add a set_state_from method to overwrite current state...

This can be useful for doing trial receptions of messages, and
if they work, update the state when successful...  Setting the
state on the old object is best as it's hard to change all references
to the new object..

copyof = strb.copy()
try:
	copyof.recv_enc(msg)
	copyof.recv_mac(mac)
except AuthenticationFailed: # failed, ignore message
	return
else: # it worked
	strb.set_state_from(copyof)

<process msg>

strobe/python/Strobe/Strobe.py

@@ -46,6 +46,12 @@ class Strobe(object):
     
     def copy(self): return Strobe(None,copy_of=self)
     def deepcopy(self): return self.copy()
+    def set_state_from(self, obj):
+        self.R,self.pos,self.posbegin,self.I0,self.F = \
+            (obj.R,obj.pos,obj.posbegin,obj.I0,
+             obj.F.copy())
+        self.st = bytearray(obj.st)
+        self.initialized = True
  
     def _runF(self):
         if self.initialized:

strobe/python/Strobe/Test/copy.py

@@ -3,6 +3,7 @@
 import unittest
 
 from Strobe.Strobe import Strobe
+from Strobe.Strobe import AuthenticationFailed
 
 class TestCopy(unittest.TestCase):
 	def test_copy(self):
@@ -19,3 +20,20 @@ class TestCopy(unittest.TestCase):
 		# that both the original and copy work
 		self.assertEqual(b'anothertest', b.recv_enc(msg))
 		self.assertEqual(b'anothertest', c.recv_enc(msg))
+
+	def test_set_state_from(self):
+		a = Strobe(b'foo')
+		b = Strobe(b'foo')
+		c = b.copy()
+
+		mac = a.send_mac(8)
+
+		# That the wrong mac fails
+		with self.assertRaises(AuthenticationFailed):
+			b.recv_mac(b'random')
+
+		# but the state can be reset
+		b.set_state_from(c)
+
+		# and then works fine
+		b.recv_mac(mac)