development on snmp

lib/net/snmp.rb

@@ -4,7 +4,7 @@
 #
 #----------------------------------------------------------------------------
 #
-# Copyright (C) 2006 by Francis Cianfrocca. All Rights Reserved.
+# Copyright (C) 2006-07 by Francis Cianfrocca. All Rights Reserved.
 #
 # Gmail: garbagecat10
 #
@@ -54,53 +54,161 @@ module Net
     class SnmpPdu
 	class Error < Exception; end
 
-	attr_reader :version, :community, :pdu_type, :request_id, :variables
+	PduTypes = [
+	    :get_request,
+	    :get_next_request,
+	    :get_response,
+	    :set_request,
+	    :trap
+	]
+	ErrorStatusCodes = { # Per RFC1157, pgh 4.1.1
+	    0 => "noError",
+	    1 => "tooBig",
+	    2 => "noSuchName",
+	    3 => "badValue",
+	    4 => "readOnly",
+	    5 => "genErr"
+	}
+
+	class << self
+	    def parse ber_object
+		n = new
+		n.send :parse, ber_object
+		n
+	    end
+	end
+
+	attr_reader :version, :community, :pdu_type, :variables, :error_status
+	attr_accessor :request_id, :error_index
+
+
+	def initialize args={}
+	    @version = args[:version] || 0
+	    @community = args[:community] || "public"
+	    @pdu_type = args[:pdu_type] # leave nil unless specified; there's no reasonable default value.
+	    @error_status = args[:error_status] || 0
+	    @error_index = args[:error_index] || 0
+	end
 
 	#--
-	# TODO, improve the error-trapping.
+	def parse ber_object
-	# 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
+	    rescue Error
+		# Pass through any SnmpPdu::Error instances
+		raise $!
+	    rescue
 		# Wrap any basic parsing error so it becomes a PDU-format error
 		raise Error.new( "snmp-pdu format error" )
 	    end
 	end
+	private :parse
 
 	def parse_ber_object ber_object
-	    @version = ber_object[0].to_i
+	    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
+	    community= ber_object[1].to_s
 
 	    data = ber_object[2]
-	    app_tag = data.ber_identifier & 31
+	    case (app_tag = data.ber_identifier & 31)
-	    case app_tag
 	    when 0
-		@pdu_type = :get_request
+		send :pdu_type=, :get_request
 		parse_get_request data
 	    else
 		raise Error.new( "unknown snmp-pdu type: #{app_tag}" )
 	    end
 	end
+	private :parse_ber_object
 
 	#--
 	# Defined in RFC1157, pgh 4.1.2.
 	def parse_get_request data
-	    @request_id = data[0].to_i
+	    send :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|
+	    data[3].each {|n,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]
+		unless v.is_a?(Net::BER::BerIdentifiedNull)
+		    raise Error.new(" invalid variable-binding in get-request" )
+		end
+		add_variable_binding n, nil
 	    }
 	end
+	private :parse_get_request
+
+	def version= ver
+	    unless [0,2].include?(ver)
+		raise Error.new("unknown snmp-version: #{ver}")
+	    end
+	    @version = ver
+	end
+
+	def pdu_type= t
+	    unless PduTypes.include?(t)
+		raise Error.new("unknown pdu-type: #{t}")
+	    end
+	    @pdu_type = t
+	end
+
+	def error_status= es
+	    unless ErrorStatusCodes.has_key?(es)
+		raise Error.new("unknown error-status: #{es}")
+	    end
+	end
+
+	def community= c
+	    @community = c.to_s
+	end
+
+	#--
+	# Syntactic sugar
+	def add_variable_binding name, value
+	    @variables ||= []
+	    @variables << [name, value]
+	end
+
+	def to_ber_string
+	    [
+		version.to_ber,
+		community.to_ber,
+		pdu_to_ber_string
+	    ].to_ber_sequence
+	end
+
+	#--
+	# Helper method that returns a PDU payload in BER form,
+	# depending on the PDU type.
+	def pdu_to_ber_string
+	    case pdu_type
+	    when :get_request
+		[
+		    request_id.to_ber,
+		    error_status.to_ber,
+		    error_index.to_ber,
+		    [
+			@variables.map {|n,v|
+			    [n.to_ber_oid, Net::BER::BerIdentifiedNull.new.to_ber].to_ber_sequence
+			}
+		    ].to_ber_sequence
+		].to_ber_contextspecific(0)
+	    when :get_response
+		[
+		    request_id.to_ber,
+		    error_status.to_ber,
+		    error_index.to_ber,
+		    [
+			@variables.map {|n,v|
+			    [n.to_ber_oid, v.to_ber].to_ber_sequence
+			}
+		    ].to_ber_sequence
+		].to_ber_contextspecific(2)
+	    else
+		raise Error.new( "unknown pdu-type: #{pdu_type}" )
+	    end
+	end
+	private :pdu_to_ber_string
 
     end
 end