=pod

---++ _restUpdateformfield

This REST function is used to update a single form field of a specified topic. 

   * =$session=   - The TWiki object associated to this session
   * =$topic=     - Name of the topic to be changed (this parameter is defined by the REST script
   * =$fieldname= - Name (key)  of the form field to be changed
   * =$newval=    - Value to be applied to the form field

The function checks for edit autharization on the topic, so username and password parameters should be passed to the REST script!

=cut


sub _restUpdateformfield {

   my ($session) = @_;
   my $web;
   my $topic = TWiki::Func::getCgiQuery()->param('topic');
   my $fieldname = TWiki::Func::getCgiQuery()->param('fieldname');
   my $newval = TWiki::Func::getCgiQuery()->param('newval');
   ($web, $topic) = TWiki::Func::normalizeWebTopicName(undef, $topic);

   unless ( TWiki::Func::topicExists ( $web, $topic )) {
     return "invalid Topic $web $topic\n";
   }

#  check accessrights in topic
   unless (TWiki::Func::checkAccessPermission(
        'EDIT', TWiki::Func::getWikiName(),
        undef, $topic, $web)) {
        my $error = "Access denied";
        print CGI::header(-status => 401);
        print $error;
        print STDERR $error;
        return undef;
    }

#   get topic content
    my ($meta, $text) = TWiki::Func::readTopic($web, $topic);

#   get chosen form field
    my $field = $meta->get('FIELD', $fieldname );
#    my $oldval = $field->{value};

    $meta->putKeyed( 'FIELD', { name => $fieldname, value => $newval } );
    my $error = TWiki::Func::saveTopic( $web, $topic, $meta, $text, { forcenewrevision => 1 } );

#    $field = $meta->get('FIELD', '$fieldname');
#    my $val = $field->{value};    

#    return "$oldval => $newval => $val : $error";
    return undef;

}