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+---
+layout: post
+category: perl
+title: More fun with Tatsumaki and Plack
+---
+
+Lately I've been toying a lot with "Plack":http://plackperl.org/ and two Perl web framework: "Tatsumaki":http://search.cpan.org/perldoc?Tatsumaki and "Dancer":http://search.cpan.org/perldoc?Dancer. I use both of them for different purposes, as their features complete each other.
+
+h3. Plack
+
+If you don't already know what Plack is, you would want to take a look at the following Plack resources:
+
+ * "Plack (redesigned) website":http://plackperl.org
+ * "Plack documentation":http://search.cpan.org/perldoc?Plack
+ * "miyagawa's screencast":http://bulknews.typepad.com/blog/2009/11/plack-and-psgi-screencast-and-feedbacks.html
+ * "Plack advent calendar":http://advent.plackperl.org/
+
+.bq As "sukria":http://www.sukria.net/ is planning to talk about "Dancer":http://perldancer.org during the "FPW 2010":http://journeesperl.fr/fpw2010/index.html, I will probably do a talk about Plack.
+
+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.
+
+h4. Plack::Middleware::ETag
+
+This middleware is really simple: for each request, an "ETag":http://en.wikipedia.org/wiki/HTTP_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 "Plack::Middleware::ConditionalGET":http://search.cpan.org/perldoc?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 "available on CPAN":http://search.cpan.org/perldoc?Plack::Middleware::ETag.
+
+Let's see how it works. First, we create a really simple application (we call it app.psgi):
+
+{% highlight 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']];
+    };
+};
+{% endhighlight %}
+
+Now we can test it:
+
+{% highlight bash %}
+> 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
+{% endhighlight %}
+
+h4. Plack::Middleware::Throttle
+
+"With this middleware":http://github.com/franckcuny/plack--middleware--throttle, 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 on github. 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:
+
+{% highlight 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']];
+    };
+};
+{% endhighlight %}
+
+then test
+
+{% highlight bash %}
+$ 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
+{% endhighlight %}
+
+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 "Dancer REST stuff":http://www.sukria.net/fr/archives/2010/03/19/let-the-dancer-rest/ "added recently":http://lumberjaph.net/blog/index.php/2010/03/19/easily-create-rest-interface-with-the-dancer-1170/.
+
+h3. another Tatsumaki application with Plack middlewares
+
+To demonstrate the use of this two middleware, "I've wrote a small application":http://github.com/franckcuny/feeddiscovery with Tatsumaki. This application fetch a page, parse it to find all the feeds declared, and return a JSON with the result.
+
+{% highlight bash %}
+    GET http://feeddiscover.tirnan0g.org/?url=http://lumberjaph.net/blog/
+{% endhighlight %}
+
+will return
+
+{% highlight javascript %}
+    [{"href":"http://lumberjaph.net/blog/index.php/feed/","type":"application/rss+xml","title":"iām a lumberjaph RSS Feed"}]
+{% endhighlight %}
+
+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:
+
+{% highlight 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;
+};
+{% endhighlight %}
+
+The application itself is really simple: for a given url, the Tatsumaki::HTTPClient fetch an url, I use "Web::Scraper":http://search.cpan.org/perldoc?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.