Add ForkData (ethereum/consensus-specs#173)

Author: hwwhww

eth/beacon/types/fork_data.py

@@ -0,0 +1,29 @@
+import rlp
+
+from eth.rlp.sedes import (
+    uint64,
+)
+
+
+class ForkData(rlp.Serializable):
+    """
+    Note: using RLP until we have standardized serialization format.
+    """
+    fields = [
+        # Previous fork version
+        ('pre_fork_version', uint64),
+        # Post fork version
+        ('post_fork_version', uint64),
+        # Fork slot number
+        ('fork_slot_number', uint64)
+    ]
+
+    def __init__(self,
+                 pre_fork_version: int,
+                 post_fork_version: int,
+                 fork_slot_number: int) -> None:
+        super().__init__(
+            pre_fork_version=pre_fork_version,
+            post_fork_version=post_fork_version,
+            fork_slot_number=fork_slot_number,
+        )

tests/beacon/conftest.py

@@ -118,6 +118,15 @@ def sample_crosslink_record_params():
     }
 
 
+@pytest.fixture
+def sample_fork_data_params():
+    return {
+        'pre_fork_version': 0,
+        'post_fork_version': 0,
+        'fork_slot_number': 2**64 - 1,
+    }
+
+
 @pytest.fixture
 def sample_proposal_signed_data_params():
     return {

tests/beacon/types/test_fork_data.py

@@ -0,0 +1,10 @@
+from eth.beacon.types.fork_data import (
+    ForkData,
+)
+
+
+def test_defaults(sample_fork_data_params):
+    fork_data = ForkData(**sample_fork_data_params)
+    assert fork_data.pre_fork_version == sample_fork_data_params['pre_fork_version']
+    assert fork_data.post_fork_version == sample_fork_data_params['post_fork_version']
+    assert fork_data.fork_slot_number == sample_fork_data_params['fork_slot_number']