Support ABI parsing of specs that use function types (#874)

See http://solidity.readthedocs.io/en/v0.4.21/types.html#function-types
This is a special case of `bytes24`, 24 bytes are right zero padded in
a 32 byte word.

manticore/ethereum.py

@@ -461,6 +461,10 @@ class ABI(object):
         elif ty.startswith('bytes') and 0 <= int(ty[5:]) <= 32:
             size = int(ty[5:])
             result = data[offset:offset + size]
+        elif ty == u'function':
+            # `function` is a special case of `bytes24`
+            size = 24
+            result = data[offset:offset + size]
         elif ty == u'address[]':
             dyn_offset = arithmetic_simplify(ABI.get_uint(data, 32, offset))
             size = arithmetic_simplify(ABI.get_uint(data, 32, dyn_offset))

tests/test_eth.py

@@ -207,6 +207,26 @@ class EthAbiTests(unittest.TestCase):
         self.assertEqual(name, 'func')
         self.assertEqual(args, tuple())
 
+    def test_function_type(self):
+        # setup ABI for function with one function param
+        func_name = 'func'
+        spec = func_name+'(function)'
+        func_id = ABI.make_function_id(spec)
+        # build bytes24 data for function value (address+selector)
+        # calls member id lookup on 'Ethereum Foundation Tip Box' (see https://www.ethereum.org/donate)
+        address = ''.join(ABI.serialize_uint(0xfB6916095ca1df60bB79Ce92cE3Ea74c37c5d359, 20))
+        selector = ABI.make_function_id('memberId(address)')
+        function_ref_data = address + selector
+        # build tx call data
+        call_data = ''.join([
+            func_id,
+            function_ref_data,
+            '\0'*8
+        ])
+        name, args = ABI.parse(spec, call_data)
+        self.assertEqual(name, func_name)
+        self.assertEqual(args, (function_ref_data,))
+
 
 class EthTests(unittest.TestCase):
     def test_emit_did_execute_end_instructions(self):