NAME
    Plack::App::GitHub::WebHook - GitHub WebHook receiver as Plack
    application

SYNOPSIS
  Basic usage
        use Plack::App::GitHub::WebHook;

        Plack::App::GitHub::WebHook->new(
            hook => sub {
                my ($payload, $event, $delivery, $logger) = @_;
                ...
            }
        )->to_app;

  Multiple task hooks
    A hook can consist of multiple tasks, given by an array reference. The
    tasks are called one by one until a task returns a false value.

        use Plack::App::GitHub::WebHook;
        use IPC::Run3;

        Plack::App::GitHub::WebHook->new(
            hook => [
                sub { $_[0]->{repository}{name} eq 'foo' }, # filter
                sub { # action
                    my ($payload, $event, $delivery, $logger) = @_;
                    run3 \@cmd, undef, $logger->{info}, $logger->{error}; 
                },
                sub { ...  }, # some more action
            ]
        )->to_app;

  Access restriction
    By default access is restricted to known GitHub WebHook IPs.

        Plack::App::GitHub::WebHook->new(
            hook => sub { ... },
            access => [
                allow => "204.232.175.64/27",
                allow => "192.30.252.0/22",
                deny  => 'all'
            ]
        )->to_app;

        # this is equivalent to
        use Plack::Builder;
        builder {
            mount 'notify' => builder {
                enable 'Access', rules => [
                    allow => "204.232.175.64/27",
                    allow => "192.30.252.0/22",
                    deny  => 'all'
                ]
                Plack::App::GitHub::WebHook->new(
                    hook => sub { ... }
                );
            }
        };

  Synchronize with a GitHub repository
    The following application automatically pulls the master branch of a
    GitHub repository into a local working directory.

        use Plack::App::GitHub::WebHook;
        use IPC::Run3;

        my $branch = "master;
        my $work_tree = "/some/path";

        Plack::App::GitHub::WebHook->new(
            events => ['push','ping'],
            hook => [
                sub { 
                    my ($payload, $event, $delivery, $log) = @_;
                    $log->info("$event $delivery");
                    $event eq 'ping' or $payload->{ref} eq "refs/heads/$branch";
                },
                sub {
                    my ($payload, $event, $delivery, $log) = @_;
                    my $origin = $payload->{repository}->{clone_url} 
                               or die "missing clone_url\n";
                    my $cmd;
                    if ( -d "$work_tree/.git") {
                        chdir $work_tree;
                        $cmd = ['git','pull',$origin,$branch];
                    } else {
                        $cmd = ['git','clone',$origin,'-b',$branch,$work_tree];
                    }
                    $log->info(join ' ', '$', @$cmd);
                    run3 $cmd, undef, $log->{info}, $log->{error};
                    1;
                },
                # sub { ...optional action after each pull... } 
            ],
        )->to_app;

DESCRIPTION
    This PSGI application receives HTTP POST requests with body parameter
    "payload" set to a JSON object. The default use case is to receive
    GitHub WebHooks <http://developer.github.com/webhooks/>, for instance
    PushEvents
    <http://developer.github.com/v3/activity/events/types/#pushevent>.

    The response of a HTTP request to this application is one of:

    HTTP 403 Forbidden
        If access was not granted (for instance because it did not origin
        from GitHub).

    HTTP 405 Method Not Allowed
        If the request was no HTTP POST.

    HTTP 400 Bad Request
        If the payload was no well-formed JSON or the "X-GitHub-Event"
        header did not match configured events.

    HTTP 200 OK
        Otherwise, if the hook was called and returned a true value.

    HTTP 202 Accepted
        Otherwise, if the hook was called and returned a false value.

    HTTP 500 Internal Server Error
        If a hook died with an exception, the error is returned as content
        body.

    This module requires at least Perl 5.10.

CONFIGURATION
    hook
        A code reference or an array of code references with tasks that are
        executed on an incoming webhook. Each task gets passed the encoded
        payload, the event <https://developer.github.com/webhooks/#events>
        and the unique delivery ID, and a logger object. If the task returns
        a true value, next the task is called or HTTP status code 200 is
        returned. Information can be passed from one task to the next by
        modifying the payload.

        If a task returns a false value or if no task was given, HTTP status
        code 202 is returned immediately. This mechanism can be used for
        conditional hooks or to detect hooks that were called successfully
        but failed to execute for some reason.

    safe
        Wrap all hook tasks in "eval { ... }" blocks to catch exceptions.
        Error messages are send to the PSGI error stream "psgi.errors". A
        dying task in safe mode is equivalent to a task that returns a false
        value, so it will result in a HTTP 202 response.

        Plack::Middleware::HTTPExceptions

        If you want errors to result in a HTTP 500 response, wrap the
        application in an eval block such as this:

            sub {
                eval { $app->(@_) } || do {
                    my $msg = $@ || 'Server Error';
                    [ 500, [ 'Content-Length' => length $msg ], [ $msg ] ];
                };
            };

    access
        Access restrictions, as passed to Plack::Middleware::Access. See
        SYNOPSIS for the default value. A recent list of official GitHub
        WebHook IPs is vailable at <https://api.github.com/meta>. One should
        only set the access value on instantiation, or manually call
        "prepare_app" after modification.

    events
        A list of event types
        <http://developer.github.com/v3/activity/events/types/> expected to
        be send with the "X-GitHub-Event" header (e.g. "['pull']").

LOGGING
    Each hook is passed a logging object as fourth parameter. It provides
    logging methods for each log level and a general log method:

        sub sample_hook {
            my ($payload, $event, $delivery, $log) = @_;

            $log->debug('message');  $log->{debug}->('message');
            $log->info('message');   $log->{info}->('message');
            $log->warn('message');   $log->{warn}->('message');
            $log->error('message');  $log->{error}->('message');
            $log->fatal('message');  $log->{fatal}->('message');

            $log->log( warn => 'message' );

            run3 \@system_command, undef,
                $log->{info},   # STDOUT to log level info
                $log->{error};  # STDERR to log level error
        }

    Trailing newlines on log messages are trimmed.

DEPLOYMENT
    Many deployment methods exist. An easy option might be to use Apache
    webserver with mod_cgi and Plack::Handler::CGI. First install Apache,
    Plack and Plack::App::GitHub::WebHook:

        sudo apt-get install apache2
        sudo apt-get install cpanminus libplack-perl
        sudo cpanm Plack::App::GitHub::WebHook

    Then add this section to "/etc/apache2/sites-enabled/default" (or
    another host configuration) and restart Apache.

        <Directory /var/www/webhooks>
           Options +ExecCGI -Indexes +SymLinksIfOwnerMatch
           AddHandler cgi-script .cgi
        </Directory>

    You can now put webhook applications in directory "/var/www/webhooks" as
    long as they are executable, have file extension ".cgi" and shebang line
    "#!/usr/bin/env plackup". You might further want to run webhooks scripts
    as another user instead of "www-data" by using Apache module SuExec.

SEE ALSO
    *   GitHub WebHooks are documented at
        <http://developer.github.com/webhooks/>.

    *   WWW::GitHub::PostReceiveHook uses Web::Simple to receive GitHub web
        hooks. A listener as exemplified by the module can also be created
        like this:

            use Plack::App::GitHub::WebHook;
            use Plack::Builder;
            build {
                mount '/myProject' => 
                    Plack::App::GitHub::WebHook->new(
                        hook => sub { my $payload = shift; }
                    );
                mount '/myOtherProject' => 
                    Plack::App::GitHub::WebHook->new(
                        hook => sub { run3 \@cmd ... }
                    );
            };

    *   Net::GitHub and Pithub provide access to GitHub APIs.

    *   App::GitHubWebhooks2Ikachan is an application that also receives
        GitHub WebHooks.

COPYRIGHT AND LICENSE
    Copyright Jakob Voss, 2014-

    This library is free software; you can redistribute it and/or modify it
    under the same terms as Perl itself.