gRPC in Go: Let's Go

Fire up GoLand and click New Project. Name the project go-grpc-demo and click Create:

To generate Go code from Protobuf definitions, you'll need to install two plugins for protoc:

1. protoc-gen-go, which generates Go code containing the messages defined in the Protobuf files.
2. protoc-gen-go-grpc, which generates Go bindings for services defined in the Protobuf files.

Open GoLand's integrated terminal and run the following commands to install protoc-gen-go and protoc-gen-go-grpc:

go install google.golang.org/protobuf/cmd/protoc-gen-go@latest
go install google.golang.org/grpc/cmd/protoc-gen-go-grpc@latest

To make sure the tools are correctly installed, run the following command, which should print the version of the installed protoc-gen-go binary:

protoc-gen-go --version

Do the same for protoc-gen-go-grpc:

protoc-gen-go-grpc --version

Writing the Protobuf Definitions

Create a new file called tasks.proto in the project's root. In this file, you'll define the messages and methods. Start by configuring the options:

syntax = 'proto3';

option go_package="src/go/tasks";

import "google/protobuf/timestamp.proto";

package tasks;

The go_package option specifies the full Go package name. Then, the Timestamp type is imported, which will be used in the Protobuf definitions. Finally, the line package tasks sets the package name for the generated code.

Defining Task

Start by defining Task, which is the fundamental unit for the task management app. A Task will have an ID, a description, an ID for the user who owns the task, a task status (complete, incomplete, or started), a deadline, and a creation date. Write the following code in tasks.proto:

enum TaskStatus {
  TASK_STATUS_COMPLETED = 0;
  TASK_STATUS_INCOMPLETE = 1;
  TASK_STATUS_STARTED = 2;
}

message Task {
  string id = 1;
  string description = 3;
  string user_id = 4;
  TaskStatus status = 5;
  google.protobuf.Timestamp deadline = 6;
  google.protobuf.Timestamp created_at = 7;
}

First, you define an enum named TaskStatus. The three values TASK_STATUS_COMPLETED, TASK_STATUS_INCOMPLETE, and TASK_STATUS_STARTED represent the three possible statuses a Task can have. The enum is then used in the Task definition for the status field. The created_at and deadline fields have the google.protobuf.Timestamp type from the timestamp.proto file that was imported earlier. The Timestamp type facilitates the conversion of timestamps from strings and the handling of timestamps.

Defining the gRPC Methods

The app will have five gRPC methods:

1. A CreateTask method that will create a task.
2. A GetTask method that will return a task given its ID.
3. A ListTasks method that will return all tasks for a given user within a given deadline. This will be a unidirectional server-side streaming endpoint.
4. A RecordTasks method, which will create a bunch of tasks. This will be a unidirectional client-side streaming endpoint.
5. A TaskChat method where multiple users can add comments to a task. This will be a bidirectional streaming endpoint.

To create RPC methods, you must define a service. Start by defining a TaskService:

service TaskService {

}

The CreateTask Method

The CreateTask method receives a task's description, user ID, and deadline and creates the task. After the task is created, the newly created task is returned as a response:

service TaskService {
  rpc CreateTask(CreateTaskRequest) returns (Task);
}

message CreateTaskRequest {
  string description = 1;
  string user_id = 2;
  google.protobuf.Timestamp deadline = 3;
}

Here, a new message named CreateTaskRequest is defined, which works as the request type of the CreateTask method. The method returns a Task, as discussed earlier.

The GetTask Method

For the GetTask method, the request only contains the task ID, and the return type is once again Task:

service TaskService {
  ...
  rpc GetTask(GetTaskRequest) returns (Task);
}

...

message GetTaskRequest {
  string task_id = 1;
}

The ListTasks Method

The ListTasks method is slightly different because it's a streaming endpoint. Instead of sending the entire list of tasks at once, it will send the data in a stream that can be consumed by the client. Thankfully, with gRPC, creating a streaming endpoint is as easy as specifying the stream keyword before the request type, the response type, or both, depending on the direction of the stream. Since this one is a server-to-client stream, the stream keyword is placed before the return type, indicating that the client will receive a stream:

service TaskService {
  ...
  rpc ListTasks(ListTasksRequest) returns (stream Task);
}

...

message ListTasksRequest {
  string user_id = 1;
  google.protobuf.Timestamp deadline = 2;
}

As before, a new message is defined for the request type. The ListTasksRequest message contains only the user ID and the deadline.

The RecordTasks Method

Like ListTasks, this one is also a streaming endpoint. However, this time, it's a client-to-server stream. So, the stream keyword is placed before the request type, indicating that the server will receive a stream:

service TaskService {
  ...
  rpc RecordTasks(stream CreateTaskRequest) returns (TaskSummary);
}

...

message TaskSummary {
  string no_of_tasks_created = 1;
}

The method returns a message named TaskSummary, which contains the number of tasks created by the server.

The TaskChat Method

The TaskChat method is a bidirectional streaming endpoint, so both the request and response types have the stream keyword. This means that both the server and the client will receive a stream. They can both read from the streams and write to them:

service TaskService {
  ...
  rpc TaskChat(stream TaskComment) returns (stream TaskComment);
}

...

message TaskComment {
  string task_id = 1;
  string user_id = 2;
  string comment = 3;
  google.protobuf.Timestamp created_at = 4;
}

The entire tasks.proto file should look like the following:

syntax = 'proto3';

option go_package="src/go/tasks";

import "google/protobuf/timestamp.proto";

package tasks;

service TaskService {
  rpc CreateTask(CreateTaskRequest) returns (Task);
  rpc GetTask(GetTaskRequest) returns (Task);
  rpc ListTasks(ListTasksRequest) returns (stream Task);
  rpc RecordTasks(stream CreateTaskRequest) returns (TaskSummary);
  rpc TaskChat(stream TaskComment) returns (stream TaskComment);
}

enum TaskStatus {
  TASK_STATUS_COMPLETED = 0;
  TASK_STATUS_INCOMPLETE = 1;
  TASK_STATUS_STARTED = 2;
}

message Task {
  string id = 1;
  string description = 3;
  string user_id = 4;
  TaskStatus status = 5;
  google.protobuf.Timestamp deadline = 6;
  google.protobuf.Timestamp created_at = 7;
}

message CreateTaskRequest {
  string description = 1;
  string user_id = 2;
  google.protobuf.Timestamp deadline = 3;
}

message GetTaskRequest {
  string task_id = 1;
}

message ListTasksRequest {
  string user_id = 1;
  google.protobuf.Timestamp deadline = 2;
}

message TaskSummary {
  string no_of_tasks_created = 1;
}

message TaskComment {
  string task_id = 1;
  string user_id = 2;
  string comment = 3;
  google.protobuf.Timestamp created_at = 4;
}

Generating the gRPC Stub

Once the Protobuf definitions are ready, generating the gRPC stub is as easy as running the protoc command with the appropriate options. But first, create the directory where the Go code will be stored:

mkdir -p src/go

Run the following code to compile the definitions from tasks.proto:

protoc --go_out=./src/go/ --go_opt=paths=source_relative --go-grpc_out=./src/go/ --go-grpc_opt=paths=source_relative tasks.proto

This will create two files, tasks.pb.go and tasks_grpc.pb.go, in the src/go directory.

If you open tasks.pb.go, you'll see that GoLand shows errors because the dependencies are not installed:

Thanks to GoLand, installing dependencies is super easy. Hover over any red line and click Sync dependencies of go-grpc-demo or press Alt+Shift+Enter (⌥+⇧+↩) . Once the dependencies are downloaded, the lines will turn green: