fix dynamic bytes decoding in abi

Author: Jan Xie

ethereum/abi.py

@@ -373,8 +373,12 @@ def decode_single(typ, data):
         return encode_hex(data[12:])
     elif base == 'hash':
         return data[32-int(sub):]
-    elif base == 'string' or base == 'bytes' or base == 'hash':
-        return data[:int(sub)] if len(sub) else data
+    elif base == 'string' or base == 'bytes':
+        if len(sub):
+            return data[:int(sub)]
+        else:
+            l = big_endian_to_int(data[0:32])
+            return data[32:][:l]
     elif base == 'uint':
         return big_endian_to_int(data)
     elif base == 'int':

ethereum/tests/test_abi.py

@@ -34,6 +34,13 @@ def test_abi_decode_single_hash():
     typ = ['hash', '8', []]
     assert b'\x01'*8 == abi.decode_single(typ, abi.encode_single(typ, b'\x01'*8))
 
+def test_abi_decode_single_bytes():
+    typ = ['bytes', '8', []]
+    assert (b'\x01\x02' + b'\x00'*6) == abi.decode_single(typ, abi.encode_single(typ, '\x01\x02'))
+
+    typ = ['bytes', '', []]
+    assert b'\x01\x02' == abi.decode_single(typ, abi.encode_single(typ, '\x01\x02'))
+
 # SETUP TESTS IN GLOBAL NAME SPACE
 def gen_func(filename, testname, testdata):
     return lambda: do_test_state(filename, testname, testdata)