#!/usr/bin/perl
# Support for external plugins written in other languages.
# Communication via XML RPC a pipe.
# See externaldemo for an example of a plugin that uses this.
package IkiWiki::Plugin::external;

use warnings;
use strict;
use IkiWiki 2.00;
use RPC::XML;
use RPC::XML::Parser;
use IPC::Open2;
use IO::Handle;

my %plugins;

sub import { #{{{
    my $self=shift;
    my $plugin=shift;
    return unless defined $plugin;

    my ($plugin_read, $plugin_write);
    my $pid = open2($plugin_read, $plugin_write,
        IkiWiki::possibly_foolish_untaint($plugin));

    # open2 doesn't respect "use open ':utf8'"
    binmode($plugin_read, ':utf8');
    binmode($plugin_write, ':utf8');

    $plugins{$plugin}={in => $plugin_read, out => $plugin_write, pid => $pid,
        accum => ""};
    $RPC::XML::ENCODING="utf-8";

    rpc_call($plugins{$plugin}, "import");
} #}}}

sub rpc_write ($$) { #{{{
    my $fh=shift;
    my $string=shift;

    $fh->print($string."\n");
    $fh->flush;
} #}}}

sub rpc_call ($$;@) { #{{{
    my $plugin=shift;
    my $command=shift;

    # send the command
    my $req=RPC::XML::request->new($command, @_);
    rpc_write($plugin->{out}, $req->as_string);

    # process incoming rpc until a result is available
    while ($_ = $plugin->{in}->getline) {
        $plugin->{accum}.=$_;
        while ($plugin->{accum} =~ /^\s*(<\?xml\s.*?<\/(?:methodCall|methodResponse)>)\n(.*)/s) {
            $plugin->{accum}=$2;
            my $r = RPC::XML::Parser->new->parse($1);
            error("XML RPC parser failure: $r") unless ref $r;
            if ($r->isa('RPC::XML::response')) {
                my $value=$r->value;
                if ($r->is_fault($value)) {
                    # throw the error as best we can
                    print STDERR $value->string."\n";
                    return "";
                }
                elsif ($value->isa('RPC::XML::array')) {
                    return @{$value->value};
                }
                elsif ($value->isa('RPC::XML::struct')) {
                    my %hash=%{$value->value};

                    # XML-RPC v1 does not allow for
                    # nil/null/None/undef values to be
                    # transmitted, so until
                    # XML::RPC::Parser honours v2
                    # (<nil/>), external plugins send
                    # a hash with one key "null" pointing
                    # to an empty string.
                    if (exists $hash{null} &&
                        $hash{null} eq "" &&
                        int(keys(%hash)) == 1) {
                        return undef;
                    }

                    return %hash;
                }
                else {
                    return $value->value;
                }
            }

            my $name=$r->name;
            my @args=map { $_->value } @{$r->args};

            # When dispatching a function, first look in 
            # IkiWiki::RPC::XML. This allows overriding
            # IkiWiki functions with RPC friendly versions.
            my $ret;
            if (exists $IkiWiki::RPC::XML::{$name}) {
                $ret=$IkiWiki::RPC::XML::{$name}($plugin, @args);