Fix timestamp parsing (#415)

Fixes #407

pyproject.toml

@@ -62,9 +62,13 @@ help = "Run tests"
 cmd  = "mypy src --ignore-missing-imports"
 help = "Check types with mypy"
 
+[tool.poe.tasks]
+_black = "black . --exclude tests/output_ --target-version py310"
+_isort = "isort . --extend-skip-glob 'tests/output_*/**/*'"
+
 [tool.poe.tasks.format]
-cmd  = "black . --exclude tests/output_ --target-version py310"
-help = "Apply black formatting to source code"
+sequence  = ["_black", "_isort"]
+help = "Apply black and isort formatting to source code"
 
 [tool.poe.tasks.docs]
 cmd  = "sphinx-build docs docs/build"

src/betterproto/__init__.py

@@ -1885,13 +1885,15 @@ def delta_to_json(delta: timedelta) -> str:
 class _Timestamp(Timestamp):
     @classmethod
     def from_datetime(cls, dt: datetime) -> "_Timestamp":
-        seconds = int(dt.timestamp())
+        # apparently 0 isn't a year in [0, 9999]??
+        seconds = int((dt - DATETIME_ZERO).total_seconds())
         nanos = int(dt.microsecond * 1e3)
         return cls(seconds, nanos)
 
     def to_datetime(self) -> datetime:
         ts = self.seconds + (self.nanos / 1e9)
-        return datetime.fromtimestamp(ts, tz=timezone.utc)
+        # if datetime.fromtimestamp ever supports -62135596800 use that instead see #407
+        return DATETIME_ZERO + timedelta(seconds=ts)
 
     @staticmethod
     def timestamp_to_json(dt: datetime) -> str:

tests/inputs/google_impl_behavior_equivalence/google_impl_behavior_equivalence.proto

@@ -1,5 +1,6 @@
 syntax = "proto3";
 
+import "google/protobuf/timestamp.proto";
 package google_impl_behavior_equivalence;
 
 message Foo { int64 bar = 1; }
@@ -12,6 +13,10 @@ message Test {
   }
 }
 
+message Spam {
+  google.protobuf.Timestamp ts = 1;
+}
+
 message Request { Empty foo = 1; }
 
-message Empty {}
+message Empty {}

tests/inputs/google_impl_behavior_equivalence/test_google_impl_behavior_equivalence.py

@@ -1,17 +1,25 @@
+from datetime import (
+    datetime,
+    timezone,
+)
+
 import pytest
 from google.protobuf import json_format
+from google.protobuf.timestamp_pb2 import Timestamp
 
 import betterproto
 from tests.output_betterproto.google_impl_behavior_equivalence import (
     Empty,
     Foo,
     Request,
+    Spam,
     Test,
 )
 from tests.output_reference.google_impl_behavior_equivalence.google_impl_behavior_equivalence_pb2 import (
     Empty as ReferenceEmpty,
     Foo as ReferenceFoo,
     Request as ReferenceRequest,
+    Spam as ReferenceSpam,
     Test as ReferenceTest,
 )
 
@@ -59,6 +67,19 @@ def test_bytes_are_the_same_for_oneof():
     assert isinstance(message_reference2.foo, ReferenceFoo)
 
 
+@pytest.mark.parametrize("dt", (datetime.min.replace(tzinfo=timezone.utc),))
+def test_datetime_clamping(dt):  # see #407
+    ts = Timestamp()
+    ts.FromDatetime(dt)
+    assert bytes(Spam(dt)) == ReferenceSpam(ts=ts).SerializeToString()
+    message_bytes = bytes(Spam(dt))
+
+    assert (
+        Spam().parse(message_bytes).ts.timestamp()
+        == ReferenceSpam.FromString(message_bytes).ts.seconds
+    )
+
+
 def test_empty_message_field():
     message = Request()
     reference_message = ReferenceRequest()