Real-time collaboration for Jupyter Notebooks, Linux Terminals, LaTeX, VS Code, R IDE, and more,
all in one place.

1
#
2
# Copyright (c) 2004 David R. Halliday
3
# All rights reserved.
4
#
5
# This SNMP library is free software.  Redistribution is permitted under the
6
# same terms and conditions as the standard Ruby distribution.  See the
7
# COPYING file in the Ruby distribution for details.
8
#
9

10
#
11
# Add ord method to Integer for forward compatibility with Ruby 1.9
12
#
13
if "a"[0].kind_of? Integer
14
    unless Integer.methods.include? :ord
15
        class Integer
16
            def ord; self; end
17
        end
18
    end
19
end
20

21
#
22
# This module implements methods for encoding and decoding SNMP packets
23
# using the ASN.1 BER (Basic Encoding Rules).
24
#
25
module SNMP
26
module BER #:nodoc:all
27

28
    # SNMP version codes
29
    SNMP_V1  = 0
30
    SNMP_V2C = 1
31
    SNMP_V3  = 3  # not supported
32

33
    # SNMP context-specific data types
34
    # See RFC 1157 for SNMPv1
35
    # See RFC 1905 for SNMPv2c
36
    GetRequest_PDU_TAG = 0xa0
37
    GetNextRequest_PDU_TAG = 0xa1
38
    Response_PDU_TAG = 0xa2
39
    SetRequest_PDU_TAG = 0xa3
40
    SNMPv1_Trap_PDU_TAG = 0xa4    # Note: valid for SNMPv1 only
41
    GetBulkRequest_PDU_TAG = 0xa5
42
    InformRequest_PDU_TAG = 0xa6
43
    SNMPv2_Trap_PDU_TAG = 0xa7
44
    Report_PDU_TAG = 0xa8  # Note: Usage not defined - not supported    
45

46
    # Primitive ASN.1 data types
47
    INTEGER_TAG = 0x02
48
    OCTET_STRING_TAG = 0x04
49
    NULL_TAG = 0x05
50
    OBJECT_IDENTIFIER_TAG = 0x06
51
    
52
    # Constructed ASN.1 data type
53
    SEQUENCE_TAG = 0x30
54
    
55
    # SNMP application data types
56
    # See RFC 1155 for SNMPv1
57
    # See RFC 1902 for SNMPv2c
58
    IpAddress_TAG = 0x40
59
    Counter32_TAG = 0x41   # Counter in SNMPv1
60
    Gauge32_TAG = 0x42     # Gauge in SNMPv1
61
    Unsigned32_TAG = 0x42  # Note: same as Gauge32
62
    TimeTicks_TAG = 0x43
63
    Opaque_TAG = 0x44
64
    Counter64_TAG = 0x46
65
    
66
    # VarBind response exceptions
67
    NoSuchObject_TAG = 0x80
68
    NoSuchInstance_TAG = 0x81
69
    EndOfMibView_TAG = 0x82
70
    
71
    # Exceptions thrown in this module
72
    class OutOfData < RuntimeError; end    
73
    class InvalidLength < RuntimeError; end
74
    class InvalidTag < RuntimeError; end
75
    class InvalidObjectId < RuntimeError; end
76

77
    def assert_no_remainder(remainder)
78
        raise ParseError, remainder.inspect if (remainder and remainder != "")
79
    end
80
    
81
    #
82
    # Decode tag-length-value data.  The data is assumed to be a string of
83
    # bytes in network byte order.  This format is returned by Socket#recv.
84
    #
85
    # Returns a tuple containing the tag, the value, and any remaining
86
    # unprocessed data.
87
    #
88
    # The data is not interpreted by this method.  Use one of the other
89
    # decoding methods to interpret the data.
90
    #
91
    # Note that ASN.1 supports an indefinite length format where the end of
92
    # content is marked by a pair of 0 octets.  SNMP does not support this
93
    # format, so only the two definite forms are implemented (single byte and
94
    # multi-byte).
95
    #
96
    def decode_tlv(data)
97
        raise OutOfData if (data.length == 2 && data[1].ord != 0) || data.length < 2
98
        tag = data[0].ord
99
        length = data[1].ord
100
        if length < 0x80
101
            value = data[2, length]
102
            remainder = data[length+2..-1]
103
        else
104
            # ASN.1 says this octet can't be 0xff
105
            raise InvalidLength, length.to_s if length == 0xff
106
            num_octets = length & 0x7f
107
            length = build_integer(data, 2, num_octets)
108
            value = data[num_octets+2, length]
109
            remainder = data[num_octets+2+length..-1]
110
        end
111
        return tag, value, remainder
112
    end
113
    
114
    #
115
    # Decode TLV data for an ASN.1 integer.
116
    #
117
    # Throws an InvalidTag exception if the tag is incorrect.
118
    #
119
    # Returns a tuple containing an integer and any remaining unprocessed data.
120
    #
121
    def decode_integer(data)
122
        tag, value, remainder = decode_tlv(data)
123
        raise InvalidTag, tag.to_s if tag != INTEGER_TAG
124
        return decode_integer_value(value), remainder
125
    end
126

127
    def decode_timeticks(data)
128
        tag, value, remainder = decode_tlv(data)
129
        raise InvalidTag, tag.to_s if tag != TimeTicks_TAG
130
        return decode_uinteger_value(value), remainder
131
    end
132
    
133
    def decode_integer_value(value)
134
        result = build_integer(value, 0, value.length)
135
        if value[0].ord[7] == 1
136
            result -= (1 << (8 * value.length))
137
        end
138
        result
139
    end
140
    
141
    ##
142
    # Decode an integer, ignoring the sign bit.  Some agents insist on
143
    # encoding 32 bit unsigned integers with four bytes even though it
144
    # should be 5 bytes (at least the way I read it).
145
    #
146
    def decode_uinteger_value(value)
147
        build_integer(value, 0, value.length)
148
    end
149
    
150
    def build_integer(data, start, num_octets)
151
        number = 0
152
        num_octets.times { |i| number = number<<8 | data[start+i].ord }
153
        return number
154
    end
155

156
    #
157
    # Decode TLV data for an ASN.1 octet string.
158
    #
159
    # Throws an InvalidTag exception if the tag is incorrect.
160
    #
161
    # Returns a tuple containing a string and any remaining unprocessed data.
162
    #    
163
    def decode_octet_string(data)
164
        tag, value, remainder = decode_tlv(data)
165
        raise InvalidTag, tag.to_s if tag != OCTET_STRING_TAG
166
        return value, remainder
167
    end
168
    
169
    def decode_ip_address(data)
170
        tag, value, remainder = decode_tlv(data)
171
        raise InvalidTag, tag.to_s if tag != IpAddress_TAG
172
        raise InvalidLength, tag.to_s if value.length != 4
173
        return value, remainder
174
    end
175
    
176
    #
177
    # Decode TLV data for an ASN.1 sequence.
178
    #
179
    # Throws an InvalidTag exception if the tag is incorrect.
180
    #
181
    # Returns a tuple containing the sequence data and any remaining 
182
    # unprocessed data that follows the sequence.
183
    #
184
    def decode_sequence(data)
185
        tag, value, remainder = decode_tlv(data)
186
        raise InvalidTag, tag.to_s if tag != SEQUENCE_TAG
187
        return value, remainder
188
    end
189
    
190
    #
191
    # Unwrap TLV data for an ASN.1 object identifier.  This method extracts
192
    # the OID value as a character string but does not decode it further.
193
    #
194
    # Throws an InvalidTag exception if the tag is incorrect.
195
    #
196
    # Returns a tuple containing the object identifier (OID) and any
197
    # remaining unprocessed data.  The OID is represented as an array
198
    # of integers.
199
    #
200
    def decode_object_id(data)
201
        tag, value, remainder = decode_tlv(data)
202
        raise InvalidTag, tag.to_s if tag != OBJECT_IDENTIFIER_TAG
203
        return decode_object_id_value(value), remainder
204
    end
205
    
206
    def decode_object_id_value(value)
207
        if value.length == 0
208
            object_id = []
209
        else
210
            value0 = value[0].ord
211
            if value0 == 0x2b
212
                object_id = [1,3]
213
            else
214
                second = value0 % 40
215
                first = (value0 - second) / 40
216
                raise InvalidObjectId, value.to_s if first > 2
217
                object_id = [first, second]
218
            end
219
            n = 0
220
            for i in 1...value.length
221
                n = (n<<7) + (value[i].ord & 0x7f)
222
                if value[i].ord < 0x80
223
                    object_id << n
224
                    n = 0
225
                end 
226
            end
227
        end
228
        return object_id
229
    end
230
    
231
    #
232
    # Encode the length field for TLV data.  Returns the length octets
233
    # as a string.
234
    #
235
    def encode_length(length)
236
        raise InvalidLength, length.to_s if length < 0
237
        if length < 0x80
238
            length.chr
239
        else
240
            data = integer_to_octets(length)
241
            (data.size | 0x80).chr << data
242
        end
243
    end
244

245
    #
246
    # Encode integer
247
    #
248
    def encode_integer(value)
249
        encode_tagged_integer(INTEGER_TAG, value)
250
    end
251
    
252
    def encode_tagged_integer(tag, value)
253
        if value > 0 && value < 0x80
254
            data = value.chr
255
        else
256
            data = integer_to_octets(value)
257
            if value > 0 && data[0].ord > 0x7f
258
                data = "\000" << data 
259
            elsif value < 0 && data[0].ord < 0x80
260
                data = "\377" << data
261
            end
262
        end
263
        encode_tlv(tag, data)
264
    end
265
    
266
    #
267
    # Helper method for encoding integer-like things.
268
    #
269
    def integer_to_octets(i)
270
        if i >= 0
271
            done = 0
272
        else
273
            done = -1
274
        end
275
        octets = ""
276
        begin
277
            octets = (i & 0xff).chr << octets
278
            i = i >> 8
279
        end until i == done
280
        octets
281
    end
282
    
283
    def encode_null
284
        NULL_TAG.chr << "\000"
285
    end
286
    
287
    #
288
    # Encode an exception.  The encoding is simply the exception tag with
289
    # no data, similar to NULL.
290
    #
291
    def encode_exception(tag)
292
        tag.chr << "\000"
293
    end
294
    
295
    #
296
    # Wraps value in a tag and length.  This method expects an
297
    # integer tag and a string value.
298
    #
299
    def encode_tlv(tag, value)
300
        data = tag.chr << encode_length(value.length)
301
        data = data << value if value.length > 0
302
        data
303
    end
304
    
305
    #
306
    # Wrap string in a octet string tag and length.
307
    #
308
    def encode_octet_string(value)
309
        encode_tlv(OCTET_STRING_TAG, value)
310
    end
311
    
312
    #
313
    # Wrap value in a sequence tag and length.
314
    #
315
    def encode_sequence(value)
316
        encode_tlv(SEQUENCE_TAG, value)
317
    end
318
    
319
    #
320
    # Encode an object id.  The input is assumed to be an array of integers
321
    # representing the object id.
322
    #
323
    def encode_object_id(value)
324
        raise InvalidObjectId, value.to_s if value.length < 1
325
        raise InvalidObjectId, value.to_s if value[0] > 2
326
        data = ""
327
        if (value.length > 1)
328
            raise InvalidObjectId if value[0] < 2 && value[1] > 40
329
            data << (40 * value[0] + value[1]).chr
330
            for i in 2...value.length
331
                if value[i] < 0x80
332
                    data << value[i].chr
333
                else
334
                    octets = ""
335
                    n = value[i]
336
                    begin
337
                        octets = (n & 0x7f | 0x80).chr << octets
338
                        n = n >> 7
339
                    end until n == 0
340
                    octets[-1] = (octets[-1].ord & 0x7f).chr
341
                    data << octets
342
                end
343
            end
344
        elsif (value.length == 1)
345
            data << (40 * value[0]).chr
346
        end
347
        encode_tlv(OBJECT_IDENTIFIER_TAG, data)
348
    end
349
    
350
end
351
end
352

353

354