gRPC Server Reflection Tutorial

Enable Server Reflection

To enable server reflection, you need to import Reflection package and register reflection service on your gRPC server.

For example, to enable server reflection in example/helloworld, we need to make the following changes:

--- a/examples/helloworld/greeter_server/main.go
+++ b/examples/helloworld/greeter_server/main.go
@@ -40,6 +40,7 @@ import (
        "google.golang.org/grpc"
        pb "google.golang.org/grpc/examples/helloworld/helloworld"
+       "google.golang.org/grpc/reflection"
 )

 const (
@@ -61,6 +62,8 @@ func main() {
        }
        s := grpc.NewServer()
        pb.RegisterGreeterService(s, &pb.GreeterService{SayHello: sayHello})
+       // Register reflection service on gRPC server.
+       reflection.Register(s)
        if err := s.Serve(lis); err != nil {
                log.Fatalf("failed to serve: %v", err)
        }

gRPCurl

After enabling Server Reflection in a server application, you can use gRPCurl to check its services. gRPCurl is built with Go and has packages available. Instructions on how to install and use gRPCurl can be found at gRPCurl Installation.

Use gRPCurl to check services

First, start grpc server:

$ go run ./server/main.go

output:

server listening at [::]:5001

NOTE: gRPCurl expects a TLS-encrypted connection by default. For all of the commands below, use the -plaintext flag to use an unencrypted connection.

List services and methods

The list command lists services exposed at a given port:

• List all the services exposed at a given port:

  $ grpcurl -plaintext localhost:50051 list
  

  output:

  grpc.examples.echo.Echo
  grpc.reflection.v1alpha.ServerReflection
  helloworld.Greeter
  

• List all the methods of a service The list command lists methods given the full service name (in the format of <package>.<service>).

  $ grpcurl -plaintext localhost:50051 list helloworld.Greeter
  

output:

helloworld.Greeter.SayHello

Describe services and methods

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

$ grpcurl -plaintext localhost:50051 describe helloworld.Greeter

• Describe all methods of a service 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 json flag indicates that the request data is in json format.

• Call a unary method

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

  output:

  {
  message: "Hello gRPCurl"
  }