MARC::File::USMARC - USMARC-specific file handling

MARC-Record documentation Contained in the MARC-Record distribution.

Index

Code Index:

NAME

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MARC::File::USMARC - USMARC-specific file handling

SYNOPSIS

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    use MARC::File::USMARC;

    my $file = MARC::File::USMARC->in( $filename );

    while ( my $marc = $file->next() ) {
        # Do something
    }
    $file->close();
    undef $file;

EXPORT

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None.

METHODS

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decode( $string [, \&filter_func ] )

Constructor for handling data from a USMARC file. This function takes care of all the tag directory parsing & mangling.

Any warnings or coercions can be checked in the warnings() function.

The $filter_func is an optional reference to a user-supplied function that determines on a tag-by-tag basis if you want the tag passed to it to be put into the MARC record. The function is passed the tag number and the raw tag data, and must return a boolean. The return of a true value tells MARC::File::USMARC::decode that the tag should get put into the resulting MARC record.

For example, if you only want title and subject tags in your MARC record, try this:

    sub filter {
        my ($tagno,$tagdata) = @_;

        return ($tagno == 245) || ($tagno >= 600 && $tagno <= 699);
    }

    my $marc = MARC::File::USMARC->decode( $string, \&filter );

Why would you want to do such a thing? The big reason is that creating fields is processor-intensive, and if your program is doing read-only data analysis and needs to be as fast as possible, you can save time by not creating fields that you'll be ignoring anyway.

Another possible use is if you're only interested in printing certain tags from the record, then you can filter them when you read from disc and not have to delete unwanted tags yourself.

update_leader()

If any changes get made to the MARC record, the first 5 bytes of the leader (the length) will be invalid. This function updates the leader with the correct length of the record as it would be if written out to a file.

_build_tag_directory()

Function for internal use only: Builds the tag directory that gets put in front of the data in a MARC record.

Returns two array references, and two lengths: The tag directory, and the data fields themselves, the length of all data (including the Leader that we expect will be added), and the size of the Leader and tag directory.

encode()

Returns a string of characters suitable for writing out to a USMARC file, including the leader, directory and all the fields.

RELATED MODULES

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MARC::Record

TODO

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Make some sort of autodispatch so that you don't have to explicitly specify the MARC::File::X subclass, sort of like how DBI knows to use DBD::Oracle or DBD::Mysql.

Create a toggle-able option to check inside the field data for end of field characters. Presumably it would be good to have it turned on all the time, but it's nice to be able to opt out if you don't want to take the performance hit.

LICENSE

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This code may be distributed under the same terms as Perl itself.

Please note that these modules are not products of or supported by the employers of the various contributors to the code.

AUTHOR

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Andy Lester, <andy@petdance.com>

MARC-Record documentation Contained in the MARC-Record distribution. 
package MARC::File::USMARC;


use strict;
use integer;

use vars qw( $ERROR );
use MARC::File::Encode qw( marc_to_utf8 );

use MARC::File;
use vars qw( @ISA ); @ISA = qw( MARC::File );

use MARC::Record qw( LEADER_LEN );
use MARC::Field;
use constant SUBFIELD_INDICATOR     => "\x1F";
use constant END_OF_FIELD           => "\x1E";
use constant END_OF_RECORD          => "\x1D";
use constant DIRECTORY_ENTRY_LEN    => 12;


sub _next {
    my $self = shift;
    my $fh = $self->{fh};

    my $reclen;
    return if eof($fh);

    local $/ = END_OF_RECORD;
    my $usmarc = <$fh>;

    # remove illegal garbage that sometimes occurs between records
    $usmarc =~ s/^[ \x00\x0a\x0d\x1a]+//;

    return $usmarc;
}


sub decode {

    my $text;
    my $location = '';

    ## decode can be called in a variety of ways
    ## $object->decode( $string )
    ## MARC::File::USMARC->decode( $string )
    ## MARC::File::USMARC::decode( $string )
    ## this bit of code covers all three

    my $self = shift;
    if ( ref($self) =~ /^MARC::File/ ) {
        $location = 'in record '.$self->{recnum};
        $text = shift;
    } else {
        $location = 'in record 1';
        $text = $self=~/MARC::File/ ? shift : $self;
    }
    my $filter_func = shift;

    # ok this the empty shell we will fill
    my $marc = MARC::Record->new();

    # Check for an all-numeric record length
    ($text =~ /^(\d{5})/)
        or return $marc->_warn( "Record length \"", substr( $text, 0, 5 ), "\" is not numeric $location" );

    my $reclen = $1;
    my $realLength = bytes::length( $text );
    $marc->_warn( "Invalid record length $location: Leader says $reclen " . 
        "bytes but it's actually $realLength" ) unless $reclen == $realLength;

    (substr($text, -1, 1) eq END_OF_RECORD)
        or $marc->_warn( "Invalid record terminator $location" );

    $marc->leader( substr( $text, 0, LEADER_LEN ) );

    # bytes 12 - 16 of leader give offset to the body of the record
    my $data_start = 0 + bytes::substr( $text, 12, 5 );

    # immediately after the leader comes the directory (no separator)
    my $dir = substr( $text, LEADER_LEN, $data_start - LEADER_LEN - 1 );  # -1 to allow for \x1e at end of directory

    # character after the directory must be \x1e
    (substr($text, $data_start-1, 1) eq END_OF_FIELD)
        or $marc->_warn( "No directory found $location" );

    # all directory entries 12 bytes long, so length % 12 must be 0
    (length($dir) % DIRECTORY_ENTRY_LEN == 0)
        or $marc->_warn( "Invalid directory length $location" );


    # go through all the fields
    my $nfields = length($dir)/DIRECTORY_ENTRY_LEN;
    for ( my $n = 0; $n < $nfields; $n++ ) {
        my ( $tagno, $len, $offset ) = unpack( "A3 A4 A5", substr($dir, $n*DIRECTORY_ENTRY_LEN, DIRECTORY_ENTRY_LEN) );

        # Check directory validity
        ($tagno =~ /^[0-9A-Za-z]{3}$/)
            or $marc->_warn( "Invalid tag in directory $location: \"$tagno\"" );

        ($len =~ /^\d{4}$/)
            or $marc->_warn( "Invalid length in directory $location tag $tagno: \"$len\"" );

        ($offset =~ /^\d{5}$/)
            or $marc->_warn( "Invalid offset in directory $location tag $tagno: \"$offset\"" );

        ($offset + $len <= $reclen)
            or $marc->_warn( "Directory entry $location runs off the end of the record tag $tagno" );

        my $tagdata = bytes::substr( $text, $data_start+$offset, $len ); 

        # if utf8 the we encode the string as utf8
        if ( $marc->encoding() eq 'UTF-8' ) {
            $tagdata = marc_to_utf8( $tagdata );
        }

        $marc->_warn( "Invalid length in directory for tag $tagno $location" )
            unless ( $len == bytes::length($tagdata) );

        if ( substr($tagdata, -1, 1) eq END_OF_FIELD ) {
            # get rid of the end-of-tag character
            chop $tagdata;
            --$len;
        } else {
            $marc->_warn( "field does not end in end of field character in tag $tagno $location" );
        }

        warn "Specs: ", join( "|", $tagno, $len, $offset, $tagdata ), "\n" if $MARC::Record::DEBUG;

        if ( $filter_func ) {
            next unless $filter_func->( $tagno, $tagdata );
        }

        if ( MARC::Field->is_controlfield_tag($tagno) ) {
            $marc->append_fields( MARC::Field->new( $tagno, $tagdata ) );
        } else {
            my @subfields = split( SUBFIELD_INDICATOR, $tagdata );
            my $indicators = shift @subfields;
            my ($ind1, $ind2);

            if ( length( $indicators ) > 2 or length( $indicators ) == 0 ) {
                $marc->_warn( "Invalid indicators \"$indicators\" forced to blanks $location for tag $tagno\n" );
                ($ind1,$ind2) = (" ", " ");
            } else {
                $ind1 = substr( $indicators,0, 1 );
                $ind2 = substr( $indicators,1, 1 );
            }

            # Split the subfield data into subfield name and data pairs
            my @subfield_data;
            for ( @subfields ) {
                if ( length > 0 ) {
                    push( @subfield_data, substr($_,0,1),substr($_,1) );
                } else {
                    $marc->_warn( "Entirely empty subfield found in tag $tagno" );
                }
            }

            if ( !@subfield_data ) {
                $marc->_warn( "no subfield data found $location for tag $tagno" );
                next;
            }

            my $field = MARC::Field->new($tagno, $ind1, $ind2, @subfield_data );
            if ( $field->warnings() ) {
                $marc->_warn( $field->warnings() );
            }
            $marc->append_fields( $field );
        }
    } # looping through all the fields


    return $marc;
}


sub update_leader() {
        my $self = shift;

        my (undef,undef,$reclen,$baseaddress) = $self->_build_tag_directory();

        $self->_set_leader_lengths( $reclen, $baseaddress );
}


sub _build_tag_directory {
        my $marc = shift;
        $marc = shift if (ref($marc)||$marc) =~ /^MARC::File/;
        die "Wanted a MARC::Record but got a ", ref($marc) unless ref($marc) eq "MARC::Record";

        my @fields;
        my @directory;

        my $dataend = 0;
        for my $field ( $marc->fields() ) {
                # Dump data into proper format
                my $str = $field->as_usmarc;
                push( @fields, $str );

                # Create directory entry
                my $len = bytes::length( $str );

                my $direntry = sprintf( "%03s%04d%05d", $field->tag, $len, $dataend );
                push( @directory, $direntry );
                $dataend += $len;
        }

        my $baseaddress =
                LEADER_LEN +    # better be 24
                ( @directory * DIRECTORY_ENTRY_LEN ) +
                                # all the directory entries
                1;              # end-of-field marker


        my $total =
                $baseaddress +  # stuff before first field
                $dataend +      # Length of the fields
                1;              # End-of-record marker



        return (\@fields, \@directory, $total, $baseaddress);
}


sub encode() {
    my $marc = shift;
    $marc = shift if (ref($marc)||$marc) =~ /^MARC::File/;

    my ($fields,$directory,$reclen,$baseaddress) = _build_tag_directory($marc);
    $marc->set_leader_lengths( $reclen, $baseaddress );

    # Glomp it all together
    return join("",$marc->leader, @$directory, END_OF_FIELD, @$fields, END_OF_RECORD);
}
1;

__END__