Convert-BER-XS/XS.pm

=head1 NAME

Convert::BER::XS - I<very> low level BER en-/decoding

=head1 SYNOPSIS

 use Convert::BER::XS ':all';

 my $ber = ber_decode $buf
    or die "unable to decode SNMP v1/v2c Message";

 # the above results in a data structure consisting of (class, tag,
 # constructed, data) tuples. here is such a message, SNMPv1 trap
 # with a cisoc mac change notification

 [ ASN_UNIVERSAL, ASN_SEQUENCE, 1,
   [
      [ ASN_UNIVERSAL, ASN_INTEGER32, 0, 0 ], # snmp version 1
      [ ASN_UNIVERSAL, 4, 0, "public" ], # community
      [ ASN_CONTEXT, 4, 1, # CHOICE, constructed
         [
            [ ASN_UNIVERSAL, ASN_OBJECT_IDENTIFIER, 0, "1.3.6.1.4.1.9.9.215.2" ], # enterprise oid
            [ ASN_APPLICATION, 0, 0, "\x0a\x00\x00\x01" ], # SNMP IpAddress, 10.0.0.1
            [ ASN_UNIVERSAL, ASN_INTEGER32, 0, 6 ], # generic trap
            [ ASN_UNIVERSAL, ASN_INTEGER32, 0, 1 ], # specific trap
            [ ASN_APPLICATION, ASN_TIMETICKS, 0, 1817903850 ], # SNMP TimeTicks
            [ ASN_UNIVERSAL, ASN_SEQUENCE, 1, # the varbindlist
               [
                  [ ASN_UNIVERSAL, ASN_SEQUENCE, 1, # a single varbind, "key value" pair
                     [
                        [ ASN_UNIVERSAL, ASN_OBJECT_IDENTIFIER, 0, "1.3.6.1.4.1.9.9.215.1.1.8.1.2.1" ], # the oid
                        [ ASN_UNIVERSAL, ASN_OCTET_STRING, 0, "...data..." # the value
                        ]
                     ]
                  ],
                  ...

 # let's decode it a bit with some helper functions

 my $msg = ber_is_seq $ber
    or die "SNMP message does not start with a sequence";

 ber_is $msg->[0], ASN_UNIVERSAL, ASN_INTEGER32, 0
    or die "SNMP message does not start with snmp version\n";

 # message is SNMP v1 or v2c?
 if ($msg->[0][BER_DATA] == 0 || $msg->[0][BER_DATA] == 1) {

    # message is v1 trap?
    if (ber_is $msg->[2], ASN_CONTEXT, 4, 1) {
       my $trap = $msg->[2][BER_DATA];

       # check whether trap is a cisco mac notification mac changed message
       if (
          (ber_is_oid $trap->[0], "1.3.6.1.4.1.9.9.215.2") # cmnInterfaceObjects
          and (ber_is_i32 $trap->[2], 6)
          and (ber_is_i32 $trap->[3], 1) # mac changed msg
       ) {
          ... and so on

 # finally, let's encode it again and hope it results in the same bit pattern

 my $buf = ber_encode $ber;

=head1 DESCRIPTION

This module implements a I<very> low level BER/DER en-/decoder.

If is tuned for low memory and high speed, while still maintaining some
level of user-friendlyness.

Currently, not much is documented, as this is an initial release to
reserve CPAN namespace, stay tuned for a few days.

=head2 ASN.1/BER/DER/... BASICS

ASN.1 is a strange language that can be sed to describe protocols and
data structures. It supports various mappings to JSON, XML, but most
importantly, to a various binary encodings such as BER, that is the topic
of this module, and is used in SNMP or LDAP for example.

While ASN.1 defines a schema that is useful to interpret encoded data,
the BER encoding is actually somehat self-describing: you might not know
whether something is a string or a number or a sequence or something else,
but you can nevertheless decode the overall structure, even if you end up
with just a binary blob for the actual value.

This works because BER values are tagged with a type and a namespace,
and also have a flag that says whther a value consists of subvalues (is
"constructed") or not (is "primitive").

Tags are simple integers, and ASN.1 defines a somewhat weird assortment of
those - for example, you have 32 bit signed integers and 16(!) different
string types, but there is no unsigned32 type for example. Different
applications work around this in different ways, for example, SNMP defines
application-specific Gauge32, Counter32 and Unsigned32, which are mapped
to two different tags: you can distinguish between Counter32 and the
others, but not between Gause32 and Unsigned32, without the ASN.1 schema.

Ugh.

=head2 DECODED BER REPRESENTATION

This module represents every BER value as a 4-element tuple (actually an
array-reference):

   [CLASS, TAG, CONSTRUCTED, DATA]

I<CLASS> is something like a namespace for I<TAG>s - there is the
C<ASN_UNIVERSAL> namespace which defines tags common to all ASN.1
implementations, the C<ASN_APPLICATION> namespace which defines tags for
specific applications (for example, the SNMP C<Unsigned32> type is in this
namespace), a special-purpose context namespace (C<ASN_CONTEXT>, used e.g.
for C<CHOICE>) and a private namespace (C<ASN_PRIVATE>).

The meaning of the I<TAG> depends on the namespace, and defines a
(partial) interpretation of the data value. For example, right now, SNMP
application namespace knowledge ix hardcoded into this module, so it
knows that SNMP C<Unsigned32> values need to be decoded into actual perl
integers.

The most common tags in the C<ASN_UNIVERSAL> namespace are
C<ASN_INTEGER32>, C<ASN_BIT_STRING>, C<ASN_NULL>, C<ASN_OCTET_STRING>,
C<ASN_OBJECT_IDENTIFIER>, C<ASN_SEQUENCE>, C<ASN_SET> and
C<ASN_IA5_STRING>.

The most common tags in SNMP's C<ASN_APPLICATION> namespace
are C<SNMP_IPADDRESS>, C<SNMP_COUNTER32>, C<SNMP_UNSIGNED32>,
C<SNMP_TIMETICKS>, C<SNMP_OPAQUE> and C<SNMP_COUNTER64>.

The I<CONSTRUCTED> flag is really just a boolean - if it is false, the
the value is "primitive" and contains no subvalues, kind of like a
non-reference perl scalar. IF it is true, then the value is "constructed"
which just means it contains a list of subvalues which this module will
en-/decode as BER tuples themselves.

The I<DATA> value is either a reference to an array of further tuples (if
the value is I<CONSTRUCTED>), some decoded representation of the value,
if this module knows how to decode it (e.g. for the integer types above)
or a binary string with the raw octets if this module doesn't know how to
interpret the namespace/tag.

Thus, you can always decode a BER data structure and at worst you get a
string in place of some nice decoded value.

See the SYNOPSIS for an example of such an encoded tuple representation.

=head2 RELATIONSHIP TO L<Convert::BER> and L<Convert::ASN1>

This module is I<not> the XS version of L<Convert::BER>, but a different
take at doing the same thing. I imagine this module would be a good base
for speeding up either of these, or write a similar module, or write your
own LDAP or SNMP module for example.

=cut

package Convert::BER::XS;

use common::sense;

use XSLoader ();
use Exporter qw(import);

our $VERSION = '0.0';

XSLoader::load __PACKAGE__, $VERSION;

our %EXPORT_TAGS = (
   const => [qw(
      BER_CLASS BER_TAG BER_CONSTRUCTED BER_DATA

      ASN_BOOLEAN ASN_INTEGER32 ASN_BIT_STRING ASN_OCTET_STRING ASN_NULL ASN_OBJECT_IDENTIFIER ASN_TAG_BER ASN_TAG_MASK
      ASN_CONSTRUCTED ASN_UNIVERSAL ASN_APPLICATION ASN_CONTEXT ASN_PRIVATE ASN_CLASS_MASK ASN_CLASS_SHIFT
      ASN_SEQUENCE
      
      SNMP_IPADDRESS SNMP_COUNTER32 SNMP_UNSIGNED32 SNMP_TIMETICKS SNMP_OPAQUE SNMP_COUNTER64
   )],
   encode => [qw(
      ber_decode
      ber_is ber_is_seq ber_is_i32 ber_is_oid
   )],
   decode => [qw(
      ber_encode
   )],
);

our @EXPORT_OK = map @$_, values %EXPORT_TAGS;

$EXPORT_TAGS{all} = \@EXPORT_OK;

1;

=head2 BUGS / SHORTCOMINGs

This module does have a number of SNMPisms hardcoded, such as the SNMP
tags for Unsigned32 and so on. More configurability is needed, and, if
ever implemented, will come in a form similar to how L<JSON::XS> and
L<CBOR::XS> respresent things, namely with an object-oriented interface.

=head1 AUTHOR

 Marc Lehmann <schmorp@schmorp.de>
 http://software.schmorp.de/pkg/Convert-BER-XS

=cut

Revision:	1.4
Committed:	Fri Apr 19 19:46:29 2019 UTC (5 years, 1 month ago) by root
Branch:	MAIN
Changes since 1.3:	+101 -9 lines
Log Message:	* empty log message *
#	Content
1	=head1 NAME
2
3	Convert::BER::XS - I<very> low level BER en-/decoding
4
5	=head1 SYNOPSIS
6
7	use Convert::BER::XS ':all';
8
9	my $ber = ber_decode $buf
10	or die "unable to decode SNMP v1/v2c Message";
11
12	# the above results in a data structure consisting of (class, tag,
13	# constructed, data) tuples. here is such a message, SNMPv1 trap
14	# with a cisoc mac change notification
15
16	[ ASN_UNIVERSAL, ASN_SEQUENCE, 1,
17	[
18	[ ASN_UNIVERSAL, ASN_INTEGER32, 0, 0 ], # snmp version 1
19	[ ASN_UNIVERSAL, 4, 0, "public" ], # community
20	[ ASN_CONTEXT, 4, 1, # CHOICE, constructed
21	[
22	[ ASN_UNIVERSAL, ASN_OBJECT_IDENTIFIER, 0, "1.3.6.1.4.1.9.9.215.2" ], # enterprise oid
23	[ ASN_APPLICATION, 0, 0, "\x0a\x00\x00\x01" ], # SNMP IpAddress, 10.0.0.1
24	[ ASN_UNIVERSAL, ASN_INTEGER32, 0, 6 ], # generic trap
25	[ ASN_UNIVERSAL, ASN_INTEGER32, 0, 1 ], # specific trap
26	[ ASN_APPLICATION, ASN_TIMETICKS, 0, 1817903850 ], # SNMP TimeTicks
27	[ ASN_UNIVERSAL, ASN_SEQUENCE, 1, # the varbindlist
28	[
29	[ ASN_UNIVERSAL, ASN_SEQUENCE, 1, # a single varbind, "key value" pair
30	[
31	[ ASN_UNIVERSAL, ASN_OBJECT_IDENTIFIER, 0, "1.3.6.1.4.1.9.9.215.1.1.8.1.2.1" ], # the oid
32	[ ASN_UNIVERSAL, ASN_OCTET_STRING, 0, "...data..." # the value
33	]
34	]
35	],
36	...
37
38	# let's decode it a bit with some helper functions
39
40	my $msg = ber_is_seq $ber
41	or die "SNMP message does not start with a sequence";
42
43	ber_is $msg->[0], ASN_UNIVERSAL, ASN_INTEGER32, 0
44	or die "SNMP message does not start with snmp version\n";
45
46	# message is SNMP v1 or v2c?
47	if ($msg->[0][BER_DATA] == 0 \|\| $msg->[0][BER_DATA] == 1) {
48
49	# message is v1 trap?
50	if (ber_is $msg->[2], ASN_CONTEXT, 4, 1) {
51	my $trap = $msg->[2][BER_DATA];
52
53	# check whether trap is a cisco mac notification mac changed message
54	if (
55	(ber_is_oid $trap->[0], "1.3.6.1.4.1.9.9.215.2") # cmnInterfaceObjects
56	and (ber_is_i32 $trap->[2], 6)
57	and (ber_is_i32 $trap->[3], 1) # mac changed msg
58	) {
59	... and so on
60
61	# finally, let's encode it again and hope it results in the same bit pattern
62
63	my $buf = ber_encode $ber;
64
65	=head1 DESCRIPTION
66
67	This module implements a I<very> low level BER/DER en-/decoder.
68
69	If is tuned for low memory and high speed, while still maintaining some
70	level of user-friendlyness.
71
72	Currently, not much is documented, as this is an initial release to
73	reserve CPAN namespace, stay tuned for a few days.
74
75	=head2 ASN.1/BER/DER/... BASICS
76
77	ASN.1 is a strange language that can be sed to describe protocols and
78	data structures. It supports various mappings to JSON, XML, but most
79	importantly, to a various binary encodings such as BER, that is the topic
80	of this module, and is used in SNMP or LDAP for example.
81
82	While ASN.1 defines a schema that is useful to interpret encoded data,
83	the BER encoding is actually somehat self-describing: you might not know
84	whether something is a string or a number or a sequence or something else,
85	but you can nevertheless decode the overall structure, even if you end up
86	with just a binary blob for the actual value.
87
88	This works because BER values are tagged with a type and a namespace,
89	and also have a flag that says whther a value consists of subvalues (is
90	"constructed") or not (is "primitive").
91
92	Tags are simple integers, and ASN.1 defines a somewhat weird assortment of
93	those - for example, you have 32 bit signed integers and 16(!) different
94	string types, but there is no unsigned32 type for example. Different
95	applications work around this in different ways, for example, SNMP defines
96	application-specific Gauge32, Counter32 and Unsigned32, which are mapped
97	to two different tags: you can distinguish between Counter32 and the
98	others, but not between Gause32 and Unsigned32, without the ASN.1 schema.
99
100	Ugh.
101
102	=head2 DECODED BER REPRESENTATION
103
104	This module represents every BER value as a 4-element tuple (actually an
105	array-reference):
106
107	[CLASS, TAG, CONSTRUCTED, DATA]
108
109	I<CLASS> is something like a namespace for I<TAG>s - there is the
110	C<ASN_UNIVERSAL> namespace which defines tags common to all ASN.1
111	implementations, the C<ASN_APPLICATION> namespace which defines tags for
112	specific applications (for example, the SNMP C<Unsigned32> type is in this
113	namespace), a special-purpose context namespace (C<ASN_CONTEXT>, used e.g.
114	for C<CHOICE>) and a private namespace (C<ASN_PRIVATE>).
115
116	The meaning of the I<TAG> depends on the namespace, and defines a
117	(partial) interpretation of the data value. For example, right now, SNMP
118	application namespace knowledge ix hardcoded into this module, so it
119	knows that SNMP C<Unsigned32> values need to be decoded into actual perl
120	integers.
121
122	The most common tags in the C<ASN_UNIVERSAL> namespace are
123	C<ASN_INTEGER32>, C<ASN_BIT_STRING>, C<ASN_NULL>, C<ASN_OCTET_STRING>,
124	C<ASN_OBJECT_IDENTIFIER>, C<ASN_SEQUENCE>, C<ASN_SET> and
125	C<ASN_IA5_STRING>.
126
127	The most common tags in SNMP's C<ASN_APPLICATION> namespace
128	are C<SNMP_IPADDRESS>, C<SNMP_COUNTER32>, C<SNMP_UNSIGNED32>,
129	C<SNMP_TIMETICKS>, C<SNMP_OPAQUE> and C<SNMP_COUNTER64>.
130
131	The I<CONSTRUCTED> flag is really just a boolean - if it is false, the
132	the value is "primitive" and contains no subvalues, kind of like a
133	non-reference perl scalar. IF it is true, then the value is "constructed"
134	which just means it contains a list of subvalues which this module will
135	en-/decode as BER tuples themselves.
136
137	The I<DATA> value is either a reference to an array of further tuples (if
138	the value is I<CONSTRUCTED>), some decoded representation of the value,
139	if this module knows how to decode it (e.g. for the integer types above)
140	or a binary string with the raw octets if this module doesn't know how to
141	interpret the namespace/tag.
142
143	Thus, you can always decode a BER data structure and at worst you get a
144	string in place of some nice decoded value.
145
146	See the SYNOPSIS for an example of such an encoded tuple representation.
147
148	=head2 RELATIONSHIP TO L<Convert::BER> and L<Convert::ASN1>
149
150	This module is I<not> the XS version of L<Convert::BER>, but a different
151	take at doing the same thing. I imagine this module would be a good base
152	for speeding up either of these, or write a similar module, or write your
153	own LDAP or SNMP module for example.
154
155	=cut
156
157	package Convert::BER::XS;
158
159	use common::sense;
160
161	use XSLoader ();
162	use Exporter qw(import);
163
164	our $VERSION = '0.0';
165
166	XSLoader::load __PACKAGE__, $VERSION;
167
168	our %EXPORT_TAGS = (
169	const => [qw(
170	BER_CLASS BER_TAG BER_CONSTRUCTED BER_DATA
171
172	ASN_BOOLEAN ASN_INTEGER32 ASN_BIT_STRING ASN_OCTET_STRING ASN_NULL ASN_OBJECT_IDENTIFIER ASN_TAG_BER ASN_TAG_MASK
173	ASN_CONSTRUCTED ASN_UNIVERSAL ASN_APPLICATION ASN_CONTEXT ASN_PRIVATE ASN_CLASS_MASK ASN_CLASS_SHIFT
174	ASN_SEQUENCE
175
176	SNMP_IPADDRESS SNMP_COUNTER32 SNMP_UNSIGNED32 SNMP_TIMETICKS SNMP_OPAQUE SNMP_COUNTER64
177	)],
178	encode => [qw(
179	ber_decode
180	ber_is ber_is_seq ber_is_i32 ber_is_oid
181	)],
182	decode => [qw(
183	ber_encode
184	)],
185	);
186
187	our @EXPORT_OK = map @$_, values %EXPORT_TAGS;
188
189	$EXPORT_TAGS{all} = \@EXPORT_OK;
190
191	1;
192
193	=head2 BUGS / SHORTCOMINGs
194
195	This module does have a number of SNMPisms hardcoded, such as the SNMP
196	tags for Unsigned32 and so on. More configurability is needed, and, if
197	ever implemented, will come in a form similar to how L<JSON::XS> and
198	L<CBOR::XS> respresent things, namely with an object-oriented interface.
199
200	=head1 AUTHOR
201
202	Marc Lehmann <schmorp@schmorp.de>
203	http://software.schmorp.de/pkg/Convert-BER-XS
204
205	=cut
206