mirror of https://github.com/grpc/grpc-go.git
150 lines
3.8 KiB
Markdown
150 lines
3.8 KiB
Markdown
# gRPC Server Reflection Tutorial
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gRPC Server Reflection provides information about publicly-accessible gRPC
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services on a server, and assists clients at runtime to construct RPC requests
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and responses without precompiled service information. It is used by gRPC CLI,
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which can be used to introspect server protos and send/receive test RPCs.
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## Enable Server Reflection
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gRPC-go Server Reflection is implemented in package
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[reflection](https://github.com/grpc/grpc-go/tree/master/reflection). To enable
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server reflection, you need to import this package and register reflection
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service on your gRPC server.
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For example, to enable server reflection in `example/helloworld`, we need to
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make the following changes:
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```diff
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--- a/examples/helloworld/greeter_server/main.go
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+++ b/examples/helloworld/greeter_server/main.go
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@@ -40,6 +40,7 @@ import (
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"google.golang.org/grpc"
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pb "google.golang.org/grpc/examples/helloworld/helloworld"
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+ "google.golang.org/grpc/reflection"
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)
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const (
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@@ -61,6 +62,8 @@ func main() {
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}
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s := grpc.NewServer()
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pb.RegisterGreeterService(s, &pb.GreeterService{SayHello: sayHello})
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+ // Register reflection service on gRPC server.
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+ reflection.Register(s)
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if err := s.Serve(lis); err != nil {
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log.Fatalf("failed to serve: %v", err)
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}
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```
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An example server with reflection registered can be found at
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`examples/features/reflection/server`.
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## gRPC CLI
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After enabling Server Reflection in a server application, you can use gRPC CLI
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to check its services. gRPC CLI is only available in c++. Instructions on how to
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build and use gRPC CLI can be found at
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[command_line_tool.md](https://github.com/grpc/grpc/blob/master/doc/command_line_tool.md).
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## Use gRPC CLI to check services
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First, start the helloworld server in grpc-go directory:
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```sh
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$ cd <grpc-go-directory>
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$ go run examples/features/reflection/server/main.go
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```
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Open a new terminal and make sure you are in the directory where grpc_cli lives:
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```sh
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$ cd <grpc-cpp-directory>/bins/opt
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```
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### List services
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`grpc_cli ls` command lists services and methods exposed at a given port:
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- List all the services exposed at a given port
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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.examples.echo.Echo
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grpc.reflection.v1alpha.ServerReflection
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helloworld.Greeter
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```
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- List one service with details
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`grpc_cli ls` command inspects a service given its full name (in the format of
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\<package\>.\<service\>). It can print information with a long listing format
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when `-l` flag is set. This flag can be used to get more details about a
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service.
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```sh
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$ ./grpc_cli ls localhost:50051 helloworld.Greeter -l
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```
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output:
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```sh
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filename: helloworld.proto
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package: helloworld;
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service Greeter {
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rpc SayHello(helloworld.HelloRequest) returns (helloworld.HelloReply) {}
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}
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```
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### List methods
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- List one method with details
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`grpc_cli ls` command also inspects a method given its full name (in the
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format of \<package\>.\<service\>.\<method\>).
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```sh
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$ ./grpc_cli ls localhost:50051 helloworld.Greeter.SayHello -l
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```
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output:
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```sh
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rpc SayHello(helloworld.HelloRequest) returns (helloworld.HelloReply) {}
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```
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### Inspect message types
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We can use`grpc_cli type` command to inspect request/response types given the
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full name of the type (in the format of \<package\>.\<type\>).
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- Get information about the request type
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```sh
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$ ./grpc_cli type localhost:50051 helloworld.HelloRequest
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```
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output:
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```sh
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message HelloRequest {
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optional string name = 1[json_name = "name"];
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}
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```
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### Call a remote method
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We can send RPCs to a server and get responses using `grpc_cli call` command.
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- Call a unary method
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```sh
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$ ./grpc_cli call localhost:50051 SayHello "name: 'gRPC CLI'"
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```
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output:
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```sh
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message: "Hello gRPC CLI"
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```
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