by Herb Torrens, ADT The middleware software market has entered the slow lane in 2009, according to a Gartner report announced on Wednesday. The report, “Market Share: Application Infrastructure and Middleware Software, Worldwide, 2008,” examines the AIM market, which includes technologies such as service-oriented architecture (SOA) solutions, business process management suites (BPMSs) and other [...]
Good evening:
I need your help please, I am new in Unix/Linux apps like middleware
Thare are thousands of documentation about middleware stuff but i would like to have a broader understanding about middleware apps, so i ask you the following questions:
1. In an Enterprise what i am working... (2 Replies)
I am trying to come up with a loop to connect to multiple servers and tun the same command on each one of them.
The number of servers will be typed in a single line separated with commas:
ex.
./test.ksh server1,server2,server3,.........
This is the code i've come up with till now:... (6 Replies)
I want to know if a server has J2EE application server installed, a webserver or any other middleware, is there a command to output a list or something like that.
Thak you (1 Reply)
Hello folks,
i want to count all apache log file but i dont want to count hits for jpg|gif|txt files. So how it is possible to count number of lines by ignore pictures extension. Pictures is like that
GET /xyz.png
GET /abcd.jpg
GET/ppp.gif (3 Replies)
Hi Guys,
How can I get the number of web server hits from the command prompt, I like shell scripting ways of finding such data.
Can anyone help? (1 Reply)
Plack::Middleware(3pm) User Contributed Perl Documentation Plack::Middleware(3pm)NAME
Plack::Middleware - Base class for easy-to-use PSGI middleware
SYNOPSIS
package Plack::Middleware::Foo;
use parent qw( Plack::Middleware );
sub call {
my($self, $env) = @_;
# Do something with $env
# $self->app is the original app
my $res = $self->app->($env);
# Do something with $res
return $res;
}
# then in app.psgi
use Plack::Builder;
my $app = sub { ... } # as usual
builder {
enable "Plack::Middleware::Foo";
enable "Plack::Middleware::Bar", %options;
$app;
};
DESCRIPTION
Plack::Middleware is a utility base class to write PSGI middleware. All you have to do is to inherit from Plack::Middleware and then
implement the callback "call" method (or "to_app" method that would return the PSGI code reference) to do the actual work. You can use
"$self->app" to call the original (wrapped) application.
Your middleware object is created at a PSGI application compile time and is persistent during the web server life cycle (unless it is a
non-persistent environment such as CGI), so you should never set or cache per-request data like $env in your middleware object. See also
"OBJECT LIFECYCLE" in Plack::Component.
See Plack::Builder how to actually enable middleware in your .psgi application file using the DSL. If you do not like our builder DSL, you
can also use "wrap" method to wrap your application with a middleware:
use Plack::Middleware::Foo;
my $app = sub { ... };
$app = Plack::Middleware::Foo->wrap($app, %options);
$app = Plack::Middleware::Bar->wrap($app, %options);
RESPONSE CALLBACK
The typical middleware is written like this:
package Plack::Middleware::Something;
use parent qw(Plack::Middleware);
sub call {
my($self, $env) = @_;
# pre-processing $env
my $res = $self->app->($env);
# post-processing $res
return $res;
}
The tricky thing about post processing the response is that it could either be an immediate 3 element array ref, or a code reference that
implements the delayed (streaming) interface.
Dealing with these two types of response in each piece of middleware is pointless, so you're recommended to use the "response_cb" wrapper
function in Plack::Util when implementing a post processing middleware.
my $res = $app->($env);
Plack::Util::response_cb($res, sub {
my $res = shift;
# do something with $res;
});
The callback function gets a PSGI response as a 3 element array reference, and you can update the reference to implement the post
processing.
package Plack::Middleware::Always500;
use parent qw(Plack::Middleware);
use Plack::Util;
sub call {
my($self, $env) = @_;
my $res = $self->app->($env);
Plack::Util::response_cb($res, sub {
my $res = shift;
$res->[0] = 500;
return;
});
}
In this example, the callback gets the $res and updates its first element (status code) to 500. Using "response_cb" makes sure that this
works with the delayed response too.
You're not required (and not recommended either) to return a new array reference - they will be simply ignored. You're suggested to
explicitly return, unless you fiddle with the content filter callback (see below).
Similarly, note that you have to keep the $res reference when you swap the entire response.
Plack::Util::response_cb($res, sub {
my $res = shift;
$res = [ $new_status, $new_headers, $new_body ]; # THIS DOES NOT WORK
return;
});
This does not work, since assigning a new anonymous array to $res doesn't update the original PSGI response value. You should instead do:
Plack::Util::response_cb($res, sub {
my $res = shift;
@$res = ($new_status, $new_headers, $new_body); # THIS WORKS
return;
});
The third element of PSGI response array ref is a body, and it could be either array ref or IO::Handle-ish object. The application could
also make use of $writer object if "psgi.streaming" is in effect. Dealing with these variants is again really painful, and "response_cb"
can take care of that too, by allowing you to return a content filter as a code reference.
# replace all "Foo" in content body with "Bar"
Plack::Util::response_cb($res, sub {
my $res = shift;
return sub {
my $chunk = shift;
return unless defined $chunk;
$chunk =~ s/Foo/Bar/g;
return $chunk;
}
});
The callback takes one argument $chunk and your callback is expected to return the updated chunk. If the given $chunk is undef, it means
the stream has reached the end, so your callback should also return undef, or return the final chunk and return undef when called next
time.
SEE ALSO
Plack Plack::Builder Plack::Component
perl v5.14.2 2011-06-22 Plack::Middleware(3pm)
