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tighten Storable's recognition of tied SVs
[perl5.git] / dist / Storable / Storable.pm
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25f64a11 1#
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2# Copyright (c) 1995-2001, Raphael Manfredi
3# Copyright (c) 2002-2013 by the Perl 5 Porters
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4#
5# You may redistribute only under the same terms as Perl 5, as specified
6# in the README file that comes with the distribution.
7#
7a6a85bf 8
71a48636 9require XSLoader;
7a6a85bf 10require Exporter;
71a48636 11package Storable; @ISA = qw(Exporter);
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12
13@EXPORT = qw(store retrieve);
14@EXPORT_OK = qw(
9e21b3d0 15 nstore store_fd nstore_fd fd_retrieve
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16 freeze nfreeze thaw
17 dclone
9e21b3d0 18 retrieve_fd
dd19458b 19 lock_store lock_nstore lock_retrieve
d4b9b6e4 20 file_magic read_magic
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21);
22
01d7b99e 23use vars qw($canonical $forgive_me $VERSION);
7a6a85bf 24
4189a2e6 25$VERSION = '2.49';
7a6a85bf 26
1541ec63
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27BEGIN {
28 if (eval { local $SIG{__DIE__}; require Log::Agent; 1 }) {
29 Log::Agent->import;
30 }
31 #
32 # Use of Log::Agent is optional. If it hasn't imported these subs then
33 # provide a fallback implementation.
34 #
81447963 35 unless ($Storable::{logcroak} && *{$Storable::{logcroak}}{CODE}) {
1541ec63 36 require Carp;
1541ec63
DL
37 *logcroak = sub {
38 Carp::croak(@_);
39 };
6fe613da 40 }
81447963 41 unless ($Storable::{logcarp} && *{$Storable::{logcarp}}{CODE}) {
6fe613da 42 require Carp;
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43 *logcarp = sub {
44 Carp::carp(@_);
45 };
46 }
47}
7a6a85bf 48
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49#
50# They might miss :flock in Fcntl
51#
52
53BEGIN {
596596d5 54 if (eval { require Fcntl; 1 } && exists $Fcntl::EXPORT_TAGS{'flock'}) {
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55 Fcntl->import(':flock');
56 } else {
57 eval q{
58 sub LOCK_SH () {1}
59 sub LOCK_EX () {2}
60 };
61 }
62}
63
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64sub CLONE {
65 # clone context under threads
66 Storable::init_perinterp();
67}
68
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69# By default restricted hashes are downgraded on earlier perls.
70
71$Storable::downgrade_restricted = 1;
e8189732 72$Storable::accept_future_minor = 1;
71a48636 73
70e1279a 74XSLoader::load('Storable', $Storable::VERSION);
b8778c7c 75
862382c7
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76#
77# Determine whether locking is possible, but only when needed.
78#
79
530b72ba 80sub CAN_FLOCK; my $CAN_FLOCK; sub CAN_FLOCK {
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81 return $CAN_FLOCK if defined $CAN_FLOCK;
82 require Config; import Config;
83 return $CAN_FLOCK =
84 $Config{'d_flock'} ||
85 $Config{'d_fcntl_can_lock'} ||
86 $Config{'d_lockf'};
87}
88
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89sub show_file_magic {
90 print <<EOM;
91#
92# To recognize the data files of the Perl module Storable,
93# the following lines need to be added to the local magic(5) file,
94# usually either /usr/share/misc/magic or /etc/magic.
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95#
960 string perl-store perl Storable(v0.6) data
8b793558
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97>4 byte >0 (net-order %d)
98>>4 byte &01 (network-ordered)
99>>4 byte =3 (major 1)
100>>4 byte =2 (major 1)
101
0a0da639 1020 string pst0 perl Storable(v0.7) data
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103>4 byte >0
104>>4 byte &01 (network-ordered)
105>>4 byte =5 (major 2)
106>>4 byte =4 (major 2)
107>>5 byte >0 (minor %d)
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108EOM
109}
110
d4b9b6e4 111sub file_magic {
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112 require IO::File;
113
d4b9b6e4 114 my $file = shift;
ed0d1802 115 my $fh = IO::File->new;
ab6f8ca1 116 open($fh, "<". $file) || die "Can't open '$file': $!";
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117 binmode($fh);
118 defined(sysread($fh, my $buf, 32)) || die "Can't read from '$file': $!";
119 close($fh);
120
121 $file = "./$file" unless $file; # ensure TRUE value
122
123 return read_magic($buf, $file);
124}
125
b8778c7c 126sub read_magic {
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127 my($buf, $file) = @_;
128 my %info;
129
130 my $buflen = length($buf);
131 my $magic;
132 if ($buf =~ s/^(pst0|perl-store)//) {
133 $magic = $1;
134 $info{file} = $file || 1;
135 }
136 else {
137 return undef if $file;
138 $magic = "";
139 }
140
141 return undef unless length($buf);
142
143 my $net_order;
144 if ($magic eq "perl-store" && ord(substr($buf, 0, 1)) > 1) {
145 $info{version} = -1;
146 $net_order = 0;
147 }
148 else {
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149 $buf =~ s/(.)//s;
150 my $major = (ord $1) >> 1;
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151 return undef if $major > 4; # sanity (assuming we never go that high)
152 $info{major} = $major;
5e12106f 153 $net_order = (ord $1) & 0x01;
d4b9b6e4 154 if ($major > 1) {
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155 return undef unless $buf =~ s/(.)//s;
156 my $minor = ord $1;
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157 $info{minor} = $minor;
158 $info{version} = "$major.$minor";
159 $info{version_nv} = sprintf "%d.%03d", $major, $minor;
160 }
161 else {
162 $info{version} = $major;
163 }
164 }
165 $info{version_nv} ||= $info{version};
166 $info{netorder} = $net_order;
167
168 unless ($net_order) {
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169 return undef unless $buf =~ s/(.)//s;
170 my $len = ord $1;
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171 return undef unless length($buf) >= $len;
172 return undef unless $len == 4 || $len == 8; # sanity
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173 @info{qw(byteorder intsize longsize ptrsize)}
174 = unpack "a${len}CCC", $buf;
175 (substr $buf, 0, $len + 3) = '';
d4b9b6e4 176 if ($info{version_nv} >= 2.002) {
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177 return undef unless $buf =~ s/(.)//s;
178 $info{nvsize} = ord $1;
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179 }
180 }
181 $info{hdrsize} = $buflen - length($buf);
182
183 return \%info;
184}
185
186sub BIN_VERSION_NV {
187 sprintf "%d.%03d", BIN_MAJOR(), BIN_MINOR();
188}
189
190sub BIN_WRITE_VERSION_NV {
191 sprintf "%d.%03d", BIN_MAJOR(), BIN_WRITE_MINOR();
b8778c7c 192}
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193
194#
195# store
196#
197# Store target object hierarchy, identified by a reference to its root.
198# The stored object tree may later be retrieved to memory via retrieve.
199# Returns undef if an I/O error occurred, in which case the file is
200# removed.
201#
202sub store {
dd19458b 203 return _store(\&pstore, @_, 0);
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204}
205
206#
207# nstore
208#
209# Same as store, but in network order.
210#
211sub nstore {
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212 return _store(\&net_pstore, @_, 0);
213}
214
215#
216# lock_store
217#
218# Same as store, but flock the file first (advisory locking).
219#
220sub lock_store {
221 return _store(\&pstore, @_, 1);
222}
223
224#
225# lock_nstore
226#
227# Same as nstore, but flock the file first (advisory locking).
228#
229sub lock_nstore {
230 return _store(\&net_pstore, @_, 1);
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231}
232
233# Internal store to file routine
234sub _store {
235 my $xsptr = shift;
236 my $self = shift;
dd19458b 237 my ($file, $use_locking) = @_;
7a6a85bf 238 logcroak "not a reference" unless ref($self);
b12202d0 239 logcroak "wrong argument number" unless @_ == 2; # No @foo in arglist
7a6a85bf 240 local *FILE;
dd19458b 241 if ($use_locking) {
6e0ac6f5 242 open(FILE, ">>$file") || logcroak "can't write into $file: $!";
862382c7 243 unless (&CAN_FLOCK) {
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244 logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O";
245 return undef;
f567092b 246 }
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247 flock(FILE, LOCK_EX) ||
248 logcroak "can't get exclusive lock on $file: $!";
249 truncate FILE, 0;
250 # Unlocking will happen when FILE is closed
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251 } else {
252 open(FILE, ">$file") || logcroak "can't create $file: $!";
dd19458b 253 }
6e0ac6f5 254 binmode FILE; # Archaic systems...
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255 my $da = $@; # Don't mess if called from exception handler
256 my $ret;
257 # Call C routine nstore or pstore, depending on network order
258 eval { $ret = &$xsptr(*FILE, $self) };
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259 # close will return true on success, so the or short-circuits, the ()
260 # expression is true, and for that case the block will only be entered
261 # if $@ is true (ie eval failed)
262 # if close fails, it returns false, $ret is altered, *that* is (also)
263 # false, so the () expression is false, !() is true, and the block is
264 # entered.
cbc736f3 265 if (!(close(FILE) or undef $ret) || $@) {
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266 unlink($file) or warn "Can't unlink $file: $!\n";
267 }
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268 logcroak $@ if $@ =~ s/\.?\n$/,/;
269 $@ = $da;
cbc736f3 270 return $ret;
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271}
272
273#
274# store_fd
275#
276# Same as store, but perform on an already opened file descriptor instead.
277# Returns undef if an I/O error occurred.
278#
279sub store_fd {
280 return _store_fd(\&pstore, @_);
281}
282
283#
284# nstore_fd
285#
286# Same as store_fd, but in network order.
287#
288sub nstore_fd {
289 my ($self, $file) = @_;
290 return _store_fd(\&net_pstore, @_);
291}
292
293# Internal store routine on opened file descriptor
294sub _store_fd {
295 my $xsptr = shift;
296 my $self = shift;
297 my ($file) = @_;
298 logcroak "not a reference" unless ref($self);
299 logcroak "too many arguments" unless @_ == 1; # No @foo in arglist
300 my $fd = fileno($file);
301 logcroak "not a valid file descriptor" unless defined $fd;
302 my $da = $@; # Don't mess if called from exception handler
303 my $ret;
304 # Call C routine nstore or pstore, depending on network order
305 eval { $ret = &$xsptr($file, $self) };
306 logcroak $@ if $@ =~ s/\.?\n$/,/;
596596d5 307 local $\; print $file ''; # Autoflush the file if wanted
7a6a85bf 308 $@ = $da;
cbc736f3 309 return $ret;
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310}
311
312#
313# freeze
314#
efaa61e2 315# Store object and its hierarchy in memory and return a scalar
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316# containing the result.
317#
318sub freeze {
319 _freeze(\&mstore, @_);
320}
321
322#
323# nfreeze
324#
325# Same as freeze but in network order.
326#
327sub nfreeze {
328 _freeze(\&net_mstore, @_);
329}
330
331# Internal freeze routine
332sub _freeze {
333 my $xsptr = shift;
334 my $self = shift;
335 logcroak "not a reference" unless ref($self);
336 logcroak "too many arguments" unless @_ == 0; # No @foo in arglist
337 my $da = $@; # Don't mess if called from exception handler
338 my $ret;
339 # Call C routine mstore or net_mstore, depending on network order
340 eval { $ret = &$xsptr($self) };
341 logcroak $@ if $@ =~ s/\.?\n$/,/;
342 $@ = $da;
343 return $ret ? $ret : undef;
344}
345
346#
347# retrieve
348#
349# Retrieve object hierarchy from disk, returning a reference to the root
350# object of that tree.
351#
352sub retrieve {
dd19458b
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353 _retrieve($_[0], 0);
354}
355
356#
357# lock_retrieve
358#
359# Same as retrieve, but with advisory locking.
360#
361sub lock_retrieve {
362 _retrieve($_[0], 1);
363}
364
365# Internal retrieve routine
366sub _retrieve {
367 my ($file, $use_locking) = @_;
7a6a85bf 368 local *FILE;
dd19458b 369 open(FILE, $file) || logcroak "can't open $file: $!";
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370 binmode FILE; # Archaic systems...
371 my $self;
372 my $da = $@; # Could be from exception handler
dd19458b 373 if ($use_locking) {
862382c7 374 unless (&CAN_FLOCK) {
8be2b38b 375 logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O";
b29b780f
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376 return undef;
377 }
8be2b38b 378 flock(FILE, LOCK_SH) || logcroak "can't get shared lock on $file: $!";
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379 # Unlocking will happen when FILE is closed
380 }
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381 eval { $self = pretrieve(*FILE) }; # Call C routine
382 close(FILE);
383 logcroak $@ if $@ =~ s/\.?\n$/,/;
384 $@ = $da;
385 return $self;
386}
387
388#
9e21b3d0 389# fd_retrieve
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390#
391# Same as retrieve, but perform from an already opened file descriptor instead.
392#
9e21b3d0 393sub fd_retrieve {
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394 my ($file) = @_;
395 my $fd = fileno($file);
396 logcroak "not a valid file descriptor" unless defined $fd;
397 my $self;
398 my $da = $@; # Could be from exception handler
399 eval { $self = pretrieve($file) }; # Call C routine
400 logcroak $@ if $@ =~ s/\.?\n$/,/;
401 $@ = $da;
402 return $self;
403}
404
1541ec63
DL
405sub retrieve_fd { &fd_retrieve } # Backward compatibility
406
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407#
408# thaw
409#
410# Recreate objects in memory from an existing frozen image created
411# by freeze. If the frozen image passed is undef, return undef.
412#
413sub thaw {
414 my ($frozen) = @_;
415 return undef unless defined $frozen;
416 my $self;
417 my $da = $@; # Could be from exception handler
418 eval { $self = mretrieve($frozen) }; # Call C routine
419 logcroak $@ if $@ =~ s/\.?\n$/,/;
420 $@ = $da;
421 return $self;
422}
423
a2307be4
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4241;
425__END__
426
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427=head1 NAME
428
f062ea6c 429Storable - persistence for Perl data structures
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430
431=head1 SYNOPSIS
432
433 use Storable;
434 store \%table, 'file';
435 $hashref = retrieve('file');
436
437 use Storable qw(nstore store_fd nstore_fd freeze thaw dclone);
438
439 # Network order
440 nstore \%table, 'file';
441 $hashref = retrieve('file'); # There is NO nretrieve()
442
443 # Storing to and retrieving from an already opened file
444 store_fd \@array, \*STDOUT;
445 nstore_fd \%table, \*STDOUT;
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446 $aryref = fd_retrieve(\*SOCKET);
447 $hashref = fd_retrieve(\*SOCKET);
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448
449 # Serializing to memory
450 $serialized = freeze \%table;
451 %table_clone = %{ thaw($serialized) };
452
453 # Deep (recursive) cloning
454 $cloneref = dclone($ref);
455
dd19458b
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456 # Advisory locking
457 use Storable qw(lock_store lock_nstore lock_retrieve)
458 lock_store \%table, 'file';
459 lock_nstore \%table, 'file';
460 $hashref = lock_retrieve('file');
461
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462=head1 DESCRIPTION
463
f062ea6c 464The Storable package brings persistence to your Perl data structures
7a6a85bf 465containing SCALAR, ARRAY, HASH or REF objects, i.e. anything that can be
c261f00e 466conveniently stored to disk and retrieved at a later time.
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467
468It can be used in the regular procedural way by calling C<store> with
469a reference to the object to be stored, along with the file name where
470the image should be written.
775ecd75 471
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472The routine returns C<undef> for I/O problems or other internal error,
473a true value otherwise. Serious errors are propagated as a C<die> exception.
474
f062ea6c
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475To retrieve data stored to disk, use C<retrieve> with a file name.
476The objects stored into that file are recreated into memory for you,
477and a I<reference> to the root object is returned. In case an I/O error
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478occurs while reading, C<undef> is returned instead. Other serious
479errors are propagated via C<die>.
480
481Since storage is performed recursively, you might want to stuff references
482to objects that share a lot of common data into a single array or hash
483table, and then store that object. That way, when you retrieve back the
484whole thing, the objects will continue to share what they originally shared.
485
486At the cost of a slight header overhead, you may store to an already
487opened file descriptor using the C<store_fd> routine, and retrieve
9e21b3d0 488from a file via C<fd_retrieve>. Those names aren't imported by default,
c261f00e 489so you will have to do that explicitly if you need those routines.
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490The file descriptor you supply must be already opened, for read
491if you're going to retrieve and for write if you wish to store.
492
493 store_fd(\%table, *STDOUT) || die "can't store to stdout\n";
9e21b3d0 494 $hashref = fd_retrieve(*STDIN);
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495
496You can also store data in network order to allow easy sharing across
497multiple platforms, or when storing on a socket known to be remotely
498connected. The routines to call have an initial C<n> prefix for I<network>,
499as in C<nstore> and C<nstore_fd>. At retrieval time, your data will be
500correctly restored so you don't have to know whether you're restoring
dd19458b
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501from native or network ordered data. Double values are stored stringified
502to ensure portability as well, at the slight risk of loosing some precision
503in the last decimals.
7a6a85bf 504
9e21b3d0 505When using C<fd_retrieve>, objects are retrieved in sequence, one
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506object (i.e. one recursive tree) per associated C<store_fd>.
507
508If you're more from the object-oriented camp, you can inherit from
509Storable and directly store your objects by invoking C<store> as
510a method. The fact that the root of the to-be-stored tree is a
511blessed reference (i.e. an object) is special-cased so that the
512retrieve does not provide a reference to that object but rather the
513blessed object reference itself. (Otherwise, you'd get a reference
514to that blessed object).
515
516=head1 MEMORY STORE
517
518The Storable engine can also store data into a Perl scalar instead, to
519later retrieve them. This is mainly used to freeze a complex structure in
520some safe compact memory place (where it can possibly be sent to another
521process via some IPC, since freezing the structure also serializes it in
522effect). Later on, and maybe somewhere else, you can thaw the Perl scalar
523out and recreate the original complex structure in memory.
524
525Surprisingly, the routines to be called are named C<freeze> and C<thaw>.
526If you wish to send out the frozen scalar to another machine, use
527C<nfreeze> instead to get a portable image.
528
529Note that freezing an object structure and immediately thawing it
530actually achieves a deep cloning of that structure:
531
532 dclone(.) = thaw(freeze(.))
533
534Storable provides you with a C<dclone> interface which does not create
535that intermediary scalar but instead freezes the structure in some
c261f00e 536internal memory space and then immediately thaws it out.
7a6a85bf 537
dd19458b
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538=head1 ADVISORY LOCKING
539
f062ea6c
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540The C<lock_store> and C<lock_nstore> routine are equivalent to
541C<store> and C<nstore>, except that they get an exclusive lock on
542the file before writing. Likewise, C<lock_retrieve> does the same
543as C<retrieve>, but also gets a shared lock on the file before reading.
dd19458b 544
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545As with any advisory locking scheme, the protection only works if you
546systematically use C<lock_store> and C<lock_retrieve>. If one side of
547your application uses C<store> whilst the other uses C<lock_retrieve>,
dd19458b
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548you will get no protection at all.
549
f062ea6c
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550The internal advisory locking is implemented using Perl's flock()
551routine. If your system does not support any form of flock(), or if
552you share your files across NFS, you might wish to use other forms
553of locking by using modules such as LockFile::Simple which lock a
554file using a filesystem entry, instead of locking the file descriptor.
dd19458b 555
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556=head1 SPEED
557
558The heart of Storable is written in C for decent speed. Extra low-level
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559optimizations have been made when manipulating perl internals, to
560sacrifice encapsulation for the benefit of greater speed.
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561
562=head1 CANONICAL REPRESENTATION
563
f062ea6c 564Normally, Storable stores elements of hashes in the order they are
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565stored internally by Perl, i.e. pseudo-randomly. If you set
566C<$Storable::canonical> to some C<TRUE> value, Storable will store
567hashes with the elements sorted by their key. This allows you to
568compare data structures by comparing their frozen representations (or
569even the compressed frozen representations), which can be useful for
570creating lookup tables for complicated queries.
571
f062ea6c 572Canonical order does not imply network order; those are two orthogonal
7a6a85bf
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573settings.
574
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575=head1 CODE REFERENCES
576
577Since Storable version 2.05, CODE references may be serialized with
578the help of L<B::Deparse>. To enable this feature, set
3c4b39be 579C<$Storable::Deparse> to a true value. To enable deserialization,
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SR
580C<$Storable::Eval> should be set to a true value. Be aware that
581deserialization is done through C<eval>, which is dangerous if the
582Storable file contains malicious data. You can set C<$Storable::Eval>
583to a subroutine reference which would be used instead of C<eval>. See
584below for an example using a L<Safe> compartment for deserialization
585of CODE references.
586
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587If C<$Storable::Deparse> and/or C<$Storable::Eval> are set to false
588values, then the value of C<$Storable::forgive_me> (see below) is
589respected while serializing and deserializing.
590
c261f00e
NC
591=head1 FORWARD COMPATIBILITY
592
593This release of Storable can be used on a newer version of Perl to
f062ea6c 594serialize data which is not supported by earlier Perls. By default,
c261f00e 595Storable will attempt to do the right thing, by C<croak()>ing if it
775ecd75 596encounters data that it cannot deserialize. However, the defaults
f062ea6c 597can be changed as follows:
c261f00e
NC
598
599=over 4
600
601=item utf8 data
602
603Perl 5.6 added support for Unicode characters with code points > 255,
604and Perl 5.8 has full support for Unicode characters in hash keys.
605Perl internally encodes strings with these characters using utf8, and
606Storable serializes them as utf8. By default, if an older version of
607Perl encounters a utf8 value it cannot represent, it will C<croak()>.
608To change this behaviour so that Storable deserializes utf8 encoded
609values as the string of bytes (effectively dropping the I<is_utf8> flag)
610set C<$Storable::drop_utf8> to some C<TRUE> value. This is a form of
611data loss, because with C<$drop_utf8> true, it becomes impossible to tell
612whether the original data was the Unicode string, or a series of bytes
613that happen to be valid utf8.
614
615=item restricted hashes
616
f062ea6c
PN
617Perl 5.8 adds support for restricted hashes, which have keys
618restricted to a given set, and can have values locked to be read only.
619By default, when Storable encounters a restricted hash on a perl
620that doesn't support them, it will deserialize it as a normal hash,
621silently discarding any placeholder keys and leaving the keys and
622all values unlocked. To make Storable C<croak()> instead, set
623C<$Storable::downgrade_restricted> to a C<FALSE> value. To restore
624the default set it back to some C<TRUE> value.
c261f00e 625
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626=item files from future versions of Storable
627
628Earlier versions of Storable would immediately croak if they encountered
629a file with a higher internal version number than the reading Storable
630knew about. Internal version numbers are increased each time new data
631types (such as restricted hashes) are added to the vocabulary of the file
632format. This meant that a newer Storable module had no way of writing a
f062ea6c 633file readable by an older Storable, even if the writer didn't store newer
e8189732
NC
634data types.
635
636This version of Storable will defer croaking until it encounters a data
637type in the file that it does not recognize. This means that it will
638continue to read files generated by newer Storable modules which are careful
639in what they write out, making it easier to upgrade Storable modules in a
640mixed environment.
641
642The old behaviour of immediate croaking can be re-instated by setting
f062ea6c 643C<$Storable::accept_future_minor> to some C<FALSE> value.
e8189732 644
c261f00e
NC
645=back
646
f062ea6c 647All these variables have no effect on a newer Perl which supports the
c261f00e
NC
648relevant feature.
649
7a6a85bf
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650=head1 ERROR REPORTING
651
652Storable uses the "exception" paradigm, in that it does not try to workaround
653failures: if something bad happens, an exception is generated from the
654caller's perspective (see L<Carp> and C<croak()>). Use eval {} to trap
655those exceptions.
656
657When Storable croaks, it tries to report the error via the C<logcroak()>
658routine from the C<Log::Agent> package, if it is available.
659
212e9bde
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660Normal errors are reported by having store() or retrieve() return C<undef>.
661Such errors are usually I/O errors (or truncated stream errors at retrieval).
662
7a6a85bf
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663=head1 WIZARDS ONLY
664
665=head2 Hooks
666
667Any class may define hooks that will be called during the serialization
668and deserialization process on objects that are instances of that class.
669Those hooks can redefine the way serialization is performed (and therefore,
c261f00e 670how the symmetrical deserialization should be conducted).
7a6a85bf
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671
672Since we said earlier:
673
674 dclone(.) = thaw(freeze(.))
675
676everything we say about hooks should also hold for deep cloning. However,
677hooks get to know whether the operation is a mere serialization, or a cloning.
678
679Therefore, when serializing hooks are involved,
680
681 dclone(.) <> thaw(freeze(.))
682
683Well, you could keep them in sync, but there's no guarantee it will always
684hold on classes somebody else wrote. Besides, there is little to gain in
f062ea6c 685doing so: a serializing hook could keep only one attribute of an object,
7a6a85bf
RG
686which is probably not what should happen during a deep cloning of that
687same object.
688
689Here is the hooking interface:
690
bbc7dcd2 691=over 4
7a6a85bf
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692
693=item C<STORABLE_freeze> I<obj>, I<cloning>
694
695The serializing hook, called on the object during serialization. It can be
696inherited, or defined in the class itself, like any other method.
697
698Arguments: I<obj> is the object to serialize, I<cloning> is a flag indicating
699whether we're in a dclone() or a regular serialization via store() or freeze().
700
701Returned value: A LIST C<($serialized, $ref1, $ref2, ...)> where $serialized
702is the serialized form to be used, and the optional $ref1, $ref2, etc... are
703extra references that you wish to let the Storable engine serialize.
704
705At deserialization time, you will be given back the same LIST, but all the
706extra references will be pointing into the deserialized structure.
707
708The B<first time> the hook is hit in a serialization flow, you may have it
709return an empty list. That will signal the Storable engine to further
710discard that hook for this class and to therefore revert to the default
711serialization of the underlying Perl data. The hook will again be normally
712processed in the next serialization.
713
714Unless you know better, serializing hook should always say:
715
716 sub STORABLE_freeze {
717 my ($self, $cloning) = @_;
718 return if $cloning; # Regular default serialization
719 ....
720 }
721
722in order to keep reasonable dclone() semantics.
723
724=item C<STORABLE_thaw> I<obj>, I<cloning>, I<serialized>, ...
725
726The deserializing hook called on the object during deserialization.
f062ea6c 727But wait: if we're deserializing, there's no object yet... right?
7a6a85bf
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728
729Wrong: the Storable engine creates an empty one for you. If you know Eiffel,
730you can view C<STORABLE_thaw> as an alternate creation routine.
731
732This means the hook can be inherited like any other method, and that
733I<obj> is your blessed reference for this particular instance.
734
735The other arguments should look familiar if you know C<STORABLE_freeze>:
736I<cloning> is true when we're part of a deep clone operation, I<serialized>
737is the serialized string you returned to the engine in C<STORABLE_freeze>,
738and there may be an optional list of references, in the same order you gave
739them at serialization time, pointing to the deserialized objects (which
740have been processed courtesy of the Storable engine).
741
212e9bde
JH
742When the Storable engine does not find any C<STORABLE_thaw> hook routine,
743it tries to load the class by requiring the package dynamically (using
744the blessed package name), and then re-attempts the lookup. If at that
745time the hook cannot be located, the engine croaks. Note that this mechanism
c261f00e 746will fail if you define several classes in the same file, but L<perlmod>
212e9bde
JH
747warned you.
748
f062ea6c 749It is up to you to use this information to populate I<obj> the way you want.
7a6a85bf
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750
751Returned value: none.
752
2f796f32
AMS
753=item C<STORABLE_attach> I<class>, I<cloning>, I<serialized>
754
755While C<STORABLE_freeze> and C<STORABLE_thaw> are useful for classes where
3c4b39be 756each instance is independent, this mechanism has difficulty (or is
2f796f32
AMS
757incompatible) with objects that exist as common process-level or
758system-level resources, such as singleton objects, database pools, caches
759or memoized objects.
760
761The alternative C<STORABLE_attach> method provides a solution for these
1e2a0f0b
RGS
762shared objects. Instead of C<STORABLE_freeze> --E<gt> C<STORABLE_thaw>,
763you implement C<STORABLE_freeze> --E<gt> C<STORABLE_attach> instead.
2f796f32
AMS
764
765Arguments: I<class> is the class we are attaching to, I<cloning> is a flag
766indicating whether we're in a dclone() or a regular de-serialization via
767thaw(), and I<serialized> is the stored string for the resource object.
768
769Because these resource objects are considered to be owned by the entire
770process/system, and not the "property" of whatever is being serialized,
771no references underneath the object should be included in the serialized
772string. Thus, in any class that implements C<STORABLE_attach>, the
773C<STORABLE_freeze> method cannot return any references, and C<Storable>
774will throw an error if C<STORABLE_freeze> tries to return references.
775
776All information required to "attach" back to the shared resource object
777B<must> be contained B<only> in the C<STORABLE_freeze> return string.
778Otherwise, C<STORABLE_freeze> behaves as normal for C<STORABLE_attach>
779classes.
780
781Because C<STORABLE_attach> is passed the class (rather than an object),
782it also returns the object directly, rather than modifying the passed
783object.
784
785Returned value: object of type C<class>
786
7a6a85bf
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787=back
788
789=head2 Predicates
790
c261f00e 791Predicates are not exportable. They must be called by explicitly prefixing
7a6a85bf
RG
792them with the Storable package name.
793
bbc7dcd2 794=over 4
7a6a85bf
RG
795
796=item C<Storable::last_op_in_netorder>
797
798The C<Storable::last_op_in_netorder()> predicate will tell you whether
799network order was used in the last store or retrieve operation. If you
800don't know how to use this, just forget about it.
801
802=item C<Storable::is_storing>
803
804Returns true if within a store operation (via STORABLE_freeze hook).
805
806=item C<Storable::is_retrieving>
807
f062ea6c 808Returns true if within a retrieve operation (via STORABLE_thaw hook).
7a6a85bf
RG
809
810=back
811
812=head2 Recursion
813
f062ea6c
PN
814With hooks comes the ability to recurse back to the Storable engine.
815Indeed, hooks are regular Perl code, and Storable is convenient when
816it comes to serializing and deserializing things, so why not use it
817to handle the serialization string?
7a6a85bf 818
f062ea6c 819There are a few things you need to know, however:
7a6a85bf 820
bbc7dcd2 821=over 4
7a6a85bf
RG
822
823=item *
824
825You can create endless loops if the things you serialize via freeze()
f062ea6c
PN
826(for instance) point back to the object we're trying to serialize in
827the hook.
7a6a85bf
RG
828
829=item *
830
831Shared references among objects will not stay shared: if we're serializing
832the list of object [A, C] where both object A and C refer to the SAME object
833B, and if there is a serializing hook in A that says freeze(B), then when
834deserializing, we'll get [A', C'] where A' refers to B', but C' refers to D,
835a deep clone of B'. The topology was not preserved.
836
837=back
838
839That's why C<STORABLE_freeze> lets you provide a list of references
840to serialize. The engine guarantees that those will be serialized in the
841same context as the other objects, and therefore that shared objects will
842stay shared.
843
844In the above [A, C] example, the C<STORABLE_freeze> hook could return:
845
846 ("something", $self->{B})
847
848and the B part would be serialized by the engine. In C<STORABLE_thaw>, you
849would get back the reference to the B' object, deserialized for you.
850
851Therefore, recursion should normally be avoided, but is nonetheless supported.
852
853=head2 Deep Cloning
854
f062ea6c 855There is a Clone module available on CPAN which implements deep cloning
7a6a85bf
RG
856natively, i.e. without freezing to memory and thawing the result. It is
857aimed to replace Storable's dclone() some day. However, it does not currently
858support Storable hooks to redefine the way deep cloning is performed.
859
0a0da639
JH
860=head1 Storable magic
861
862Yes, there's a lot of that :-) But more precisely, in UNIX systems
863there's a utility called C<file>, which recognizes data files based on
864their contents (usually their first few bytes). For this to work,
8b793558 865a certain file called F<magic> needs to taught about the I<signature>
0a0da639 866of the data. Where that configuration file lives depends on the UNIX
f062ea6c 867flavour; often it's something like F</usr/share/misc/magic> or
8b793558
JH
868F</etc/magic>. Your system administrator needs to do the updating of
869the F<magic> file. The necessary signature information is output to
f062ea6c
PN
870STDOUT by invoking Storable::show_file_magic(). Note that the GNU
871implementation of the C<file> utility, version 3.38 or later,
872is expected to contain support for recognising Storable files
873out-of-the-box, in addition to other kinds of Perl files.
0a0da639 874
d4b9b6e4
GA
875You can also use the following functions to extract the file header
876information from Storable images:
877
878=over
879
880=item $info = Storable::file_magic( $filename )
881
882If the given file is a Storable image return a hash describing it. If
883the file is readable, but not a Storable image return C<undef>. If
884the file does not exist or is unreadable then croak.
885
886The hash returned has the following elements:
887
888=over
889
890=item C<version>
891
892This returns the file format version. It is a string like "2.7".
893
894Note that this version number is not the same as the version number of
895the Storable module itself. For instance Storable v0.7 create files
896in format v2.0 and Storable v2.15 create files in format v2.7. The
897file format version number only increment when additional features
898that would confuse older versions of the module are added.
899
900Files older than v2.0 will have the one of the version numbers "-1",
901"0" or "1". No minor number was used at that time.
902
903=item C<version_nv>
904
905This returns the file format version as number. It is a string like
906"2.007". This value is suitable for numeric comparisons.
907
908The constant function C<Storable::BIN_VERSION_NV> returns a comparable
b846e6a6
FC
909number that represents the highest file version number that this
910version of Storable fully supports (but see discussion of
d4b9b6e4
GA
911C<$Storable::accept_future_minor> above). The constant
912C<Storable::BIN_WRITE_VERSION_NV> function returns what file version
913is written and might be less than C<Storable::BIN_VERSION_NV> in some
c4a6f826 914configurations.
d4b9b6e4
GA
915
916=item C<major>, C<minor>
917
918This also returns the file format version. If the version is "2.7"
919then major would be 2 and minor would be 7. The minor element is
920missing for when major is less than 2.
921
922=item C<hdrsize>
923
924The is the number of bytes that the Storable header occupies.
925
926=item C<netorder>
927
928This is TRUE if the image store data in network order. This means
929that it was created with nstore() or similar.
930
931=item C<byteorder>
932
933This is only present when C<netorder> is FALSE. It is the
934$Config{byteorder} string of the perl that created this image. It is
935a string like "1234" (32 bit little endian) or "87654321" (64 bit big
936endian). This must match the current perl for the image to be
937readable by Storable.
938
939=item C<intsize>, C<longsize>, C<ptrsize>, C<nvsize>
940
941These are only present when C<netorder> is FALSE. These are the sizes of
942various C datatypes of the perl that created this image. These must
943match the current perl for the image to be readable by Storable.
944
945The C<nvsize> element is only present for file format v2.2 and
946higher.
947
948=item C<file>
949
950The name of the file.
951
952=back
953
954=item $info = Storable::read_magic( $buffer )
955
956=item $info = Storable::read_magic( $buffer, $must_be_file )
957
958The $buffer should be a Storable image or the first few bytes of it.
959If $buffer starts with a Storable header, then a hash describing the
960image is returned, otherwise C<undef> is returned.
961
962The hash has the same structure as the one returned by
963Storable::file_magic(). The C<file> element is true if the image is a
964file image.
965
966If the $must_be_file argument is provided and is TRUE, then return
967C<undef> unless the image looks like it belongs to a file dump.
968
969The maximum size of a Storable header is currently 21 bytes. If the
970provided $buffer is only the first part of a Storable image it should
971at least be this long to ensure that read_magic() will recognize it as
972such.
973
974=back
975
7a6a85bf
RG
976=head1 EXAMPLES
977
978Here are some code samples showing a possible usage of Storable:
979
980 use Storable qw(store retrieve freeze thaw dclone);
981
982 %color = ('Blue' => 0.1, 'Red' => 0.8, 'Black' => 0, 'White' => 1);
983
2359510d 984 store(\%color, 'mycolors') or die "Can't store %a in mycolors!\n";
7a6a85bf 985
2359510d
SD
986 $colref = retrieve('mycolors');
987 die "Unable to retrieve from mycolors!\n" unless defined $colref;
7a6a85bf
RG
988 printf "Blue is still %lf\n", $colref->{'Blue'};
989
990 $colref2 = dclone(\%color);
991
992 $str = freeze(\%color);
993 printf "Serialization of %%color is %d bytes long.\n", length($str);
994 $colref3 = thaw($str);
995
996which prints (on my machine):
997
998 Blue is still 0.100000
999 Serialization of %color is 102 bytes long.
1000
d2b96869
SR
1001Serialization of CODE references and deserialization in a safe
1002compartment:
1003
197b90bc
SR
1004=for example begin
1005
d2b96869
SR
1006 use Storable qw(freeze thaw);
1007 use Safe;
1008 use strict;
1009 my $safe = new Safe;
197b90bc 1010 # because of opcodes used in "use strict":
d1e2299c 1011 $safe->permit(qw(:default require));
d2b96869
SR
1012 local $Storable::Deparse = 1;
1013 local $Storable::Eval = sub { $safe->reval($_[0]) };
197b90bc 1014 my $serialized = freeze(sub { 42 });
d2b96869 1015 my $code = thaw($serialized);
197b90bc
SR
1016 $code->() == 42;
1017
1018=for example end
1019
1020=for example_testing
1021 is( $code->(), 42 );
d2b96869 1022
664f237a
SM
1023=head1 SECURITY WARNING
1024
1025B<Do not accept Storable documents from untrusted sources!>
1026
1027Some features of Storable can lead to security vulnerabilities if you
1028accept Storable documents from untrusted sources. Most obviously, the
1029optional (off by default) CODE reference serialization feature allows
1030transfer of code to the deserializing process. Furthermore, any
1031serialized object will cause Storable to helpfully load the module
1032corresponding to the class of the object in the deserializing module.
1033For manipulated module names, this can load almost arbitrary code.
1034Finally, the deserialized object's destructors will be invoked when
1035the objects get destroyed in the deserializing process. Maliciously
1036crafted Storable documents may put such objects in the value of
1037a hash key that is overridden by another key/value pair in the
1038same hash, thus causing immediate destructor execution.
1039
1040In a future version of Storable, we intend to provide options to disable
1041loading modules for classes and to disable deserializing objects
1042altogether. I<Nonetheless, Storable deserializing documents from
1043untrusted sources is expected to have other, yet undiscovered,
1044security concerns such as allowing an attacker to cause the deserializer
1045to crash hard.>
1046
1047B<Therefore, let me repeat: Do not accept Storable documents from
1048untrusted sources!>
1049
1050If your application requires accepting data from untrusted sources, you
1051are best off with a less powerful and more-likely safe serialization format
efaa61e2 1052and implementation. If your data is sufficiently simple, JSON is a good
664f237a
SM
1053choice and offers maximum interoperability.
1054
7a6a85bf
RG
1055=head1 WARNING
1056
1057If you're using references as keys within your hash tables, you're bound
f062ea6c 1058to be disappointed when retrieving your data. Indeed, Perl stringifies
7a6a85bf
RG
1059references used as hash table keys. If you later wish to access the
1060items via another reference stringification (i.e. using the same
1061reference that was used for the key originally to record the value into
1062the hash table), it will work because both references stringify to the
1063same string.
1064
6fe6778b
PN
1065It won't work across a sequence of C<store> and C<retrieve> operations,
1066however, because the addresses in the retrieved objects, which are
1067part of the stringified references, will probably differ from the
1068original addresses. The topology of your structure is preserved,
1069but not hidden semantics like those.
7a6a85bf
RG
1070
1071On platforms where it matters, be sure to call C<binmode()> on the
1072descriptors that you pass to Storable functions.
1073
1074Storing data canonically that contains large hashes can be
1075significantly slower than storing the same data normally, as
c261f00e 1076temporary arrays to hold the keys for each hash have to be allocated,
7a6a85bf
RG
1077populated, sorted and freed. Some tests have shown a halving of the
1078speed of storing -- the exact penalty will depend on the complexity of
1079your data. There is no slowdown on retrieval.
1080
1081=head1 BUGS
1082
eda690a0 1083You can't store GLOB, FORMLINE, REGEXP, etc.... If you can define semantics
197b90bc
SR
1084for those operations, feel free to enhance Storable so that it can
1085deal with them.
7a6a85bf
RG
1086
1087The store functions will C<croak> if they run into such references
1088unless you set C<$Storable::forgive_me> to some C<TRUE> value. In that
1089case, the fatal message is turned in a warning and some
1090meaningless string is stored instead.
1091
1092Setting C<$Storable::canonical> may not yield frozen strings that
1093compare equal due to possible stringification of numbers. When the
f062ea6c 1094string version of a scalar exists, it is the form stored; therefore,
7a6a85bf
RG
1095if you happen to use your numbers as strings between two freezing
1096operations on the same data structures, you will get different
1097results.
1098
dd19458b
JH
1099When storing doubles in network order, their value is stored as text.
1100However, you should also not expect non-numeric floating-point values
1101such as infinity and "not a number" to pass successfully through a
1102nstore()/retrieve() pair.
1103
1104As Storable neither knows nor cares about character sets (although it
1105does know that characters may be more than eight bits wide), any difference
1106in the interpretation of character codes between a host and a target
1107system is your problem. In particular, if host and target use different
1108code points to represent the characters used in the text representation
1109of floating-point numbers, you will not be able be able to exchange
1110floating-point data, even with nstore().
1111
c261f00e
NC
1112C<Storable::drop_utf8> is a blunt tool. There is no facility either to
1113return B<all> strings as utf8 sequences, or to attempt to convert utf8
1114data back to 8 bit and C<croak()> if the conversion fails.
1115
ee0f7aac
NC
1116Prior to Storable 2.01, no distinction was made between signed and
1117unsigned integers on storing. By default Storable prefers to store a
1118scalars string representation (if it has one) so this would only cause
3c4b39be 1119problems when storing large unsigned integers that had never been converted
ee0f7aac
NC
1120to string or floating point. In other words values that had been generated
1121by integer operations such as logic ops and then not used in any string or
1122arithmetic context before storing.
1123
1124=head2 64 bit data in perl 5.6.0 and 5.6.1
1125
1126This section only applies to you if you have existing data written out
1127by Storable 2.02 or earlier on perl 5.6.0 or 5.6.1 on Unix or Linux which
1128has been configured with 64 bit integer support (not the default)
1129If you got a precompiled perl, rather than running Configure to build
1130your own perl from source, then it almost certainly does not affect you,
1131and you can stop reading now (unless you're curious). If you're using perl
1132on Windows it does not affect you.
1133
1134Storable writes a file header which contains the sizes of various C
1135language types for the C compiler that built Storable (when not writing in
1136network order), and will refuse to load files written by a Storable not
1137on the same (or compatible) architecture. This check and a check on
1138machine byteorder is needed because the size of various fields in the file
1139are given by the sizes of the C language types, and so files written on
1140different architectures are incompatible. This is done for increased speed.
1141(When writing in network order, all fields are written out as standard
1142lengths, which allows full interworking, but takes longer to read and write)
1143
1144Perl 5.6.x introduced the ability to optional configure the perl interpreter
1145to use C's C<long long> type to allow scalars to store 64 bit integers on 32
1146bit systems. However, due to the way the Perl configuration system
1147generated the C configuration files on non-Windows platforms, and the way
1148Storable generates its header, nothing in the Storable file header reflected
1149whether the perl writing was using 32 or 64 bit integers, despite the fact
1150that Storable was storing some data differently in the file. Hence Storable
1151running on perl with 64 bit integers will read the header from a file
1152written by a 32 bit perl, not realise that the data is actually in a subtly
1153incompatible format, and then go horribly wrong (possibly crashing) if it
1154encountered a stored integer. This is a design failure.
1155
1156Storable has now been changed to write out and read in a file header with
1157information about the size of integers. It's impossible to detect whether
1158an old file being read in was written with 32 or 64 bit integers (they have
1159the same header) so it's impossible to automatically switch to a correct
1160backwards compatibility mode. Hence this Storable defaults to the new,
1161correct behaviour.
1162
1163What this means is that if you have data written by Storable 1.x running
1164on perl 5.6.0 or 5.6.1 configured with 64 bit integers on Unix or Linux
1165then by default this Storable will refuse to read it, giving the error
efaa61e2 1166I<Byte order is not compatible>. If you have such data then you
ee0f7aac
NC
1167should set C<$Storable::interwork_56_64bit> to a true value to make this
1168Storable read and write files with the old header. You should also
1169migrate your data, or any older perl you are communicating with, to this
1170current version of Storable.
1171
1172If you don't have data written with specific configuration of perl described
1173above, then you do not and should not do anything. Don't set the flag -
1174not only will Storable on an identically configured perl refuse to load them,
1175but Storable a differently configured perl will load them believing them
1176to be correct for it, and then may well fail or crash part way through
1177reading them.
1178
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1179=head1 CREDITS
1180
1181Thank you to (in chronological order):
1182
1183 Jarkko Hietaniemi <jhi@iki.fi>
1184 Ulrich Pfeifer <pfeifer@charly.informatik.uni-dortmund.de>
51f77169 1185 Benjamin A. Holzman <bholzman@earthlink.net>
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1186 Andrew Ford <A.Ford@ford-mason.co.uk>
1187 Gisle Aas <gisle@aas.no>
1188 Jeff Gresham <gresham_jeffrey@jpmorgan.com>
1189 Murray Nesbitt <murray@activestate.com>
1190 Marc Lehmann <pcg@opengroup.org>
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1191 Justin Banks <justinb@wamnet.com>
1192 Jarkko Hietaniemi <jhi@iki.fi> (AGAIN, as perl 5.7.0 Pumpkin!)
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1193 Salvador Ortiz Garcia <sog@msg.com.mx>
1194 Dominic Dunlop <domo@computer.org>
1195 Erik Haugan <erik@solbors.no>
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1196 Benjamin A. Holzman <ben.holzman@grantstreet.com>
1197 Reini Urban <rurban@cpanel.net>
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1198
1199for their bug reports, suggestions and contributions.
1200
1201Benjamin Holzman contributed the tied variable support, Andrew Ford
1202contributed the canonical order for hashes, and Gisle Aas fixed
f062ea6c 1203a few misunderstandings of mine regarding the perl internals,
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1204and optimized the emission of "tags" in the output streams by
1205simply counting the objects instead of tagging them (leading to
1206a binary incompatibility for the Storable image starting at version
f062ea6c 12070.6--older images are, of course, still properly understood).
7a6a85bf 1208Murray Nesbitt made Storable thread-safe. Marc Lehmann added overloading
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1209and references to tied items support. Benjamin Holzman added a performance
1210improvement for overloaded classes; thanks to Grant Street Group for footing
1211the bill.
7a6a85bf 1212
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1213=head1 AUTHOR
1214
0ba8809e 1215Storable was written by Raphael Manfredi F<E<lt>Raphael_Manfredi@pobox.comE<gt>>
775ecd75 1216Maintenance is now done by the perl5-porters F<E<lt>perl5-porters@perl.orgE<gt>>
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1217
1218Please e-mail us with problems, bug fixes, comments and complaints,
d119459b 1219although if you have compliments you should send them to Raphael.
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1220Please don't e-mail Raphael with problems, as he no longer works on
1221Storable, and your message will be delayed while he forwards it to us.
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1222
1223=head1 SEE ALSO
1224
c261f00e 1225L<Clone>.
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1226
1227=cut