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153 lines
4.0 KiB
Markdown
153 lines
4.0 KiB
Markdown
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# 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
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requests and responses without precompiled service information. It is used by
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gRPC CLI, which can be used to introspect server protos and send/receive test
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RPCs.
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## Enable Server Reflection
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gRPC-go Server Reflection is implemented in package [reflection](https://github.com/grpc/grpc-go/tree/master/reflection). To enable server reflection, you need to import this package and register reflection service on your gRPC server.
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For example, to enable server reflection in `example/helloworld`, we need to 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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"golang.org/x/net/context"
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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.RegisterGreeterServer(s, &server{})
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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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We have made this change in `example/helloworld`, and we will use it as an example to show the use of gRPC server reflection and gRPC CLI in this tutorial.
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## gRPC CLI
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After enabling Server Reflection in a server application, you can use gRPC CLI to check its services.
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gRPC CLI is only available in c++. Instructions on how to use gRPC CLI can be found at [command_line_tool.md](https://github.com/grpc/grpc/blob/master/doc/command_line_tool.md).
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To build gRPC CLI:
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```sh
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git clone https://github.com/grpc/grpc
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cd grpc
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make grpc_cli
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cd bins/opt # grpc_cli is in directory bins/opt/
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```
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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/helloworld/greeter_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-dirctory>/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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helloworld.Greeter
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grpc.reflection.v1alpha.ServerReflection
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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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