Get your teeth into Plack
 

Get your teeth into Plack

on

  • 9,159 views

A short introduction to Plack/PSGI with references.

A short introduction to Plack/PSGI with references.

Statistics

Views

Total Views
9,159
Views on SlideShare
9,159
Embed Views
0

Actions

Likes
0
Downloads
3
Comments
0

0 Embeds 0

No embeds

Accessibility

Categories

Upload Details

Uploaded via as Adobe PDF

Usage Rights

© All Rights Reserved

Report content

Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
  • Full Name Full Name Comment goes here.
    Are you sure you want to
    Your message goes here
    Processing…
Post Comment
Edit your comment

Get your teeth into Plack Get your teeth into Plack Presentation Transcript

  • Getting Your Teeth Into Plack: A short introduction to the next generation of web service. Steven Lembark Workhorse Computing
  • No! This is not a Listerine ad!● Sorry, no jingle in the background.● Plack is an interface for web request handlers.● It simplifies the interface to a usable level.● Permits more portable code.● Allows you to focus on your content handler, not the API specs.
  • In the beginning...● Was CGI: – It was simple enough to implement. – Proved platform and language agnostic. – Lived outside of the server, with simple variables and print statements moving the data in and out of back-end code. – Became the standard for most work on the web.
  • CGI has problems. ● It was designed for shell-ish environments. – Each iteration of the site required re-launching the CGI “script” as a separate process. – This caused too much overhead to re-process the source code for every request. – Let alone the overhead of creating new processes, especially on non-*NIX systems.● Fixes involved avoiding the re-processing and dodging CGI altogether.
  • Inside the beast: mod_foobar● The alternative was ditching all of CGI.● Code moved inside the server itself. – Apache created the mod_<thingy> interfaces. – This allowed the code a low-level view of the request and server state to process its requests. – For example: mod_perl.● And things seemed good, for a while...
  • Be careful what you ask for!● We have probably all dealt with mod_perl by now: – Once you are inside the beast, you have to deal with it. – All of it.● Do you really enjoy dealing with circular documentation, fragmentation of objects, details of the HTTP lifecycle within Apache? Then have fun!● mod_perl code is also largely non-portable. – Even upgrading Apache can cause major headaches.
  • The search for a better way● Hardware and O/S performance have improved since 80486s were “modern”.● Weve also learned a few things about how to design objects.● This led to multiple approaches for layers between apache internals and the request handler code.● All of them encapsulate specifics of the server. – Avoid all of us re-inventing the interface wheel.
  • More than one way to do it...● Catalyst is one approach.● Python & Ruby took another approach with WSGI & Rack.● Tatsuhiko Miyagawa developed Perl Web Server Gateway Interface (PSGI) and Plack. – Note that PSGI is not Plack.
  • Example: PSGI my $app = sub● Environment arrives as { an argument.     my $env = shift;     return● Return     [         200, [status, header, body ]         [          Content­Type,  text/plain to caller for response.         ],         [● Note these are             HelloWorld arrayrefs, not hashes.         ],     ] };
  • A few nice things● The encapsulated source “$env” is limited to the current request. – Less likely to get polluted or contain extraneous values than %ENV in CGI. – Return values are server and language agnostic.
  • Meanwhile, back at the server...● Plack::Handler provides the interface from PSGI to the server internals. – This includes modules for Apache, FCGI, Starman (Unicorn.rb).● There are also stand-alone Perly servers – Twiggy Non-blocking, AnyEvent. – Dancer Tries to simplify things. – Starlet Simpler server. – plackup Just runs your code – comes with plack.
  • What does this mean to you?● Ever try to debug mod_perl code with printf?● What if your server were pure perl, executable with “perl -d ...”? – You could fondle the structures interactively. – Hardwire breakpoints. – Fix things a whole lot faster...● perl -d plackup /path/to/your/module;
  • Example: Dancer● Callbacks added by location. #!/bin/env perl● Return the content with options for headers. use Dancer;● Thats about all you need. get / => sub { Hello World }; dance;
  • Catalyst can also handle PSGIuse My::Catalyst::App;My::Catalyst::App­>setup_engine( PSGI );my $app = sub{ My::Catalyst::App­>run( @_ )};
  • What Plack gets you● Plack::Handler What your app sees.● plackup Command-line startup.● Plack::Loader Autoload plack servers● Plack::Middleware PSGI Middleware● Plack::Builder OO Layer under middleware● Plack::Apps● Plack::Test
  • Simplest case: plackup# read your app from app.psgi file  plackup# choose .psgi file from ARGV[0] (or with ­a option)  plackup hello.psgi# switch server implementation with ­­server (or ­s)  plackup ­­server HTTP::Server::Simple ­­port 9090   ­­host 127.0.0.1 test.psgi# use UNIX socket to run FCGI daemon  plackup ­s FCGI ­­listen /tmp/fcgi.sock myapp.psgi# launch FCGI external server on port 9090  plackup ­s FCGI ­­port 9090
  • Having it both ways: #! or plackup if( caller ) {● Debugging or     # plackup, twiggy, etc. testing are simpler     $server from code run via } else perl -d. {     # standalone application● PSGI servers are better for real use.     require Plack::Runner;● Have both:     my $run = Plack::Runner­>new; Without a caller     $run­>parse_options( @ARGV ); this runs itself.     $run­>run( $server ); }
  • Server code is simple● With only $env to worry about, extracting the request is easy.● Standard errors can be canned.● Even the headers are largely re-usable.● Switches on $env offer simple handler branching.
  • my $server= sub{$DB::single = 1; my $env     = shift;   given( $env ) { when( fasta ) { return        [ # hand back javascript for viewing W­curve           200,           $canned_hdrz{ js },           $wc­>read_seq( $env­>{ fasta } )­>format        ] } ... return [ 200, [], [Unhandled Request] ] }};
  • Summary● PSGI & Plack bring back the simplicity and portability of CGI. – Flexible enough to support a variety of frameworks above it. – Portable enough to run on any server.● Check the references for lots of examples.
  • References The main Plack site: http://plackperl.org/Tatsuhiko Miyagawa has good documentation for Plack along with the modules:http://search.cpan.org/~miyagawa/Leo Lapworth has multiple Slideshare items about Plack:http://www.slideshare.net/ranguard/plack­basics­for­perl­websites­yapceu­2011Article: Catalyst 5.9: (Less Code, More Plack!)http://jjnapiorkowski.typepad.com/modern­perl/2011/08/catalyst­59­less­code­more­plack.html