Add helper method to get a struct message as JSON

Structs containing any Bytes types would error out with the standard
json.dumps call, since it does not support json-encoding bytes by default.

Additionally, this adds __eq__ and __hash__ functions to structs - the need
arose due to some comparisons I wanted to make during new tests.

Author: ajrgrubbs

eip712_structs/struct.py

@@ -1,11 +1,14 @@
+import functools
+import json
+import operator
 import re
 from collections import OrderedDict, defaultdict
 from typing import List, Tuple, NamedTuple
 
 from eth_utils.crypto import keccak
 
 import eip712_structs
-from eip712_structs.types import Array, EIP712Type, from_solidity_type
+from eip712_structs.types import Array, EIP712Type, from_solidity_type, BytesJSONEncoder
 
 
 class OrderedAttributesMeta(type):
@@ -180,6 +183,10 @@ def to_message(self, domain: 'EIP712Struct' = None) -> dict:
 
         return result
 
+    def to_message_json(self, domain: 'EIP712Struct' = None) -> str:
+        message = self.to_message(domain)
+        return json.dumps(message, cls=BytesJSONEncoder)
+
     def signable_bytes(self, domain: 'EIP712Struct' = None) -> bytes:
         """Return a ``bytes`` object suitable for signing, as specified for EIP712.
 
@@ -251,6 +258,24 @@ def from_message(cls, message_dict: dict) -> 'StructTuple':
 
         return result
 
+    def __eq__(self, other):
+        if not other:
+            # Null check
+            return False
+        if self is other:
+            # Check identity
+            return True
+        if not isinstance(other, EIP712Struct):
+            # Check class
+            return False
+        # Our structs are considered equal if their type signature and encoded value signature match.
+        # E.g., like computing signable bytes but without a domain separator
+        return self.encode_type() == other.encode_type() and self.encode_value() == other.encode_value()
+
+    def __hash__(self):
+        value_hashes = [hash(k) ^ hash(v) for k, v in self.values.items()]
+        return functools.reduce(operator.xor, value_hashes, hash(self.type_name))
+
 
 class StructTuple(NamedTuple):
     message: EIP712Struct

eip712_structs/types.py

@@ -1,8 +1,9 @@
 import re
+from json import JSONEncoder
 from typing import Any, Union, Type
 
 from eth_utils.crypto import keccak
-from eth_utils.conversions import to_int
+from eth_utils.conversions import to_bytes, to_hex, to_int
 
 
 class EIP712Type:
@@ -124,6 +125,10 @@ def __init__(self, length: int = 0):
 
     def _encode_value(self, value):
         """Static bytesN types are encoded by right-padding to 32 bytes. Dynamic bytes types are keccak256 hashed."""
+        if isinstance(value, str):
+            # Try converting to a bytestring, assuming that it's been given as hex
+            value = to_bytes(hexstr=value)
+
         if self.length == 0:
             return keccak(value)
         else:
@@ -229,3 +234,11 @@ def from_solidity_type(solidity_type: str):
         return result
     else:
         return type_instance
+
+
+class BytesJSONEncoder(JSONEncoder):
+    def default(self, o):
+        if isinstance(o, bytes):
+            return to_hex(o)
+        else:
+            return super(BytesJSONEncoder, self).default(o)

tests/test_encode_data.py

@@ -187,3 +187,44 @@ def test_validation_errors():
         bool_type.encode_value(0)
     with pytest.raises(ValueError, match='Must be True or False.'):
         bool_type.encode_value(1)
+
+
+def test_struct_eq():
+    class Foo(EIP712Struct):
+        s = String()
+    foo = Foo(s='hello world')
+    foo_copy = Foo(s='hello world')
+    foo_2 = Foo(s='blah')
+
+    assert foo == foo
+    assert foo is not foo_copy
+    assert foo == foo_copy
+    assert foo != foo_2
+
+    def make_different_foo():
+        # We want another struct defined with the same name but different member types
+        class Foo(EIP712Struct):
+            b = Bytes()
+        return Foo
+
+    def make_same_foo():
+        # For good measure, recreate the exact same class and ensure they can still compare
+        class Foo(EIP712Struct):
+            s = String()
+        return Foo
+
+    OtherFooClass = make_different_foo()
+    wrong_type = OtherFooClass(b=b'hello world')
+    assert wrong_type != foo
+    assert OtherFooClass != Foo
+
+    SameFooClass = make_same_foo()
+    right_type = SameFooClass(s='hello world')
+    assert right_type == foo
+    assert SameFooClass != Foo
+
+    # Different name, same members
+    class Bar(EIP712Struct):
+        s = String()
+    bar = Bar(s='hello world')
+    assert bar != foo

tests/test_message_json.py

@@ -1,4 +1,7 @@
-from eip712_structs import EIP712Struct, String, make_domain
+import json
+import os
+
+from eip712_structs import EIP712Struct, String, make_domain, Bytes
 
 
 def test_flat_struct_to_message():
@@ -105,3 +108,20 @@ class Foo(EIP712Struct):
     assert bar_val.get_data_value('s') == 'bar'
 
     assert foo.hash_struct() == new_struct.hash_struct()
+
+
+def test_bytes_json_encoder():
+    class Foo(EIP712Struct):
+        b = Bytes(32)
+    domain = make_domain(name='domain')
+
+    bytes_val = os.urandom(32)
+    foo = Foo(b=bytes_val)
+    result = foo.to_message_json(domain)
+
+    expected_substring = f'"b": "0x{bytes_val.hex()}"'
+    assert expected_substring in result
+
+    reconstructed = EIP712Struct.from_message(json.loads(result))
+    assert reconstructed.domain == domain
+    assert reconstructed.message == foo