DirDB::FTP - Perl extension to use a remote directory as a database

  use DirDB::FTP;
  my $ftp = DirDB::FTP->new('some.host.name',$username,$password);
  tie my %entries, DirDB::FTP, $ftp, => "/blog_entries";
  $entries{'entry for '.localtime} = $entry_text;

package DirDB::FTP;

require 5.005;
use strict;
# use warnings;
use Carp;

use Net::FTP;
use Net::FTP::blat;

use vars '$VERSION';

$VERSION = '0.03';

sub new{
# DirDB::FTP -> new ( $hostname, $user, $pass );
	shift; # we don't need the package name
	my $f = Net::FTP->new( $_[0] , timeout => 300 ) or croak
	   "cannot connect to $_[0]";
	my $pl = 0+length $_[2];
	$f->login($_[1], $_[2]) or croak
	   "cannot login with username $_[1] and $pl char passwd";
	$f->binary();
	$f;
};


sub TIEHASH {
	my ($self, $ftp, $rootpath) = @_;
	ref($ftp) eq 'Net::FTP' or croak <<'EOSYNTAX';
Syntax:
tie my %hash, DirDB::FTP => $ftp_object [, "/some/directory"];
EOSYNTAX

    if(defined $rootpath){
	$rootpath =~ s#/+$##; # lose trailing slash(es)
	if (length $rootpath){
	  $ftp->cwd($rootpath) or $ftp->mkdir($rootpath,'recurse')   
	   or
	     croak "could not change to or create dir $rootpath: "
	     . $ftp->message;
	};
    }else{
    	$rootpath = $ftp->pwd();
    };
	bless [$ftp,"$rootpath/"], $self;
};

sub TIEARRAY {
	confess "DirDB does not support arrays yet";
};

sub TIESCALAR {
	confess "DirDB does not support scalars yet -- try Tie::Slurp";
};


sub EXISTS {
	my ($ftp,$rootpath) = @{+shift};
	my $key = shift;
	$key =~ s/^ /  /; #escape leading space into two spaces
	$key eq '' and $key = ' EMPTY';
	my $mdtm = $ftp->mdtm("$rootpath$key");
	$ftp->message =~ m/no such/i and return 0;
	return 1;

	# my @mdtm = $ftp->ls("$rootpath$key");
	# print "Debug: $mdtm\n";
	defined $mdtm and return 1;
	$ftp->message =~ m/ not a plain file/ and return 1;
	0;
};

sub FETCH {
	my $ref = shift;
	my ($ftp,$rootpath) = @{$ref};
	my $key = shift;
	$key =~ s/^ /  /; #escape leading space into two spaces
	$key eq '' and $key = ' EMPTY';
# FIXME
# Our goal here is to mimic the DirDB semantics, using
# commands defined in Net::FTP, plus slurp and blat.
# We are allowing some error message reading but want
# to keep that down to as little as possible.

	
	sleep 1 while $ftp->ls( "$rootpath LOCK$key");
	my $result = $ftp->slurp( "$rootpath$key" );
	# print "DEBUG: ",$ftp->message(),"\n";
	
	defined $result and return $result;

	$ftp->message =~ /no such/i and return undef;
	
	# assume a directory, ...
	tie my %newhash, ref($ref),$ftp,"$rootpath$key"
	  or croak "Could not fetch [$rootpath$key]: ".$ftp->message;
 	return \%newhash;
};

{
my %CircleTracker;
sub STORE {
	my ($ref , $key, $value) = @_;
	my ($ftp,$rootpath) = @{$ref};
	
	my $rnd = rand(10000).{}.$$;
	$rnd =~ tr/a-zA-Z0-9//cd;
	$key =~ s/^ /  /; #escape leading space into two spaces
	$key eq '' and $key = ' EMPTY';
	my $refvalue = ref $value;
	if ($refvalue){

		if ( $CircleTracker{$value}++ ){
	          croak "$ref version $VERSION cannot store circular structures\n";
		};

		$refvalue eq 'HASH' or	
	          croak 
		   "$ref version $VERSION only stores references to HASH, not $refvalue\n";

		if (tied (%$value)){
			# recursive copy
		   tie my %tmp, ref($ref), $ftp, "$rootpath TMP$rnd" or
		   die "tie failed";
		 eval{
		 	# %tmp = %$value

			my ($k,$v);
			while(($k,$v) = each %$value){
				$tmp{$k}=$v;
			};
		 };
		 # print "$rootpath TMP$rnd should now contain @{[%$value]}\n";
		 if($@){
		    my $message = $@;
		    eval {$ftp->rmdir( "$rootpath TMP$rnd", 1)};
		    croak "trouble writing [$value] to [$rootpath$key]: $message";

		};
	
		# print "lock (tied)";
		 sleep 1 while !$ftp->mkdir( "$rootpath LOCK$key");
		 {
		  # no warnings;
		  $ftp->rename( "$rootpath$key", "$rootpath GARBAGE$rnd"); 
		 };
		 $ftp->rename( "$rootpath TMP$rnd", "$rootpath$key");

		}else{
			# cache, bless, restore
			my @cache = %$value;
			%$value = ();
		# print "lock (untied)";
			while( !$ftp->mkdir( "$rootpath LOCK$key")){
				# print "lock conflivt: $!";
				sleep 1;
			};
			{
			 # no warnings;
		         $ftp->rename( "$rootpath$key","$rootpath GARBAGE$rnd");
		        };
		        tie %$value, ref($ref), $ftp, "$rootpath$key" or
		          warn "tie to [$rootpath$key] failed: ".$ftp->message;
		# print "assignment";
			%$value = @cache;
		};
		
		$ftp->rmdir( "$rootpath LOCK$key");
		delete $CircleTracker{$value};
		
		# print "GC";
		 eval {$ftp->rmdir( "$rootpath GARBAGE$rnd",'recurse')};
		 if($@){
			croak "GC problem: $@";
		 };
		 return;

	};

	# store a scalar using write-to-temp-and-rename
	$ftp->blat($value,"$rootpath TMP$rnd") or croak $ftp->message;
	$ftp->rename( "$rootpath TMP$rnd" , "$rootpath$key") or
	  croak
	     " could not rename temp file to [$rootpath$key]: ".$ftp->message;
};
};

sub DELETE {
	my ($ref , $key) = @_;
	my ($ftp,$rootpath) = @{$ref};
	
	my $retval = undef;
	
	if(defined wantarray){
		$retval = FETCH( $ref,$key );
		if (ref $retval) {
			my %hash;
			my @keys = keys %$retval;
			my $k;
			foreach $k (@keys) {
				$hash{$k} = delete $retval->{$k};
			};
			$retval = \%hash;
		};
	};

	$key =~ s/^ /  /; #escape leading space into two spaces
	$key eq '' and $key = ' EMPTY';

	# -e "$rootpath$key" or return undef;
	$ftp->delete( "$rootpath$key" ) or 
	$ftp->rmdir( "$rootpath$key", 'recurse' );
	
	return $retval;
};

sub CLEAR{
	my ($ref , $key, $value) = @_;
	my ($ftp,$rootpath) = @{$ref};
	
	# maybe we can delete the whole thing? 
	# we will check to make sure this succeeds because we
	# want to support clearing a whole directory that we
	# have been issued by an administrator
	
	$ftp->rmdir($rootpath, 'recurse')
	and	
	$ftp->mkdir($rootpath)
	and
	return;

	my @dirents = $ftp->ls($rootpath);
	for my $ent (@dirents){
		$ftp->delete("$rootpath$ent")
		or
		$ftp->rmdir("$rootpath$ent",1)
	};
		
};

{

   my %IteratorListings;

   sub FIRSTKEY {
	my ($ref , $key, $value) = @_;
	my ($ftp,$rootpath) = @{$ref};
	# opendir FSDBFH, $path or croak "opendir $path: $!";
	# $IteratorListings{$ref} = [ grep {!($_ =~ /^\.\.?\Z/)} readdir FSDBFH ];
	$IteratorListings{$ref} = [ $ftp->ls ];

	$ref->NEXTKEY;
   };

   sub NEXTKEY{
	my $ref = shift;
	my ($ftp,$rootpath) = @{$ref};
	#print "next key in path <$$ref> will be shifted from <@{$IteratorListings{$ref}}>\n";
	@{$IteratorListings{$ref}} or return undef;
	my $key = shift @{$IteratorListings{$ref}};
	if ($key =~ s/^ //){
		if ($key = m/^ /){
			# we have unescaped a leading space.
		}elsif ($key eq 'EMPTY'){
			$key = ''
		#}elsif($key eq 'REF'){
		# 	return $ref->NEXTKEY();	# next
		#}elsif($key =~ m/^ARRAY){
		# 	return $ref->NEXTKEY();	# next
		}else{
			# per-container metadata does not
			# appear in iterations through data.
			return $ref->NEXTKEY();	# next
		}
	};
	wantarray or return $key;
	return @{[$key, $ref->FETCH($key)]};
   };
   
   sub DESTROY{
       # no warnings;
       delete $IteratorListings{$_[0]};
   };
 
};




1;
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