Refactor how registering grpcio servicer works

We now have a grpcio module in betterproto that defines the ServicerBase
Abstract Base Class and a register_servicers function.
Register_servicers takes multiple ServicerBase instances, and registers
them to the grpc AIO server.

The generated servicers now inherit from ServicerBase.

Author: roblabla

pyproject.toml

@@ -19,6 +19,7 @@ dataclasses = { version = "^0.7", python = ">=3.6, <3.7" }
 grpclib = "^0.4.1"
 jinja2 = { version = "^2.11.2", optional = true }
 protobuf = { version = "^3.12.2", optional = true }
+grpcio = { version = "^1.35.0", optional = true }
 
 [tool.poetry.dev-dependencies]
 black = "^20.8b1"
@@ -42,6 +43,7 @@ protoc-gen-python_betterproto = "betterproto.plugin:main"
 
 [tool.poetry.extras]
 compiler = ["black", "jinja2", "protobuf"]
+grpcio = ["grpcio"]
 
 [tool.poe.tasks]
 # Dev workflow tasks

src/betterproto/grpc/grpcio_server.py

@@ -0,0 +1,34 @@
+from typing import Dict, TYPE_CHECKING
+from abc import ABC, abstractmethod
+
+if TYPE_CHECKING:
+    import grpc
+
+class ServicerBase(ABC):
+    """
+    Base class for async grpcio servers.
+    """
+
+    @property
+    @abstractmethod
+    def __rpc_methods__(self) -> Dict[str, "grpc.RpcMethodHandler"]:
+        ...
+
+    @property
+    @abstractmethod
+    def __proto_path__(self) -> str:
+        ...
+
+
+def register_servicers(server: "grpc.aio.Server", *servicers: ServicerBase):
+    from grpc import method_handlers_generic_handler
+
+    server.add_generic_rpc_handlers(
+        tuple(
+            method_handlers_generic_handler(
+                servicer.__proto_path__,
+                servicer.__rpc_handlers__
+            )
+            for servicer in servicers
+        )
+    )

src/betterproto/templates/template.py.j2

@@ -23,6 +23,7 @@ import grpclib
 {% endif %}
 {% if output_file.services and output_file.parent_request.options.grpc_kind == "grpcio" %}
 import grpc
+from betterproto.grpc.grpcio_server import ServicerBase
 {% endif %}
 
 
@@ -249,7 +250,7 @@ class {{ service.py_name }}Base(ServiceBase):
 
 {% if output_file.parent_request.options.grpc_kind == "grpcio" %}
 {% for service in output_file.services %}
-class {{ service.py_name }}Base:
+class {{ service.py_name }}Base(ServicerBase):
     {% if service.comment %}
 {{ service.comment }}
 
@@ -275,8 +276,11 @@ class {{ service.py_name }}Base:
 
     {% endfor %}
 
-    def register_to_server(self, server: grpc.aio.Server):
-        rpc_method_handlers = {
+    __proto_path__ = "{{ service.proto_path }}"
+
+    @property
+    def __rpc_methods__(self):
+        return {
         {% for method in service.methods %}
             "{{ method.proto_name }}":
             {% if not method.client_streaming and not method.server_streaming %}
@@ -294,9 +298,6 @@ class {{ service.py_name }}Base:
                 ),
         {% endfor %}
         }
-        generic_handler = grpc.method_handlers_generic_handler(
-            "{{ service.proto_path }}", rpc_method_handlers)
-        server.add_generic_rpc_handlers((generic_handler,))
 
 {% endfor %}
 {% endif %}