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# -*- ruby encoding: utf-8 -*-
require 'stringio'
# Implements Basic Encoding Rules parsing to be mixed into types as needed.
module Net::BER::BERParser
primitive = {
1 => :boolean,
2 => :integer,
4 => :string,
5 => :null,
6 => :oid,
10 => :integer,
13 => :string # (relative OID)
}
constructed = {
16 => :array,
17 => :array,
}
universal = { :primitive => primitive, :constructed => constructed }
primitive = { 10 => :integer }
context = { :primitive => primitive }
# The universal, built-in ASN.1 BER syntax.
BuiltinSyntax = Net::BER.compile_syntax(:universal => universal,
:context_specific => context)
##
# This is an extract of our BER object parsing to simplify our
# understanding of how we parse basic BER object types.
def parse_ber_object(syntax, id, data)
# Find the object type from either the provided syntax lookup table or
# the built-in syntax lookup table.
#
# This exceptionally clever bit of code is verrrry slow.
object_type = (syntax && syntax[id]) || BuiltinSyntax[id]
# == is expensive so sort this so the common cases are at the top.
if object_type == :string
s = Net::BER::BerIdentifiedString.new(data || "")
s.ber_identifier = id
s
elsif object_type == :integer
neg = !(data.unpack("C").first & 0x80).zero?
int = 0
data.each_byte do |b|
int = (int << 8) + (neg ? 255 - b : b)
end
if neg
(int + 1) * -1
else
int
end
elsif object_type == :oid
# See X.690 pgh 8.19 for an explanation of this algorithm.
# This is potentially not good enough. We may need a
# BerIdentifiedOid as a subclass of BerIdentifiedArray, to
# get the ber identifier and also a to_s method that produces
# the familiar dotted notation.
oid = data.unpack("w*")
f = oid.shift
g = if f < 40
[0, f]
elsif f < 80
[1, f - 40]
else
# f - 80 can easily be > 80. What a weird optimization.
[2, f - 80]
end
oid.unshift g.last
oid.unshift g.first
# Net::BER::BerIdentifiedOid.new(oid)
oid
elsif object_type == :array
seq = Net::BER::BerIdentifiedArray.new
seq.ber_identifier = id
sio = StringIO.new(data || "")
# Interpret the subobject, but note how the loop is built:
# nil ends the loop, but false (a valid BER value) does not!
while (e = sio.read_ber(syntax)) != nil
seq << e
end
seq
elsif object_type == :boolean
data != "\000"
elsif object_type == :null
n = Net::BER::BerIdentifiedNull.new
n.ber_identifier = id
n
else
raise Net::BER::BerError, "Unsupported object type: id=#{id}"
end
end
private :parse_ber_object
##
# This is an extract of how our BER object length parsing is done to
# simplify the primary call. This is defined in X.690 section 8.1.3.
#
# The BER length will either be a single byte or up to 126 bytes in
# length. There is a special case of a BER length indicating that the
# content-length is undefined and will be identified by the presence of
# two null values (0x00 0x00).
#
# <table>
# <tr>
# <th>Range</th>
# <th>Length</th>
# </tr>
# <tr>
# <th>0x00 -- 0x7f<br />0b00000000 -- 0b01111111</th>
# <td>0 - 127 bytes</td>
# </tr>
# <tr>
# <th>0x80<br />0b10000000</th>
# <td>Indeterminate (end-of-content marker required)</td>
# </tr>
# <tr>
# <th>0x81 -- 0xfe<br />0b10000001 -- 0b11111110</th>
# <td>1 - 126 bytes of length as an integer value</td>
# </tr>
# <tr>
# <th>0xff<br />0b11111111</th>
# <td>Illegal (reserved for future expansion)</td>
# </tr>
# </table>
#
#--
# This has been modified from the version that was previously inside
# #read_ber to handle both the indeterminate terminator case and the
# invalid BER length case. Because the "lengthlength" value was not used
# inside of #read_ber, we no longer return it.
def read_ber_length
n = getbyte
if n <= 0x7f
n
elsif n == 0x80
-1
elsif n == 0xff
raise Net::BER::BerError, "Invalid BER length 0xFF detected."
else
v = 0
read(n & 0x7f).each_byte do |b|
v = (v << 8) + b
end
v
end
end
private :read_ber_length
##
# Reads a BER object from the including object. Requires that #getbyte is
# implemented on the including object and that it returns a Fixnum value.
# Also requires #read(bytes) to work.
#
# Yields the object type `id` and the data `content_length` if a block is
# given. This is namely to support instrumentation.
#
# This does not work with non-blocking I/O.
def read_ber(syntax = nil)
# TODO: clean this up so it works properly with partial packets coming
# from streams that don't block when we ask for more data (like
# StringIOs). At it is, this can throw TypeErrors and other nasties.
id = getbyte or return nil # don't trash this value, we'll use it later
content_length = read_ber_length
yield id, content_length if block_given?
if -1 == content_length
raise Net::BER::BerError,
"Indeterminite BER content length not implemented."
end
data = read(content_length)
parse_ber_object(syntax, id, data)
end
end
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