Provided by: libperlbal-perl_1.80-3_all 
NAME
Perlbal::Manual::Plugins - Creating and using plugins
VERSION
Perlbal 1.78.
DESCRIPTION
How to create and use Perlbal plugins.
How to use a plugin
Perlbal supports plugins through modules under "Perlbal::Plugin::*" that implement a set
of functions described further down this document.
Some of these plugins are shipped with Perlbal itself, while others can be found on CPAN
(you can also create your own plugin and have it available only locally).
In order to use a plugin you first have to load it; on your Perlbal's configuration file
add something like:
Load MyPlugin
This loads plugin "Perlbal::Plugin::MyPlugin".
Each plugin will have its own way of being configured (some don't require any
configuration at all), so you'll have to refer to their documentation (or code).
Typically (but not always), a plugin will allow you to set additional parameters to a
service; for instance:
LOAD MaxContentLength
CREATE SERVICE example
SET max_content_length = 100000
SET plugins = MaxContentLength
"max_content_length" is a parameter of Perlbal::Plugin::MaxContentLength.
If you're worried that two plugins may have the same parameter, of if you simply want to
define those variables all in the same spot and thus will be doing it outside of the
plugin's context, you can use the more verbose syntax:
SET my_service.my_plugin.my_variable = my_value
Notice that some plugins need to be stated service by service; hence, this line:
SET plugins = MaxContentLength
The "plugins" parameter (a list of strings separated by commas or spaces) defines which
plugins are acceptable for a service.
Troubleshooting
If you try to load a plugin and receive the following error message:
ERROR: Can't locate Perlbal/Plugin/MyPlugin.pm in @INC
That means that either the plugin isn't installed or perlbal couldn't find it. (perhaps it
is installed in a different version of perl other than the one used to run perlbal?)
How to create a plugin
A Perlbal plugin consists in a package under the "Perlbal::Plugin" namespace that
implements a number of functions: "register", "unregister", "load" and "unload".
These steps and functions (plus some helper functions you can define or use) are described
below.
PLEASE KEEP IN MIND: Perlbal is a single-process, asynchronous web server. You must not do
things in plugins which will cause it to block, or no other requests can be served at the
same time.
Creating a package
While there are many ways of creating a package, we'd recommend that you use something to
do it for you. A good option is Module::Starter.
(note: if you really want to, you can just create a file with your package and use it; by
using something like Module::Starter you're making sure that several pitfalls are avoided,
lots of basic rules are followed and that your package can easily be made available as a
distribution that you can deploy on any machine - or, if you feel so inclined, upload to
CPAN - in a simple way)
Let's assume you want to create a plugin that checks requests for a "X-Magic" header and,
if present, add an header "X-Color" to the response when serving a file. Let's assume your
plugin will be called "Perlbal::Plugin::ColorOfMagic".
Having installed Module::Starter, here's a command you can run that will create your
package for you:
$ module-starter --module=Perlbal::Plugin::ColorOfMagic --author="My name" --email=my@email.address
That should create a file tree that you can get better acquainted with by reading
Module::Starter's fine documentation. For this example, the file you really need should
now reside in "lib/Perlbal/Plugin/ColorOfMagic.pm".
This file probably starts with something like the following:
package Perlbal::Plugin::ColorOfMagic;
use warnings;
use strict;
You'll have to add a few functions to this file. These are described below.
(note: upon creating this package, some boilerplate documentation will also be present on
the file; you should revise it and even remove bits that don't feel right for your plugin)
register
"register" is called when the plugin is being added to a service. This is where you
register your plugin's hooks, if required (see Perlbal::Manual::Hooks for the list of
existing hooks and further documentation on how they work).
For the sake of our example ("Perlbal::Plugin::ColorOfMagic", see above), what we want to
do is register a hook that modifies the response headers; that means we want a
"modify_response_headers" hook.
Here's what you'd do:
sub register {
my ($class, $service) = @_;
my $my_hook_code = sub {
my Perlbal::ClientHTTPBase $cp = shift;
if ( $cp->{req_headers}->header('X-Magic') ) {
$cp->{res_headers}->header( 'X-Color', 'Octarine' );
}
return 0;
};
$service->register_hook('ColorOfMagic','modify_response_headers', $my_hook_code);
}
Inside "register", we're calling "register_hook" to register our "ColorOfMagic"
"modify_response_headers" hook. Its code, that will run "when we've set all the headers,
and are about to serve a file" (see Perlbal::Manual::Hooks), receives a
Perlbal::ClientHTTPBase object (you can see what kind of object your hook will receive on
Perlbal::Manual::Hooks). We're checking to see if "X-Magic" is defined on the request and,
if so, we're setting header "X-Color" on the response to "Octarine".
Notice that the hook ends with "return 0". This is because returning a true value means
that you want to cancel the connection to the backend and send the response to the client
yourself.
unregister
"unregister" is called when the plugin is removed from a service. It's a standard good
practice to unregister your plugin's hooks here, like so:
sub unregister {
my ($class, $service) = @_;
$service->unregister_hooks('ColorOfMagic');
return 1;
}
You can also use "unregister_hook" to unregister one single hook:
$service->unregister_hook('ColorOfMagic', 'modify_response_headers');
load
"load" is called when your plugin is loaded (or reloaded).
This is where you should perform your plugin's initialization, which can go from setting
up some variables to registering a management command (to register commands see the
documentation for "manage_command" further down this document).
my $color;
sub load {
my $class = shift;
$color = 'Octarine';
return 1;
}
"load" must always be defined, but if you really don't need it you can have it simply
returning a true value:
sub load { return 1; }
unload
"unload" is called when your plugin is unloaded. This is where you should perform any
clean up tasks.
"unload" must always be defined, but if you really don't need it you can have it simply
returning a true value:
sub unload { return 1; }
Don't forget to call "unregister_global_hook" if you have registered any (see the
documentation for "manage_command" further down this document and you'll see what we're
talking about).
register vs. load
"load" is called when the plugin is loaded, while "register" is called whenever the plugin
is set for a service.
This means that you should use "load" for anything that is global, such as registering a
global hook, and you should use "register" for things that are specific to a service, such
as registering service hooks.
dumpconfig
"dumpconfig" is not required.
When managing Perlbal (see Perlbal::Manual::Management) you can send a "dumpconfig"
command that will result in a configuration dump.
Apart from the global configuration, each plugin that implements a "dumpconfig" function
will also have that function called.
"dumpconfig" should return an array of messages to be displayed.
sub dumpconfig {
my ($class, $service) = @_;
my @messages;
push @messages, "COLOROFMAGIC is $color";
return @messages;
}
Again, "dumpconfig" is not required, so implement it only if it makes sense for your
plugin.
Helper functions
add_tunable
Adding a tunable will allow you to set its value within each plugin:
LOAD MyPlugin
CREATE SERVICE my_service
SET my_new_parameter = 42
SET plugins = MyPlugin
ENABLE my_service
"add_tunable" can be used by plugins that want to add tunables so that the config file can
have more options for service settings.
sub load {
Perlbal::Service::add_tunable(
my_new_parameter => {
check_role => '*',
check_type => 'int',
des => "description of my new parameter",
default => 0,
},
);
return 1;
}
"check_role" defines for which roles the value can be set ("reverse_proxy", "web_server",
etc). A value of "*" mean that the value can be set for any role.
The acceptable values for "check_type" are "enum", "regexp", "bool", "int", "size",
"file", "file_or_none" and "directory_or_none". An Unknown check_type error message will
be displayed whenever you try to set a value that has an unknown "check_type".
"check_type" can also contain a code reference that will be used to validate the type.
check_type => sub {
my $self = shift;
my $val = shift;
my $emesg = shift;
...
},
This code reference should return a true or false value. If returning false, the contents
of $emesg (which is passed as a reference to the function) will be used as the error
message.
Here's a better explanation of the acceptable values for "check_type":
bool
Boolean value. Must be defined and will be checked as a Perl value.
directory_or_none
The value needs to be defined and the content must be an existing directory (validated
against perl's -d switch).
enum
An array reference containing the acceptable values:
check_type => [enum => ["yellow", "blue", "green"]],
file
A filename, validated against perl's -f switch.
file_or_none
A filename, validated against perl's -f switch, or the default value.
int An integer value, validated against "/^\d+$/".
regexp
Regular expression.
The correct form of setting a regexp tunable is by setting it as an array reference
containing the type ("regexp"), the regular expression and a message that can explain
it:
check_type => ["regexp", qr/^\d+\.\d+\.\d+\.\d+:\d+$/, "Expecting IP:port of form a.b.c.d:port."],
size
A size, validated against "/^(\d+)[bkm]$/".
manage_command
Perlbal catches unknown configuration commands and tries to match them against hooks in
the form of "manage_command.*".
Let's say that you want to set a management command "time" that will allow you to see what
time it is on the server.
sub load {
Perlbal::register_global_hook('manage_command.time', sub {
my $time = localtime time;
return [ "It is now:", $time ];
});
return 1;
}
If you want to display a text message you should return an array reference; each of the
values will be printed with a trailing newline character:
time
It is now:
Wed Dec 1 19:08:58 2010
If you need to parse additional parameters on your hook, you can use "parse" and "args" on
the Perlbal::ManageCommand object that your function will receive:
my $mc = shift;
$mc->parse(qr/^time\s+(today|tomorrow)$/, "usage: TIME [today|tomorrow]");
my ($cmd, $choice) = $mc->args;
This would allow you to call your command with an argument that would have to be one of
"today" or "tomorrow".
register_setter
"register_setter" allows you to define parameters that can be set for your plugin, using a
syntax such as:
SET my_service.my_plugin.my_variable = my_value
For instance:
SET discworld.colorofmagic.color = 'Orange'
Here's how you'd configure a new setter, by using "register_setter" inside "load":
my $color;
sub load {
$color = 'Octarine';
$svc->register_setter('ColorOfMagic', 'color', sub {
my ($out, $what, $val) = @_;
return 0 unless $what && $val;
$color = $val;
$out->("OK") if $out;
return 1;
});
return 1;
}
selector
For plugins that will work with a "selector" service, sometimes you'll want to override
the "selector" itself.
You can do this in "register":
sub register {
my ($class, $svc) = @_;
$svc->selector(\&my_selector_function);
Don't forget to unregister your function on the way out:
sub unregister {
my ($class, $svc) = @_;
$svc->selector(undef);
return 1;
}
Your "selector" function receives a Perlbal::ClientHTTPBase object.
my Perlbal::ClientHTTPBase $cb = shift;
Inside your "selector" function you can set which service to forward the request to like
this:
my $service = Perlbal->service($service_name);
$service->adopt_base_client($cb);
return 1;
See Perlbal::Plugin::Vhosts or Perlbal::Plugin::Vpaths for examples on how to do this.
Known plugins
The following is a list of known plugins:
• Perlbal::Plugin::AccessControl (Perlbal core)
Basic access control based on IPs and Netmasks.
• Perlbal::Plugin::Addheader
Add Headers to Perlbal webserver responses.
• Perlbal::Plugin::AutoRemoveLeadingDir (Perlbal core)
Auto-removal of leading directory path components in the URL.
• Perlbal::Plugin::BackendHeaders
See which backend served the request.
• Perlbal::Plugin::Cgilike (Perlbal core)
Handle Perlbal requests with a Perl subroutine.
• Perlbal::Plugin::EchoService (Perlbal core)
Simple plugin demonstrating how to create an add-on service for Perlbal using the
plugin infrastructure.
• Perlbal::Plugin::ExpandSSL
Add a custom header according to the SSL of a service.
• Perlbal::Plugin::FlvStreaming (Perlbal core)
Enable FLV streaming with reverse proxy.
• Perlbal::Plugin::ForwardedFor
Rename the X-Forwarded-For header in Perlbal.
• Perlbal::Plugin::Highpri (Perlbal core)
Makes some requests high priority.
• Perlbal::Plugin::Include (Perlbal core)
Allows multiple, nesting configuration files.
• Perlbal::Plugin::LazyCDN (Perlbal core)
Support for Content Delivery Networks.
• Perlbal::Plugin::MaxContentLength (Perlbal core)
Reject large requests.
• Perlbal::Plugin::NotModified (Perlbal core)
Automatic 304 Not Modified responses when clients send a "If-Modified-Since" header.
• Perlbal::Plugin::PSGI
PSGI web server on Perlbal.
• Perlbal::Plugin::Palimg (Perlbal core)
Plugin that allows Perlbal to serve palette altered images.
• Perlbal::Plugin::Queues (Perlbal core)
Simple queue length header inclusion plugin.
• Perlbal::Plugin::Redirect (Perlbal core)
Plugin to do redirecting in Perlbal land.
• Perlbal::Plugin::Stats (Perlbal core)
Basic Perlbal statistics gatherer.
• Perlbal::Plugin::StickySessions
Session affinity for Perlbal.
• Perlbal::Plugin::Throttle (Perlbal core)
Throttle connections from hosts that connect too frequently.
• Perlbal::Plugin::TrustHeader
Remove untrusted headers.
• Perlbal::Plugin::UrlGroup
Let URL match it in regular expression.
• Perlbal::Plugin::Vhosts (Perlbal core)
Name-based virtual hosts.
• Perlbal::Plugin::Vpaths (Perlbal core)
Select by path (selector role only).
• Perlbal::Plugin::XFFExtras (Perlbal core)
Perlbal plugin that can optionally add an X-Forwarded-Port and/or X-Forwarded-Proto
header to reverse proxied requests.
SEE ALSO
Perlbal::Manual::Hooks, Perlbal::Manual::Internals.
There are sample configuration files under conf/; some of these are examples on how to use
and configure existing plugins: echoservice.conf for Perlbal::Plugin::EchoService,
virtual-hosts.conf for Perlbal::Plugin::VHosts, etc.