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.\" ========================================================================
.\"
.IX Title "Plack::Builder 3pm"
.TH Plack::Builder 3pm 2024-01-20 "perl v5.38.2" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH NAME
Plack::Builder \- OO and DSL to enable Plack Middlewares
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 2
\&  # in .psgi
\&  use Plack::Builder;
\&
\&  my $app = sub { ... };
\&
\&  builder {
\&      enable "Deflater";
\&      enable "Session", store => "File";
\&      enable "Debug", panels => [ qw(DBITrace Memory Timer) ];
\&      enable "+My::Plack::Middleware";
\&      $app;
\&  };
\&
\&  # use URLMap
\&
\&  builder {
\&      mount "/foo" => builder {
\&          enable "Foo";
\&          $app;
\&      };
\&
\&      mount "/bar" => $app2;
\&      mount "http://example.com/" => builder { $app3 };
\&  };
\&
\&  # using OO interface
\&  my $builder = Plack::Builder\->new;
\&  $builder\->add_middleware(\*(AqFoo\*(Aq, opt => 1);
\&  $builder\->add_middleware(\*(AqBar\*(Aq);
\&  $builder\->wrap($app);
.Ve
.SH DESCRIPTION
.IX Header "DESCRIPTION"
Plack::Builder gives you a quick domain specific language (DSL) to
wrap your application with Plack::Middleware subclasses. The
middleware you're trying to use should use Plack::Middleware as a
base class to use this DSL, inspired by Rack::Builder.
.PP
Whenever you call \f(CW\*(C`enable\*(C'\fR on any middleware, the middleware app is
pushed to the stack inside the builder, and then reversed when it
actually creates a wrapped application handler. \f(CW"Plack::Middleware::"\fR
is added as a prefix by default. So:
.PP
.Vb 5
\&  builder {
\&      enable "Foo";
\&      enable "Bar", opt => "val";
\&      $app;
\&  };
.Ve
.PP
is syntactically equal to:
.PP
.Vb 2
\&  $app = Plack::Middleware::Bar\->wrap($app, opt => "val");
\&  $app = Plack::Middleware::Foo\->wrap($app);
.Ve
.PP
In other words, you're supposed to \f(CW\*(C`enable\*(C'\fR middleware from outer to inner.
.SH "INLINE MIDDLEWARE"
.IX Header "INLINE MIDDLEWARE"
Plack::Builder allows you to code middleware inline using a nested
code reference.
.PP
If the first argument to \f(CW\*(C`enable\*(C'\fR is a code reference, it will be
passed an \f(CW$app\fR and should return another code reference
which is a PSGI application that consumes \f(CW$env\fR at runtime. So:
.PP
.Vb 10
\&  builder {
\&      enable sub {
\&          my $app = shift;
\&          sub {
\&              my $env = shift;
\&              # do preprocessing
\&              my $res = $app\->($env);
\&              # do postprocessing
\&              return $res;
\&          };
\&      };
\&      $app;
\&  };
.Ve
.PP
is equal to:
.PP
.Vb 4
\&  my $mw = sub {
\&      my $app = shift;
\&      sub { my $env = shift; $app\->($env) };
\&  };
\&
\&  $app = $mw\->($app);
.Ve
.SH "URLMap support"
.IX Header "URLMap support"
Plack::Builder has a native support for Plack::App::URLMap via the \f(CW\*(C`mount\*(C'\fR method.
.PP
.Vb 8
\&  use Plack::Builder;
\&  my $app = builder {
\&      mount "/foo" => $app1;
\&      mount "/bar" => builder {
\&          enable "Foo";
\&          $app2;
\&      };
\&  };
.Ve
.PP
See Plack::App::URLMap's \f(CW\*(C`map\*(C'\fR method to see what they mean. With
\&\f(CW\*(C`builder\*(C'\fR you can't use \f(CW\*(C`map\*(C'\fR as a DSL, for the obvious reason :)
.PP
\&\fBNOTE\fR: Once you use \f(CW\*(C`mount\*(C'\fR in your builder code, you have to use
\&\f(CW\*(C`mount\*(C'\fR for all the paths, including the root path (\f(CW\*(C`/\*(C'\fR). You can't
have the default app in the last line of \f(CW\*(C`builder\*(C'\fR like:
.PP
.Vb 4
\&  my $app = sub {
\&      my $env = shift;
\&      ...
\&  };
\&
\&  builder {
\&      mount "/foo" => sub { ... };
\&      $app; # THIS DOESN\*(AqT WORK
\&  };
.Ve
.PP
You'll get warnings saying that your mount configuration will be
ignored. Instead you should use \f(CW\*(C`mount "/" => ...\*(C'\fR in the last
line to set the default fallback app.
.PP
.Vb 4
\&  builder {
\&      mount "/foo" => sub { ... };
\&      mount "/" => $app;
\&  }
.Ve
.PP
Note that the \f(CW\*(C`builder\*(C'\fR DSL returns a whole new PSGI application, which means
.IP \(bu 4
\&\f(CW\*(C`builder { ... }\*(C'\fR should normally be the last statement of a \f(CW\*(C`.psgi\*(C'\fR
file, because the return value of \f(CW\*(C`builder\*(C'\fR is the application that
is actually executed.
.IP \(bu 4
You can nest your \f(CW\*(C`builder\*(C'\fR blocks, mixed with \f(CW\*(C`mount\*(C'\fR statements (see "URLMap support"
above):
.Sp
.Vb 5
\&  builder {
\&      mount "/foo" => builder {
\&          mount "/bar" => $app;
\&      }
\&  }
.Ve
.Sp
will locate the \f(CW$app\fR under \f(CW\*(C`/foo/bar\*(C'\fR, since the inner \f(CW\*(C`builder\*(C'\fR
block puts it under \f(CW\*(C`/bar\*(C'\fR and it results in a new PSGI application
which is located under \f(CW\*(C`/foo\*(C'\fR because of the outer \f(CW\*(C`builder\*(C'\fR block.
.SH "CONDITIONAL MIDDLEWARE SUPPORT"
.IX Header "CONDITIONAL MIDDLEWARE SUPPORT"
You can use \f(CW\*(C`enable_if\*(C'\fR to conditionally enable middleware based on
the runtime environment.
.PP
.Vb 4
\&  builder {
\&      enable_if { $_[0]\->{REMOTE_ADDR} eq \*(Aq127.0.0.1\*(Aq } \*(AqStackTrace\*(Aq, force => 1;
\&      $app;
\&  };
.Ve
.PP
See Plack::Middleware::Conditional for details.
.SH "OBJECT ORIENTED INTERFACE"
.IX Header "OBJECT ORIENTED INTERFACE"
Object oriented interface supports the same functionality with the DSL
version in a clearer interface, probably with more typing required.
.PP
.Vb 6
\&  # With mount
\&  my $builder = Plack::Builder\->new;
\&  $builder\->add_middleware(\*(AqFoo\*(Aq, opt => 1);
\&  $builder\->mount(\*(Aq/foo\*(Aq => $foo_app);
\&  $builder\->mount(\*(Aq/\*(Aq => $root_app);
\&  $builder\->to_app;
\&
\&  # Nested builders. Equivalent to:
\&  # builder {
\&  #     mount \*(Aq/foo\*(Aq => builder {
\&  #         enable \*(AqFoo\*(Aq;
\&  #         $app;
\&  #     };
\&  #     mount \*(Aq/\*(Aq => $app2;
\&  # };
\&  my $builder_out = Plack::Builder\->new;
\&  my $builder_in  = Plack::Builder\->new;
\&  $builder_in\->add_middleware(\*(AqFoo\*(Aq);
\&  $builder_out\->mount("/foo" => $builder_in\->wrap($app));
\&  $builder_out\->mount("/" => $app2);
\&  $builder_out\->to_app;
\&
\&  # conditional. You can also directly use Plack::Middleware::Conditional
\&  my $builder = Plack::Builder\->new;
\&  $builder\->add_middleware_if(sub { $_[0]\->{REMOTE_ADDR} eq \*(Aq127.0.0.1\*(Aq }, \*(AqStackTrace\*(Aq);
\&  $builder\->wrap($app);
.Ve
.SH "SEE ALSO"
.IX Header "SEE ALSO"
Plack::Middleware Plack::App::URLMap Plack::Middleware::Conditional