Go gRPC server utilities

This repo contains utilities to build gRPC server. These include useful interceptors, health checks, metrics, and functions to start and stop the gRPC server.

Installation

go get github.com/moveaxlab/go-grpc-server

Create the server

This package provides utilities to create, start, and stop gRPC servers.

package main

import (
	"fmt"
	"os"
	"os/signal"
	"sync"
	"syscall"

	"github.com/moveaxlab/go-grpc-server"
)

func main() {
	server := grpc_server.NewGrpcServer(40051)
	wg := &sync.WaitGroup{}
	channel := make(chan os.Signal, 1)

	// register your gRPC services
	var myService mypackage.MyServiceServer
	// initialize the myService variable
	mypackage.RegisterMyServiceServer(server.GetServer(), myService)

	// start the server
	server.Start()

	// stop the server gracefully
	signal.Notify(channel, syscall.SIGINT)
	signal.Notify(channel, syscall.SIGTERM)

	wg.Add(1)
	go func() {
		defer wg.Done()
		select {
		case <-channel:
			err := server.Stop()
			if err != nil {
				fmt.Printf("server stop returned an error: %v", err)
			}
		}

	}()
	wg.Wait()
}

Implementing a new gRPC service requires the following steps:

1. generate code from your proto files, using protoc, protoc-gen-go, and protoc-gen-go-grpc
2. implement the service with a struct that embeds the mypackage.MyServiceServer interface
3. register it before the gRPC server start with mypackage.RegisterMyServiceServer, passing it the result of server.GetServer() as first argument

The server registers automatically the standard health service, and sets its status to running as soon as the gRPC server is started.

Metrics

The gRPC server provides metrics with the GetMetrics() method, which returns a list of github.com/prometheus/client_golang/prometheus.Collector.

Using interceptors will enable different metrics.

Interceptors

The gRPC server constructor function accepts a list of google.golang.org/grpc.UnaryServerInterceptor that will be registered in the order they are passed.

We provide a few useful interceptors. The suggested order of registration is the following:

• StatusInterceptor handles non-application errors
• NewMetricsInterceptor() tracks prometheus metrics for your application
• ValidationInterceptor validates requests using protoc-gen-validate
• NewErrorInterceptor() handles application errors
• RecoverInterceptor recovers from panics occurring in the application

Recovering from panics

The grpc_server.RecoverInterceptor recovers from panics downstream in your application. Add it at the end of your interceptor list, and you can panic as much as you want inside your application code.

The recovered errors will be returned as the second result from the handler function in upstream interceptors.

Handling application errors

This package provides the grpc_server.ApplicationError interface that can be implemented by your application errors. This interface requires you to implement the GRPCStatus() method, that converts the error to a google.golang.org/grpc/status.Status object, and the Trailer() method that returns the trailing metadata that must be returned to the caller.

Once you have defined your application errors, call the grpc_server.NewErrorInterceptor() to initialize the interceptor, and add it to your gRPC server.

Initializing this interceptor adds the grpc_request_application_error_count_total prometheus metric to the gRPC server, which counts application errors.

Validating requests

If you are using protoc-gen-validate on incoming requests, you can add the grpc_server.ValidationInterceptor to your gRPC server. This interceptor will validate incoming requests, and return an error if validation does not pass.

Collecting metrics

You can use the grpc_server.NewMetricsInterceptor function to create an interceptor that collects metrics on requests you received using prometheus. Initializing this interceptor will register the following metrics:

• grpc_request_time_ms tracks time taken by all requests
• grpc_request_count_total tracks the number of requests received
• grpc_request_error_count_total tracks the number of requests that failed for any reason

The function that creates the interceptor takes in input a list of endpoints that will be ignored. This can be used if you don't want to track metrics on certain endpoints, e.g. for the health check endpoint.

Unhandled errors

The grpc_server.StatusInterceptor adds the internal status code to responses if the service returned an error and it was not handled by other interceptors.

This should be your first interceptor.

Custom interceptors

You can implement custom interceptors that use your custom application logic.

This interceptor extracts user info from the request metadata, and stores them in the request context:

import (
	"context"

	"google.golang.org/grpc"
	"google.golang.org/grpc/metadata"
)

func SecurityInterceptor(
	ctx context.Context,
	req interface{},
	info *grpc.UnaryServerInfo,
	handler grpc.UnaryHandler,
) (resp interface{}, err error) {
	md, hasMetadata := metadata.FromIncomingContext(ctx)

	if hasMetadata {
		ctx = AddUserToContext(ctx, md)
	}

	return handler(ctx, req)
}

This is what a Sentry interceptor would look like, that sends non-application errors to Sentry and tracks user info:

import (
	"context"

	"github.com/moveaxlab/go-grpc-server"
	"github.com/getsentry/sentry-go"
	"google.golang.org/grpc"
)

func SentryInterceptor(
	ctx context.Context,
	req interface{},
	info *grpc.UnaryServerInfo,
	handler grpc.UnaryHandler,
) (resp interface{}, err error) {
	resp, err = handler(ctx, req)

	// skip reporting application errors to sentry
	if err == nil || grpc_server.IsApplicationError(err) {
		return resp, nil
	}

	sentry.WithScope(func(scope *sentry.Scope) {
		// your custom logic to retrieve the user from the context
		if user, hasUser := GetUser(ctx); hasUser {
			scope.SetUser(sentry.User{
				ID: user.Id(),
			})
		}

		scope.SetExtras(map[string]interface{}{
			"endpoint": info.FullMethod,
			"request":  req,
		})

		sentry.CaptureException(err)
	})

	return nil, err
}

This interceptor should be registered after the SecurityInterceptor example given above.