mirror of
https://github.com/rapid7/metasploit-framework
synced 2024-11-12 11:52:01 +01:00
111 lines
3.6 KiB
Ruby
111 lines
3.6 KiB
Ruby
module BinData
|
|
# The enviroment in which a lazily evaluated lamba is called. These lambdas
|
|
# are those that are passed to data objects as parameters. Each lambda
|
|
# has access to the following:
|
|
#
|
|
# parent:: the environment of the parent data object
|
|
# params:: any extra parameters that have been passed to the data object.
|
|
# The value of a parameter is either a lambda, a symbol or a
|
|
# literal value (such as a Fixnum).
|
|
#
|
|
# Unknown methods are resolved in the context of the parent environment,
|
|
# first as keys in the extra parameters, and secondly as methods in the
|
|
# parent data object. This makes the lambda easier to read as we just write
|
|
# <tt>field</tt> instead of <tt>obj.field</tt>.
|
|
class LazyEvalEnv
|
|
# An empty hash shared by all instances
|
|
@@empty_hash = Hash.new.freeze
|
|
|
|
@@variables_cache = {}
|
|
|
|
# Creates a new environment. +parent+ is the environment of the
|
|
# parent data object.
|
|
def initialize(parent = nil)
|
|
@parent = parent
|
|
@variables = @@empty_hash
|
|
@overrides = @@empty_hash
|
|
@params = @@empty_hash
|
|
end
|
|
attr_reader :parent, :params
|
|
attr_accessor :data_object
|
|
|
|
# only accessible by another LazyEvalEnv
|
|
protected :data_object
|
|
|
|
# Set the parameters for this environment.
|
|
def params=(p)
|
|
@params = (p.nil? or p.empty?) ? @@empty_hash : p
|
|
end
|
|
|
|
# Add a variable with a pre-assigned value to this environment. +sym+
|
|
# will be accessible as a variable for any lambda evaluated
|
|
# with #lazy_eval.
|
|
def add_variable(sym, value)
|
|
sym = sym.to_sym
|
|
if @variables.equal?(@@empty_hash)
|
|
# optimise the case where only 1 variable is added as this
|
|
# is the most common occurance (BinData::Arrays adding index)
|
|
key = [sym, value]
|
|
@variables = @@variables_cache[key]
|
|
if @variables.nil?
|
|
# cache this variable and value so it can be shared with
|
|
# other LazyEvalEnvs to keep memory usage down
|
|
@variables = {sym => value}.freeze
|
|
@@variables_cache[key] = @variables
|
|
end
|
|
else
|
|
if @variables.length == 1
|
|
key = @variables.keys[0]
|
|
@variables = {key => @variables[key]}
|
|
end
|
|
@variables[sym] = value
|
|
end
|
|
end
|
|
|
|
# TODO: offset_of needs to be better thought out
|
|
def offset_of(sym)
|
|
@parent.data_object.offset_of(sym)
|
|
rescue
|
|
nil
|
|
end
|
|
|
|
# Returns the data_object for the parent environment.
|
|
def parent_data_object
|
|
@parent.nil? ? nil : @parent.data_object
|
|
end
|
|
|
|
# Evaluates +obj+ in the context of this environment. Evaluation
|
|
# recurses until it yields a value that is not a symbol or lambda.
|
|
# +overrides+ is an optional +params+ like hash
|
|
def lazy_eval(obj, overrides = nil)
|
|
result = obj
|
|
@overrides = overrides if overrides
|
|
if obj.is_a? Symbol
|
|
# treat :foo as lambda { foo }
|
|
result = __send__(obj)
|
|
elsif obj.respond_to? :arity
|
|
result = instance_eval(&obj)
|
|
end
|
|
@overrides = @@empty_hash
|
|
result
|
|
end
|
|
|
|
def method_missing(symbol, *args)
|
|
if @overrides.include?(symbol)
|
|
@overrides[symbol]
|
|
elsif @variables.include?(symbol)
|
|
@variables[symbol]
|
|
elsif @parent
|
|
obj = symbol
|
|
if @parent.params and @parent.params.has_key?(symbol)
|
|
obj = @parent.params[symbol]
|
|
elsif @parent.data_object and @parent.data_object.respond_to?(symbol)
|
|
obj = @parent.data_object.__send__(symbol, *args)
|
|
end
|
|
@parent.lazy_eval(obj)
|
|
else
|
|
super
|
|
end
|
|
end
|
|
end
|
|
end |