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