Storable.pm revision 1.1
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 8require DynaLoader; 9require Exporter; 10package 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 22use AutoLoader; 23use FileHandle; 24use vars qw($canonical $forgive_me $VERSION); 25 26$VERSION = '2.22'; 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 38require Carp; 39 40# 41# They might miss :flock in Fcntl 42# 43 44BEGIN { 45 if (eval { require Fcntl; 1 } && exists $Fcntl::EXPORT_TAGS{'flock'}) { 46 Fcntl->import(':flock'); 47 } else { 48 eval q{ 49 sub LOCK_SH () {1} 50 sub LOCK_EX () {2} 51 }; 52 } 53} 54 55sub CLONE { 56 # clone context under threads 57 Storable::init_perinterp(); 58} 59 60# Can't Autoload cleanly as this clashes 8.3 with &retrieve 61sub retrieve_fd { &fd_retrieve } # Backward compatibility 62 63# By default restricted hashes are downgraded on earlier perls. 64 65$Storable::downgrade_restricted = 1; 66$Storable::accept_future_minor = 1; 67bootstrap Storable; 681; 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 75sub logcroak { 76 Carp::croak(@_); 77} 78 79sub logcarp { 80 Carp::carp(@_); 81} 82 83# 84# Determine whether locking is possible, but only when needed. 85# 86 87sub 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 96sub 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# 1030 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 1090 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) 115EOM 116} 117 118sub 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, $file); 129} 130 131sub read_magic { 132 my($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 192sub BIN_VERSION_NV { 193 sprintf "%d.%03d", BIN_MAJOR(), BIN_MINOR(); 194} 195 196sub 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# 208sub store { 209 return _store(\&pstore, @_, 0); 210} 211 212# 213# nstore 214# 215# Same as store, but in network order. 216# 217sub 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# 226sub 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# 235sub lock_nstore { 236 return _store(\&net_pstore, @_, 1); 237} 238 239# Internal store to file routine 240sub _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 ? $ret : undef; 270} 271 272# 273# store_fd 274# 275# Same as store, but perform on an already opened file descriptor instead. 276# Returns undef if an I/O error occurred. 277# 278sub store_fd { 279 return _store_fd(\&pstore, @_); 280} 281 282# 283# nstore_fd 284# 285# Same as store_fd, but in network order. 286# 287sub nstore_fd { 288 my ($self, $file) = @_; 289 return _store_fd(\&net_pstore, @_); 290} 291 292# Internal store routine on opened file descriptor 293sub _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# 317sub freeze { 318 _freeze(\&mstore, @_); 319} 320 321# 322# nfreeze 323# 324# Same as freeze but in network order. 325# 326sub nfreeze { 327 _freeze(\&net_mstore, @_); 328} 329 330# Internal freeze routine 331sub _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 ? $ret : undef; 343} 344 345# 346# retrieve 347# 348# Retrieve object hierarchy from disk, returning a reference to the root 349# object of that tree. 350# 351sub retrieve { 352 _retrieve($_[0], 0); 353} 354 355# 356# lock_retrieve 357# 358# Same as retrieve, but with advisory locking. 359# 360sub lock_retrieve { 361 _retrieve($_[0], 1); 362} 363 364# Internal retrieve routine 365sub _retrieve { 366 my ($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 $self; 385} 386 387# 388# fd_retrieve 389# 390# Same as retrieve, but perform from an already opened file descriptor instead. 391# 392sub fd_retrieve { 393 my ($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 $self; 402} 403 404# 405# thaw 406# 407# Recreate objects in memory from an existing frozen image created 408# by freeze. If the frozen image passed is undef, return undef. 409# 410sub thaw { 411 my ($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 4211; 422__END__ 423 424=head1 NAME 425 426Storable - 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 461The Storable package brings persistence to your Perl data structures 462containing SCALAR, ARRAY, HASH or REF objects, i.e. anything that can be 463conveniently stored to disk and retrieved at a later time. 464 465It can be used in the regular procedural way by calling C<store> with 466a reference to the object to be stored, along with the file name where 467the image should be written. 468 469The routine returns C<undef> for I/O problems or other internal error, 470a true value otherwise. Serious errors are propagated as a C<die> exception. 471 472To retrieve data stored to disk, use C<retrieve> with a file name. 473The objects stored into that file are recreated into memory for you, 474and a I<reference> to the root object is returned. In case an I/O error 475occurs while reading, C<undef> is returned instead. Other serious 476errors are propagated via C<die>. 477 478Since storage is performed recursively, you might want to stuff references 479to objects that share a lot of common data into a single array or hash 480table, and then store that object. That way, when you retrieve back the 481whole thing, the objects will continue to share what they originally shared. 482 483At the cost of a slight header overhead, you may store to an already 484opened file descriptor using the C<store_fd> routine, and retrieve 485from a file via C<fd_retrieve>. Those names aren't imported by default, 486so you will have to do that explicitly if you need those routines. 487The file descriptor you supply must be already opened, for read 488if 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 493You can also store data in network order to allow easy sharing across 494multiple platforms, or when storing on a socket known to be remotely 495connected. The routines to call have an initial C<n> prefix for I<network>, 496as in C<nstore> and C<nstore_fd>. At retrieval time, your data will be 497correctly restored so you don't have to know whether you're restoring 498from native or network ordered data. Double values are stored stringified 499to ensure portability as well, at the slight risk of loosing some precision 500in the last decimals. 501 502When using C<fd_retrieve>, objects are retrieved in sequence, one 503object (i.e. one recursive tree) per associated C<store_fd>. 504 505If you're more from the object-oriented camp, you can inherit from 506Storable and directly store your objects by invoking C<store> as 507a method. The fact that the root of the to-be-stored tree is a 508blessed reference (i.e. an object) is special-cased so that the 509retrieve does not provide a reference to that object but rather the 510blessed object reference itself. (Otherwise, you'd get a reference 511to that blessed object). 512 513=head1 MEMORY STORE 514 515The Storable engine can also store data into a Perl scalar instead, to 516later retrieve them. This is mainly used to freeze a complex structure in 517some safe compact memory place (where it can possibly be sent to another 518process via some IPC, since freezing the structure also serializes it in 519effect). Later on, and maybe somewhere else, you can thaw the Perl scalar 520out and recreate the original complex structure in memory. 521 522Surprisingly, the routines to be called are named C<freeze> and C<thaw>. 523If you wish to send out the frozen scalar to another machine, use 524C<nfreeze> instead to get a portable image. 525 526Note that freezing an object structure and immediately thawing it 527actually achieves a deep cloning of that structure: 528 529 dclone(.) = thaw(freeze(.)) 530 531Storable provides you with a C<dclone> interface which does not create 532that intermediary scalar but instead freezes the structure in some 533internal memory space and then immediately thaws it out. 534 535=head1 ADVISORY LOCKING 536 537The C<lock_store> and C<lock_nstore> routine are equivalent to 538C<store> and C<nstore>, except that they get an exclusive lock on 539the file before writing. Likewise, C<lock_retrieve> does the same 540as C<retrieve>, but also gets a shared lock on the file before reading. 541 542As with any advisory locking scheme, the protection only works if you 543systematically use C<lock_store> and C<lock_retrieve>. If one side of 544your application uses C<store> whilst the other uses C<lock_retrieve>, 545you will get no protection at all. 546 547The internal advisory locking is implemented using Perl's flock() 548routine. If your system does not support any form of flock(), or if 549you share your files across NFS, you might wish to use other forms 550of locking by using modules such as LockFile::Simple which lock a 551file using a filesystem entry, instead of locking the file descriptor. 552 553=head1 SPEED 554 555The heart of Storable is written in C for decent speed. Extra low-level 556optimizations have been made when manipulating perl internals, to 557sacrifice encapsulation for the benefit of greater speed. 558 559=head1 CANONICAL REPRESENTATION 560 561Normally, Storable stores elements of hashes in the order they are 562stored internally by Perl, i.e. pseudo-randomly. If you set 563C<$Storable::canonical> to some C<TRUE> value, Storable will store 564hashes with the elements sorted by their key. This allows you to 565compare data structures by comparing their frozen representations (or 566even the compressed frozen representations), which can be useful for 567creating lookup tables for complicated queries. 568 569Canonical order does not imply network order; those are two orthogonal 570settings. 571 572=head1 CODE REFERENCES 573 574Since Storable version 2.05, CODE references may be serialized with 575the help of L<B::Deparse>. To enable this feature, set 576C<$Storable::Deparse> to a true value. To enable deserialization, 577C<$Storable::Eval> should be set to a true value. Be aware that 578deserialization is done through C<eval>, which is dangerous if the 579Storable file contains malicious data. You can set C<$Storable::Eval> 580to a subroutine reference which would be used instead of C<eval>. See 581below for an example using a L<Safe> compartment for deserialization 582of CODE references. 583 584If C<$Storable::Deparse> and/or C<$Storable::Eval> are set to false 585values, then the value of C<$Storable::forgive_me> (see below) is 586respected while serializing and deserializing. 587 588=head1 FORWARD COMPATIBILITY 589 590This release of Storable can be used on a newer version of Perl to 591serialize data which is not supported by earlier Perls. By default, 592Storable will attempt to do the right thing, by C<croak()>ing if it 593encounters data that it cannot deserialize. However, the defaults 594can be changed as follows: 595 596=over 4 597 598=item utf8 data 599 600Perl 5.6 added support for Unicode characters with code points > 255, 601and Perl 5.8 has full support for Unicode characters in hash keys. 602Perl internally encodes strings with these characters using utf8, and 603Storable serializes them as utf8. By default, if an older version of 604Perl encounters a utf8 value it cannot represent, it will C<croak()>. 605To change this behaviour so that Storable deserializes utf8 encoded 606values as the string of bytes (effectively dropping the I<is_utf8> flag) 607set C<$Storable::drop_utf8> to some C<TRUE> value. This is a form of 608data loss, because with C<$drop_utf8> true, it becomes impossible to tell 609whether the original data was the Unicode string, or a series of bytes 610that happen to be valid utf8. 611 612=item restricted hashes 613 614Perl 5.8 adds support for restricted hashes, which have keys 615restricted to a given set, and can have values locked to be read only. 616By default, when Storable encounters a restricted hash on a perl 617that doesn't support them, it will deserialize it as a normal hash, 618silently discarding any placeholder keys and leaving the keys and 619all values unlocked. To make Storable C<croak()> instead, set 620C<$Storable::downgrade_restricted> to a C<FALSE> value. To restore 621the default set it back to some C<TRUE> value. 622 623=item files from future versions of Storable 624 625Earlier versions of Storable would immediately croak if they encountered 626a file with a higher internal version number than the reading Storable 627knew about. Internal version numbers are increased each time new data 628types (such as restricted hashes) are added to the vocabulary of the file 629format. This meant that a newer Storable module had no way of writing a 630file readable by an older Storable, even if the writer didn't store newer 631data types. 632 633This version of Storable will defer croaking until it encounters a data 634type in the file that it does not recognize. This means that it will 635continue to read files generated by newer Storable modules which are careful 636in what they write out, making it easier to upgrade Storable modules in a 637mixed environment. 638 639The old behaviour of immediate croaking can be re-instated by setting 640C<$Storable::accept_future_minor> to some C<FALSE> value. 641 642=back 643 644All these variables have no effect on a newer Perl which supports the 645relevant feature. 646 647=head1 ERROR REPORTING 648 649Storable uses the "exception" paradigm, in that it does not try to workaround 650failures: if something bad happens, an exception is generated from the 651caller's perspective (see L<Carp> and C<croak()>). Use eval {} to trap 652those exceptions. 653 654When Storable croaks, it tries to report the error via the C<logcroak()> 655routine from the C<Log::Agent> package, if it is available. 656 657Normal errors are reported by having store() or retrieve() return C<undef>. 658Such errors are usually I/O errors (or truncated stream errors at retrieval). 659 660=head1 WIZARDS ONLY 661 662=head2 Hooks 663 664Any class may define hooks that will be called during the serialization 665and deserialization process on objects that are instances of that class. 666Those hooks can redefine the way serialization is performed (and therefore, 667how the symmetrical deserialization should be conducted). 668 669Since we said earlier: 670 671 dclone(.) = thaw(freeze(.)) 672 673everything we say about hooks should also hold for deep cloning. However, 674hooks get to know whether the operation is a mere serialization, or a cloning. 675 676Therefore, when serializing hooks are involved, 677 678 dclone(.) <> thaw(freeze(.)) 679 680Well, you could keep them in sync, but there's no guarantee it will always 681hold on classes somebody else wrote. Besides, there is little to gain in 682doing so: a serializing hook could keep only one attribute of an object, 683which is probably not what should happen during a deep cloning of that 684same object. 685 686Here is the hooking interface: 687 688=over 4 689 690=item C<STORABLE_freeze> I<obj>, I<cloning> 691 692The serializing hook, called on the object during serialization. It can be 693inherited, or defined in the class itself, like any other method. 694 695Arguments: I<obj> is the object to serialize, I<cloning> is a flag indicating 696whether we're in a dclone() or a regular serialization via store() or freeze(). 697 698Returned value: A LIST C<($serialized, $ref1, $ref2, ...)> where $serialized 699is the serialized form to be used, and the optional $ref1, $ref2, etc... are 700extra references that you wish to let the Storable engine serialize. 701 702At deserialization time, you will be given back the same LIST, but all the 703extra references will be pointing into the deserialized structure. 704 705The B<first time> the hook is hit in a serialization flow, you may have it 706return an empty list. That will signal the Storable engine to further 707discard that hook for this class and to therefore revert to the default 708serialization of the underlying Perl data. The hook will again be normally 709processed in the next serialization. 710 711Unless you know better, serializing hook should always say: 712 713 sub STORABLE_freeze { 714 my ($self, $cloning) = @_; 715 return if $cloning; # Regular default serialization 716 .... 717 } 718 719in order to keep reasonable dclone() semantics. 720 721=item C<STORABLE_thaw> I<obj>, I<cloning>, I<serialized>, ... 722 723The deserializing hook called on the object during deserialization. 724But wait: if we're deserializing, there's no object yet... right? 725 726Wrong: the Storable engine creates an empty one for you. If you know Eiffel, 727you can view C<STORABLE_thaw> as an alternate creation routine. 728 729This means the hook can be inherited like any other method, and that 730I<obj> is your blessed reference for this particular instance. 731 732The other arguments should look familiar if you know C<STORABLE_freeze>: 733I<cloning> is true when we're part of a deep clone operation, I<serialized> 734is the serialized string you returned to the engine in C<STORABLE_freeze>, 735and there may be an optional list of references, in the same order you gave 736them at serialization time, pointing to the deserialized objects (which 737have been processed courtesy of the Storable engine). 738 739When the Storable engine does not find any C<STORABLE_thaw> hook routine, 740it tries to load the class by requiring the package dynamically (using 741the blessed package name), and then re-attempts the lookup. If at that 742time the hook cannot be located, the engine croaks. Note that this mechanism 743will fail if you define several classes in the same file, but L<perlmod> 744warned you. 745 746It is up to you to use this information to populate I<obj> the way you want. 747 748Returned value: none. 749 750=item C<STORABLE_attach> I<class>, I<cloning>, I<serialized> 751 752While C<STORABLE_freeze> and C<STORABLE_thaw> are useful for classes where 753each instance is independent, this mechanism has difficulty (or is 754incompatible) with objects that exist as common process-level or 755system-level resources, such as singleton objects, database pools, caches 756or memoized objects. 757 758The alternative C<STORABLE_attach> method provides a solution for these 759shared objects. Instead of C<STORABLE_freeze> --E<gt> C<STORABLE_thaw>, 760you implement C<STORABLE_freeze> --E<gt> C<STORABLE_attach> instead. 761 762Arguments: I<class> is the class we are attaching to, I<cloning> is a flag 763indicating whether we're in a dclone() or a regular de-serialization via 764thaw(), and I<serialized> is the stored string for the resource object. 765 766Because these resource objects are considered to be owned by the entire 767process/system, and not the "property" of whatever is being serialized, 768no references underneath the object should be included in the serialized 769string. Thus, in any class that implements C<STORABLE_attach>, the 770C<STORABLE_freeze> method cannot return any references, and C<Storable> 771will throw an error if C<STORABLE_freeze> tries to return references. 772 773All information required to "attach" back to the shared resource object 774B<must> be contained B<only> in the C<STORABLE_freeze> return string. 775Otherwise, C<STORABLE_freeze> behaves as normal for C<STORABLE_attach> 776classes. 777 778Because C<STORABLE_attach> is passed the class (rather than an object), 779it also returns the object directly, rather than modifying the passed 780object. 781 782Returned value: object of type C<class> 783 784=back 785 786=head2 Predicates 787 788Predicates are not exportable. They must be called by explicitly prefixing 789them with the Storable package name. 790 791=over 4 792 793=item C<Storable::last_op_in_netorder> 794 795The C<Storable::last_op_in_netorder()> predicate will tell you whether 796network order was used in the last store or retrieve operation. If you 797don't know how to use this, just forget about it. 798 799=item C<Storable::is_storing> 800 801Returns true if within a store operation (via STORABLE_freeze hook). 802 803=item C<Storable::is_retrieving> 804 805Returns true if within a retrieve operation (via STORABLE_thaw hook). 806 807=back 808 809=head2 Recursion 810 811With hooks comes the ability to recurse back to the Storable engine. 812Indeed, hooks are regular Perl code, and Storable is convenient when 813it comes to serializing and deserializing things, so why not use it 814to handle the serialization string? 815 816There are a few things you need to know, however: 817 818=over 4 819 820=item * 821 822You 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 824the hook. 825 826=item * 827 828Shared references among objects will not stay shared: if we're serializing 829the list of object [A, C] where both object A and C refer to the SAME object 830B, and if there is a serializing hook in A that says freeze(B), then when 831deserializing, we'll get [A', C'] where A' refers to B', but C' refers to D, 832a deep clone of B'. The topology was not preserved. 833 834=back 835 836That's why C<STORABLE_freeze> lets you provide a list of references 837to serialize. The engine guarantees that those will be serialized in the 838same context as the other objects, and therefore that shared objects will 839stay shared. 840 841In the above [A, C] example, the C<STORABLE_freeze> hook could return: 842 843 ("something", $self->{B}) 844 845and the B part would be serialized by the engine. In C<STORABLE_thaw>, you 846would get back the reference to the B' object, deserialized for you. 847 848Therefore, recursion should normally be avoided, but is nonetheless supported. 849 850=head2 Deep Cloning 851 852There is a Clone module available on CPAN which implements deep cloning 853natively, i.e. without freezing to memory and thawing the result. It is 854aimed to replace Storable's dclone() some day. However, it does not currently 855support Storable hooks to redefine the way deep cloning is performed. 856 857=head1 Storable magic 858 859Yes, there's a lot of that :-) But more precisely, in UNIX systems 860there's a utility called C<file>, which recognizes data files based on 861their contents (usually their first few bytes). For this to work, 862a certain file called F<magic> needs to taught about the I<signature> 863of the data. Where that configuration file lives depends on the UNIX 864flavour; often it's something like F</usr/share/misc/magic> or 865F</etc/magic>. Your system administrator needs to do the updating of 866the F<magic> file. The necessary signature information is output to 867STDOUT by invoking Storable::show_file_magic(). Note that the GNU 868implementation of the C<file> utility, version 3.38 or later, 869is expected to contain support for recognising Storable files 870out-of-the-box, in addition to other kinds of Perl files. 871 872You can also use the following functions to extract the file header 873information from Storable images: 874 875=over 876 877=item $info = Storable::file_magic( $filename ) 878 879If the given file is a Storable image return a hash describing it. If 880the file is readable, but not a Storable image return C<undef>. If 881the file does not exist or is unreadable then croak. 882 883The hash returned has the following elements: 884 885=over 886 887=item C<version> 888 889This returns the file format version. It is a string like "2.7". 890 891Note that this version number is not the same as the version number of 892the Storable module itself. For instance Storable v0.7 create files 893in format v2.0 and Storable v2.15 create files in format v2.7. The 894file format version number only increment when additional features 895that would confuse older versions of the module are added. 896 897Files older than v2.0 will have the one of the version numbers "-1", 898"0" or "1". No minor number was used at that time. 899 900=item C<version_nv> 901 902This returns the file format version as number. It is a string like 903"2.007". This value is suitable for numeric comparisons. 904 905The constant function C<Storable::BIN_VERSION_NV> returns a comparable 906number that represent the highest file version number that this 907version of Storable fully support (but see discussion of 908C<$Storable::accept_future_minor> above). The constant 909C<Storable::BIN_WRITE_VERSION_NV> function returns what file version 910is written and might be less than C<Storable::BIN_VERSION_NV> in some 911configuations. 912 913=item C<major>, C<minor> 914 915This also returns the file format version. If the version is "2.7" 916then major would be 2 and minor would be 7. The minor element is 917missing for when major is less than 2. 918 919=item C<hdrsize> 920 921The is the number of bytes that the Storable header occupies. 922 923=item C<netorder> 924 925This is TRUE if the image store data in network order. This means 926that it was created with nstore() or similar. 927 928=item C<byteorder> 929 930This is only present when C<netorder> is FALSE. It is the 931$Config{byteorder} string of the perl that created this image. It is 932a string like "1234" (32 bit little endian) or "87654321" (64 bit big 933endian). This must match the current perl for the image to be 934readable by Storable. 935 936=item C<intsize>, C<longsize>, C<ptrsize>, C<nvsize> 937 938These are only present when C<netorder> is FALSE. These are the sizes of 939various C datatypes of the perl that created this image. These must 940match the current perl for the image to be readable by Storable. 941 942The C<nvsize> element is only present for file format v2.2 and 943higher. 944 945=item C<file> 946 947The 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 955The $buffer should be a Storable image or the first few bytes of it. 956If $buffer starts with a Storable header, then a hash describing the 957image is returned, otherwise C<undef> is returned. 958 959The hash has the same structure as the one returned by 960Storable::file_magic(). The C<file> element is true if the image is a 961file image. 962 963If the $must_be_file argument is provided and is TRUE, then return 964C<undef> unless the image looks like it belongs to a file dump. 965 966The maximum size of a Storable header is currently 21 bytes. If the 967provided $buffer is only the first part of a Storable image it should 968at least be this long to ensure that read_magic() will recognize it as 969such. 970 971=back 972 973=head1 EXAMPLES 974 975Here 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 993which prints (on my machine): 994 995 Blue is still 0.100000 996 Serialization of %color is 102 bytes long. 997 998Serialization of CODE references and deserialization in a safe 999compartment: 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( $code->(), 42 ); 1019 1020=head1 WARNING 1021 1022If you're using references as keys within your hash tables, you're bound 1023to be disappointed when retrieving your data. Indeed, Perl stringifies 1024references used as hash table keys. If you later wish to access the 1025items via another reference stringification (i.e. using the same 1026reference that was used for the key originally to record the value into 1027the hash table), it will work because both references stringify to the 1028same string. 1029 1030It won't work across a sequence of C<store> and C<retrieve> operations, 1031however, because the addresses in the retrieved objects, which are 1032part of the stringified references, will probably differ from the 1033original addresses. The topology of your structure is preserved, 1034but not hidden semantics like those. 1035 1036On platforms where it matters, be sure to call C<binmode()> on the 1037descriptors that you pass to Storable functions. 1038 1039Storing data canonically that contains large hashes can be 1040significantly slower than storing the same data normally, as 1041temporary arrays to hold the keys for each hash have to be allocated, 1042populated, sorted and freed. Some tests have shown a halving of the 1043speed of storing -- the exact penalty will depend on the complexity of 1044your data. There is no slowdown on retrieval. 1045 1046=head1 BUGS 1047 1048You can't store GLOB, FORMLINE, REGEXP, etc.... If you can define semantics 1049for those operations, feel free to enhance Storable so that it can 1050deal with them. 1051 1052The store functions will C<croak> if they run into such references 1053unless you set C<$Storable::forgive_me> to some C<TRUE> value. In that 1054case, the fatal message is turned in a warning and some 1055meaningless string is stored instead. 1056 1057Setting C<$Storable::canonical> may not yield frozen strings that 1058compare equal due to possible stringification of numbers. When the 1059string version of a scalar exists, it is the form stored; therefore, 1060if you happen to use your numbers as strings between two freezing 1061operations on the same data structures, you will get different 1062results. 1063 1064When storing doubles in network order, their value is stored as text. 1065However, you should also not expect non-numeric floating-point values 1066such as infinity and "not a number" to pass successfully through a 1067nstore()/retrieve() pair. 1068 1069As Storable neither knows nor cares about character sets (although it 1070does know that characters may be more than eight bits wide), any difference 1071in the interpretation of character codes between a host and a target 1072system is your problem. In particular, if host and target use different 1073code points to represent the characters used in the text representation 1074of floating-point numbers, you will not be able be able to exchange 1075floating-point data, even with nstore(). 1076 1077C<Storable::drop_utf8> is a blunt tool. There is no facility either to 1078return B<all> strings as utf8 sequences, or to attempt to convert utf8 1079data back to 8 bit and C<croak()> if the conversion fails. 1080 1081Prior to Storable 2.01, no distinction was made between signed and 1082unsigned integers on storing. By default Storable prefers to store a 1083scalars string representation (if it has one) so this would only cause 1084problems when storing large unsigned integers that had never been converted 1085to string or floating point. In other words values that had been generated 1086by integer operations such as logic ops and then not used in any string or 1087arithmetic context before storing. 1088 1089=head2 64 bit data in perl 5.6.0 and 5.6.1 1090 1091This section only applies to you if you have existing data written out 1092by Storable 2.02 or earlier on perl 5.6.0 or 5.6.1 on Unix or Linux which 1093has been configured with 64 bit integer support (not the default) 1094If you got a precompiled perl, rather than running Configure to build 1095your own perl from source, then it almost certainly does not affect you, 1096and you can stop reading now (unless you're curious). If you're using perl 1097on Windows it does not affect you. 1098 1099Storable writes a file header which contains the sizes of various C 1100language types for the C compiler that built Storable (when not writing in 1101network order), and will refuse to load files written by a Storable not 1102on the same (or compatible) architecture. This check and a check on 1103machine byteorder is needed because the size of various fields in the file 1104are given by the sizes of the C language types, and so files written on 1105different architectures are incompatible. This is done for increased speed. 1106(When writing in network order, all fields are written out as standard 1107lengths, which allows full interworking, but takes longer to read and write) 1108 1109Perl 5.6.x introduced the ability to optional configure the perl interpreter 1110to use C's C<long long> type to allow scalars to store 64 bit integers on 32 1111bit systems. However, due to the way the Perl configuration system 1112generated the C configuration files on non-Windows platforms, and the way 1113Storable generates its header, nothing in the Storable file header reflected 1114whether the perl writing was using 32 or 64 bit integers, despite the fact 1115that Storable was storing some data differently in the file. Hence Storable 1116running on perl with 64 bit integers will read the header from a file 1117written by a 32 bit perl, not realise that the data is actually in a subtly 1118incompatible format, and then go horribly wrong (possibly crashing) if it 1119encountered a stored integer. This is a design failure. 1120 1121Storable has now been changed to write out and read in a file header with 1122information about the size of integers. It's impossible to detect whether 1123an old file being read in was written with 32 or 64 bit integers (they have 1124the same header) so it's impossible to automatically switch to a correct 1125backwards compatibility mode. Hence this Storable defaults to the new, 1126correct behaviour. 1127 1128What this means is that if you have data written by Storable 1.x running 1129on perl 5.6.0 or 5.6.1 configured with 64 bit integers on Unix or Linux 1130then by default this Storable will refuse to read it, giving the error 1131I<Byte order is not compatible>. If you have such data then you you 1132should set C<$Storable::interwork_56_64bit> to a true value to make this 1133Storable read and write files with the old header. You should also 1134migrate your data, or any older perl you are communicating with, to this 1135current version of Storable. 1136 1137If you don't have data written with specific configuration of perl described 1138above, then you do not and should not do anything. Don't set the flag - 1139not only will Storable on an identically configured perl refuse to load them, 1140but Storable a differently configured perl will load them believing them 1141to be correct for it, and then may well fail or crash part way through 1142reading them. 1143 1144=head1 CREDITS 1145 1146Thank 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 1162for their bug reports, suggestions and contributions. 1163 1164Benjamin Holzman contributed the tied variable support, Andrew Ford 1165contributed the canonical order for hashes, and Gisle Aas fixed 1166a few misunderstandings of mine regarding the perl internals, 1167and optimized the emission of "tags" in the output streams by 1168simply counting the objects instead of tagging them (leading to 1169a binary incompatibility for the Storable image starting at version 11700.6--older images are, of course, still properly understood). 1171Murray Nesbitt made Storable thread-safe. Marc Lehmann added overloading 1172and references to tied items support. 1173 1174=head1 AUTHOR 1175 1176Storable was written by Raphael Manfredi F<E<lt>Raphael_Manfredi@pobox.comE<gt>> 1177Maintenance is now done by the perl5-porters F<E<lt>perl5-porters@perl.orgE<gt>> 1178 1179Please e-mail us with problems, bug fixes, comments and complaints, 1180although if you have compliments you should send them to Raphael. 1181Please don't e-mail Raphael with problems, as he no longer works on 1182Storable, and your message will be delayed while he forwards it to us. 1183 1184=head1 SEE ALSO 1185 1186L<Clone>. 1187 1188=cut 1189