[Aio] Correct the typing of input Metadata (#27768)

src/python/grpcio/grpc/aio/_base_channel.py

@@ -19,8 +19,8 @@ from typing import Any, Optional
 import grpc
 
 from . import _base_call
-from ._metadata import Metadata
 from ._typing import DeserializingFunction
+from ._typing import MetadataType
 from ._typing import RequestIterableType
 from ._typing import SerializingFunction
 
@@ -34,7 +34,7 @@ class UnaryUnaryMultiCallable(abc.ABC):
         request: Any,
         *,
         timeout: Optional[float] = None,
-        metadata: Optional[Metadata] = None,
+        metadata: Optional[MetadataType] = None,
         credentials: Optional[grpc.CallCredentials] = None,
         wait_for_ready: Optional[bool] = None,
         compression: Optional[grpc.Compression] = None
@@ -73,7 +73,7 @@ class UnaryStreamMultiCallable(abc.ABC):
         request: Any,
         *,
         timeout: Optional[float] = None,
-        metadata: Optional[Metadata] = None,
+        metadata: Optional[MetadataType] = None,
         credentials: Optional[grpc.CallCredentials] = None,
         wait_for_ready: Optional[bool] = None,
         compression: Optional[grpc.Compression] = None
@@ -111,7 +111,7 @@ class StreamUnaryMultiCallable(abc.ABC):
         self,
         request_iterator: Optional[RequestIterableType] = None,
         timeout: Optional[float] = None,
-        metadata: Optional[Metadata] = None,
+        metadata: Optional[MetadataType] = None,
         credentials: Optional[grpc.CallCredentials] = None,
         wait_for_ready: Optional[bool] = None,
         compression: Optional[grpc.Compression] = None
@@ -150,7 +150,7 @@ class StreamStreamMultiCallable(abc.ABC):
         self,
         request_iterator: Optional[RequestIterableType] = None,
         timeout: Optional[float] = None,
-        metadata: Optional[Metadata] = None,
+        metadata: Optional[MetadataType] = None,
         credentials: Optional[grpc.CallCredentials] = None,
         wait_for_ready: Optional[bool] = None,
         compression: Optional[grpc.Compression] = None

src/python/grpcio/grpc/aio/_base_server.py

@@ -19,6 +19,7 @@ from typing import Generic, Iterable, Mapping, Optional, Sequence
 import grpc
 
 from ._metadata import Metadata
+from ._typing import MetadataType
 from ._typing import RequestType
 from ._typing import ResponseType
 
@@ -159,7 +160,8 @@ class ServicerContext(Generic[RequestType, ResponseType], abc.ABC):
         """
 
     @abc.abstractmethod
-    async def send_initial_metadata(self, initial_metadata: Metadata) -> None:
+    async def send_initial_metadata(self,
+                                    initial_metadata: MetadataType) -> None:
         """Sends the initial metadata value to the client.
 
         This method need not be called by implementations if they have no
@@ -174,7 +176,7 @@ class ServicerContext(Generic[RequestType, ResponseType], abc.ABC):
         self,
         code: grpc.StatusCode,
         details: str = '',
-        trailing_metadata: Metadata = tuple()) -> None:
+        trailing_metadata: MetadataType = tuple()) -> None:
         """Raises an exception to terminate the RPC with a non-OK status.
 
         The code and details passed as arguments will supercede any existing
@@ -194,7 +196,7 @@ class ServicerContext(Generic[RequestType, ResponseType], abc.ABC):
         """
 
     @abc.abstractmethod
-    def set_trailing_metadata(self, trailing_metadata: Metadata) -> None:
+    def set_trailing_metadata(self, trailing_metadata: MetadataType) -> None:
         """Sends the trailing metadata for the RPC.
 
         This method need not be called by implementations if they have no

src/python/grpcio/grpc/aio/_typing.py

@@ -27,7 +27,7 @@ ResponseType = TypeVar('ResponseType')
 SerializingFunction = Callable[[Any], bytes]
 DeserializingFunction = Callable[[bytes], Any]
 MetadatumType = Tuple[MetadataKey, MetadataValue]
-MetadataType = Metadata
+MetadataType = Union[Metadata, Sequence[MetadatumType]]
 ChannelArgumentType = Sequence[Tuple[str, Any]]
 EOFType = type(EOF)
 DoneCallbackType = Callable[[Any], None]