diff -r ffa851df0825 -r 2fb8b9db1c86 symbian-qemu-0.9.1-12/python-2.6.1/Lib/Bastion.py --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/symbian-qemu-0.9.1-12/python-2.6.1/Lib/Bastion.py Fri Jul 31 15:01:17 2009 +0100 @@ -0,0 +1,180 @@ +"""Bastionification utility. + +A bastion (for another object -- the 'original') is an object that has +the same methods as the original but does not give access to its +instance variables. Bastions have a number of uses, but the most +obvious one is to provide code executing in restricted mode with a +safe interface to an object implemented in unrestricted mode. + +The bastionification routine has an optional second argument which is +a filter function. Only those methods for which the filter method +(called with the method name as argument) returns true are accessible. +The default filter method returns true unless the method name begins +with an underscore. + +There are a number of possible implementations of bastions. We use a +'lazy' approach where the bastion's __getattr__() discipline does all +the work for a particular method the first time it is used. This is +usually fastest, especially if the user doesn't call all available +methods. The retrieved methods are stored as instance variables of +the bastion, so the overhead is only occurred on the first use of each +method. + +Detail: the bastion class has a __repr__() discipline which includes +the repr() of the original object. This is precomputed when the +bastion is created. + +""" +from warnings import warnpy3k +warnpy3k("the Bastion module has been removed in Python 3.0", stacklevel=2) +del warnpy3k + +__all__ = ["BastionClass", "Bastion"] + +from types import MethodType + + +class BastionClass: + + """Helper class used by the Bastion() function. + + You could subclass this and pass the subclass as the bastionclass + argument to the Bastion() function, as long as the constructor has + the same signature (a get() function and a name for the object). + + """ + + def __init__(self, get, name): + """Constructor. + + Arguments: + + get - a function that gets the attribute value (by name) + name - a human-readable name for the original object + (suggestion: use repr(object)) + + """ + self._get_ = get + self._name_ = name + + def __repr__(self): + """Return a representation string. + + This includes the name passed in to the constructor, so that + if you print the bastion during debugging, at least you have + some idea of what it is. + + """ + return "" % self._name_ + + def __getattr__(self, name): + """Get an as-yet undefined attribute value. + + This calls the get() function that was passed to the + constructor. The result is stored as an instance variable so + that the next time the same attribute is requested, + __getattr__() won't be invoked. + + If the get() function raises an exception, this is simply + passed on -- exceptions are not cached. + + """ + attribute = self._get_(name) + self.__dict__[name] = attribute + return attribute + + +def Bastion(object, filter = lambda name: name[:1] != '_', + name=None, bastionclass=BastionClass): + """Create a bastion for an object, using an optional filter. + + See the Bastion module's documentation for background. + + Arguments: + + object - the original object + filter - a predicate that decides whether a function name is OK; + by default all names are OK that don't start with '_' + name - the name of the object; default repr(object) + bastionclass - class used to create the bastion; default BastionClass + + """ + + raise RuntimeError, "This code is not secure in Python 2.2 and later" + + # Note: we define *two* ad-hoc functions here, get1 and get2. + # Both are intended to be called in the same way: get(name). + # It is clear that the real work (getting the attribute + # from the object and calling the filter) is done in get1. + # Why can't we pass get1 to the bastion? Because the user + # would be able to override the filter argument! With get2, + # overriding the default argument is no security loophole: + # all it does is call it. + # Also notice that we can't place the object and filter as + # instance variables on the bastion object itself, since + # the user has full access to all instance variables! + + def get1(name, object=object, filter=filter): + """Internal function for Bastion(). See source comments.""" + if filter(name): + attribute = getattr(object, name) + if type(attribute) == MethodType: + return attribute + raise AttributeError, name + + def get2(name, get1=get1): + """Internal function for Bastion(). See source comments.""" + return get1(name) + + if name is None: + name = repr(object) + return bastionclass(get2, name) + + +def _test(): + """Test the Bastion() function.""" + class Original: + def __init__(self): + self.sum = 0 + def add(self, n): + self._add(n) + def _add(self, n): + self.sum = self.sum + n + def total(self): + return self.sum + o = Original() + b = Bastion(o) + testcode = """if 1: + b.add(81) + b.add(18) + print "b.total() =", b.total() + try: + print "b.sum =", b.sum, + except: + print "inaccessible" + else: + print "accessible" + try: + print "b._add =", b._add, + except: + print "inaccessible" + else: + print "accessible" + try: + print "b._get_.func_defaults =", map(type, b._get_.func_defaults), + except: + print "inaccessible" + else: + print "accessible" + \n""" + exec testcode + print '='*20, "Using rexec:", '='*20 + import rexec + r = rexec.RExec() + m = r.add_module('__main__') + m.b = b + r.r_exec(testcode) + + +if __name__ == '__main__': + _test()