[ViewVC] Annotation of: cvs/CBOR-XS/README

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

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

DESCRIPTION
    WARNING! THIS IS A PRE-ALPHA RELEASE! IT WILL CRASH, CORRUPT YOUR DATA
    AND EAT YOUR CHILDREN! (Actually, apart from being untested and a bit
    feature-limited, it might already be useful).

    This module converts Perl data structures to the Concise Binary Object
    Representation (CBOR) and vice versa. CBOR is a fast binary
    serialisation format that aims to use a superset of the JSON data model,
    i.e. when you can represent something in JSON, you should be able to
    represent it in CBOR.

    This makes it a faster and more compact binary alternative to JSON.

    The primary goal of this module is to be *correct* and the secondary
    goal is to be *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.

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

    $cbor_data = encode_cbor $perl_scalar
        Converts the given Perl data structure to CBOR representation.
        Croaks on error.

    $perl_scalar = decode_cbor $cbor_data
        The opposite of "encode_cbor": expects a valid CBOR string to parse,
        returning the resulting perl scalar. Croaks on error.

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

    $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
        *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]});

    $cbor = $cbor->max_depth ([$maximum_nesting_depth])
    $max_depth = $cbor->get_max_depth
        Sets the maximum nesting level (default 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
        "{" or "[" 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.

    $cbor = $cbor->max_size ([$maximum_string_size])
    $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 0, meaning no limit.
        When "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 "encode" (yet).

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

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

    $cbor_data = $cbor->encode ($perl_scalar)
        Converts the given Perl data structure (a scalar value) to its CBOR
        representation.

    $perl_scalar = $cbor->decode ($cbor_data)
        The opposite of "encode": expects CBOR data and tries to parse it,
        returning the resulting simple scalar or reference. Croaks on error.

    ($perl_scalar, $octets) = $cbor->decode_prefix ($cbor_data)
        This works like the "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)

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 *perl* refers to the Perl interpreter, while uppercase *Perl*
    refers to the abstract Perl language itself.

  CBOR -> PERL
    integers
        CBOR integers become (numeric) perl scalars. On perls without 64 bit
        support, 64 bit integers will be truncated or otherwise corrupted.

    byte strings
        Byte strings will become octet strings in Perl (the byte values
        0..255 will simply become characters of the same value in Perl).

    UTF-8 strings
        UTF-8 strings in CBOR will be decoded, i.e. the UTF-8 octets will be
        decoded into proper Unicode code points. At the moment, the validity
        of the UTF-8 octets will not be validated - corrupt input will
        result in corrupted Perl strings.

    arrays, maps
        CBOR arrays and CBOR maps will be converted into references to a
        Perl array or hash, respectively. The keys of the map will be
        stringified during this process.

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

    null, undefined
        CBOR null and undefined values becomes "undef" in Perl (in the
        future, Undefined may raise an exception or something else).

    tags
        Tagged items consists of a numeric tag and another CBOR value. The
        tag 55799 is ignored (this tag implements the magic header).

        All other tags are currently converted into a CBOR::XS::Tagged
        object, which is simply a blessed array reference consistsing of the
        numeric tag value followed by the (decoded) BOR value.

    anything else
        Anything else (e.g. unsupported simple values) will raise a decoding
        error.

  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.

    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.

        Currently, tied hashes will use the indefinite-length format, while
        normal hashes will use the fixed-length format.

    array references
        Perl array references become fixed-length CBOR arrays.

    other references
        Other unblessed references are generally not allowed and will cause
        an exception to be thrown, except for references to the integers 0
        and 1, which get turned into false and true in CBOR.

    CBOR::XS::Tagged objects
        Objects of this type must be arrays consisting of a single "[tag,
        value]" pair. The (numerical) tag will be encoded as a CBOR tag, the
        value will be encoded as appropriate for the value.

    CBOR::XS::true, CBOR::XS::false
        These special values become CBOR true and CBOR false values,
        respectively. You can also use "\1" and "\0" directly if you want.

    blessed objects
        Other blessed objects currently need to have a "TO_CBOR" method. It
        will be called on every object that is being serialised, and must
        return something that can be encoded in CBOR.

    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 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 :).

        Perl values that seem to be integers generally use the shortest
        possible representation. Floating-point values will use either the
        IEEE single format if possible without loss of precision, otherwise
        the IEEE double format will be used. Perls that use formats other
        than IEEE double to represent numerical values are supported, but
        might suffer loss of precision.

  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 $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.

  CBOR and JSON
    CBOR is supposed to implement a superset of the JSON data model, and is,
    with some coercion, able to represent all JSON texts (something that
    other "binary JSON" formats such as BSON generally do not support).

    CBOR implements some extra hints and support for JSON interoperability,
    and the spec offers further guidance for conversion between CBOR and
    JSON. None of this is currently implemented in CBOR, and the guidelines
    in the spec do not result in correct round-tripping of data. If JSON
    interoperability is improved in the future, then the goal will be to
    ensure that decoded JSON data will round-trip encoding and decoding to
    CBOR intact.

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 "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.

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.

THREADS
    This module is *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 *much* faster, cheaper, better).

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

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.

SEE ALSO
    The JSON and JSON::XS modules that do similar, but human-readable,
    serialisation.

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

Revision:	1.4
Committed:	Sat Oct 26 23:02:55 2013 UTC (10 years, 6 months ago) by root
Branch:	MAIN
CVS Tags:	rel-0_03
Changes since 1.3:	+79 -24 lines
Log Message:	0.03
#	User	Rev	Content
1	root	1.2	NAME
2			CBOR::XS - Concise Binary Object Representation (CBOR, RFC7049)
3
4			SYNOPSIS
5			use CBOR::XS;
6
7			$binary_cbor_data = encode_cbor $perl_value;
8			$perl_value = decode_cbor $binary_cbor_data;
9
10			# OO-interface
11
12			$coder = CBOR::XS->new;
13			#TODO
14
15			DESCRIPTION
16			WARNING! THIS IS A PRE-ALPHA RELEASE! IT WILL CRASH, CORRUPT YOUR DATA
17	root	1.4	AND EAT YOUR CHILDREN! (Actually, apart from being untested and a bit
18			feature-limited, it might already be useful).
19	root	1.2
20	root	1.4	This module converts Perl data structures to the Concise Binary Object
21			Representation (CBOR) and vice versa. CBOR is a fast binary
22			serialisation format that aims to use a superset of the JSON data model,
23			i.e. when you can represent something in JSON, you should be able to
24			represent it in CBOR.
25
26			This makes it a faster and more compact binary alternative to JSON.
27
28			The primary goal of this module is to be correct and the secondary
29			goal is to be fast. To reach the latter goal it was written in C.
30	root	1.2
31			See MAPPING, below, on how CBOR::XS maps perl values to CBOR values and
32			vice versa.
33
34			FUNCTIONAL INTERFACE
35			The following convenience methods are provided by this module. They are
36			exported by default:
37
38			$cbor_data = encode_cbor $perl_scalar
39			Converts the given Perl data structure to CBOR representation.
40			Croaks on error.
41
42			$perl_scalar = decode_cbor $cbor_data
43			The opposite of "encode_cbor": expects a valid CBOR string to parse,
44			returning the resulting perl scalar. Croaks on error.
45
46			OBJECT-ORIENTED INTERFACE
47			The object oriented interface lets you configure your own encoding or
48			decoding style, within the limits of supported formats.
49
50			$cbor = new CBOR::XS
51			Creates a new CBOR::XS object that can be used to de/encode CBOR
52			strings. All boolean flags described below are by default
53			disabled.
54
55			The mutators for flags all return the CBOR object again and thus
56			calls can be chained:
57
58			#TODO my $cbor = CBOR::XS->new->encode ({a => [1,2]});
59
60			$cbor = $cbor->max_depth ([$maximum_nesting_depth])
61			$max_depth = $cbor->get_max_depth
62			Sets the maximum nesting level (default 512) accepted while encoding
63			or decoding. If a higher nesting level is detected in CBOR data or a
64			Perl data structure, then the encoder and decoder will stop and
65			croak at that point.
66
67			Nesting level is defined by number of hash- or arrayrefs that the
68			encoder needs to traverse to reach a given point or the number of
69			"{" or "[" characters without their matching closing parenthesis
70			crossed to reach a given character in a string.
71
72			Setting the maximum depth to one disallows any nesting, so that
73			ensures that the object is only a single hash/object or array.
74
75			If no argument is given, the highest possible setting will be used,
76			which is rarely useful.
77
78			Note that nesting is implemented by recursion in C. The default
79			value has been chosen to be as large as typical operating systems
80			allow without crashing.
81
82			See SECURITY CONSIDERATIONS, below, for more info on why this is
83			useful.
84
85			$cbor = $cbor->max_size ([$maximum_string_size])
86			$max_size = $cbor->get_max_size
87			Set the maximum length a CBOR string may have (in bytes) where
88			decoding is being attempted. The default is 0, meaning no limit.
89			When "decode" is called on a string that is longer then this many
90			bytes, it will not attempt to decode the string but throw an
91			exception. This setting has no effect on "encode" (yet).
92
93			If no argument is given, the limit check will be deactivated (same
94			as when 0 is specified).
95
96			See SECURITY CONSIDERATIONS, below, for more info on why this is
97			useful.
98
99			$cbor_data = $cbor->encode ($perl_scalar)
100			Converts the given Perl data structure (a scalar value) to its CBOR
101			representation.
102
103			$perl_scalar = $cbor->decode ($cbor_data)
104			The opposite of "encode": expects CBOR data and tries to parse it,
105			returning the resulting simple scalar or reference. Croaks on error.
106
107			($perl_scalar, $octets) = $cbor->decode_prefix ($cbor_data)
108			This works like the "decode" method, but instead of raising an
109			exception when there is trailing garbage after the CBOR string, it
110			will silently stop parsing there and return the number of characters
111			consumed so far.
112
113			This is useful if your CBOR texts are not delimited by an outer
114			protocol and you need to know where the first CBOR string ends amd
115			the next one starts.
116
117			CBOR::XS->new->decode_prefix ("......")
118			=> ("...", 3)
119
120			MAPPING
121			This section describes how CBOR::XS maps Perl values to CBOR values and
122			vice versa. These mappings are designed to "do the right thing" in most
123			circumstances automatically, preserving round-tripping characteristics
124			(what you put in comes out as something equivalent).
125
126			For the more enlightened: note that in the following descriptions,
127			lowercase perl refers to the Perl interpreter, while uppercase Perl
128			refers to the abstract Perl language itself.
129
130			CBOR -> PERL
131	root	1.4	integers
132			CBOR integers become (numeric) perl scalars. On perls without 64 bit
133			support, 64 bit integers will be truncated or otherwise corrupted.
134
135			byte strings
136			Byte strings will become octet strings in Perl (the byte values
137			0..255 will simply become characters of the same value in Perl).
138
139			UTF-8 strings
140			UTF-8 strings in CBOR will be decoded, i.e. the UTF-8 octets will be
141			decoded into proper Unicode code points. At the moment, the validity
142			of the UTF-8 octets will not be validated - corrupt input will
143			result in corrupted Perl strings.
144
145			arrays, maps
146			CBOR arrays and CBOR maps will be converted into references to a
147			Perl array or hash, respectively. The keys of the map will be
148			stringified during this process.
149
150			true, false
151	root	1.2	These CBOR values become "CBOR::XS::true" and "CBOR::XS::false",
152			respectively. They are overloaded to act almost exactly like the
153			numbers 1 and 0. You can check whether a scalar is a CBOR boolean by
154			using the "CBOR::XS::is_bool" function.
155
156	root	1.4	null, undefined
157			CBOR null and undefined values becomes "undef" in Perl (in the
158			future, Undefined may raise an exception or something else).
159
160			tags
161			Tagged items consists of a numeric tag and another CBOR value. The
162			tag 55799 is ignored (this tag implements the magic header).
163
164			All other tags are currently converted into a CBOR::XS::Tagged
165			object, which is simply a blessed array reference consistsing of the
166			numeric tag value followed by the (decoded) BOR value.
167
168			anything else
169			Anything else (e.g. unsupported simple values) will raise a decoding
170			error.
171	root	1.2
172			PERL -> CBOR
173			The mapping from Perl to CBOR is slightly more difficult, as Perl is a
174			truly typeless language, so we can only guess which CBOR type is meant
175			by a Perl value.
176
177			hash references
178			Perl hash references become CBOR maps. As there is no inherent
179			ordering in hash keys (or CBOR maps), they will usually be encoded
180			in a pseudo-random order.
181
182	root	1.4	Currently, tied hashes will use the indefinite-length format, while
183			normal hashes will use the fixed-length format.
184
185	root	1.2	array references
186	root	1.4	Perl array references become fixed-length CBOR arrays.
187	root	1.2
188			other references
189			Other unblessed references are generally not allowed and will cause
190			an exception to be thrown, except for references to the integers 0
191	root	1.4	and 1, which get turned into false and true in CBOR.
192
193			CBOR::XS::Tagged objects
194			Objects of this type must be arrays consisting of a single "[tag,
195			value]" pair. The (numerical) tag will be encoded as a CBOR tag, the
196			value will be encoded as appropriate for the value.
197	root	1.2
198			CBOR::XS::true, CBOR::XS::false
199	root	1.4	These special values become CBOR true and CBOR false values,
200	root	1.2	respectively. You can also use "\1" and "\0" directly if you want.
201
202			blessed objects
203	root	1.4	Other blessed objects currently need to have a "TO_CBOR" method. It
204			will be called on every object that is being serialised, and must
205			return something that can be encoded in CBOR.
206	root	1.2
207			simple scalars
208			TODO Simple Perl scalars (any scalar that is not a reference) are
209			the most difficult objects to encode: CBOR::XS will encode undefined
210	root	1.4	scalars as CBOR null values, scalars that have last been used in a
211	root	1.2	string context before encoding as CBOR strings, and anything else as
212			number value:
213
214			# dump as number
215			encode_cbor [2] # yields [2]
216			encode_cbor [-3.0e17] # yields [-3e+17]
217			my $value = 5; encode_cbor [$value] # yields [5]
218
219			# used as string, so dump as string
220			print $value;
221			encode_cbor [$value] # yields ["5"]
222
223			# undef becomes null
224			encode_cbor [undef] # yields [null]
225
226			You can force the type to be a CBOR string by stringifying it:
227
228			my $x = 3.1; # some variable containing a number
229			"$x"; # stringified
230			$x .= ""; # another, more awkward way to stringify
231			print $x; # perl does it for you, too, quite often
232
233			You can force the type to be a CBOR number by numifying it:
234
235			my $x = "3"; # some variable containing a string
236			$x += 0; # numify it, ensuring it will be dumped as a number
237			$x *= 1; # same thing, the choice is yours.
238
239			You can not currently force the type in other, less obscure, ways.
240			Tell me if you need this capability (but don't forget to explain why
241			it's needed :).
242
243	root	1.4	Perl values that seem to be integers generally use the shortest
244			possible representation. Floating-point values will use either the
245			IEEE single format if possible without loss of precision, otherwise
246			the IEEE double format will be used. Perls that use formats other
247			than IEEE double to represent numerical values are supported, but
248			might suffer loss of precision.
249	root	1.2
250	root	1.3	MAGIC HEADER
251			There is no way to distinguish CBOR from other formats programmatically.
252			To make it easier to distinguish CBOR from other formats, the CBOR
253			specification has a special "magic string" that can be prepended to any
254			CBOR string without changing it's meaning.
255
256			This string is available as $CBOR::XS::MAGIC. This module does not
257			prepend this string tot he CBOR data it generates, but it will ignroe it
258			if present, so users can prepend this string as a "file type" indicator
259			as required.
260
261	root	1.2	CBOR and JSON
262	root	1.4	CBOR is supposed to implement a superset of the JSON data model, and is,
263			with some coercion, able to represent all JSON texts (something that
264			other "binary JSON" formats such as BSON generally do not support).
265
266			CBOR implements some extra hints and support for JSON interoperability,
267			and the spec offers further guidance for conversion between CBOR and
268			JSON. None of this is currently implemented in CBOR, and the guidelines
269			in the spec do not result in correct round-tripping of data. If JSON
270			interoperability is improved in the future, then the goal will be to
271			ensure that decoded JSON data will round-trip encoding and decoding to
272			CBOR intact.
273	root	1.2
274			SECURITY CONSIDERATIONS
275			When you are using CBOR in a protocol, talking to untrusted potentially
276			hostile creatures requires relatively few measures.
277
278			First of all, your CBOR decoder should be secure, that is, should not
279			have any buffer overflows. Obviously, this module should ensure that and
280			I am trying hard on making that true, but you never know.
281
282			Second, you need to avoid resource-starving attacks. That means you
283			should limit the size of CBOR data you accept, or make sure then when
284			your resources run out, that's just fine (e.g. by using a separate
285			process that can crash safely). The size of a CBOR string in octets is
286			usually a good indication of the size of the resources required to
287			decode it into a Perl structure. While CBOR::XS can check the size of
288			the CBOR text, it might be too late when you already have it in memory,
289			so you might want to check the size before you accept the string.
290
291			Third, CBOR::XS recurses using the C stack when decoding objects and
292			arrays. The C stack is a limited resource: for instance, on my amd64
293			machine with 8MB of stack size I can decode around 180k nested arrays
294			but only 14k nested CBOR objects (due to perl itself recursing deeply on
295			croak to free the temporary). If that is exceeded, the program crashes.
296			To be conservative, the default nesting limit is set to 512. If your
297			process has a smaller stack, you should adjust this setting accordingly
298			with the "max_depth" method.
299
300			Something else could bomb you, too, that I forgot to think of. In that
301			case, you get to keep the pieces. I am always open for hints, though...
302
303			Also keep in mind that CBOR::XS might leak contents of your Perl data
304			structures in its error messages, so when you serialise sensitive
305			information you might want to make sure that exceptions thrown by
306			CBOR::XS will not end up in front of untrusted eyes.
307
308			CBOR IMPLEMENTATION NOTES
309			This section contains some random implementation notes. They do not
310			describe guaranteed behaviour, but merely behaviour as-is implemented
311			right now.
312
313			64 bit integers are only properly decoded when Perl was built with 64
314			bit support.
315
316			Strings and arrays are encoded with a definite length. Hashes as well,
317			unless they are tied (or otherwise magical).
318
319			Only the double data type is supported for NV data types - when Perl
320			uses long double to represent floating point values, they might not be
321			encoded properly. Half precision types are accepted, but not encoded.
322
323			Strict mode and canonical mode are not implemented.
324
325			THREADS
326			This module is not guaranteed to be thread safe and there are no plans
327			to change this until Perl gets thread support (as opposed to the
328			horribly slow so-called "threads" which are simply slow and bloated
329			process simulations - use fork, it's much faster, cheaper, better).
330
331			(It might actually work, but you have been warned).
332
333			BUGS
334			While the goal of this module is to be correct, that unfortunately does
335			not mean it's bug-free, only that I think its design is bug-free. If you
336			keep reporting bugs they will be fixed swiftly, though.
337
338			Please refrain from using rt.cpan.org or any other bug reporting
339			service. I put the contact address into my modules for a reason.
340
341			SEE ALSO
342			The JSON and JSON::XS modules that do similar, but human-readable,
343			serialisation.
344
345			AUTHOR
346			Marc Lehmann <schmorp@schmorp.de>
347			http://home.schmorp.de/
348