Initial commit, work in progress

lib/netlink/message.rb

@@ -0,0 +1,151 @@
+require 'netlink/constants'
+
+module Netlink
+  # Base class for Netlink messages
+  class Message
+    # Map of numeric message type code => message class
+    CODE_TO_MESSAGE = {}
+
+    # You can initialize a message from a Hash or from another
+    # instance of itself.
+    #
+    #   class Foo < Message
+    #     field :foo, "C", 0xff
+    #     field :bar, "L", 0
+    #   end
+    #   msg = Foo.new(:bar => 123)  # or ("bar" => 123)
+    #   msg2 = Foo.new(msg)
+    #   msg3 = Foo.new(:qux => 999) # error, no method qux=
+    def initialize(h={})
+      if h.instance_of?(self.class)
+        @attrs = h.to_hash.dup
+      else
+        @attrs = self.class::DEFAULTS.dup
+        h.each { |k,v| self[k] = v }
+      end
+    end
+    
+    def to_hash
+      @attrs
+    end
+    
+    def each(&blk)
+      @attrs.each(&blk)
+    end
+    
+    # Set a field by name. Can use either symbol or string as key.
+    def []=(k,v)
+      send "#{k}=", v
+    end
+
+    # Retrieve a field by name. Must use symbol as key.
+    def [](k)
+      @attrs[k]
+    end
+    
+    def self.inherited(subclass) #:nodoc:
+      subclass.const_set(:FIELDS, [])
+      subclass.const_set(:FORMAT, "")
+      subclass.const_set(:DEFAULTS, {})
+    end
+
+    # Define which message type code(s) use this structure
+    def self.code(*codes)
+      codes.each { |code| CODE_TO_MESSAGE[code] = self }
+    end
+    
+    # Define a field for this message, which creates accessor methods. The
+    # "pattern" is the Array#pack or String#unpack code to extract this field.    
+    def self.field(name, pattern, default=nil, opt={})
+      self::FIELDS << name
+      self::FORMAT << pattern
+      self::DEFAULTS[name] = default
+      define_method name do
+        @attrs.fetch name
+      end
+      define_method "#{name}=" do |val|
+        @attrs.store name, val
+      end
+    end
+
+    def self.uchar(name, *args);	field name, "C", 0, *args; end
+    def self.uint16(name, *args);	field name, "S", 0, *args; end
+    def self.uint32(name, *args);	field name, "L", 0, *args; end
+    def self.char(name, *args);		field name, "c", 0, *args; end
+    def self.int16(name, *args);	field name, "s", 0, *args; end
+    def self.int32(name, *args);	field name, "l", 0, *args; end
+    def self.ushort(name, *args);	field name, "S_", 0, *args; end
+    def self.uint(name, *args);		field name, "I", 0, *args; end
+    def self.ulong(name, *args);	field name, "L_", 0, *args; end
+    def self.short(name, *args);	field name, "s_", 0, *args; end
+    def self.int(name, *args);		field name, "i", 0, *args; end
+    def self.long(name, *args);		field name, "l_", 0, *args; end
+    
+    # Returns the packed binary representation of this message (without
+    # header, and not padded to NLMSG_ALIGNTO bytes)    
+    def to_s
+      self.class::FIELDS.map { |key| self[key] }.pack(self.class::FORMAT)
+    end
+
+    def inspect
+      "#<#{self.class} #{@attrs.inspect}>"
+    end
+    
+    # Convert a binary representation of this message into an object instance
+    def self.parse(str)
+      res = new
+      str.unpack(self::FORMAT).zip(self::FIELDS).each do |val, key|
+        res[key] = val
+      end
+      res
+    end
+
+    NLMSG_ALIGNTO_1 = NLMSG_ALIGNTO-1 #:nodoc:
+    NLMSG_ALIGNTO_1_MASK = ~NLMSG_ALIGNTO_1 #:nodoc:
+
+    # Round up a length to a multiple of NLMSG_ALIGNTO bytes
+    def self.align(n)
+      (n + NLMSG_ALIGNTO_1) & NLMSG_ALIGNTO_1_MASK
+    end
+
+    PADDING = ("\000" * NLMSG_ALIGNTO).freeze #:nodoc:
+
+    # Pad a string up to a multiple of NLMSG_ALIGNTO bytes. Returns str.
+    def self.pad(str)
+      str << PADDING[0, align(str.bytesize) - str.bytesize]
+    end
+
+  end
+
+  class Link < Message
+    code RTM_NEWLINK, RTM_DELLINK, RTM_GETLINK
+    uchar :family
+    uchar :pad
+    ushort :type
+    int :index
+    uint :flags
+    uint :change
+  end
+
+  class Addr < Message
+    code RTM_NEWADDR, RTM_DELADDR, RTM_GETADDR
+    uchar :family
+    uchar :prefixlen
+    uchar :flags
+    uchar :scope
+    int :index
+  end
+
+  class Route < Message
+    code RTM_NEWROUTE, RTM_DELROUTE, RTM_GETROUTE
+    uchar :family
+    uchar :dst_len
+    uchar :src_len
+    uchar :tos
+    uchar :table
+    uchar :protocol
+    uchar :scope
+    uchar :type
+    uint :flags
+  end
+end