CBOR-XS/XS.pm

=head1 NAME

CBOR::XS - Concise Binary Object Representation (CBOR, RFC7049)

=encoding utf-8

=head1 SYNOPSIS

 use CBOR::XS;

 $binary_cbor_data = encode_cbor $perl_value;
 $perl_value       = decode_cbor $binary_cbor_data;

 # OO-interface

 $coder = CBOR::XS->new;
 #TODO

=head1 DESCRIPTION

WARNING! THIS IS A PRE-ALPHA RELEASE! IT WILL CRASH, CORRUPT YOUR DATA AND
EAT YOUR CHILDREN!

This module converts Perl data structures to CBOR and vice versa. Its
primary goal is to be I<correct> and its secondary goal is to be
I<fast>. To reach the latter goal it was written in C.

See MAPPING, below, on how CBOR::XS maps perl values to CBOR values and
vice versa.

=cut

package CBOR::XS;

use common::sense;

our $VERSION = 0.02;
our @ISA = qw(Exporter);

our @EXPORT = qw(encode_cbor decode_cbor);

use Exporter;
use XSLoader;

our $MAGIC = "\xd9\xd9\xf7";

=head1 FUNCTIONAL INTERFACE

The following convenience methods are provided by this module. They are
exported by default:

=over 4

=item $cbor_data = encode_cbor $perl_scalar

Converts the given Perl data structure to CBOR representation. Croaks on
error.

=item $perl_scalar = decode_cbor $cbor_data

The opposite of C<encode_cbor>: expects a valid CBOR string to parse,
returning the resulting perl scalar. Croaks on error.

=back


=head1 OBJECT-ORIENTED INTERFACE

The object oriented interface lets you configure your own encoding or
decoding style, within the limits of supported formats.

=over 4

=item $cbor = new CBOR::XS

Creates a new CBOR::XS object that can be used to de/encode CBOR
strings. All boolean flags described below are by default I<disabled>.

The mutators for flags all return the CBOR object again and thus calls can
be chained:

#TODO
   my $cbor = CBOR::XS->new->encode ({a => [1,2]});

=item $cbor = $cbor->max_depth ([$maximum_nesting_depth])

=item $max_depth = $cbor->get_max_depth

Sets the maximum nesting level (default C<512>) accepted while encoding
or decoding. If a higher nesting level is detected in CBOR data or a Perl
data structure, then the encoder and decoder will stop and croak at that
point.

Nesting level is defined by number of hash- or arrayrefs that the encoder
needs to traverse to reach a given point or the number of C<{> or C<[>
characters without their matching closing parenthesis crossed to reach a
given character in a string.

Setting the maximum depth to one disallows any nesting, so that ensures
that the object is only a single hash/object or array.

If no argument is given, the highest possible setting will be used, which
is rarely useful.

Note that nesting is implemented by recursion in C. The default value has
been chosen to be as large as typical operating systems allow without
crashing.

See SECURITY CONSIDERATIONS, below, for more info on why this is useful.

=item $cbor = $cbor->max_size ([$maximum_string_size])

=item $max_size = $cbor->get_max_size

Set the maximum length a CBOR string may have (in bytes) where decoding
is being attempted. The default is C<0>, meaning no limit. When C<decode>
is called on a string that is longer then this many bytes, it will not
attempt to decode the string but throw an exception. This setting has no
effect on C<encode> (yet).

If no argument is given, the limit check will be deactivated (same as when
C<0> is specified).

See SECURITY CONSIDERATIONS, below, for more info on why this is useful.

=item $cbor_data = $cbor->encode ($perl_scalar)

Converts the given Perl data structure (a scalar value) to its CBOR
representation.

=item $perl_scalar = $cbor->decode ($cbor_data)

The opposite of C<encode>: expects CBOR data and tries to parse it,
returning the resulting simple scalar or reference. Croaks on error.

=item ($perl_scalar, $octets) = $cbor->decode_prefix ($cbor_data)

This works like the C<decode> method, but instead of raising an exception
when there is trailing garbage after the CBOR string, it will silently
stop parsing there and return the number of characters consumed so far.

This is useful if your CBOR texts are not delimited by an outer protocol
and you need to know where the first CBOR string ends amd the next one
starts.

   CBOR::XS->new->decode_prefix ("......")
   => ("...", 3)

=back


=head1 MAPPING

This section describes how CBOR::XS maps Perl values to CBOR values and
vice versa. These mappings are designed to "do the right thing" in most
circumstances automatically, preserving round-tripping characteristics
(what you put in comes out as something equivalent).

For the more enlightened: note that in the following descriptions,
lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl>
refers to the abstract Perl language itself.


=head2 CBOR -> PERL

=over 4

=item True, False

These CBOR values become C<CBOR::XS::true> and C<CBOR::XS::false>,
respectively. They are overloaded to act almost exactly like the numbers
C<1> and C<0>. You can check whether a scalar is a CBOR boolean by using
the C<CBOR::XS::is_bool> function.

=item Null, Undefined

CBOR Null and Undefined values becomes C<undef> in Perl (in the future,
Undefined may raise an exception).

=back


=head2 PERL -> CBOR

The mapping from Perl to CBOR is slightly more difficult, as Perl is a
truly typeless language, so we can only guess which CBOR type is meant by
a Perl value.

=over 4

=item hash references

Perl hash references become CBOR maps. As there is no inherent ordering
in hash keys (or CBOR maps), they will usually be encoded in a
pseudo-random order.

=item array references

Perl array references become CBOR arrays.

=item other references

Other unblessed references are generally not allowed and will cause an
exception to be thrown, except for references to the integers C<0> and
C<1>, which get turned into C<False> and C<True> in CBOR.

=item CBOR::XS::true, CBOR::XS::false

These special values become CBOR True and CBOR False values,
respectively. You can also use C<\1> and C<\0> directly if you want.

=item blessed objects

Blessed objects are not directly representable in CBOR. TODO
See the
C<allow_blessed> and C<convert_blessed> methods on various options on
how to deal with this: basically, you can choose between throwing an
exception, encoding the reference as if it weren't blessed, or provide
your own serialiser method.

=item simple scalars

TODO
Simple Perl scalars (any scalar that is not a reference) are the most
difficult objects to encode: CBOR::XS will encode undefined scalars as
CBOR C<Null> values, scalars that have last been used in a string context
before encoding as CBOR strings, and anything else as number value:

   # dump as number
   encode_cbor [2]                      # yields [2]
   encode_cbor [-3.0e17]                # yields [-3e+17]
   my $value = 5; encode_cbor [$value]  # yields [5]

   # used as string, so dump as string
   print $value;
   encode_cbor [$value]                 # yields ["5"]

   # undef becomes null
   encode_cbor [undef]                  # yields [null]

You can force the type to be a CBOR string by stringifying it:

   my $x = 3.1; # some variable containing a number
   "$x";        # stringified
   $x .= "";    # another, more awkward way to stringify
   print $x;    # perl does it for you, too, quite often

You can force the type to be a CBOR number by numifying it:

   my $x = "3"; # some variable containing a string
   $x += 0;     # numify it, ensuring it will be dumped as a number
   $x *= 1;     # same thing, the choice is yours.

You can not currently force the type in other, less obscure, ways. Tell me
if you need this capability (but don't forget to explain why it's needed
:).

Note that numerical precision has the same meaning as under Perl (so
binary to decimal conversion follows the same rules as in Perl, which
can differ to other languages). Also, your perl interpreter might expose
extensions to the floating point numbers of your platform, such as
infinities or NaN's - these cannot be represented in CBOR, and it is an
error to pass those in.

=back


=head2 MAGIC HEADER

There is no way to distinguish CBOR from other formats
programmatically. To make it easier to distinguish CBOR from other
formats, the CBOR specification has a special "magic string" that can be
prepended to any CBOR string without changing it's meaning.

This string is available as C<$CBOR::XS::MAGIC>. This module does not
prepend this string tot he CBOR data it generates, but it will ignroe it
if present, so users can prepend this string as a "file type" indicator as
required.


=head2 CBOR and JSON

TODO


=head1 SECURITY CONSIDERATIONS

When you are using CBOR in a protocol, talking to untrusted potentially
hostile creatures requires relatively few measures.

First of all, your CBOR decoder should be secure, that is, should not have
any buffer overflows. Obviously, this module should ensure that and I am
trying hard on making that true, but you never know.

Second, you need to avoid resource-starving attacks. That means you should
limit the size of CBOR data you accept, or make sure then when your
resources run out, that's just fine (e.g. by using a separate process that
can crash safely). The size of a CBOR string in octets is usually a good
indication of the size of the resources required to decode it into a Perl
structure. While CBOR::XS can check the size of the CBOR text, it might be
too late when you already have it in memory, so you might want to check
the size before you accept the string.

Third, CBOR::XS recurses using the C stack when decoding objects and
arrays. The C stack is a limited resource: for instance, on my amd64
machine with 8MB of stack size I can decode around 180k nested arrays but
only 14k nested CBOR objects (due to perl itself recursing deeply on croak
to free the temporary). If that is exceeded, the program crashes. To be
conservative, the default nesting limit is set to 512. If your process
has a smaller stack, you should adjust this setting accordingly with the
C<max_depth> method.

Something else could bomb you, too, that I forgot to think of. In that
case, you get to keep the pieces. I am always open for hints, though...

Also keep in mind that CBOR::XS might leak contents of your Perl data
structures in its error messages, so when you serialise sensitive
information you might want to make sure that exceptions thrown by CBOR::XS
will not end up in front of untrusted eyes.

=head1 CBOR IMPLEMENTATION NOTES

This section contains some random implementation notes. They do not
describe guaranteed behaviour, but merely behaviour as-is implemented
right now.

64 bit integers are only properly decoded when Perl was built with 64 bit
support.

Strings and arrays are encoded with a definite length. Hashes as well,
unless they are tied (or otherwise magical).

Only the double data type is supported for NV data types - when Perl uses
long double to represent floating point values, they might not be encoded
properly. Half precision types are accepted, but not encoded.

Strict mode and canonical mode are not implemented.


=head1 THREADS

This module is I<not> guaranteed to be thread safe and there are no
plans to change this until Perl gets thread support (as opposed to the
horribly slow so-called "threads" which are simply slow and bloated
process simulations - use fork, it's I<much> faster, cheaper, better).

(It might actually work, but you have been warned).


=head1 BUGS

While the goal of this module is to be correct, that unfortunately does
not mean it's bug-free, only that I think its design is bug-free. If you
keep reporting bugs they will be fixed swiftly, though.

Please refrain from using rt.cpan.org or any other bug reporting
service. I put the contact address into my modules for a reason.

=cut

our $true  = do { bless \(my $dummy = 1), "CBOR::XS::Boolean" };
our $false = do { bless \(my $dummy = 0), "CBOR::XS::Boolean" };

sub true()  { $true  }
sub false() { $false }

sub is_bool($) {
   UNIVERSAL::isa $_[0], "CBOR::XS::Boolean"
#      or UNIVERSAL::isa $_[0], "CBOR::Literal"
}

XSLoader::load "CBOR::XS", $VERSION;

package CBOR::XS::Boolean;

use overload
   "0+"     => sub { ${$_[0]} },
   "++"     => sub { $_[0] = ${$_[0]} + 1 },
   "--"     => sub { $_[0] = ${$_[0]} - 1 },
   fallback => 1;

1;

=head1 SEE ALSO

The L<JSON> and L<JSON::XS> modules that do similar, but human-readable,
serialisation.

=head1 AUTHOR

 Marc Lehmann <schmorp@schmorp.de>
 http://home.schmorp.de/

=cut

Revision:	1.3
Committed:	Sat Oct 26 11:08:34 2013 UTC (10 years, 6 months ago) by root
Branch:	MAIN
CVS Tags:	rel-0_02
Changes since 1.2:	+16 -1 lines
Log Message:	0.02
#	Content
1	=head1 NAME
2
3	CBOR::XS - Concise Binary Object Representation (CBOR, RFC7049)
4
5	=encoding utf-8
6
7	=head1 SYNOPSIS
8
9	use CBOR::XS;
10
11	$binary_cbor_data = encode_cbor $perl_value;
12	$perl_value = decode_cbor $binary_cbor_data;
13
14	# OO-interface
15
16	$coder = CBOR::XS->new;
17	#TODO
18
19	=head1 DESCRIPTION
20
21	WARNING! THIS IS A PRE-ALPHA RELEASE! IT WILL CRASH, CORRUPT YOUR DATA AND
22	EAT YOUR CHILDREN!
23
24	This module converts Perl data structures to CBOR and vice versa. Its
25	primary goal is to be I<correct> and its secondary goal is to be
26	I<fast>. To reach the latter goal it was written in C.
27
28	See MAPPING, below, on how CBOR::XS maps perl values to CBOR values and
29	vice versa.
30
31	=cut
32
33	package CBOR::XS;
34
35	use common::sense;
36
37	our $VERSION = 0.02;
38	our @ISA = qw(Exporter);
39
40	our @EXPORT = qw(encode_cbor decode_cbor);
41
42	use Exporter;
43	use XSLoader;
44
45	our $MAGIC = "\xd9\xd9\xf7";
46
47	=head1 FUNCTIONAL INTERFACE
48
49	The following convenience methods are provided by this module. They are
50	exported by default:
51
52	=over 4
53
54	=item $cbor_data = encode_cbor $perl_scalar
55
56	Converts the given Perl data structure to CBOR representation. Croaks on
57	error.
58
59	=item $perl_scalar = decode_cbor $cbor_data
60
61	The opposite of C<encode_cbor>: expects a valid CBOR string to parse,
62	returning the resulting perl scalar. Croaks on error.
63
64	=back
65
66
67	=head1 OBJECT-ORIENTED INTERFACE
68
69	The object oriented interface lets you configure your own encoding or
70	decoding style, within the limits of supported formats.
71
72	=over 4
73
74	=item $cbor = new CBOR::XS
75
76	Creates a new CBOR::XS object that can be used to de/encode CBOR
77	strings. All boolean flags described below are by default I<disabled>.
78
79	The mutators for flags all return the CBOR object again and thus calls can
80	be chained:
81
82	#TODO
83	my $cbor = CBOR::XS->new->encode ({a => [1,2]});
84
85	=item $cbor = $cbor->max_depth ([$maximum_nesting_depth])
86
87	=item $max_depth = $cbor->get_max_depth
88
89	Sets the maximum nesting level (default C<512>) accepted while encoding
90	or decoding. If a higher nesting level is detected in CBOR data or a Perl
91	data structure, then the encoder and decoder will stop and croak at that
92	point.
93
94	Nesting level is defined by number of hash- or arrayrefs that the encoder
95	needs to traverse to reach a given point or the number of C<{> or C<[>
96	characters without their matching closing parenthesis crossed to reach a
97	given character in a string.
98
99	Setting the maximum depth to one disallows any nesting, so that ensures
100	that the object is only a single hash/object or array.
101
102	If no argument is given, the highest possible setting will be used, which
103	is rarely useful.
104
105	Note that nesting is implemented by recursion in C. The default value has
106	been chosen to be as large as typical operating systems allow without
107	crashing.
108
109	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
110
111	=item $cbor = $cbor->max_size ([$maximum_string_size])
112
113	=item $max_size = $cbor->get_max_size
114
115	Set the maximum length a CBOR string may have (in bytes) where decoding
116	is being attempted. The default is C<0>, meaning no limit. When C<decode>
117	is called on a string that is longer then this many bytes, it will not
118	attempt to decode the string but throw an exception. This setting has no
119	effect on C<encode> (yet).
120
121	If no argument is given, the limit check will be deactivated (same as when
122	C<0> is specified).
123
124	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
125
126	=item $cbor_data = $cbor->encode ($perl_scalar)
127
128	Converts the given Perl data structure (a scalar value) to its CBOR
129	representation.
130
131	=item $perl_scalar = $cbor->decode ($cbor_data)
132
133	The opposite of C<encode>: expects CBOR data and tries to parse it,
134	returning the resulting simple scalar or reference. Croaks on error.
135
136	=item ($perl_scalar, $octets) = $cbor->decode_prefix ($cbor_data)
137
138	This works like the C<decode> method, but instead of raising an exception
139	when there is trailing garbage after the CBOR string, it will silently
140	stop parsing there and return the number of characters consumed so far.
141
142	This is useful if your CBOR texts are not delimited by an outer protocol
143	and you need to know where the first CBOR string ends amd the next one
144	starts.
145
146	CBOR::XS->new->decode_prefix ("......")
147	=> ("...", 3)
148
149	=back
150
151
152	=head1 MAPPING
153
154	This section describes how CBOR::XS maps Perl values to CBOR values and
155	vice versa. These mappings are designed to "do the right thing" in most
156	circumstances automatically, preserving round-tripping characteristics
157	(what you put in comes out as something equivalent).
158
159	For the more enlightened: note that in the following descriptions,
160	lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl>
161	refers to the abstract Perl language itself.
162
163
164	=head2 CBOR -> PERL
165
166	=over 4
167
168	=item True, False
169
170	These CBOR values become C<CBOR::XS::true> and C<CBOR::XS::false>,
171	respectively. They are overloaded to act almost exactly like the numbers
172	C<1> and C<0>. You can check whether a scalar is a CBOR boolean by using
173	the C<CBOR::XS::is_bool> function.
174
175	=item Null, Undefined
176
177	CBOR Null and Undefined values becomes C<undef> in Perl (in the future,
178	Undefined may raise an exception).
179
180	=back
181
182
183	=head2 PERL -> CBOR
184
185	The mapping from Perl to CBOR is slightly more difficult, as Perl is a
186	truly typeless language, so we can only guess which CBOR type is meant by
187	a Perl value.
188
189	=over 4
190
191	=item hash references
192
193	Perl hash references become CBOR maps. As there is no inherent ordering
194	in hash keys (or CBOR maps), they will usually be encoded in a
195	pseudo-random order.
196
197	=item array references
198
199	Perl array references become CBOR arrays.
200
201	=item other references
202
203	Other unblessed references are generally not allowed and will cause an
204	exception to be thrown, except for references to the integers C<0> and
205	C<1>, which get turned into C<False> and C<True> in CBOR.
206
207	=item CBOR::XS::true, CBOR::XS::false
208
209	These special values become CBOR True and CBOR False values,
210	respectively. You can also use C<\1> and C<\0> directly if you want.
211
212	=item blessed objects
213
214	Blessed objects are not directly representable in CBOR. TODO
215	See the
216	C<allow_blessed> and C<convert_blessed> methods on various options on
217	how to deal with this: basically, you can choose between throwing an
218	exception, encoding the reference as if it weren't blessed, or provide
219	your own serialiser method.
220
221	=item simple scalars
222
223	TODO
224	Simple Perl scalars (any scalar that is not a reference) are the most
225	difficult objects to encode: CBOR::XS will encode undefined scalars as
226	CBOR C<Null> values, scalars that have last been used in a string context
227	before encoding as CBOR strings, and anything else as number value:
228
229	# dump as number
230	encode_cbor [2] # yields [2]
231	encode_cbor [-3.0e17] # yields [-3e+17]
232	my $value = 5; encode_cbor [$value] # yields [5]
233
234	# used as string, so dump as string
235	print $value;
236	encode_cbor [$value] # yields ["5"]
237
238	# undef becomes null
239	encode_cbor [undef] # yields [null]
240
241	You can force the type to be a CBOR string by stringifying it:
242
243	my $x = 3.1; # some variable containing a number
244	"$x"; # stringified
245	$x .= ""; # another, more awkward way to stringify
246	print $x; # perl does it for you, too, quite often
247
248	You can force the type to be a CBOR number by numifying it:
249
250	my $x = "3"; # some variable containing a string
251	$x += 0; # numify it, ensuring it will be dumped as a number
252	$x *= 1; # same thing, the choice is yours.
253
254	You can not currently force the type in other, less obscure, ways. Tell me
255	if you need this capability (but don't forget to explain why it's needed
256	:).
257
258	Note that numerical precision has the same meaning as under Perl (so
259	binary to decimal conversion follows the same rules as in Perl, which
260	can differ to other languages). Also, your perl interpreter might expose
261	extensions to the floating point numbers of your platform, such as
262	infinities or NaN's - these cannot be represented in CBOR, and it is an
263	error to pass those in.
264
265	=back
266
267
268	=head2 MAGIC HEADER
269
270	There is no way to distinguish CBOR from other formats
271	programmatically. To make it easier to distinguish CBOR from other
272	formats, the CBOR specification has a special "magic string" that can be
273	prepended to any CBOR string without changing it's meaning.
274
275	This string is available as C<$CBOR::XS::MAGIC>. This module does not
276	prepend this string tot he CBOR data it generates, but it will ignroe it
277	if present, so users can prepend this string as a "file type" indicator as
278	required.
279
280
281	=head2 CBOR and JSON
282
283	TODO
284
285
286	=head1 SECURITY CONSIDERATIONS
287
288	When you are using CBOR in a protocol, talking to untrusted potentially
289	hostile creatures requires relatively few measures.
290
291	First of all, your CBOR decoder should be secure, that is, should not have
292	any buffer overflows. Obviously, this module should ensure that and I am
293	trying hard on making that true, but you never know.
294
295	Second, you need to avoid resource-starving attacks. That means you should
296	limit the size of CBOR data you accept, or make sure then when your
297	resources run out, that's just fine (e.g. by using a separate process that
298	can crash safely). The size of a CBOR string in octets is usually a good
299	indication of the size of the resources required to decode it into a Perl
300	structure. While CBOR::XS can check the size of the CBOR text, it might be
301	too late when you already have it in memory, so you might want to check
302	the size before you accept the string.
303
304	Third, CBOR::XS recurses using the C stack when decoding objects and
305	arrays. The C stack is a limited resource: for instance, on my amd64
306	machine with 8MB of stack size I can decode around 180k nested arrays but
307	only 14k nested CBOR objects (due to perl itself recursing deeply on croak
308	to free the temporary). If that is exceeded, the program crashes. To be
309	conservative, the default nesting limit is set to 512. If your process
310	has a smaller stack, you should adjust this setting accordingly with the
311	C<max_depth> method.
312
313	Something else could bomb you, too, that I forgot to think of. In that
314	case, you get to keep the pieces. I am always open for hints, though...
315
316	Also keep in mind that CBOR::XS might leak contents of your Perl data
317	structures in its error messages, so when you serialise sensitive
318	information you might want to make sure that exceptions thrown by CBOR::XS
319	will not end up in front of untrusted eyes.
320
321	=head1 CBOR IMPLEMENTATION NOTES
322
323	This section contains some random implementation notes. They do not
324	describe guaranteed behaviour, but merely behaviour as-is implemented
325	right now.
326
327	64 bit integers are only properly decoded when Perl was built with 64 bit
328	support.
329
330	Strings and arrays are encoded with a definite length. Hashes as well,
331	unless they are tied (or otherwise magical).
332
333	Only the double data type is supported for NV data types - when Perl uses
334	long double to represent floating point values, they might not be encoded
335	properly. Half precision types are accepted, but not encoded.
336
337	Strict mode and canonical mode are not implemented.
338
339
340	=head1 THREADS
341
342	This module is I<not> guaranteed to be thread safe and there are no
343	plans to change this until Perl gets thread support (as opposed to the
344	horribly slow so-called "threads" which are simply slow and bloated
345	process simulations - use fork, it's I<much> faster, cheaper, better).
346
347	(It might actually work, but you have been warned).
348
349
350	=head1 BUGS
351
352	While the goal of this module is to be correct, that unfortunately does
353	not mean it's bug-free, only that I think its design is bug-free. If you
354	keep reporting bugs they will be fixed swiftly, though.
355
356	Please refrain from using rt.cpan.org or any other bug reporting
357	service. I put the contact address into my modules for a reason.
358
359	=cut
360
361	our $true = do { bless \(my $dummy = 1), "CBOR::XS::Boolean" };
362	our $false = do { bless \(my $dummy = 0), "CBOR::XS::Boolean" };
363
364	sub true() { $true }
365	sub false() { $false }
366
367	sub is_bool($) {
368	UNIVERSAL::isa $_[0], "CBOR::XS::Boolean"
369	# or UNIVERSAL::isa $_[0], "CBOR::Literal"
370	}
371
372	XSLoader::load "CBOR::XS", $VERSION;
373
374	package CBOR::XS::Boolean;
375
376	use overload
377	"0+" => sub { ${$_[0]} },
378	"++" => sub { $_[0] = ${$_[0]} + 1 },
379	"--" => sub { $_[0] = ${$_[0]} - 1 },
380	fallback => 1;
381
382	1;
383
384	=head1 SEE ALSO
385
386	The L<JSON> and L<JSON::XS> modules that do similar, but human-readable,
387	serialisation.
388
389	=head1 AUTHOR
390
391	Marc Lehmann <schmorp@schmorp.de>
392	http://home.schmorp.de/
393
394	=cut
395