File Coverage

blib/lib/File/ReadBackwards.pm

Criterion	Covered	Total	%
statement	77	79	97.4
branch	18	24	75.0
condition	11	15	73.3
subroutine	11	11	100.0
pod	6	6	100.0
total	123	135	91.1

# File::ReadBackwards.pm

# Copyright (C) 2000-2021 by Uri Guttman. All rights reserved.
# mail bugs, comments and feedback to [e-mail]

package File::ReadBackwards ;

use strict ;
use Symbol ;
use Fcntl qw( :seek O_RDONLY ) ;
use Carp ;

our $VERSION = '1.06' ;

my $max_read_size = 1 << 13 ;

my $default_rec_sep ;

BEGIN {

# set the default record separator according to this OS
# this needs testing and expansion.

# look for CR/LF types
# then look for CR types
# else it's a LF type

	if ( $^O =~ /win32/i || $^O =~ /vms/i ) {

		$default_rec_sep = "\015\012" ;
	}
	elsif ( $^O =~ /mac/i ) {

		$default_rec_sep = "\015" ;
	}
	else {
		$default_rec_sep = "\012" ;
	}

# the tied interface is exactly the same as the object one, so all we
# need to do is to alias the subs with typeglobs

	*TIEHANDLE = \&new ;
	*READLINE = \&readline ;
 	*EOF = \&eof ;
 	*CLOSE = \&close ;
 	*TELL = \&tell ;

# added getline alias for compatibility with IO::Handle

	*getline = \&readline ;
}


# constructor for File::ReadBackwards

sub new {

	my( $class, $filename, $rec_sep, $sep_is_regex ) = @_ ;

# check that we have a filename

	defined( $filename ) || return ;

# see if this file uses the default of a cr/lf separator
# those files will get cr/lf converted to \n

	$rec_sep ||= $default_rec_sep ;
	my $is_crlf = $rec_sep eq "\015\012" ;

# get a handle and open the file

	my $handle = gensym ;
	sysopen( $handle, $filename, O_RDONLY ) || return ;
	binmode $handle ;

# seek to the end of the file and get its size

	my $seek_pos = sysseek( $handle, 0, SEEK_END ) or return ;

# get the size of the first block to read,
# either a trailing partial one (the % size) or full sized one (max read size)

	my $read_size = $seek_pos % $max_read_size || $max_read_size ;

# create the object

	my $self = bless {
			'file_name'	=> $filename,
			'handle'	=> $handle,
			'read_size'	=> $read_size,
			'seek_pos'	=> $seek_pos,
			'lines'		=> [],
			'is_crlf'	=> $is_crlf,
			'rec_sep'	=> $rec_sep,
			'sep_is_regex'	=> $sep_is_regex,

		}, $class ;

	return( $self ) ;
}

# read the previous record from the file
#
sub readline {

	my( $self, $line_ref ) = @_ ;

	my $read_buf ;

# get the buffer of lines

	my $lines_ref = $self->{'lines'} ;

	return unless $lines_ref ;

	while( 1 ) {

# see if there is more than 1 line in the buffer

		if ( @{$lines_ref} > 1 ) {

# we have a complete line so return it
# and convert those damned cr/lf lines to \n

			$lines_ref->[-1] =~ s/\015\012/\n/
					if $self->{'is_crlf'} ;

			return( pop @{$lines_ref} ) ;
		}

# we don't have a complete, so have to read blocks until we do

		my $seek_pos = $self->{'seek_pos'} ;

# see if we are at the beginning of the file

		if ( $seek_pos == 0 ) {

# the last read never made more lines, so return the last line in the buffer
# if no lines left then undef will be returned
# and convert those damned cr/lf lines to \n

			$lines_ref->[-1] =~ s/\015\012/\n/
					if @{$lines_ref} && $self->{'is_crlf'} ;

			return( pop @{$lines_ref} ) ;
		}

# we have to read more text so get the handle and the current read size

		my $handle = $self->{'handle'} ;
		my $read_size = $self->{'read_size'} ;

# after the first read, always read the maximum size

		$self->{'read_size'} = $max_read_size ;

# seek to the beginning of this block and save the new seek position

		$seek_pos -= $read_size ;
		sysseek( $handle, $seek_pos, SEEK_SET ) ;
		$self->{'seek_pos'} = $seek_pos ;

# read in the next (previous) block of text

		my $read_cnt = sysread( $handle, $read_buf, $read_size ) ;

# prepend the read buffer to the leftover (possibly partial) line

		my $text = $read_buf ;
		$text .= shift @{$lines_ref} if @{$lines_ref} ;

# split the buffer into a list of lines
# this may want to be $/ but reading files backwards assumes plain text and
# newline separators

		@{$lines_ref} = ( $self->{'sep_is_regex'} ) ?
	 		$text =~ /(.*?$self->{'rec_sep'}|.+)/gs :
			$text =~ /(.*?\Q$self->{'rec_sep'}\E|.+)/gs ;

#print "Lines \n=>", join( "<=\n=>", @{$lines_ref} ), "<=\n" ;

	}
}

sub eof {

	my ( $self ) = @_ ;

	my $seek_pos = $self->{'seek_pos'} ;
	my $lines_count = @{ $self->{'lines'} } ;
	return( $seek_pos == 0 && $lines_count == 0 ) ;
}

sub tell {
	my ( $self ) = @_ ;

	my $seek_pos = $self->{'seek_pos'} ;
	$seek_pos + length(join "", @{ $self->{'lines'} });
}

sub get_handle {
	my ( $self ) = @_ ;

	my $handle = $self->{handle} ;
	seek( $handle, $self->tell, SEEK_SET ) ;
	return $handle ;
}

sub close {

	my ( $self ) = @_ ;

	my $handle = delete( $self->{'handle'} ) ;
	delete( $self->{'lines'} ) ;

	CORE::close( $handle ) ;
}

__END__