lumberjaph.net/p5-plack-middleware-throttle.git/][With this
+middleware]], you can control how many times you want to provide an
+access to your application. This module is not yet on CPAN, has I want
+to add some features, but you can get the code from git. There is four
+methods to control access:
+
+-  Plack::Middleware::Throttle::Hourly: how many times in one hour
+   someone can access the application
+-  P::M::T::Daily: the same, but for a day
+-  P::M::T::Interval: which interval the client must wait between two
+   query
+-  by combining the three previous methods
+
+To store sessions informations, you can use any cache backend that
+provides =get=, =set= and =incr= methods. By default, if no backend is
+provided, it will store informations in a hash. You can easily modify
+the defaults throttling strategies by subclassing all the classes.
+
+Let's write another application to test it:
+
+#+BEGIN_SRC perl
+    #!/usr/bin/env perl
+    use strict;
+    use warnings;
+    use Plack::Builder;
+
+    builder {
+        enable "Plack::Middleware::Throttle::Hourly", max => 2;
+        sub {
+            ['200', ['Content-Type' => 'text/html'], ['Hello world']];
+        };
+    };
+#+END_SRC
+
+then test
+
+#+BEGIN_EXAMPLE
+    % curl -D - http://localhost:5000/
+    HTTP/1.0 200 OK
+    Date: Sat, 03 Apr 2010 09:57:40 GMT
+    Server: HTTP::Server::PSGI
+    Content-Type: text/html
+    X-RateLimit-Limit: 2
+    X-RateLimit-Remaining: 1
+    X-RateLimit-Reset: 140
+    Content-Length: 11
+
+    Hello world
+
+    % curl -D - http://localhost:5000/
+    HTTP/1.0 200 OK
+    Date: Sat, 03 Apr 2010 09:57:40 GMT
+    Server: HTTP::Server::PSGI
+    Content-Type: text/html
+    X-RateLimit-Limit: 2
+    X-RateLimit-Remaining: 0
+    X-RateLimit-Reset: 140
+    Content-Length: 11
+
+    Hello world
+
+    % curl -D - http://localhost:5000/
+    HTTP/1.0 503 Service Unavailable
+    Date: Sat, 03 Apr 2010 09:57:41 GMT
+    Server: HTTP::Server::PSGI
+    Content-Type: text/plain
+    X-RateLimit-Reset: 139
+    Content-Length: 15
+
+    Over rate limit
+#+END_EXAMPLE
+
+Some HTTP headers are added to the response :
+
+-  *X-RateLimit-Limit*: how many request can be done
+-  *X-RateLimit-Remaining*: how many requests are available
+-  *X-RateLimit-Reset*: when will the counter be reseted (in seconds)
+
+This middleware could be a very good companion to the
+[[http://www.sukria.net/fr/archives/2010/03/19/let-the-dancer-rest/][Dancer
+REST stuff]]
+[[/easily-create-rest-interface-with-the-dancer-1.170/][added
+recently]].
+
+** another Tatsumaki application with Plack middlewares
+
+To demonstrate the use of this two middleware,
+[[http://git.lumberjaph.net/p5-feeddiscovery.git/][I wrote a small
+application]] with Tatsumaki. This application fetch a page, parse it to
+find all the feeds declared, and return a JSON with the result.
+
+#+BEGIN_EXAMPLE
+    % GET http://feeddiscover.tirnan0g.org/?url=http://lumberjaph.net/blog/
+#+END_EXAMPLE
+
+will return
+
+#+BEGIN_EXAMPLE
+    % [{"href":"http://lumberjaph.net/blog/index.php/feed/","type":"application/rss+xml","title":"i'm a lumberjaph RSS Feed"}]
+#+END_EXAMPLE
+
+This application is composed of one handler, that handle only *GET*
+request. The request will fetch the url given in the *url* parameter,
+scrap the content to find the links to feeds, and cache the result with
+Redis. The response is a JSON string with the informations.
+
+The interesting part is the app.psgi file:
+
+#+BEGIN_SRC perl
+    my $app = Tatsumaki::Application->new(['/' => 'FeedDiscovery::Handler'],);
+
+    builder {
+        enable "Plack::Middleware::ConditionalGET";
+        enable "Plack::Middleware::ETag";
+        enable "Plack::Middleware::Throttle::Hourly",
+            backend => Redis->new(server => '127.0.0.1:6379',),
+            max     => 100;
+        $app;
+    };
+#+END_SRC
+
+The application itself is really simple: for a given url, the
+Tatsumaki::HTTPClient fetch an url, I use
+[[http://search.cpan.org/perldoc?Web::Scraper][Web::Scraper]] to find
+the *link rel="alternate"* from the page, if something is found, it's
+stored in Redis, then a JSON string is returned to the client.