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gRPC Reflection Example

The reflection example has a Hello World server with ProtoReflectionServiceV1 registered.

Build the example

To build the example server, from the grpc-java/examples/examples-reflection directory:

$ ../gradlew installDist

This creates the scripts build/install/example-reflection/bin/reflection-server.

Run the example

gRPC Server Reflection provides information about publicly-accessible gRPC services on a server, and assists clients at runtime to construct RPC requests and responses without precompiled service information. It is used by gRPCurl, which can be used to introspect server protos and send/receive test RPCs.

  1. To start the reflection example server on its default port of 50051, run:
$ ./build/install/example-reflection/bin/reflection-server
  1. After enabling Server Reflection in a server application, you can use gRPCurl to check its services. Instructions on how to install and use gRPCurl can be found at gRPCurl Installation

After installing gRPCurl, open a new terminal and run the commands from the new terminal.

List all the services exposed at a given port

$ grpcurl -plaintext localhost:50051 list

Output

grpc.reflection.v1alpha.ServerReflection
helloworld.Greeter

List all the methods of a service

$ grpcurl -plaintext localhost:50051 list helloworld.Greeter

Output

helloworld.Greeter.SayHello

Describe services and methods

The describe command inspects a method given its full name(in the format of <package>.<service>.<method>).

$ grpcurl -plaintext localhost:50051 describe helloworld.Greeter.SayHello

Output

helloworld.Greeter.SayHello is a method:
rpc SayHello ( .helloworld.HelloRequest ) returns ( .helloworld.HelloReply );

Inspect message types

We can use the describe command to inspect request/response types given the full name of the type (in the format of <package>.<type>).

Get information about the request type:

$ grpcurl -plaintext localhost:50051 describe helloworld.HelloRequest

Output

helloworld.HelloRequest is a message:
message HelloRequest {
  string name = 1;
}

Call a remote method

We can send RPCs to a server and get responses using the full method name (in the format of <package>.<service>.<method>). The -d <string> flag represents the request data and the -format text flag indicates that the request data is in text format.

$ grpcurl -plaintext -format text -d 'name: "gRPCurl"' \
  localhost:50051 helloworld.Greeter.SayHello

Output

message: "Hello gRPCurl"