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Bootstrap Go

It is hard to write bootstrap tool to quickly create Go service. So I write this guide instead. This is a quick checklist for me every damn time I need to write a Go service from scratch. Also, this is my personal opinion, so feel free to comment.

Structure

main.go
internal
| business
| | http
| | | handler.go
| | | service.go
| | | models.go
| | grpc
| | | handler.go
| | | models.go
| | consumer
| | | handler.go
| | | service.go
| | | models.go
| | service.go
| | repository.go
| | models.go

All business codes are inside internal. Each business has a different directory business.

Inside each business, there are 2 handlers: http, grpc:

http is for public APIs (Android, iOS, ... are clients).
grpc is for internal APIs (other services are clients).
consumer is for consuming messages from queue (Kafka, RabbitMQ, ...).

For each handler, there are usually 3 layers: handler, service, repository:

handler interacts directly with gRPC, REST or consumer using specific codes (cookies, ...) In case gRPC, there are frameworks outside handle for us so we can write business/logic codes here too. But remember, gRPC only.
service is where we write business/logic codes, and only business/logic codes is written here.
repository is where we write codes which interacts with database/cache like MySQL, Redis, ...
models is where we put all request, response, data models.

Location:

handler must exist inside grpc, http, consumer.
service, models can exist directly inside of business if both grpc, http, consumer has same business/logic.
repository should be placed directly inside of business.

Do not repeat!

If we have too many services, some of the logic will be overlapped.

For example, service A and service B both need to make POST call API to service C. If service A and service B both have libs to call service C to do that API, we need to move the libs to some common pkg libs. So in the future, service D which needs to call C will not need to copy libs to handle service C api but only need to import from common pkg libs.

Another bad practice is adapter service. No need to write a new service if what we need is just common pkg libs.

Taste on style guide

Stop using global var

If I see someone using global var, I swear I will shoot them twice in the face.

Why?

Can not write unit test.
Is not thread safe.

Use functional options, but don't overuse it!

For simple struct with 1 or 2 fields, no need to use functional options.

Example:

func main() {
	s := NewS(WithA(1), WithB("b"))
	fmt.Printf("%+v\n", s)
}

type S struct {
	fieldA int
	fieldB string
}

type OptionS func(s *S)

func WithA(a int) OptionS {
	return func(s *S) {
		s.fieldA = a
	}
}

func WithB(b string) OptionS {
	return func(s *S) {
		s.fieldB = b
	}
}

func NewS(opts ...OptionS) *S {
	s := &S{}
	for _, opt := range opts {
		opt(s)
	}
	return s
}

In above example, I construct s with WithA and WithB option. No need to pass direct field inside s.

Use errgroup as much as possible

If business logic involves calling too many APIs, but they are not depend on each other. We can fire them parallel :)

Personally, I prefer errgroup to WaitGroup (https://pkg.go.dev/sync#WaitGroup). Because I always need deal with error.

Example:

eg, egCtx := errgroup.WithContext(ctx)

eg.Go(func() error {
	// Do some thing
	return nil
})

eg.Go(func() error {
	// Do other thing
	return nil
})

if err := eg.Wait(); err != nil {
	// Handle error
}

Use semaphore when need to implement WorkerPool

Please don't use external libs for WorkerPool, I don't want to deal with dependency hell.

External libs

No need `vendor`

Only need if you need something from vendor, to generate mock or something else.

Use `build.go` to include build tools in go.mod

To easily control version of build tools.

For example build.go:

//go:build tools
// +build tools

package main

import (
	_ "github.com/golang/protobuf/protoc-gen-go"
)

And then in Makefile:

build:
    go install github.com/golang/protobuf/protoc-gen-go

We always get the version of build tools in go.mod each time we install it. Future contributors will not cry anymore.

Don't use cli libs (spf13/cobra, urfave/cli) just for Go service

What is the point to pass many params (do-it, --abc, --xyz) when what we only need is start service?

In my case, service starts with only config, and config should be read from file or environment like The Twelve Factors guide.

Don't use grpc-ecosystem/grpc-gateway

Just don't.

Use protocolbuffers/protobuf-go, grpc/grpc-go for gRPC.

Write 1 for both gRPC, REST sounds good, but in the end, it is not worth it.

Don't use uber/prototool, use bufbuild/buf

prototool is deprecated, and buf can generate, lint, format as good as prototool.

Use gin-gonic/gin for REST.

Don't use gin.Context when pass context from handler layer to service layer, use gin.Context.Request.Context() instead.

If you want log, just use uber-go/zap

It is fast!

Don't overuse func (*Logger) With. Because if log line is too long, there is a possibility that we can lost it.
Use MarshalLogObject when we need to hide some field of object when log (field is long or has sensitive value)
Don't use Panic. Use Fatal for errors when start service to check dependencies. If you really need panic level, use DPanic.
If doubt, use zap.Any.
Use contextID or traceID in every log lines for easily debug.

To read config, use spf13/viper

Only init config in main or cmd layer. Do not use viper.Get... in business layer or inside business layer.

Why?

Hard to mock and test
Put all config in single place for easily tracking

Also, be careful if config value is empty. You should decide to continue or stop the service if there is no config.

Don't overuse ORM libs, no need to handle another layer above SQL.

Each ORM libs has each different syntax. To learn and use those libs correctly is time consuming. So just stick to plain SQL. It is easier to debug when something is wrong.

But database/sql has its own limit. For example, it is hard to get primary key after insert/update. So may be you want to use ORM for those cases. I hear that go-gorm/gorm, ent/ent is good.

If you want test, just use stretchr/testify.

It is easy to write a suite test, thanks to testify. Also, for mocking, there are many options out there. Pick 1 then sleep peacefully.

If need to mock, choose matryer/moq or golang/mock

The first is easy to use but not powerful as the later. If you want to make sure mock func is called with correct times, use the later.

Example with matryer/moq:

// Only gen mock if source code file is newer than mock file
// https://jonwillia.ms/2019/12/22/conditional-gomock-mockgen
//go:generate sh -c "test service_mock_generated.go -nt $GOFILE && exit 0; moq -rm -out service_mock_generated.go . Service"

Be careful with spf13/cast

Don't cast proto enum:

// Bad
a := cast.ToInt32(servicev1.ReasonCode_ABC)

// Good
a := int32(servicev1.ReasonCode_ABC)

Use stringer if you want your type enum can be print as string

type Drink int

const (
	Beer Drink = iota
	Water
	OrangeJuice
)

go install golang.org/x/tools/cmd/stringer@latest

# Run inside directory which contains Drink
stringer -type=Drink

Don't waste your time rewrite rate limiter if your use case is simple, use rate or go-redis/redis_rate

rate if you want rate limiter locally in your single instance of service. redis_rate if you want rate limiter distributed across all your instances of service.

Replace `go fmt`, `goimports` with mvdan/gofumpt.

gofumpt provides more rules when format Go codes.

Use golangci/golangci-lint.

No need to say more. Lint or get the f out!

If you get fieldalignment error, use fieldalignment to fix them.

# Install
go install golang.org/x/tools/go/analysis/passes/fieldalignment/cmd/fieldalignment@latest

# Fix
fieldalignment -fix ./internal/business/*.go

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