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121 lines
4.5 KiB
121 lines
4.5 KiB
# gRPC Python Server Reflection |
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This document shows how to use gRPC Server Reflection in gRPC Python. |
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Please see [C++ Server Reflection Tutorial] for general information |
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and more examples how to use server reflection. |
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## Enable server reflection in Python servers |
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gRPC Python Server Reflection is an add-on library. To use it, first install |
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the [grpcio-reflection] PyPI package into your project. |
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Note that with Python you need to manually register the service |
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descriptors with the reflection service implementation when creating a server |
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(this isn't necessary with e.g. C++ or Java) |
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```python |
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# add the following import statement to use server reflection |
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from grpc_reflection.v1alpha import reflection |
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# ... |
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def serve(): |
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server = grpc.server(futures.ThreadPoolExecutor(max_workers=10)) |
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helloworld_pb2_grpc.add_GreeterServicer_to_server(Greeter(), server) |
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# the reflection service will be aware of "Greeter" and "ServerReflection" services. |
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SERVICE_NAMES = ( |
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helloworld_pb2.DESCRIPTOR.services_by_name['Greeter'].full_name, |
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reflection.SERVICE_NAME, |
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) |
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reflection.enable_server_reflection(SERVICE_NAMES, server) |
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server.add_insecure_port('[::]:50051') |
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server.start() |
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``` |
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Please see [greeter_server_with_reflection.py] in the examples directory for the full |
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example, which extends the gRPC [Python `Greeter` example] on a reflection-enabled server. |
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After starting the server, you can verify that the server reflection |
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is working properly by using the [`grpc_cli` command line tool]: |
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```sh |
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$ grpc_cli ls localhost:50051 |
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``` |
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output: |
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```sh |
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grpc.reflection.v1alpha.ServerReflection |
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helloworld.Greeter |
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``` |
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For more examples and instructions how to use the `grpc_cli` tool, |
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please refer to the [`grpc_cli` documentation] and the |
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[C++ Server Reflection Tutorial]. |
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## Use Server Reflection in a Python client |
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Server Reflection can be used by clients to get information about gRPC services |
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at runtime. We've provided a descriptor database called |
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[ProtoReflectionDescriptorDatabase](../../src/python/grpcio_reflection/v1alpha/proto_reflection_descriptor_database.h) |
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which implements the |
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[DescriptorDatabase](https://googleapis.dev/python/protobuf/latest/google/protobuf/descriptor_database.html#google.protobuf.descriptor_database.DescriptorDatabase) |
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interface. It manages the communication between clients and reflection services |
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and the storage of received information. Clients can use it as using a local |
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descriptor database. |
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- To use Server Reflection with ProtoReflectionDescriptorDatabase, first |
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initialize an instance with a channel. |
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```Python |
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import grpc |
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from grpc_reflection.v1alpha.proto_reflection_descriptor_database import ProtoReflectionDescriptorDatabase |
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channel = grpc.secure_channel(server_address, creds) |
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reflection_db = ProtoReflectionDescriptorDatabase(channel) |
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``` |
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- Then use this instance to feed a |
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[DescriptorPool](https://googleapis.dev/python/protobuf/latest/google/protobuf/descriptor_pool.html#google.protobuf.descriptor_pool.DescriptorPool). |
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```Python |
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from google.protobuf.descriptor_pool import DescriptorPool |
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desc_pool = DescriptorPool(reflection_db) |
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``` |
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- Example usage of this descriptor pool: |
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* Get Service/method descriptors. |
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```Python |
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service_desc = desc_pool.FindServiceByName("helloworld.Greeter") |
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method_desc = service_desc.FindMethodByName("helloworld.Greeter.SayHello") |
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``` |
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* Get message type descriptors and create messages dynamically. |
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```Python |
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request_desc = desc_pool.FindMessageTypeByName("helloworld.HelloRequest") |
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request = MessageFactory(desc_pool).GetPrototype(request_desc)() |
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``` |
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- You can also use the Reflection Database to list all the services: |
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```Python |
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services = reflection_db.get_services() |
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``` |
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## Additional Resources |
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The [Server Reflection Protocol] provides detailed |
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information about how the server reflection works and describes the server reflection |
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protocol in detail. |
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[C++ Server Reflection Tutorial]: ../server_reflection_tutorial.md |
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[grpcio-reflection]: https://pypi.org/project/grpcio-reflection/ |
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[greeter_server_with_reflection.py]: https://github.com/grpc/grpc/blob/master/examples/python/helloworld/greeter_server_with_reflection.py |
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[Python `Greeter` example]: https://github.com/grpc/grpc/tree/master/examples/python/helloworld |
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[`grpc_cli` command line tool]: https://github.com/grpc/grpc/blob/master/doc/command_line_tool.md |
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[`grpc_cli` documentation]: ../command_line_tool.md |
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[C++ Server Reflection Tutorial]: ../server_reflection_tutorial.md |
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[Server Reflection Protocol]: ../server-reflection.md
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