Add ability to provide metadata, timeout & deadline args to requests

This is an enhancement of the ServiceStub abstract class that makes
it more useful by making it possible to pass all arguments supported
by the underlying grpclib request function.

It extends to the existing high level API by allowing values to be
set on the stub instance, and the low level API by allowing values
to be set per call.

betterproto/__init__.py

@@ -11,10 +11,12 @@ from typing import (
     Any,
     AsyncGenerator,
     Callable,
+    Collection,
     Dict,
     Generator,
     Iterable,
     List,
+    Mapping,
     Optional,
     SupportsBytes,
     Tuple,
@@ -1000,20 +1002,57 @@ def _get_wrapper(proto_type: str) -> Type:
     }[proto_type]
 
 
+_Value = Union[str, bytes]
+_MetadataLike = Union[Mapping[str, _Value], Collection[Tuple[str, _Value]]]
+
+
 class ServiceStub(ABC):
     """
     Base class for async gRPC service stubs.
     """
 
-    def __init__(self, channel: grpclib.client.Channel) -> None:
+    def __init__(
+        self,
+        channel: grpclib.client.Channel,
+        *,
+        timeout: Optional[float] = None,
+        deadline: Optional[grpclib.metadata.Deadline] = None,
+        metadata: Optional[_MetadataLike] = None,
+    ) -> None:
         self.channel = channel
+        self.timeout = timeout
+        self.deadline = deadline
+        self.metadata = metadata
+
+    def __resolve_request_kwargs(
+        self,
+        timeout: Optional[float],
+        deadline: Optional[grpclib.metadata.Deadline],
+        metadata: Optional[_MetadataLike],
+    ):
+        return {
+            "timeout": self.timeout if timeout is None else timeout,
+            "deadline": self.deadline if deadline is None else deadline,
+            "metadata": self.metadata if metadata is None else metadata,
+        }
 
     async def _unary_unary(
-        self, route: str, request: "IProtoMessage", response_type: Type[T]
+        self,
+        route: str,
+        request: "IProtoMessage",
+        response_type: Type[T],
+        *,
+        timeout: Optional[float] = None,
+        deadline: Optional[grpclib.metadata.Deadline] = None,
+        metadata: Optional[_MetadataLike] = None,
     ) -> T:
         """Make a unary request and return the response."""
         async with self.channel.request(
-            route, grpclib.const.Cardinality.UNARY_UNARY, type(request), response_type
+            route,
+            grpclib.const.Cardinality.UNARY_UNARY,
+            type(request),
+            response_type,
+            **self.__resolve_request_kwargs(timeout, deadline, metadata),
         ) as stream:
             await stream.send_message(request, end=True)
             response = await stream.recv_message()
@@ -1021,11 +1060,22 @@ class ServiceStub(ABC):
             return response
 
     async def _unary_stream(
-        self, route: str, request: "IProtoMessage", response_type: Type[T]
+        self,
+        route: str,
+        request: "IProtoMessage",
+        response_type: Type[T],
+        *,
+        timeout: Optional[float] = None,
+        deadline: Optional[grpclib.metadata.Deadline] = None,
+        metadata: Optional[_MetadataLike] = None,
     ) -> AsyncGenerator[T, None]:
         """Make a unary request and return the stream response iterator."""
         async with self.channel.request(
-            route, grpclib.const.Cardinality.UNARY_STREAM, type(request), response_type
+            route,
+            grpclib.const.Cardinality.UNARY_STREAM,
+            type(request),
+            response_type,
+            **self.__resolve_request_kwargs(timeout, deadline, metadata),
         ) as stream:
             await stream.send_message(request, end=True)
             async for message in stream: