setbookmark.pl

#!/usr/bin/perl

use strict;

# Syntax: perl setbookmark.pl onetimepad_file new_bookmark

# This sets the value of the bookmark in the given one-time pad and erases the data
# between the old bookmark and the bookmark.

my $True = 1;
my $False = 0;

# Execution starts here
&main;

sub main()
{
	my $intNumArgs = $#ARGV + 1;
	if ($intNumArgs != 2)
	{
		print "Syntax: perl setbookmark.pl onetimepad_file new_bookmark\n";
		exit 1;
	}
	
	# Read the arguments on the command line
	my $strPadFilename = $ARGV[0];
	my $lngNewBookmark = $ARGV[1];

	my $lngCurrentBookmark = ReadBookmark($strPadFilename);
	if ($lngCurrentBookmark == 0)
	{
		exit 1;
	}
	print "Current bookmark is ".$lngCurrentBookmark."\n";

	if ($lngNewBookmark <= $lngCurrentBookmark)
	{
		print "ERROR:New bookmark must be set after current bookmark\n";
		exit 1;
	}

	my $lngFileSize = -s $strPadFilename;
	print "File size is ".$lngFileSize."\n";
	if ($lngNewBookmark > $lngFileSize )
	{
		print "ERROR:New bookmark is beyond the end of the file\n";
		exit 1;
	}

	if (SetBookmarkAndDeleteData($strPadFilename, $lngCurrentBookmark, $lngNewBookmark) == $False)
	{
		exit 1;
	}
	exit 0;
}

sub ReadBookmark($)
{
	my $strPadFilename = $_[0];

	if (!open PAD_FILE, "<$strPadFilename")
	{
		print "ERROR:Can't open file $strPadFilename\n";
		return 0;
	}
	# Handle the file as bytes instead of text
	binmode PAD_FILE;

	my $lngBookmark = unpack('L', <PAD_FILE>);
	close PAD_FILE;

	return $lngBookmark;
}

sub SetBookmarkAndDeleteData($$$)
{
	my $strPadFilename = $_[0];
	my $lngCurrentBookmark = $_[1];
	my $lngNewBookmark = $_[2];

	if (!open PAD_FILE, "+<$strPadFilename")
	{
		print "ERROR:Can't open file $strPadFilename\n";
		return $False;
	}
	# Handle the file as bytes instead of text
	binmode PAD_FILE;

	# Write the new bookmark at the start of the file
	seek(PAD_FILE, 0, 0);
	print PAD_FILE pack('L', $lngNewBookmark);
	print "Bookmark updated to ".$lngNewBookmark."\n";

	# Delete data between old and new bookmarks
	seek(PAD_FILE, $lngCurrentBookmark, 0);

	for(my $lngCounter = $lngCurrentBookmark; $lngCounter < $lngNewBookmark; $lngCounter++)
	{
		my $byte = 0;
		print PAD_FILE pack('C', $byte);
	}	
	print "Data up to new bookmark deleted\n";

	close PAD_FILE;
	return $True;
}

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