addressing comments

Signed-off-by: Tim Li <ltim@uber.com>

Author: timl3136

cadence/_internal/activity/_heartbeat.py

@@ -37,5 +37,6 @@ async def send_heartbeat(self, *details: Any) -> None:
                     identity=self._identity,
                 )
             )
+            self._previous_details = payload
         except Exception:
             _logger.warning("Heartbeat failed", exc_info=True)

cadence/data_converter.py

@@ -30,6 +30,9 @@ def from_data(
         if not payload.data:
             return DefaultDataConverter._convert_into([], type_hints)
 
+        if not type_hints:
+            type_hints = [None]
+
         payload_str = payload.data.decode()
 
         return self._decode_whitespace_delimited(payload_str, type_hints)
@@ -39,7 +42,7 @@ def _decode_whitespace_delimited(
     ) -> List[Any]:
         results: List[Any] = []
         start, end = 0, len(payload)
-        while start < end and (not type_hints or len(results) < len(type_hints)):
+        while start < end and len(results) < len(type_hints):
             remaining = payload[start:end]
             (value, value_end) = self._decoder.raw_decode(remaining)
             start += value_end + 1
@@ -51,8 +54,6 @@ def _decode_whitespace_delimited(
     def _convert_into(
         values: List[Any], type_hints: Sequence[Type | None]
     ) -> List[Any]:
-        if not type_hints:
-            return list(values)
         results: List[Any] = []
         for i, type_hint in enumerate(type_hints):
             if not type_hint or type_hint is Any:

tests/cadence/_internal/activity/test_heartbeat.py

@@ -67,3 +67,30 @@ async def test_heartbeat_no_details(sender, worker_stub):
     call = worker_stub.RecordActivityTaskHeartbeat.call_args[0][0]
     assert call.task_token == b"task_token"
     assert call.identity == "test-identity"
+
+
+async def test_heartbeat_updates_previous_details(sender, worker_stub):
+    await sender.send_heartbeat("step1", 10)
+
+    details = sender.get_details(str, int)
+    assert details == ["step1", 10]
+
+
+async def test_heartbeat_details_not_updated_on_failure(
+    worker_stub, data_converter,
+):
+    worker_stub.RecordActivityTaskHeartbeat = AsyncMock(
+        side_effect=Exception("rpc error")
+    )
+    sender = _HeartbeatSender(
+        worker_stub=worker_stub,
+        data_converter=data_converter,
+        task_token=b"task_token",
+        identity="test-identity",
+        previous_details=Payload(data=b'"old"'),
+    )
+
+    await sender.send_heartbeat("new_value")
+
+    details = sender.get_details(str)
+    assert details == ["old"]