535 lines
16 KiB
Ruby
535 lines
16 KiB
Ruby
# Class for packed binary data, with defined bitfields and accessors for them.
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# See {intro.txt}[link:../doc/files/intro_txt.html] for an overview.
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#
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# Data after the end of the defined fields is accessible using the +rest+
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# declaration. See examples/ip.rb. Nested fields can be declared using +nest+.
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# See examples/nest.rb.
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#
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# Note that all string methods are still available: length, grep, etc.
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# The String#replace method is useful.
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#
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class BitStruct < String
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class Field
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# Offset of field in bits.
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attr_reader :offset
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# Length of field in bits.
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attr_reader :length
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alias size length
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# Name of field (used for its accessors).
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attr_reader :name
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# Options, such as :default (varies for each field subclass).
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# In general, options can be provided as strings or as symbols.
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attr_reader :options
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# Display name of field (used for printing).
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attr_reader :display_name
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# Default value.
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attr_reader :default
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# Format for printed value of field.
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attr_reader :format
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# Subclasses can override this to define a default for all fields of this
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# class, not just the one currently being added to a BitStruct class, a
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# "default default" if you will. The global default, if #default returns
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# nil, is to fill the field with zero. Most field classes just let this
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# default stand. The default can be overridden per-field when a BitStruct
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# class is defined.
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def self.default; nil; end
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# Used in describe.
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def self.class_name
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@class_name ||= name[/\w+$/]
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end
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# Used in describe. Can be overridden per-subclass, as in NestedField.
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def class_name
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self.class.class_name
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end
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# Yield the description of this field, as an array of 5 strings: byte
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# offset, type, name, size, and description. The opts hash may have:
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#
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# :expand :: if the value is true, expand complex fields
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#
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# (Subclass implementations may yield more than once for complex fields.)
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#
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def describe opts
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bits = size
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if bits > 32 and bits % 8 == 0
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len_str = "%dB" % (bits/8)
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else
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len_str = "%db" % bits
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end
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byte_offset = offset / 8 + (opts[:byte_offset] || 0)
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yield ["@%d" % byte_offset, class_name, name, len_str, display_name]
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end
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# Options are _display_name_, _default_, and _format_ (subclasses of Field
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# may add other options).
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def initialize(offset, length, name, opts = {})
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@offset, @length, @name, @options =
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offset, length, name, opts
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@display_name = opts[:display_name] || opts["display_name"]
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@default = opts[:default] || opts["default"] || self.class.default
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@format = opts[:format] || opts["format"]
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end
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# Inspect the value of this field in the specified _obj_.
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def inspect_in_object(obj, opts)
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val = obj.send(name)
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str =
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begin
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val.inspect(opts)
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rescue ArgumentError # assume: "wrong number of arguments (1 for 0)"
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val.inspect
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end
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(f=@format) ? (f % str) : str
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end
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# Normally, all fields show up in inspect, but some, such as padding,
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# should not.
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def inspectable?; true; end
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end
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NULL_FIELD = Field.new(0, 0, :null, :display_name => "null field")
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# Raised when a field is added after an instance has been created. Fields
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# cannot be added after this point.
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class ClosedClassError < StandardError; end
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# Raised if the chosen field name is not allowed, either because another
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# field by that name exists, or because a method by that name exists.
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class FieldNameError < StandardError; end
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@default_options = {}
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class << self
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# ------------------------
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# :section: field access methods
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#
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# For introspection and metaprogramming.
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#
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# ------------------------
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# Return the list of fields for this class.
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def fields
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@fields ||= self == BitStruct ? [] : superclass.fields.dup
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end
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# Return the list of fields defined by this class, not inherited
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# from the superclass.
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def own_fields
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@own_fields ||= []
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end
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# Add a field to the BitStruct (usually, this is only used internally).
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def add_field(name, length, opts = {})
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round_byte_length ## just to make sure this has been calculated
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## before adding anything
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name = name.to_sym
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if @closed
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raise ClosedClassError, "Cannot add field #{name}: " +
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"The definition of the #{self.inspect} BitStruct class is closed."
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end
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if fields.find {|f|f.name == name}
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raise FieldNameError, "Field #{name} is already defined as a field."
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end
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if instance_methods(true).find {|m| m == name}
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if opts[:allow_method_conflict] || opts["allow_method_conflict"]
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warn "Field #{name} is already defined as a method."
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else
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raise FieldNameError,"Field #{name} is already defined as a method."
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end
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end
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field_class = opts[:field_class]
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prev = fields[-1] || NULL_FIELD
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offset = prev.offset + prev.length
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field = field_class.new(offset, length, name, opts)
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field.add_accessors_to(self)
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fields << field
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own_fields << field
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@bit_length += field.length
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@round_byte_length = (bit_length/8.0).ceil
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if @initial_value
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diff = @round_byte_length - @initial_value.length
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if diff > 0
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@initial_value << "\0" * diff
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end
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end
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field
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end
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def parse_options(ary, default_name, default_field_class) # :nodoc:
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opts = ary.grep(Hash).first || {}
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opts = default_options.merge(opts)
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opts[:display_name] = ary.grep(String).first || default_name
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opts[:field_class] = ary.grep(Class).first || default_field_class
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opts
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end
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# Get or set the hash of default options for the class, which apply to all
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# fields. Changes take effect immediately, so can be used alternatingly with
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# blocks of field declarations. If +h+ is provided, update the default
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# options with that hash. Default options are inherited.
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#
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# This is especially useful with the <tt>:endian => val</tt> option.
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def default_options h = nil
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@default_options ||= superclass.default_options.dup
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if h
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@default_options.merge! h
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end
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@default_options
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end
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# Length, in bits, of this object.
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def bit_length
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@bit_length ||= fields.inject(0) {|a, f| a + f.length}
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end
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# Length, in bytes (rounded up), of this object.
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def round_byte_length
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@round_byte_length ||= (bit_length/8.0).ceil
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end
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def closed! # :nodoc:
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@closed = true
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end
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def field_by_name name
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@field_by_name ||= {}
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field = @field_by_name[name]
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unless field
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field = fields.find {|f| f.name == name}
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@field_by_name[name] = field if field
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end
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field
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end
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end
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# Return the list of fields for this class.
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def fields
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self.class.fields
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end
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# Return the field with the given name.
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def field_by_name name
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self.class.field_by_name name
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end
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# ------------------------
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# :section: metadata inspection methods
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#
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# Methods to textually describe the format of a BitStruct subclass.
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#
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# ------------------------
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class << self
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# Default format for describe. Fields are byte, type, name, size,
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# and description.
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DESCRIBE_FORMAT = "%8s: %-12s %-14s[%4s] %s"
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# Can be overridden to use a different format.
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def describe_format
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DESCRIBE_FORMAT
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end
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# Textually describe the fields of this class of BitStructs.
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# Returns a printable table (array of line strings), based on +fmt+,
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# which defaults to #describe_format, which defaults to +DESCRIBE_FORMAT+.
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def describe(fmt = nil, opts = {})
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if fmt.kind_of? Hash
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opts = fmt; fmt = nil
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end
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if block_given?
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fields.each do |field|
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field.describe(opts) do |desc|
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yield desc
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end
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end
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nil
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else
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fmt ||= describe_format
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result = []
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unless opts[:omit_header]
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result << fmt % ["byte", "type", "name", "size", "description"]
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result << "-"*70
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end
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fields.each do |field|
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field.describe(opts) do |desc|
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result << fmt % desc
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end
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end
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unless opts[:omit_footer]
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result << @note if @note
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end
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result
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end
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end
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# Subclasses can use this to append a string (or several) to the #describe
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# output. Notes are not cumulative with inheritance. When used with no
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# arguments simply returns the note string
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def note(*str)
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@note = str unless str.empty?
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@note
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end
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end
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# ------------------------
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# :section: initialization and conversion methods
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#
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# ------------------------
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# Initialize the string with the given string or bitstruct, or with a hash of
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# field=>value pairs, or with the defaults for the BitStruct subclass, or
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# with an IO or other object with a #read method. Fields can be strings or
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# symbols. Finally, if a block is given, yield the instance for modification
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# using accessors.
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def initialize(value = nil) # :yields: instance
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self << self.class.initial_value
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case value
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when Hash
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value.each do |k, v|
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send "#{k}=", v
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end
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when nil
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else
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if value.respond_to?(:read)
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value = value.read(self.class.round_byte_length)
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end
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self[0, value.length] = value
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end
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self.class.closed!
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yield self if block_given?
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end
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DEFAULT_TO_H_OPTS = {
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:convert_keys => :to_sym,
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:include_rest => true
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}
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# Returns a hash of {name=>value,...} for each field. By default, include
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# the rest field.
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# Keys are symbols derived from field names using +to_sym+, unless
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# <tt>opts[:convert_keys]<\tt> is set to some other method name.
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def to_h(opts = DEFAULT_TO_H_OPTS)
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converter = opts[:convert_keys] || :to_sym
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fields_for_to_h = fields
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if opts[:include_rest] and (rest_field = self.class.rest_field)
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fields_for_to_h += [rest_field]
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end
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fields_for_to_h.inject({}) do |h,f|
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h[f.name.send(converter)] = send(f.name)
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h
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end
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end
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# Returns an array of values of the fields of the BitStruct. By default,
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# include the rest field.
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def to_a(include_rest = true)
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ary =
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fields.map do |f|
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send(f.name)
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end
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if include_rest and (rest_field = self.class.rest_field)
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ary << send(rest_field.name)
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end
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end
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class << self
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# The unique "prototype" object from which new instances are copied.
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# The fields of this instance can be modified in the class definition
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# to set default values for the fields in that class. (Otherwise, defaults
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# defined by the fields themselves are used.) A copy of this object is
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# inherited in subclasses, which they may override using defaults and
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# by writing to the initial_value object itself.
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#
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# If called with a block, yield the initial value object before returning
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# it. Useful for customization within a class definition.
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#
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def initial_value # :yields: the initial value
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unless @initial_value
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iv = defined?(superclass.initial_value) ?
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superclass.initial_value.dup : ""
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if iv.length < round_byte_length
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iv << "\0" * (round_byte_length - iv.length)
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end
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@initial_value = "" # Serves as initval while the real initval is inited
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@initial_value = new(iv)
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@closed = false # only creating the first _real_ instance closes.
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fields.each do |field|
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@initial_value.send("#{field.name}=", field.default) if field.default
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end
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end
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yield @initial_value if block_given?
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@initial_value
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end
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# Take +data+ (a string or BitStruct) and parse it into instances of
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# the +classes+, returning them in an array. The classes can be given
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# as an array or a separate arguments. (For parsing a string into a _single_
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# BitStruct instance, just use the #new method with the string as an arg.)
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def parse(data, *classes)
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classes.flatten.map do |c|
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c.new(data.slice!(0...c.round_byte_length))
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end
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end
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# Join the given structs (array or multiple args) as a string.
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# Actually, the inherited String#+ instance method is the same, as is using
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# Array#join.
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def join(*structs)
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structs.flatten.map {|struct| struct.to_s}.join("")
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end
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end
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# ------------------------
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# :section: inspection methods
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#
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# ------------------------
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DEFAULT_INSPECT_OPTS = {
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:format => "#<%s %s>",
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:field_format => "%s=%s",
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:separator => ", ",
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:field_name_meth => :name,
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:include_rest => true,
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:brackets => ["[", "]"],
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:include_class => true,
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:simple_format => "<%s>"
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}
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DETAILED_INSPECT_OPTS = {
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:format => "%s:\n%s",
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:field_format => "%30s = %s",
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:separator => "\n",
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:field_name_meth => :display_name,
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:include_rest => true,
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:brackets => [nil, "\n"],
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:include_class => true,
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:simple_format => "\n%s"
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}
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# A standard inspect method which does not add newlines.
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def inspect(opts = DEFAULT_INSPECT_OPTS)
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field_format = opts[:field_format]
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field_name_meth = opts[:field_name_meth]
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fields_for_inspect = fields.select {|field| field.inspectable?}
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if opts[:include_rest] and (rest_field = self.class.rest_field)
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fields_for_inspect << rest_field
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end
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ary = fields_for_inspect.map do |field|
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field_format %
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[field.send(field_name_meth),
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field.inspect_in_object(self, opts)]
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end
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body = ary.join(opts[:separator])
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if opts[:include_class]
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opts[:format] % [self.class, body]
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else
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opts[:simple_format] % body
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end
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end
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# A more visually appealing inspect method that puts each field/value on
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# a separate line. Very useful when output is scrolling by on a screen.
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#
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# (This is actually a convenience method to call #inspect with the
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# DETAILED_INSPECT_OPTS opts.)
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def inspect_detailed
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inspect(DETAILED_INSPECT_OPTS)
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end
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# ------------------------
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# :section: field declaration methods
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#
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# ------------------------
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# Define accessors for a variable length substring from the end of
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# the defined fields to the end of the BitStruct. The _rest_ may behave as
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# a String or as some other String or BitStruct subclass.
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#
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# This does not add a field, which is useful because a superclass can have
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# a rest method which accesses subclass data. In particular, #rest does
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# not affect the #round_byte_length class method. Of course, any data
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# in rest does add to the #length of the BitStruct, calculated as a string.
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# Also, _rest_ is not inherited.
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#
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# The +ary+ argument(s) work as follows:
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#
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# If a class is provided, use it for the Field class (String by default).
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# If a string is provided, use it for the display_name (+name+ by default).
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# If a hash is provided, use it for options.
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#
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# *Warning*: the rest reader method returns a copy of the field, so
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# accessors on that returned value do not affect the original rest field.
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#
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def self.rest(name, *ary)
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if @rest_field
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raise ArgumentError, "Duplicate rest field: #{name.inspect}."
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end
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opts = parse_options(ary, name, String)
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offset = round_byte_length
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byte_range = offset..-1
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class_eval do
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field_class = opts[:field_class]
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define_method name do ||
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field_class.new(self[byte_range])
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end
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define_method "#{name}=" do |val|
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self[byte_range] = val
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end
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@rest_field = Field.new(offset, -1, name, {
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:display_name => opts[:display_name],
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:rest_class => field_class
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})
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end
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end
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# Not included with the other fields, but accessible separately.
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def self.rest_field; @rest_field; end
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end
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