SNMP GetRequest parsing

lib/net/snmp.rb

@@ -51,5 +51,57 @@ module Net
 
     end
 
+    class SnmpPdu
+	class Error < Exception; end
+
+	attr_reader :version, :community, :pdu_type, :request_id, :variables
+
+	#--
+	# TODO, improve the error-trapping.
+	# We want to wrap up Ruby errors like array-ranges, which can appear if we get bad data.
+	# We should probably do the whole parse under a catch-all block.
+	def initialize ber_object
+	    begin
+		parse_ber_object ber_object
+	    rescue RuntimeError
+		# Wrap any basic parsing error so it becomes a PDU-format error
+		raise Error.new( "snmp-pdu format error" )
+	    end
+	end
+
+	def parse_ber_object ber_object
+	    @version = ber_object[0].to_i
+	    unless [0,2].include?(@version)
+		raise Error.new("unknown snmp-version: #{@version}")
+	    end
+
+	    @community = ber_object[1].to_s
+
+	    data = ber_object[2]
+	    app_tag = data.ber_identifier & 31
+	    case app_tag
+	    when 0
+		@pdu_type = :get_request
+		parse_get_request data
+	    else
+		raise Error.new( "unknown snmp-pdu type: #{app_tag}" )
+	    end
+	end
+
+	#--
+	# Defined in RFC1157, pgh 4.1.2.
+	def parse_get_request data
+	    @request_id = data[0].to_i
+	    # data[1] is error-status, always 0.
+	    # data[2] is error-index, always 0.
+	    @variables = data[3].map {|v|
+		# A variable-binding, of which there may be several,
+		# consists of an OID and a BER null.
+		# We're ignoring the null, we might want to verify it instead.
+		v[0]
+	    }
+	end
+
+    end
 end