fix decoder, also fix bug in pyssz, see PR 74

test_libs/pyspec/eth2spec/fuzzing/decoder.py

@@ -72,7 +72,7 @@ def translate_value(value, typ):
         return value
     elif spec_ssz.is_vector_type(typ):
         elem_typ = spec_ssz.read_elem_type(typ)
-        return typ(translate_value(elem, elem_typ) for elem in value)
+        return typ(*(translate_value(elem, elem_typ) for elem in value))
     elif spec_ssz.is_bytesn_type(typ):
         return typ(value)
     elif spec_ssz.is_bytes_type(typ):

test_libs/pyspec/eth2spec/fuzzing/test_decoder.py

@@ -0,0 +1,39 @@
+from eth2spec.fuzzing.decoder import translate_typ, translate_value
+from eth2spec.phase0 import spec
+from preset_loader import loader
+from eth2spec.utils.ssz import ssz_impl as spec_ssz_impl
+from random import Random
+from eth2spec.debug import random_value
+
+
+def test_decoder():
+    configs_path = "../../../../configs/"
+    config_name = "minimal"
+    presets = loader.load_presets(configs_path, config_name)
+    spec.apply_constants_preset(presets)
+
+    rng = Random(123)
+
+    # check these types only, Block covers a lot of operation types already.
+    for typ in [spec.BeaconBlock, spec.BeaconState, spec.IndexedAttestation, spec.AttestationDataAndCustodyBit]:
+        # create a random pyspec value
+        original = random_value.get_random_ssz_object(rng, typ, 100, 10,
+                                                      mode=random_value.RandomizationMode.mode_random,
+                                                      chaos=True)
+        # serialize it, using pyspec
+        pyspec_data = spec_ssz_impl.serialize(original)
+        # get the py-ssz type for it
+        block_sedes = translate_typ(typ)
+        # try decoding using the py-ssz type
+        raw_value = block_sedes.deserialize(pyspec_data)
+
+        # serialize it using py-ssz
+        pyssz_data = block_sedes.serialize(raw_value)
+        # now check if the serialized form is equal. If so, we confirmed decoding and encoding to work.
+        assert pyspec_data == pyssz_data
+
+        # now translate the py-ssz value in a pyspec-value
+        block = translate_value(raw_value, typ)
+
+        # and see if the hash-tree-root of the original matches the hash-tree-root of the decoded & translated value.
+        assert spec_ssz_impl.hash_tree_root(original) == spec_ssz_impl.hash_tree_root(block)