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1 # 2 # Copyright (c) 1995-2000, Raphael Manfredi 3 # 4 # You may redistribute only under the same terms as Perl 5, as specified 5 # in the README file that comes with the distribution. 6 # 7 8 require DynaLoader; 9 require Exporter; 10 package Storable; @ISA = qw(Exporter DynaLoader); 11 12 @EXPORT = qw(store retrieve); 13 @EXPORT_OK = qw( 14 nstore store_fd nstore_fd fd_retrieve 15 freeze nfreeze thaw 16 dclone 17 retrieve_fd 18 lock_store lock_nstore lock_retrieve 19 file_magic read_magic 20 ); 21 22 use AutoLoader; 23 use FileHandle; 24 use vars qw($canonical $forgive_me $VERSION); 25 26 $VERSION = '2.18'; 27 *AUTOLOAD = \&AutoLoader::AUTOLOAD; # Grrr... 28 29 # 30 # Use of Log::Agent is optional 31 # 32 33 { 34 local $SIG{__DIE__}; 35 eval "use Log::Agent"; 36 } 37 38 require Carp; 39 40 # 41 # They might miss :flock in Fcntl 42 # 43 44 BEGIN { 45 if (eval { require Fcntl; 1 } && exists $Fcntl::EXPORT_TAGS{'flock'}) { 46 Fcntl->import(':flock'); 47 } else { 48 eval q{ 49 sub LOCK_SH () {1} 50 sub LOCK_EX () {2} 51 }; 52 } 53 } 54 55 sub CLONE { 56 # clone context under threads 57 Storable::init_perinterp(); 58 } 59 60 # Can't Autoload cleanly as this clashes 8.3 with &retrieve 61 sub retrieve_fd { &fd_retrieve } # Backward compatibility 62 63 # By default restricted hashes are downgraded on earlier perls. 64 65 $Storable::downgrade_restricted = 1; 66 $Storable::accept_future_minor = 1; 67 bootstrap Storable; 68 1; 69 __END__ 70 # 71 # Use of Log::Agent is optional. If it hasn't imported these subs then 72 # Autoloader will kindly supply our fallback implementation. 73 # 74 75 sub logcroak { 76 Carp::croak(@_); 77 } 78 79 sub logcarp { 80 Carp::carp(@_); 81 } 82 83 # 84 # Determine whether locking is possible, but only when needed. 85 # 86 87 sub CAN_FLOCK; my $CAN_FLOCK; sub CAN_FLOCK { 88 return $CAN_FLOCK if defined $CAN_FLOCK; 89 require Config; import Config; 90 return $CAN_FLOCK = 91 $Config{'d_flock'} || 92 $Config{'d_fcntl_can_lock'} || 93 $Config{'d_lockf'}; 94 } 95 96 sub show_file_magic { 97 print <<EOM; 98 # 99 # To recognize the data files of the Perl module Storable, 100 # the following lines need to be added to the local magic(5) file, 101 # usually either /usr/share/misc/magic or /etc/magic. 102 # 103 0 string perl-store perl Storable(v0.6) data 104 >4 byte >0 (net-order %d) 105 >>4 byte &01 (network-ordered) 106 >>4 byte =3 (major 1) 107 >>4 byte =2 (major 1) 108 109 0 string pst0 perl Storable(v0.7) data 110 >4 byte >0 111 >>4 byte &01 (network-ordered) 112 >>4 byte =5 (major 2) 113 >>4 byte =4 (major 2) 114 >>5 byte >0 (minor %d) 115 EOM 116 } 117 118 sub file_magic { 119 my $file = shift; 120 my $fh = new FileHandle; 121 open($fh, "<". $file) || die "Can't open '$file': $!"; 122 binmode($fh); 123 defined(sysread($fh, my $buf, 32)) || die "Can't read from '$file': $!"; 124 close($fh); 125 126 $file = "./$file" unless $file; # ensure TRUE value 127 128 return read_magic($buf, $file); 129 } 130 131 sub read_magic { 132 my($buf, $file) = @_; 133 my %info; 134 135 my $buflen = length($buf); 136 my $magic; 137 if ($buf =~ s/^(pst0|perl-store)//) { 138 $magic = $1; 139 $info{file} = $file || 1; 140 } 141 else { 142 return undef if $file; 143 $magic = ""; 144 } 145 146 return undef unless length($buf); 147 148 my $net_order; 149 if ($magic eq "perl-store" && ord(substr($buf, 0, 1)) > 1) { 150 $info{version} = -1; 151 $net_order = 0; 152 } 153 else { 154 $net_order = ord(substr($buf, 0, 1, "")); 155 my $major = $net_order >> 1; 156 return undef if $major > 4; # sanity (assuming we never go that high) 157 $info{major} = $major; 158 $net_order &= 0x01; 159 if ($major > 1) { 160 return undef unless length($buf); 161 my $minor = ord(substr($buf, 0, 1, "")); 162 $info{minor} = $minor; 163 $info{version} = "$major.$minor"; 164 $info{version_nv} = sprintf "%d.%03d", $major, $minor; 165 } 166 else { 167 $info{version} = $major; 168 } 169 } 170 $info{version_nv} ||= $info{version}; 171 $info{netorder} = $net_order; 172 173 unless ($net_order) { 174 return undef unless length($buf); 175 my $len = ord(substr($buf, 0, 1, "")); 176 return undef unless length($buf) >= $len; 177 return undef unless $len == 4 || $len == 8; # sanity 178 $info{byteorder} = substr($buf, 0, $len, ""); 179 $info{intsize} = ord(substr($buf, 0, 1, "")); 180 $info{longsize} = ord(substr($buf, 0, 1, "")); 181 $info{ptrsize} = ord(substr($buf, 0, 1, "")); 182 if ($info{version_nv} >= 2.002) { 183 return undef unless length($buf); 184 $info{nvsize} = ord(substr($buf, 0, 1, "")); 185 } 186 } 187 $info{hdrsize} = $buflen - length($buf); 188 189 return \%info; 190 } 191 192 sub BIN_VERSION_NV { 193 sprintf "%d.%03d", BIN_MAJOR(), BIN_MINOR(); 194 } 195 196 sub BIN_WRITE_VERSION_NV { 197 sprintf "%d.%03d", BIN_MAJOR(), BIN_WRITE_MINOR(); 198 } 199 200 # 201 # store 202 # 203 # Store target object hierarchy, identified by a reference to its root. 204 # The stored object tree may later be retrieved to memory via retrieve. 205 # Returns undef if an I/O error occurred, in which case the file is 206 # removed. 207 # 208 sub store { 209 return _store(\&pstore, @_, 0); 210 } 211 212 # 213 # nstore 214 # 215 # Same as store, but in network order. 216 # 217 sub nstore { 218 return _store(\&net_pstore, @_, 0); 219 } 220 221 # 222 # lock_store 223 # 224 # Same as store, but flock the file first (advisory locking). 225 # 226 sub lock_store { 227 return _store(\&pstore, @_, 1); 228 } 229 230 # 231 # lock_nstore 232 # 233 # Same as nstore, but flock the file first (advisory locking). 234 # 235 sub lock_nstore { 236 return _store(\&net_pstore, @_, 1); 237 } 238 239 # Internal store to file routine 240 sub _store { 241 my $xsptr = shift; 242 my $self = shift; 243 my ($file, $use_locking) = @_; 244 logcroak "not a reference" unless ref($self); 245 logcroak "wrong argument number" unless @_ == 2; # No @foo in arglist 246 local *FILE; 247 if ($use_locking) { 248 open(FILE, ">>$file") || logcroak "can't write into $file: $!"; 249 unless (&CAN_FLOCK) { 250 logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O"; 251 return undef; 252 } 253 flock(FILE, LOCK_EX) || 254 logcroak "can't get exclusive lock on $file: $!"; 255 truncate FILE, 0; 256 # Unlocking will happen when FILE is closed 257 } else { 258 open(FILE, ">$file") || logcroak "can't create $file: $!"; 259 } 260 binmode FILE; # Archaic systems... 261 my $da = $@; # Don't mess if called from exception handler 262 my $ret; 263 # Call C routine nstore or pstore, depending on network order 264 eval { $ret = &$xsptr(*FILE, $self) }; 265 close(FILE) or $ret = undef; 266 unlink($file) or warn "Can't unlink $file: $!\n" if $@ || !defined $ret; 267 logcroak $@ if $@ =~ s/\.?\n$/,/; 268 $@ = $da; 269 return $ret ? $ret : undef; 270 } 271 272 # 273 # store_fd 274 # 275 # Same as store, but perform on an already opened file descriptor instead. 276 # Returns undef if an I/O error occurred. 277 # 278 sub store_fd { 279 return _store_fd(\&pstore, @_); 280 } 281 282 # 283 # nstore_fd 284 # 285 # Same as store_fd, but in network order. 286 # 287 sub nstore_fd { 288 my ($self, $file) = @_; 289 return _store_fd(\&net_pstore, @_); 290 } 291 292 # Internal store routine on opened file descriptor 293 sub _store_fd { 294 my $xsptr = shift; 295 my $self = shift; 296 my ($file) = @_; 297 logcroak "not a reference" unless ref($self); 298 logcroak "too many arguments" unless @_ == 1; # No @foo in arglist 299 my $fd = fileno($file); 300 logcroak "not a valid file descriptor" unless defined $fd; 301 my $da = $@; # Don't mess if called from exception handler 302 my $ret; 303 # Call C routine nstore or pstore, depending on network order 304 eval { $ret = &$xsptr($file, $self) }; 305 logcroak $@ if $@ =~ s/\.?\n$/,/; 306 local $\; print $file ''; # Autoflush the file if wanted 307 $@ = $da; 308 return $ret ? $ret : undef; 309 } 310 311 # 312 # freeze 313 # 314 # Store oject and its hierarchy in memory and return a scalar 315 # containing the result. 316 # 317 sub freeze { 318 _freeze(\&mstore, @_); 319 } 320 321 # 322 # nfreeze 323 # 324 # Same as freeze but in network order. 325 # 326 sub nfreeze { 327 _freeze(\&net_mstore, @_); 328 } 329 330 # Internal freeze routine 331 sub _freeze { 332 my $xsptr = shift; 333 my $self = shift; 334 logcroak "not a reference" unless ref($self); 335 logcroak "too many arguments" unless @_ == 0; # No @foo in arglist 336 my $da = $@; # Don't mess if called from exception handler 337 my $ret; 338 # Call C routine mstore or net_mstore, depending on network order 339 eval { $ret = &$xsptr($self) }; 340 logcroak $@ if $@ =~ s/\.?\n$/,/; 341 $@ = $da; 342 return $ret ? $ret : undef; 343 } 344 345 # 346 # retrieve 347 # 348 # Retrieve object hierarchy from disk, returning a reference to the root 349 # object of that tree. 350 # 351 sub retrieve { 352 _retrieve($_[0], 0); 353 } 354 355 # 356 # lock_retrieve 357 # 358 # Same as retrieve, but with advisory locking. 359 # 360 sub lock_retrieve { 361 _retrieve($_[0], 1); 362 } 363 364 # Internal retrieve routine 365 sub _retrieve { 366 my ($file, $use_locking) = @_; 367 local *FILE; 368 open(FILE, $file) || logcroak "can't open $file: $!"; 369 binmode FILE; # Archaic systems... 370 my $self; 371 my $da = $@; # Could be from exception handler 372 if ($use_locking) { 373 unless (&CAN_FLOCK) { 374 logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O"; 375 return undef; 376 } 377 flock(FILE, LOCK_SH) || logcroak "can't get shared lock on $file: $!"; 378 # Unlocking will happen when FILE is closed 379 } 380 eval { $self = pretrieve(*FILE) }; # Call C routine 381 close(FILE); 382 logcroak $@ if $@ =~ s/\.?\n$/,/; 383 $@ = $da; 384 return $self; 385 } 386 387 # 388 # fd_retrieve 389 # 390 # Same as retrieve, but perform from an already opened file descriptor instead. 391 # 392 sub fd_retrieve { 393 my ($file) = @_; 394 my $fd = fileno($file); 395 logcroak "not a valid file descriptor" unless defined $fd; 396 my $self; 397 my $da = $@; # Could be from exception handler 398 eval { $self = pretrieve($file) }; # Call C routine 399 logcroak $@ if $@ =~ s/\.?\n$/,/; 400 $@ = $da; 401 return $self; 402 } 403 404 # 405 # thaw 406 # 407 # Recreate objects in memory from an existing frozen image created 408 # by freeze. If the frozen image passed is undef, return undef. 409 # 410 sub thaw { 411 my ($frozen) = @_; 412 return undef unless defined $frozen; 413 my $self; 414 my $da = $@; # Could be from exception handler 415 eval { $self = mretrieve($frozen) }; # Call C routine 416 logcroak $@ if $@ =~ s/\.?\n$/,/; 417 $@ = $da; 418 return $self; 419 } 420 421 1; 422 __END__ 423 424 =head1 NAME 425 426 Storable - persistence for Perl data structures 427 428 =head1 SYNOPSIS 429 430 use Storable; 431 store \%table, 'file'; 432 $hashref = retrieve('file'); 433 434 use Storable qw(nstore store_fd nstore_fd freeze thaw dclone); 435 436 # Network order 437 nstore \%table, 'file'; 438 $hashref = retrieve('file'); # There is NO nretrieve() 439 440 # Storing to and retrieving from an already opened file 441 store_fd \@array, \*STDOUT; 442 nstore_fd \%table, \*STDOUT; 443 $aryref = fd_retrieve(\*SOCKET); 444 $hashref = fd_retrieve(\*SOCKET); 445 446 # Serializing to memory 447 $serialized = freeze \%table; 448 %table_clone = %{ thaw($serialized) }; 449 450 # Deep (recursive) cloning 451 $cloneref = dclone($ref); 452 453 # Advisory locking 454 use Storable qw(lock_store lock_nstore lock_retrieve) 455 lock_store \%table, 'file'; 456 lock_nstore \%table, 'file'; 457 $hashref = lock_retrieve('file'); 458 459 =head1 DESCRIPTION 460 461 The Storable package brings persistence to your Perl data structures 462 containing SCALAR, ARRAY, HASH or REF objects, i.e. anything that can be 463 conveniently stored to disk and retrieved at a later time. 464 465 It can be used in the regular procedural way by calling C<store> with 466 a reference to the object to be stored, along with the file name where 467 the image should be written. 468 469 The routine returns C<undef> for I/O problems or other internal error, 470 a true value otherwise. Serious errors are propagated as a C<die> exception. 471 472 To retrieve data stored to disk, use C<retrieve> with a file name. 473 The objects stored into that file are recreated into memory for you, 474 and a I<reference> to the root object is returned. In case an I/O error 475 occurs while reading, C<undef> is returned instead. Other serious 476 errors are propagated via C<die>. 477 478 Since storage is performed recursively, you might want to stuff references 479 to objects that share a lot of common data into a single array or hash 480 table, and then store that object. That way, when you retrieve back the 481 whole thing, the objects will continue to share what they originally shared. 482 483 At the cost of a slight header overhead, you may store to an already 484 opened file descriptor using the C<store_fd> routine, and retrieve 485 from a file via C<fd_retrieve>. Those names aren't imported by default, 486 so you will have to do that explicitly if you need those routines. 487 The file descriptor you supply must be already opened, for read 488 if you're going to retrieve and for write if you wish to store. 489 490 store_fd(\%table, *STDOUT) || die "can't store to stdout\n"; 491 $hashref = fd_retrieve(*STDIN); 492 493 You can also store data in network order to allow easy sharing across 494 multiple platforms, or when storing on a socket known to be remotely 495 connected. The routines to call have an initial C<n> prefix for I<network>, 496 as in C<nstore> and C<nstore_fd>. At retrieval time, your data will be 497 correctly restored so you don't have to know whether you're restoring 498 from native or network ordered data. Double values are stored stringified 499 to ensure portability as well, at the slight risk of loosing some precision 500 in the last decimals. 501 502 When using C<fd_retrieve>, objects are retrieved in sequence, one 503 object (i.e. one recursive tree) per associated C<store_fd>. 504 505 If you're more from the object-oriented camp, you can inherit from 506 Storable and directly store your objects by invoking C<store> as 507 a method. The fact that the root of the to-be-stored tree is a 508 blessed reference (i.e. an object) is special-cased so that the 509 retrieve does not provide a reference to that object but rather the 510 blessed object reference itself. (Otherwise, you'd get a reference 511 to that blessed object). 512 513 =head1 MEMORY STORE 514 515 The Storable engine can also store data into a Perl scalar instead, to 516 later retrieve them. This is mainly used to freeze a complex structure in 517 some safe compact memory place (where it can possibly be sent to another 518 process via some IPC, since freezing the structure also serializes it in 519 effect). Later on, and maybe somewhere else, you can thaw the Perl scalar 520 out and recreate the original complex structure in memory. 521 522 Surprisingly, the routines to be called are named C<freeze> and C<thaw>. 523 If you wish to send out the frozen scalar to another machine, use 524 C<nfreeze> instead to get a portable image. 525 526 Note that freezing an object structure and immediately thawing it 527 actually achieves a deep cloning of that structure: 528 529 dclone(.) = thaw(freeze(.)) 530 531 Storable provides you with a C<dclone> interface which does not create 532 that intermediary scalar but instead freezes the structure in some 533 internal memory space and then immediately thaws it out. 534 535 =head1 ADVISORY LOCKING 536 537 The C<lock_store> and C<lock_nstore> routine are equivalent to 538 C<store> and C<nstore>, except that they get an exclusive lock on 539 the file before writing. Likewise, C<lock_retrieve> does the same 540 as C<retrieve>, but also gets a shared lock on the file before reading. 541 542 As with any advisory locking scheme, the protection only works if you 543 systematically use C<lock_store> and C<lock_retrieve>. If one side of 544 your application uses C<store> whilst the other uses C<lock_retrieve>, 545 you will get no protection at all. 546 547 The internal advisory locking is implemented using Perl's flock() 548 routine. If your system does not support any form of flock(), or if 549 you share your files across NFS, you might wish to use other forms 550 of locking by using modules such as LockFile::Simple which lock a 551 file using a filesystem entry, instead of locking the file descriptor. 552 553 =head1 SPEED 554 555 The heart of Storable is written in C for decent speed. Extra low-level 556 optimizations have been made when manipulating perl internals, to 557 sacrifice encapsulation for the benefit of greater speed. 558 559 =head1 CANONICAL REPRESENTATION 560 561 Normally, Storable stores elements of hashes in the order they are 562 stored internally by Perl, i.e. pseudo-randomly. If you set 563 C<$Storable::canonical> to some C<TRUE> value, Storable will store 564 hashes with the elements sorted by their key. This allows you to 565 compare data structures by comparing their frozen representations (or 566 even the compressed frozen representations), which can be useful for 567 creating lookup tables for complicated queries. 568 569 Canonical order does not imply network order; those are two orthogonal 570 settings. 571 572 =head1 CODE REFERENCES 573 574 Since Storable version 2.05, CODE references may be serialized with 575 the help of L<B::Deparse>. To enable this feature, set 576 C<$Storable::Deparse> to a true value. To enable deserialization, 577 C<$Storable::Eval> should be set to a true value. Be aware that 578 deserialization is done through C<eval>, which is dangerous if the 579 Storable file contains malicious data. You can set C<$Storable::Eval> 580 to a subroutine reference which would be used instead of C<eval>. See 581 below for an example using a L<Safe> compartment for deserialization 582 of CODE references. 583 584 If C<$Storable::Deparse> and/or C<$Storable::Eval> are set to false 585 values, then the value of C<$Storable::forgive_me> (see below) is 586 respected while serializing and deserializing. 587 588 =head1 FORWARD COMPATIBILITY 589 590 This release of Storable can be used on a newer version of Perl to 591 serialize data which is not supported by earlier Perls. By default, 592 Storable will attempt to do the right thing, by C<croak()>ing if it 593 encounters data that it cannot deserialize. However, the defaults 594 can be changed as follows: 595 596 =over 4 597 598 =item utf8 data 599 600 Perl 5.6 added support for Unicode characters with code points > 255, 601 and Perl 5.8 has full support for Unicode characters in hash keys. 602 Perl internally encodes strings with these characters using utf8, and 603 Storable serializes them as utf8. By default, if an older version of 604 Perl encounters a utf8 value it cannot represent, it will C<croak()>. 605 To change this behaviour so that Storable deserializes utf8 encoded 606 values as the string of bytes (effectively dropping the I<is_utf8> flag) 607 set C<$Storable::drop_utf8> to some C<TRUE> value. This is a form of 608 data loss, because with C<$drop_utf8> true, it becomes impossible to tell 609 whether the original data was the Unicode string, or a series of bytes 610 that happen to be valid utf8. 611 612 =item restricted hashes 613 614 Perl 5.8 adds support for restricted hashes, which have keys 615 restricted to a given set, and can have values locked to be read only. 616 By default, when Storable encounters a restricted hash on a perl 617 that doesn't support them, it will deserialize it as a normal hash, 618 silently discarding any placeholder keys and leaving the keys and 619 all values unlocked. To make Storable C<croak()> instead, set 620 C<$Storable::downgrade_restricted> to a C<FALSE> value. To restore 621 the default set it back to some C<TRUE> value. 622 623 =item files from future versions of Storable 624 625 Earlier versions of Storable would immediately croak if they encountered 626 a file with a higher internal version number than the reading Storable 627 knew about. Internal version numbers are increased each time new data 628 types (such as restricted hashes) are added to the vocabulary of the file 629 format. This meant that a newer Storable module had no way of writing a 630 file readable by an older Storable, even if the writer didn't store newer 631 data types. 632 633 This version of Storable will defer croaking until it encounters a data 634 type in the file that it does not recognize. This means that it will 635 continue to read files generated by newer Storable modules which are careful 636 in what they write out, making it easier to upgrade Storable modules in a 637 mixed environment. 638 639 The old behaviour of immediate croaking can be re-instated by setting 640 C<$Storable::accept_future_minor> to some C<FALSE> value. 641 642 =back 643 644 All these variables have no effect on a newer Perl which supports the 645 relevant feature. 646 647 =head1 ERROR REPORTING 648 649 Storable uses the "exception" paradigm, in that it does not try to workaround 650 failures: if something bad happens, an exception is generated from the 651 caller's perspective (see L<Carp> and C<croak()>). Use eval {} to trap 652 those exceptions. 653 654 When Storable croaks, it tries to report the error via the C<logcroak()> 655 routine from the C<Log::Agent> package, if it is available. 656 657 Normal errors are reported by having store() or retrieve() return C<undef>. 658 Such errors are usually I/O errors (or truncated stream errors at retrieval). 659 660 =head1 WIZARDS ONLY 661 662 =head2 Hooks 663 664 Any class may define hooks that will be called during the serialization 665 and deserialization process on objects that are instances of that class. 666 Those hooks can redefine the way serialization is performed (and therefore, 667 how the symmetrical deserialization should be conducted). 668 669 Since we said earlier: 670 671 dclone(.) = thaw(freeze(.)) 672 673 everything we say about hooks should also hold for deep cloning. However, 674 hooks get to know whether the operation is a mere serialization, or a cloning. 675 676 Therefore, when serializing hooks are involved, 677 678 dclone(.) <> thaw(freeze(.)) 679 680 Well, you could keep them in sync, but there's no guarantee it will always 681 hold on classes somebody else wrote. Besides, there is little to gain in 682 doing so: a serializing hook could keep only one attribute of an object, 683 which is probably not what should happen during a deep cloning of that 684 same object. 685 686 Here is the hooking interface: 687 688 =over 4 689 690 =item C<STORABLE_freeze> I<obj>, I<cloning> 691 692 The serializing hook, called on the object during serialization. It can be 693 inherited, or defined in the class itself, like any other method. 694 695 Arguments: I<obj> is the object to serialize, I<cloning> is a flag indicating 696 whether we're in a dclone() or a regular serialization via store() or freeze(). 697 698 Returned value: A LIST C<($serialized, $ref1, $ref2, ...)> where $serialized 699 is the serialized form to be used, and the optional $ref1, $ref2, etc... are 700 extra references that you wish to let the Storable engine serialize. 701 702 At deserialization time, you will be given back the same LIST, but all the 703 extra references will be pointing into the deserialized structure. 704 705 The B<first time> the hook is hit in a serialization flow, you may have it 706 return an empty list. That will signal the Storable engine to further 707 discard that hook for this class and to therefore revert to the default 708 serialization of the underlying Perl data. The hook will again be normally 709 processed in the next serialization. 710 711 Unless you know better, serializing hook should always say: 712 713 sub STORABLE_freeze { 714 my ($self, $cloning) = @_; 715 return if $cloning; # Regular default serialization 716 .... 717 } 718 719 in order to keep reasonable dclone() semantics. 720 721 =item C<STORABLE_thaw> I<obj>, I<cloning>, I<serialized>, ... 722 723 The deserializing hook called on the object during deserialization. 724 But wait: if we're deserializing, there's no object yet... right? 725 726 Wrong: the Storable engine creates an empty one for you. If you know Eiffel, 727 you can view C<STORABLE_thaw> as an alternate creation routine. 728 729 This means the hook can be inherited like any other method, and that 730 I<obj> is your blessed reference for this particular instance. 731 732 The other arguments should look familiar if you know C<STORABLE_freeze>: 733 I<cloning> is true when we're part of a deep clone operation, I<serialized> 734 is the serialized string you returned to the engine in C<STORABLE_freeze>, 735 and there may be an optional list of references, in the same order you gave 736 them at serialization time, pointing to the deserialized objects (which 737 have been processed courtesy of the Storable engine). 738 739 When the Storable engine does not find any C<STORABLE_thaw> hook routine, 740 it tries to load the class by requiring the package dynamically (using 741 the blessed package name), and then re-attempts the lookup. If at that 742 time the hook cannot be located, the engine croaks. Note that this mechanism 743 will fail if you define several classes in the same file, but L<perlmod> 744 warned you. 745 746 It is up to you to use this information to populate I<obj> the way you want. 747 748 Returned value: none. 749 750 =item C<STORABLE_attach> I<class>, I<cloning>, I<serialized> 751 752 While C<STORABLE_freeze> and C<STORABLE_thaw> are useful for classes where 753 each instance is independent, this mechanism has difficulty (or is 754 incompatible) with objects that exist as common process-level or 755 system-level resources, such as singleton objects, database pools, caches 756 or memoized objects. 757 758 The alternative C<STORABLE_attach> method provides a solution for these 759 shared objects. Instead of C<STORABLE_freeze> --E<gt> C<STORABLE_thaw>, 760 you implement C<STORABLE_freeze> --E<gt> C<STORABLE_attach> instead. 761 762 Arguments: I<class> is the class we are attaching to, I<cloning> is a flag 763 indicating whether we're in a dclone() or a regular de-serialization via 764 thaw(), and I<serialized> is the stored string for the resource object. 765 766 Because these resource objects are considered to be owned by the entire 767 process/system, and not the "property" of whatever is being serialized, 768 no references underneath the object should be included in the serialized 769 string. Thus, in any class that implements C<STORABLE_attach>, the 770 C<STORABLE_freeze> method cannot return any references, and C<Storable> 771 will throw an error if C<STORABLE_freeze> tries to return references. 772 773 All information required to "attach" back to the shared resource object 774 B<must> be contained B<only> in the C<STORABLE_freeze> return string. 775 Otherwise, C<STORABLE_freeze> behaves as normal for C<STORABLE_attach> 776 classes. 777 778 Because C<STORABLE_attach> is passed the class (rather than an object), 779 it also returns the object directly, rather than modifying the passed 780 object. 781 782 Returned value: object of type C<class> 783 784 =back 785 786 =head2 Predicates 787 788 Predicates are not exportable. They must be called by explicitly prefixing 789 them with the Storable package name. 790 791 =over 4 792 793 =item C<Storable::last_op_in_netorder> 794 795 The C<Storable::last_op_in_netorder()> predicate will tell you whether 796 network order was used in the last store or retrieve operation. If you 797 don't know how to use this, just forget about it. 798 799 =item C<Storable::is_storing> 800 801 Returns true if within a store operation (via STORABLE_freeze hook). 802 803 =item C<Storable::is_retrieving> 804 805 Returns true if within a retrieve operation (via STORABLE_thaw hook). 806 807 =back 808 809 =head2 Recursion 810 811 With hooks comes the ability to recurse back to the Storable engine. 812 Indeed, hooks are regular Perl code, and Storable is convenient when 813 it comes to serializing and deserializing things, so why not use it 814 to handle the serialization string? 815 816 There are a few things you need to know, however: 817 818 =over 4 819 820 =item * 821 822 You can create endless loops if the things you serialize via freeze() 823 (for instance) point back to the object we're trying to serialize in 824 the hook. 825 826 =item * 827 828 Shared references among objects will not stay shared: if we're serializing 829 the list of object [A, C] where both object A and C refer to the SAME object 830 B, and if there is a serializing hook in A that says freeze(B), then when 831 deserializing, we'll get [A', C'] where A' refers to B', but C' refers to D, 832 a deep clone of B'. The topology was not preserved. 833 834 =back 835 836 That's why C<STORABLE_freeze> lets you provide a list of references 837 to serialize. The engine guarantees that those will be serialized in the 838 same context as the other objects, and therefore that shared objects will 839 stay shared. 840 841 In the above [A, C] example, the C<STORABLE_freeze> hook could return: 842 843 ("something", $self->{B}) 844 845 and the B part would be serialized by the engine. In C<STORABLE_thaw>, you 846 would get back the reference to the B' object, deserialized for you. 847 848 Therefore, recursion should normally be avoided, but is nonetheless supported. 849 850 =head2 Deep Cloning 851 852 There is a Clone module available on CPAN which implements deep cloning 853 natively, i.e. without freezing to memory and thawing the result. It is 854 aimed to replace Storable's dclone() some day. However, it does not currently 855 support Storable hooks to redefine the way deep cloning is performed. 856 857 =head1 Storable magic 858 859 Yes, there's a lot of that :-) But more precisely, in UNIX systems 860 there's a utility called C<file>, which recognizes data files based on 861 their contents (usually their first few bytes). For this to work, 862 a certain file called F<magic> needs to taught about the I<signature> 863 of the data. Where that configuration file lives depends on the UNIX 864 flavour; often it's something like F</usr/share/misc/magic> or 865 F</etc/magic>. Your system administrator needs to do the updating of 866 the F<magic> file. The necessary signature information is output to 867 STDOUT by invoking Storable::show_file_magic(). Note that the GNU 868 implementation of the C<file> utility, version 3.38 or later, 869 is expected to contain support for recognising Storable files 870 out-of-the-box, in addition to other kinds of Perl files. 871 872 You can also use the following functions to extract the file header 873 information from Storable images: 874 875 =over 876 877 =item $info = Storable::file_magic( $filename ) 878 879 If the given file is a Storable image return a hash describing it. If 880 the file is readable, but not a Storable image return C<undef>. If 881 the file does not exist or is unreadable then croak. 882 883 The hash returned has the following elements: 884 885 =over 886 887 =item C<version> 888 889 This returns the file format version. It is a string like "2.7". 890 891 Note that this version number is not the same as the version number of 892 the Storable module itself. For instance Storable v0.7 create files 893 in format v2.0 and Storable v2.15 create files in format v2.7. The 894 file format version number only increment when additional features 895 that would confuse older versions of the module are added. 896 897 Files older than v2.0 will have the one of the version numbers "-1", 898 "0" or "1". No minor number was used at that time. 899 900 =item C<version_nv> 901 902 This returns the file format version as number. It is a string like 903 "2.007". This value is suitable for numeric comparisons. 904 905 The constant function C<Storable::BIN_VERSION_NV> returns a comparable 906 number that represent the highest file version number that this 907 version of Storable fully support (but see discussion of 908 C<$Storable::accept_future_minor> above). The constant 909 C<Storable::BIN_WRITE_VERSION_NV> function returns what file version 910 is written and might be less than C<Storable::BIN_VERSION_NV> in some 911 configuations. 912 913 =item C<major>, C<minor> 914 915 This also returns the file format version. If the version is "2.7" 916 then major would be 2 and minor would be 7. The minor element is 917 missing for when major is less than 2. 918 919 =item C<hdrsize> 920 921 The is the number of bytes that the Storable header occupies. 922 923 =item C<netorder> 924 925 This is TRUE if the image store data in network order. This means 926 that it was created with nstore() or similar. 927 928 =item C<byteorder> 929 930 This is only present when C<netorder> is FALSE. It is the 931 $Config{byteorder} string of the perl that created this image. It is 932 a string like "1234" (32 bit little endian) or "87654321" (64 bit big 933 endian). This must match the current perl for the image to be 934 readable by Storable. 935 936 =item C<intsize>, C<longsize>, C<ptrsize>, C<nvsize> 937 938 These are only present when C<netorder> is FALSE. These are the sizes of 939 various C datatypes of the perl that created this image. These must 940 match the current perl for the image to be readable by Storable. 941 942 The C<nvsize> element is only present for file format v2.2 and 943 higher. 944 945 =item C<file> 946 947 The name of the file. 948 949 =back 950 951 =item $info = Storable::read_magic( $buffer ) 952 953 =item $info = Storable::read_magic( $buffer, $must_be_file ) 954 955 The $buffer should be a Storable image or the first few bytes of it. 956 If $buffer starts with a Storable header, then a hash describing the 957 image is returned, otherwise C<undef> is returned. 958 959 The hash has the same structure as the one returned by 960 Storable::file_magic(). The C<file> element is true if the image is a 961 file image. 962 963 If the $must_be_file argument is provided and is TRUE, then return 964 C<undef> unless the image looks like it belongs to a file dump. 965 966 The maximum size of a Storable header is currently 21 bytes. If the 967 provided $buffer is only the first part of a Storable image it should 968 at least be this long to ensure that read_magic() will recognize it as 969 such. 970 971 =back 972 973 =head1 EXAMPLES 974 975 Here are some code samples showing a possible usage of Storable: 976 977 use Storable qw(store retrieve freeze thaw dclone); 978 979 %color = ('Blue' => 0.1, 'Red' => 0.8, 'Black' => 0, 'White' => 1); 980 981 store(\%color, 'mycolors') or die "Can't store %a in mycolors!\n"; 982 983 $colref = retrieve('mycolors'); 984 die "Unable to retrieve from mycolors!\n" unless defined $colref; 985 printf "Blue is still %lf\n", $colref->{'Blue'}; 986 987 $colref2 = dclone(\%color); 988 989 $str = freeze(\%color); 990 printf "Serialization of %%color is %d bytes long.\n", length($str); 991 $colref3 = thaw($str); 992 993 which prints (on my machine): 994 995 Blue is still 0.100000 996 Serialization of %color is 102 bytes long. 997 998 Serialization of CODE references and deserialization in a safe 999 compartment: 1000 1001 =for example begin 1002 1003 use Storable qw(freeze thaw); 1004 use Safe; 1005 use strict; 1006 my $safe = new Safe; 1007 # because of opcodes used in "use strict": 1008 $safe->permit(qw(:default require)); 1009 local $Storable::Deparse = 1; 1010 local $Storable::Eval = sub { $safe->reval($_[0]) }; 1011 my $serialized = freeze(sub { 42 }); 1012 my $code = thaw($serialized); 1013 $code->() == 42; 1014 1015 =for example end 1016 1017 =for example_testing 1018 is( $code->(), 42 ); 1019 1020 =head1 WARNING 1021 1022 If you're using references as keys within your hash tables, you're bound 1023 to be disappointed when retrieving your data. Indeed, Perl stringifies 1024 references used as hash table keys. If you later wish to access the 1025 items via another reference stringification (i.e. using the same 1026 reference that was used for the key originally to record the value into 1027 the hash table), it will work because both references stringify to the 1028 same string. 1029 1030 It won't work across a sequence of C<store> and C<retrieve> operations, 1031 however, because the addresses in the retrieved objects, which are 1032 part of the stringified references, will probably differ from the 1033 original addresses. The topology of your structure is preserved, 1034 but not hidden semantics like those. 1035 1036 On platforms where it matters, be sure to call C<binmode()> on the 1037 descriptors that you pass to Storable functions. 1038 1039 Storing data canonically that contains large hashes can be 1040 significantly slower than storing the same data normally, as 1041 temporary arrays to hold the keys for each hash have to be allocated, 1042 populated, sorted and freed. Some tests have shown a halving of the 1043 speed of storing -- the exact penalty will depend on the complexity of 1044 your data. There is no slowdown on retrieval. 1045 1046 =head1 BUGS 1047 1048 You can't store GLOB, FORMLINE, etc.... If you can define semantics 1049 for those operations, feel free to enhance Storable so that it can 1050 deal with them. 1051 1052 The store functions will C<croak> if they run into such references 1053 unless you set C<$Storable::forgive_me> to some C<TRUE> value. In that 1054 case, the fatal message is turned in a warning and some 1055 meaningless string is stored instead. 1056 1057 Setting C<$Storable::canonical> may not yield frozen strings that 1058 compare equal due to possible stringification of numbers. When the 1059 string version of a scalar exists, it is the form stored; therefore, 1060 if you happen to use your numbers as strings between two freezing 1061 operations on the same data structures, you will get different 1062 results. 1063 1064 When storing doubles in network order, their value is stored as text. 1065 However, you should also not expect non-numeric floating-point values 1066 such as infinity and "not a number" to pass successfully through a 1067 nstore()/retrieve() pair. 1068 1069 As Storable neither knows nor cares about character sets (although it 1070 does know that characters may be more than eight bits wide), any difference 1071 in the interpretation of character codes between a host and a target 1072 system is your problem. In particular, if host and target use different 1073 code points to represent the characters used in the text representation 1074 of floating-point numbers, you will not be able be able to exchange 1075 floating-point data, even with nstore(). 1076 1077 C<Storable::drop_utf8> is a blunt tool. There is no facility either to 1078 return B<all> strings as utf8 sequences, or to attempt to convert utf8 1079 data back to 8 bit and C<croak()> if the conversion fails. 1080 1081 Prior to Storable 2.01, no distinction was made between signed and 1082 unsigned integers on storing. By default Storable prefers to store a 1083 scalars string representation (if it has one) so this would only cause 1084 problems when storing large unsigned integers that had never been converted 1085 to string or floating point. In other words values that had been generated 1086 by integer operations such as logic ops and then not used in any string or 1087 arithmetic context before storing. 1088 1089 =head2 64 bit data in perl 5.6.0 and 5.6.1 1090 1091 This section only applies to you if you have existing data written out 1092 by Storable 2.02 or earlier on perl 5.6.0 or 5.6.1 on Unix or Linux which 1093 has been configured with 64 bit integer support (not the default) 1094 If you got a precompiled perl, rather than running Configure to build 1095 your own perl from source, then it almost certainly does not affect you, 1096 and you can stop reading now (unless you're curious). If you're using perl 1097 on Windows it does not affect you. 1098 1099 Storable writes a file header which contains the sizes of various C 1100 language types for the C compiler that built Storable (when not writing in 1101 network order), and will refuse to load files written by a Storable not 1102 on the same (or compatible) architecture. This check and a check on 1103 machine byteorder is needed because the size of various fields in the file 1104 are given by the sizes of the C language types, and so files written on 1105 different architectures are incompatible. This is done for increased speed. 1106 (When writing in network order, all fields are written out as standard 1107 lengths, which allows full interworking, but takes longer to read and write) 1108 1109 Perl 5.6.x introduced the ability to optional configure the perl interpreter 1110 to use C's C<long long> type to allow scalars to store 64 bit integers on 32 1111 bit systems. However, due to the way the Perl configuration system 1112 generated the C configuration files on non-Windows platforms, and the way 1113 Storable generates its header, nothing in the Storable file header reflected 1114 whether the perl writing was using 32 or 64 bit integers, despite the fact 1115 that Storable was storing some data differently in the file. Hence Storable 1116 running on perl with 64 bit integers will read the header from a file 1117 written by a 32 bit perl, not realise that the data is actually in a subtly 1118 incompatible format, and then go horribly wrong (possibly crashing) if it 1119 encountered a stored integer. This is a design failure. 1120 1121 Storable has now been changed to write out and read in a file header with 1122 information about the size of integers. It's impossible to detect whether 1123 an old file being read in was written with 32 or 64 bit integers (they have 1124 the same header) so it's impossible to automatically switch to a correct 1125 backwards compatibility mode. Hence this Storable defaults to the new, 1126 correct behaviour. 1127 1128 What this means is that if you have data written by Storable 1.x running 1129 on perl 5.6.0 or 5.6.1 configured with 64 bit integers on Unix or Linux 1130 then by default this Storable will refuse to read it, giving the error 1131 I<Byte order is not compatible>. If you have such data then you you 1132 should set C<$Storable::interwork_56_64bit> to a true value to make this 1133 Storable read and write files with the old header. You should also 1134 migrate your data, or any older perl you are communicating with, to this 1135 current version of Storable. 1136 1137 If you don't have data written with specific configuration of perl described 1138 above, then you do not and should not do anything. Don't set the flag - 1139 not only will Storable on an identically configured perl refuse to load them, 1140 but Storable a differently configured perl will load them believing them 1141 to be correct for it, and then may well fail or crash part way through 1142 reading them. 1143 1144 =head1 CREDITS 1145 1146 Thank you to (in chronological order): 1147 1148 Jarkko Hietaniemi <jhi@iki.fi> 1149 Ulrich Pfeifer <pfeifer@charly.informatik.uni-dortmund.de> 1150 Benjamin A. Holzman <bah@ecnvantage.com> 1151 Andrew Ford <A.Ford@ford-mason.co.uk> 1152 Gisle Aas <gisle@aas.no> 1153 Jeff Gresham <gresham_jeffrey@jpmorgan.com> 1154 Murray Nesbitt <murray@activestate.com> 1155 Marc Lehmann <pcg@opengroup.org> 1156 Justin Banks <justinb@wamnet.com> 1157 Jarkko Hietaniemi <jhi@iki.fi> (AGAIN, as perl 5.7.0 Pumpkin!) 1158 Salvador Ortiz Garcia <sog@msg.com.mx> 1159 Dominic Dunlop <domo@computer.org> 1160 Erik Haugan <erik@solbors.no> 1161 1162 for their bug reports, suggestions and contributions. 1163 1164 Benjamin Holzman contributed the tied variable support, Andrew Ford 1165 contributed the canonical order for hashes, and Gisle Aas fixed 1166 a few misunderstandings of mine regarding the perl internals, 1167 and optimized the emission of "tags" in the output streams by 1168 simply counting the objects instead of tagging them (leading to 1169 a binary incompatibility for the Storable image starting at version 1170 0.6--older images are, of course, still properly understood). 1171 Murray Nesbitt made Storable thread-safe. Marc Lehmann added overloading 1172 and references to tied items support. 1173 1174 =head1 AUTHOR 1175 1176 Storable was written by Raphael Manfredi F<E<lt>Raphael_Manfredi@pobox.comE<gt>> 1177 Maintenance is now done by the perl5-porters F<E<lt>perl5-porters@perl.orgE<gt>> 1178 1179 Please e-mail us with problems, bug fixes, comments and complaints, 1180 although if you have complements you should send them to Raphael. 1181 Please don't e-mail Raphael with problems, as he no longer works on 1182 Storable, and your message will be delayed while he forwards it to us. 1183 1184 =head1 SEE ALSO 1185 1186 L<Clone>. 1187 1188 =cut
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