Provided by: libalien-build-perl_2.80-2_all 
NAME
Alien::Build::Manual::PluginAuthor - Alien::Build plugin author documentation
VERSION
version 2.80
SYNOPSIS
your plugin:
package Alien::Build::Plugin::Build::MyPlugin;
use strict;
use warnings;
use Alien::Build::Plugin;
has arg1 => 'default_for arg1';
has arg2 => sub { [ 'default', 'for', 'arg2' ] };
sub init
{
my($self, $meta) = @_;
...
}
1;
and then from alienfile:
use alienfile;
plugin 'Build::MyPlugin' => (
arg1 => 'override for arg1',
arg2 => [ 'something', 'else' ],
);
Perlish pseudo code for how plugins are called:
my $probe;
my $override = override();
if($override eq 'system') {
$probe = probe();
if($probe ne 'system') {
die 'system tool or library not found';
}
}
elsif($override eq 'default') {
$probe = probe();
} else { # $override eq 'share'
# note that in this instance the
# probe hook is never called
$probe = 'share';
}
if($probe eq 'system') {
gather_system();
} else { # $probe eq 'share'
download();
extract();
patch();
build();
gather_share();
# Check to see if there isa build_ffi hook
if(defined &build_ffi) {
patch_ffi();
build_ffi();
gather_ffi();
}
}
# By default this just returns the value of $ENV{ALIEN_INSTALL_TYPE}
sub override {
return $ENV{ALIEN_INSTALL_TYPE};
}
# Default download implementation; can be
# replaced by specifying a different download
# hook. See Alien::Build::Plugin::Core::Download
# for detailed implementation.
sub download {
my $response = fetch();
if($response->{type} eq 'html' || $response->{type} eq 'dir_listing') {
# decode will transform an HTML listing (html) or a FTP directory
# listing (dir_listing) into a regular list
$response = decode($response);
}
if($response->{type} eq 'list') {
# prefer will filter bad entries in the list
# and sort them so that the first one is
# the one that we want
$response = prefer($response);
my $first_preferred = $res->{list}->[0];
# prefer can sometimes infer the version from the
# filename.
if(defined $first_preferred->{version}) {
# not a hook
runtime_prop->{version} = $first_preferred->{version};
}
$response = fetch($first_preferred);
}
if($response->{type} eq 'file') {
# not a hook
write_file_to_disk $response;
}
}
DESCRIPTION
This document explains how to write Alien::Build plugins using the Alien::Build::Plugin
base class.
Writing plugins
Plugins use Alien::Build::Plugin, which sets the appropriate base class, and provides you
with the "has" property builder. "has" takes two arguments, the name of the property and
the default value. (As with Moose and Moo, you should use a code reference to specify
default values for non-string defaults). No not set this as your plugin's base class
directly:
use parent qw( Alien::Build::Plugin ); # wrong
use Alien::Build::Plugin; # right
The only method that you need to implement is "init". From this method you can add hooks
to change the behavior of the alienfile recipe. This is a very simple example of a probe
hook, with the actual probe logic removed:
sub init
{
my($self, $meta) = @_;
$meta->register_hook(
probe => sub {
my($build) = @_;
if( ... )
{
return 'system';
}
else
{
return 'share';
}
},
);
}
Hooks get the Alien::Build instance as their first argument, and depending on the hook may
get additional arguments.
Modifying hooks
You can also modify hooks using "before_hook", "around_hook" and "after_hook", similar to
Moose modifiers:
sub init
{
my($self, $meta) = @_;
$meta->before_hook(
build => sub {
my($build) = @_;
$build->log('this runs before the build');
},
);
$meta->after_hook(
build => sub {
my($build) = @_;
$build->log('this runs after the build');
},
);
$meta->around_hook(
build => sub {
my $orig = shift;
# around hooks are useful for setting environment variables
local $ENV{CPPFLAGS} = '-I/foo/include';
$orig->(@_);
},
);
}
Testing plugins
You can and should write tests for your plugin. The best way to do this is using
Test::Alien::Build, which allows you to write an inline alienfile in your test. Here is
an example:
use Test::V0;
use Test::Alien::Build;
my $build = alienfile_ok q{
use alienfile;
plugin 'Build::MyPlugin' => (
arg1 => 'override for arg1',
arg2 => [ 'something', 'else' ],
);
...
};
# you can interrogate $build, it is an instance of L<Alien::Build>.
my $alien = alien_build_ok;
# you can interrogate $alien, it is an instance of L<Alien::Base>.
Negotiator plugins
A Negotiator plugin doesn't itself typically implement anything on its own, but picks the
best plugin to achieve a particular goal.
The "best" plugin can in some cases vary depending on the platform or tools that are
available. For example The download negotiator might choose to use the fetch plugin that
relies on the command line "curl", or it might choose the fetch plugin that relies on the
Perl module HTTP::Tiny depending on the platform and what is already installed. (For
either to be useful they have to support SSL).
The Negotiator plugin is by convention named something like
"Alien::Build::Plugin::*::Negotiate", but is typically invoked without the "::Negotiate"
suffix. For example:
plugin 'Download'; # is short for Alien::Build::Plugin::Download::Negotiator
Here is a simple example of a negotiator which picks "curl" if already installed and
HTTP::Tiny otherwise. (The actual download plugin is a lot smarter and complicated than
this, but this is a good simplified example).
package Alien::Build::Plugin::Download::Negotiate;
use strict;
use warnings;
use Alien::Build::Plugin;
use File::Which qw( which );
sub init
{
my($self, $meta) = @_;
if(which('curl')) {
$meta->apply_plugin('Fetch::Curl');
} else {
$meta->apply_plugin('Fetch::HTTPTiny');
}
}
Hooks
The remainder of this document is a reference for the hooks that you can register.
Generally speaking you can register any hook that you like, but some care must be taken as
some hooks have default behavior that will be overridden when you register a hook. The
hooks are presented in alphabetical order. The execution order is shown in the flowchart
above (if you are browsing the HTML version of this document), or the Perlish pseudo code
in the synopsis section.
HOOKS
build hook
$meta->register_hook( build => sub {
my($build) = @_;
...
});
This does the main build of the alienized project and installs it into the staging area.
The current directory is the build root. You need to run whatever tools are necessary for
the project, and install them into "$build-"install_prop->{prefix}>
("%{.install.prefix}").
build_ffi hook
$meta->register_hook( build_ffi => sub {
my($build) = @_;
...
});
This is the same as build, except it fires only on a FFI build.
decode hook
$meta->register_hook( decode => sub {
my($build, $res) = @_;
...
}
This hook takes a response hash reference from the "fetch" hook above with a type of
"html" or "dir_listing" and converts it into a response hash reference of type "list". In
short it takes an HTML or FTP file listing response from a fetch hook and converts it into
a list of filenames and links that can be used by the prefer hook to choose the correct
file to download. See the fetch hook for the specification of the input and response hash
references.
check_digest hook
# implement the well known FOO-92 digest
$meta->register_hook( check_digest => sub {
my($build, $file, $algorithm, $digest) = @_;
if($algorithm ne 'FOO92') {
return 0;
}
my $actual = foo92_hex_digest($file);
if($actual eq $digest) {
return 1;
} else {
die "Digest FOO92 does not match: got $actual, expected $digest";
}
});
This hook should check the given $file (the format is the same as used by the fetch hook)
matches the given $digest using the given $algorithm. If the plugin does not support the
given algorithm, then it should return a false value. If the digest does not match, it
should throw an exception. If the digest matches, it should return a true value.
clean_install
$meta->register_hook( clean_install => sub {
my($build) = @_;
});
This hook allows you to remove files from the final install location before the files are
installed by the installer layer (examples: Alien::Build::MM, Alien::Build::MB or
App::af). This hook is not called by default, and must be enabled via the interface to
the installer layer (example: "clean_install" in Alien::Build::MM).
This hook SHOULD NOT remove the "_alien" directory or its content from the install
location.
The default implementation removes all the files EXCEPT the "_alien" directory and its
content.
download hook
$meta->register_hook( download => sub {
my($build) = @_;
...
});
This hook is used to download from the internet the source. Either as an archive (like
tar, zip, etc), or as a directory of files ("git clone", etc). When the hook is called,
the current working directory will be a new empty directory, so you can save the download
to the current directory. If you store a single file in the directory, Alien::Build will
assume that it is an archive, which will be processed by the extract hook. If you store
multiple files, Alien::Build will assume the current directory is the source root. If no
files are stored at all, an exception with an appropriate diagnostic will be thrown.
Note: If you register this hook, then the fetch, decode and prefer hooks will NOT be
called, unless you call them yourself from this hook.
extract hook
$meta->register_hook( extract => sub {
my($build, $archive) = @_;
...
});
This hook is used to extract an archive that has already been downloaded. Alien::Build
already has plugins for the most common archive formats, so you will likely only need this
to add support for new or novel archive formats. When this hook is called, the current
working directory will be a new empty directory, so you can save the content of the
archive to the current directory. If a single directory is written to the current
directory, Alien::Build will assume that is the root directory of the package. If
multiple files and/or directories are present, that will indicate that the current working
directory is the root of the package. The logic typically handles correctly the default
behavior for tar (where packages are typically extracted to a subdirectory) and for zip
(where packages are typically extracted to the current directory).
fetch hook
package Alien::Build::Plugin::MyPlugin;
use strict;
use warnings;
use Alien::Build::Plugin;
use Carp ();
has '+url' => sub { Carp::croak "url is required property" };
sub init
{
my($self, $meta) = @_;
$meta->register_hook( fetch => sub {
my($build, $url, %options) = @_;
...
}
}
1;
Used to fetch a resource. The first time it will be called without an argument (or with
$url set to "undef", so the configuration used to find the resource should be specified by
the plugin's properties. On subsequent calls the first argument will be a URL.
The %options hash may contain these options:
http_headers
HTTP request headers, if an appropriate protocol is being used. The headers are
provided as an array reference of key/value pairs, which allows for duplicate header
keys with multiple values.
If a non-HTTP protocol is used, or if the plugin cannot otherwise send HTTP request
headers, the plugin SHOULD issue a warning using the "$build->log" method, but because
this option wasn't part of the original spec, the plugin MAY no issue that warning
while ignoring it.
Note that versions of Alien::Build prior to 2.39 did not pass the options hash into the
fetch plugin.
Normally the first fetch will be to either a file or a directory listing. If it is a file
then the content should be returned as a hash reference with the following keys:
# content of file stored in Perl
return {
type => 'file',
filename => $filename,
content => $content,
version => $version, # optional, if known
protocol => $protocol, # AB 2.60 optional, but recommended
};
# content of file stored in the filesystem
return {
type => 'file',
filename => $filename,
path => $path, # full file system path to file
version => $version, # optional, if known
tmp => $tmp, # optional
protocol => $protocol, # AB 2.60 optional, but recommended
};
$tmp if set will indicate if the file is temporary or not, and can be used by Alien::Build
to save a copy in some cases. The default is true, so Alien::Build assumes the file or
directory is temporary if you don't tell it otherwise. Probably the most common situation
when you would set "tmp" to false, is when the file is bundled inside the Alien
distribution. See Alien::Build::Plugin::Fetch::Local for example.
If the URL points to a directory listing you should return it as either a hash reference
containing a list of files:
return {
type => 'list',
list => [
# filename: each filename should be just the
# filename portion, no path or url.
# url: each url should be the complete url
# needed to fetch the file.
# version: OPTIONAL, may be provided by some fetch or prefer
{ filename => $filename1, url => $url1, version => $version1 },
{ filename => $filename2, url => $url2, version => $version2 },
],
protocol => $protocol, # AB 2.60 optional, but recommended
};
or if the listing is in HTML format as a hash reference containing the HTML information:
return {
type => 'html',
charset => $charset, # optional
base => $base, # the base URL: used for computing relative URLs
content => $content, # the HTML content
protocol => $protocol, # optional, but recommended
};
or a directory listing (usually produced by an FTP servers) as a hash reference:
return {
type => 'dir_listing',
base => $base,
content => $content,
protocol => $protocol, # AB 2.60 optional, but recommended
};
[version 2.60]
For all of these responses $protocol is optional, since it was not part of the original
spec, however it is strongly recommended that you include this field, because future
versions of Alien::Build will use this to determine if a file was downloaded securely
(that is via a secure protocol such as SSL).
Some plugins (like decode plugins ) trans late a file hash from one type to another, they
should maintain the $protocol from the old to the new representation of the file.
gather_ffi hook
$meta->register_hook( gather_ffi => sub {
my($build) = @_;
$build->runtime_prop->{cflags} = ...;
$build->runtime_prop->{libs} = ...;
$build->runtime_prop->{version} = ...;
});
This hook is called for a FFI build to determine the properties necessary for using the
library or tool. These properties should be stored in the runtime_prop hash as shown
above. Typical properties that are needed for libraries are cflags and libs. If at all
possible you should also try to determine the version of the library or tool.
gather_share hook
$meta->register_hook( gather_share => sub {
my($build) = @_;
$build->runtime_prop->{cflags} = ...;
$build->runtime_prop->{libs} = ...;
$build->runtime_prop->{version} = ...;
});
This hook is called for a share install to determine the properties necessary for using
the library or tool. These properties should be stored in the runtime_prop hash as shown
above. Typical properties that are needed for libraries are cflags and libs. If at all
possible you should also try to determine the version of the library or tool.
gather_system hook
$meta->register_hook( gather_system => sub {
my($build) = @_;
$build->runtime_prop->{cflags} = ...;
$build->runtime_prop->{libs} = ...;
$build->runtime_prop->{version} = ...;
});
This hook is called for a system install to determine the properties necessary for using
the library or tool. These properties should be stored in the runtime_prop hash as shown
above. Typical properties that are needed for libraries are cflags and libs. If at all
possible you should also try to determine the version of the library or tool.
override hook
$meta->register_hook( override => sub {
my($build) = @_;
return $ENV{ALIEN_INSTALL_TYPE} || '';
});
This allows you to alter the override logic. It should return one of "share", "system",
"default" or ''. The default implementation is shown above.
Alien::Build::Plugin::Probe::Override and Alien::Build::Plugin::Probe::OverrideCI are
examples of how you can use this hook.
patch hook
$meta->register_hook( patch => sub {
my($build) = @_;
...
});
This hook is completely optional. If registered, it will be triggered after extraction
and before build. It allows you to apply any patches or make any modifications to the
source if they are necessary.
patch_ffi hook
$meta->register_hook( patch_ffi => sub {
my($build) = @_;
...
});
This hook is exactly like the patch hook, except it fires only on an FFI build.
prefer hook
$meta->register_hook( prefer => sub {
my($build, $res) = @_;
return {
type => 'list',
list => [sort @{ $res->{list} }],
};
}
This hook sorts candidates from a listing generated from either the "fetch" or "decode"
hooks. It should return a new list hash reference with the candidates sorted from best to
worst. It may also remove candidates that are totally unacceptable.
probe hook
$meta->register_hook( probe => sub {
my($build) = @_;
return 'system' if ...; # system install
return 'share'; # otherwise
});
$meta->register_hook( probe => [ $command ] );
This hook should return the string "system" if the operating system provides the library
or tool. It should return "share" otherwise.
You can also use a command that returns true when the tool or library is available. For
example for use with "pkg-config":
$meta->register_hook( probe =>
[ '%{pkgconf} --exists libfoo' ] );
Or if you needed a minimum version:
$meta->register_hook( probe =>
[ '%{pkgconf} --atleast-version=1.00 libfoo' ] );
Note that this hook SHOULD NOT gather system properties, such as cflags, libs, versions,
etc, because the probe hook will be skipped in the event the environment variable
"ALIEN_INSTALL_TYPE" is set. The detection of these properties should instead be done by
the gather_system hook.
Multiple probe hooks can be given. These will be used in sequence, stopping at the first
that detects a system installation.
SEE ALSO
Alien::Build::Manual
Other Alien::Build manuals.
AUTHOR
Author: Graham Ollis <plicease@cpan.org>
Contributors:
Diab Jerius (DJERIUS)
Roy Storey (KIWIROY)
Ilya Pavlov
David Mertens (run4flat)
Mark Nunberg (mordy, mnunberg)
Christian Walde (Mithaldu)
Brian Wightman (MidLifeXis)
Zaki Mughal (zmughal)
mohawk (mohawk2, ETJ)
Vikas N Kumar (vikasnkumar)
Flavio Poletti (polettix)
Salvador Fandiño (salva)
Gianni Ceccarelli (dakkar)
Pavel Shaydo (zwon, trinitum)
Kang-min Liu (劉康民, gugod)
Nicholas Shipp (nshp)
Juan Julián Merelo Guervós (JJ)
Joel Berger (JBERGER)
Petr Písař (ppisar)
Lance Wicks (LANCEW)
Ahmad Fatoum (a3f, ATHREEF)
José Joaquín Atria (JJATRIA)
Duke Leto (LETO)
Shoichi Kaji (SKAJI)
Shawn Laffan (SLAFFAN)
Paul Evans (leonerd, PEVANS)
Håkon Hægland (hakonhagland, HAKONH)
nick nauwelaerts (INPHOBIA)
Florian Weimer
COPYRIGHT AND LICENSE
This software is copyright (c) 2011-2022 by Graham Ollis.
This is free software; you can redistribute it and/or modify it under the same terms as
the Perl 5 programming language system itself.