Introduction to PSGI and Plack.

1. PSGI and Plack
Tatsuhiko Miyagawa

2. PSGI
Perl Web Server Gateway Interface

3. Plack
PSGI ref. implementations
Utilities

4. A Perl port of:
Python’s WSGI and Ruby’s Rack
(will talk about them later)

5. WHY

6. Web Frameworks

7. Maypole Mason Mojo Sledge Catalyst Spoon PageKit
AxKit Egg Gantry Continuity Solstice Mojolicious
Tripletail Konstrukt Reflection Jifty Cyclone3
OpenInteract Squatting Dancer CGI::Application Nanoa
Ark Angelos Noe Schenker

8. Most of them run on
mod_perl and CGI

9. Some run on FCGI

10. Some run standalone

11. Very few supports
non-blocking

12. Because:

13. No common server
environment layers

14. CGI.pm

15. Runs fine on:
CGI, FastCGI, mod_perl (1 & 2)
Standalone (with HTTP::Server::Simple)

16. CGI.pm = LCD
It’s also Perl core

17. > grep ‘(CGI.pm|ENV)’ lib/MT/App.pm
if ( my $path_info = $ENV{PATH_INFO} ) {
# defined which interferes with CGI.pm determining the
delete $ENV{PATH_INFO};
# CGI.pm has this terrible flaw in that if a POST is in effect,
my $query_string = $ENV{'QUERY_STRING'}
if defined $ENV{'QUERY_STRING'};
$query_string ||= $ENV{'REDIRECT_QUERY_STRING'}
if defined $ENV{'REDIRECT_QUERY_STRING'};
my $len = $ENV{CONTENT_LENGTH} || 0;
return $ENV{ 'HTTP_' . $key };
$app->{request_method} = $ENV{REQUEST_METHOD} || '';
## Older versions of CGI.pm didn't have an 'upload' method.
if ( my $host = $ENV{HTTP_HOST} ) {
: $ENV{REMOTE_ADDR});
$cwd = $ENV{DOCUMENT_ROOT} || $app->mt_dir;

18. Not cool.

19. Catalyst
The most popular framework as of today

20. Catalyst::Engine::*
Server abstractions.
Well supported Apache, FCGI and Standalone

21. Problems:
Duplicated efforts
No fair performance evaluations

22. Catalyst::Engine
for the rest of us

23. = HTTP::Engine

24. HTTP::Engine
Lots of adapters (FCGI, Apache2, POE)
Clean Request/Response API
Written by Yappo, tokuhirom and others

25. Problem

26. Mo[ou]se everywhere
Mouse is light but still overspec for some env.

27. Monolithic
All implementations share HTTP::Engine roles
and builders, which is sometimes hard to adapt
and has less place for optimizations.

28. APIs everywhere
Most frameworks have their request/response API
Sometimes there are gaps.
Annoying to write bridges and wrappers

29. Solution

30. Steal good stuff
from Python/Ruby

31. WSGI (Python)
Rack

32. WSGI (PEP-333)
mod_wsgi, Tornado, Paste, GAE
Django, CherryPy, Pylons

33. Rack
Passenger, Thin, rack, Heroku
Rails, Merb, Sinatra

34. Split HTTP::Engine
into three parts

35. Interface
Implementations
Utilities

36. PSGI (interface)
Plack::Server (implementations)
Plack::* (utilities)

37. PSGI

38. Interface

39. my $app = sub {
my $env = shift;
# ...
return [ $status, $header, $body ];
};

40. PSGI application
code reference
$app = sub {...};

41. environment hash
$env: CGI-like env variables
+ psgi.input, psgi.errors etc.

42. Why a big hash?
Easy to adapt if you have CGI adapter
Also follows what WSGI/Rack do

43. Response
array ref with three elements
status code, headers (array ref)
and body (IO-like or array ref)

44. $body
IO::Handle-like
getline() and close()

45. IO::Handle-like
We really envy Python/Ruby
for built-in iterators
(Perl’s filehandle is also an object, but it really sucks)

46. Frameworks
Write an adapter to return
PSGI application code ref.

47. Servers
Set up $env, run the app
and emits response out of $res

48. Middleware
Plays both side
“Application wrapper”

49. Plack

50. Plack::Server
reference server implementations
Standalone, FCGI, Apache2, CGI
Standalone, Prefork, AnyEvent, Coro

51. Very fast
5000 QPS on standalone
15000 QPS with prefork :)

52. Framework Adapters
CGI::Application, Catalyst, Maypole
Mason, Squatting, Mojo, HTTP::Engine etc.

53. Applications
MT::App, WebGUI

54. Utilities

55. Plackup
Run PSGI app instantly from CLI
(inspired by rackup)

56. DEMO

57. Middlewares

58. my $app = sub {
my $env = shift;
return [ $status, $header, $body ];
};
my $mw = sub {
my $env = shift;
# do something with $env
my $res = $app->($env);
# do something with $res;
return $res;
};

59. Middlewares
Static, AccessLog, ConditionalGET
ErrorDocument, StackTrace etc.

60. Plack::Middleware
reusable and extensible
Middleware framework
Plack::Builder DSL in .psgi

61. CGI::PSGI
Easy migration from CGI.pm

62. Plack::Request
like libapreq (Apache::Request)
wrapper APIs for framework developers

63. Plack::Test
Unified interface to write tests
with Mock HTTP and Live HTTP

64. use Plack::Test;
use HTTP::Request::Common;
my $app = sub {
my $env = shift;
return [ $status, $header, $body ];
};
test_psgi app => $app, client => sub {
my $cb = shift;
my $req = GET “http://localhost/foo”;
my $res = $cb->($req);
# test $res;
};

65. use Plack::Test;
use HTTP::Request::Common;
$Plack::Test::Impl = “Server”;
my $app = sub {
my $env = shift;
return [ $status, $header, $body ];
};
test_psgi app => $app, client => sub {
my $cb = shift;
my $req = GET “http://localhost/foo”;
my $res = $cb->($req);
# test $res;
};

66. Streaming
event loop / long-poll

67. use IO::Handle::Util qw(io_from_getline);
my $app = sub {
my $env = shift;
my $io = io_from_getline sub {
return $chunk; # undef when done
};
return [ $status, $header, $io ];
};

68. use IO::Writer; # TBD: API might change
use AnyEvent::Timer;
my $app = sub {
my $env = shift;
my $io = writer {
my $h = shift;
my $t; $t = AE::timer 0, 1, sub {
$t;
$h->push_write($stuff);
};
};
return [ $status, $header, $io ];
};

69. Other Servers

70. nginx embedded perl
http://github.com/yappo/nginx-psgi-patchs

71. mod_psgi
http://github.com/spiritloose/mod_psgi

72. Gearman Dispatcher?

73. Cloud

74. WSGI (PEP-333)
mod_wsgi, Tornado, Paste, GAE
Django, CherryPy, Pylons

75. Rack
Passenger, Thin, rack, Heroku
Rails, Merb, Sinatra

76. What if GAE Perl
comes with PSGI ...

77. Summary
• PSGI is an interface, Plack is the code.
• We have many (pretty fast) servers.
• We have adapters and tools for most web
frameworks.
• Use it!

78. http://github.com/miyagawa/Plack
http://plackperl.org/

79. Questions?