Generating Code in Go

Different approach to some challenges

Gopher: https://github.com/egonelbre/gophers

(no AI)

Who am I?

Staff Backend Engineer at Pento

Daniel Antos

I used to hate generated code.

What are we talking about today?

Why?
Basics of generating code in Go.
Generate your APIs: gRPC, GraphQL.
Generate your ORM.
Generating decorators.
Everyday life with generated code.

Why?

Compile time safety
To reduce abstraction and complexity
Computer is better at repetitive task

Error while building:
 # github.com/antosdaniel/go-presentation-generate-code/internal/grpc
internal/grpc/payrollServiceWithAuth.go:16:9: ... (missing method GetPayslip)

Basics of generating code in Go

Generators are just CLI tools:

go generate <path>

go generate ./...

Generate your APIs: gRPC, GraphQL

syntax = "proto3";

package payroll.v1;

service PayrollService {
  rpc AddPayroll(AddPayrollRequest) returns (AddPayrollResponse);
  rpc AddPayslip(AddPayslipRequest) returns (AddPayslipResponse);
  rpc GetPayroll(GetPayrollRequest) returns (GetPayrollResponse);
}

message AddPayrollRequest {
  string payroll_id = 1;
  string tenant_id = 2;
  Date   payday = 3;
}

// ...

Generate your APIs: gRPC, GraphQL, REST

// PayrollServiceHandler is an implementation of the payroll.v1.PayrollService service.
type PayrollServiceHandler interface {
  AddPayroll(context.Context, *connect_go.Request[payrollv1.AddPayrollRequest]) (*connect_go.Response[payrollv1.AddPayrollResponse], error)
  AddPayslip(context.Context, *connect_go.Request[payrollv1.AddPayslipRequest]) (*connect_go.Response[payrollv1.AddPayslipResponse], error)
  GetPayroll(context.Context, *connect_go.Request[payrollv1.GetPayrollRequest]) (*connect_go.Response[payrollv1.GetPayrollResponse], error)
}

// Now we only have to implement it:
func (s *payrollServiceServer) AddPayroll(
  ctx context.Context,
  request *connect_go.Request[payrollv1.AddPayrollRequest],
) (*connect_go.Response[payrollv1.AddPayrollResponse], error) {
  // TODO: business logic

  return &connect_go.Response[payrollv1.AddPayrollResponse]{
    Msg: &payrollv1.AddPayrollResponse{ PayrollId: id, },
  }, nil
}

Generate your ORM

create table payrolls (
    id        uuid not null primary key,
    tenant_id uuid not null,
    payday    date not null
);

type PayrollModel struct {
	ID       string `orm:"id"`
	TenantID string `orm:"tenant_id"`
	Payday   string `orm:"payday"`
}

The ugly side of abstraction

func FindPayroll(ctx context.Context, exec boil.ContextExecutor, iD string, selectCols ...string) (*Payroll, error) {
	payrollObj := &Payroll{}

	sel := "*"
	if len(selectCols) > 0 {
		sel = strings.Join(strmangle.IdentQuoteSlice(dialect.LQ, dialect.RQ, selectCols), ",")
	}
	query := fmt.Sprintf(
		"select %s from \"payrolls\" where \"id\"=$1", sel,
	)

	q := queries.Raw(query, iD)

	err := q.Bind(ctx, exec, payrollObj)
	if err != nil {
		if errors.Is(err, sql.ErrNoRows) {
			return nil, sql.ErrNoRows
		}
		return nil, errors.Wrap(err, "models: unable to select from payrolls")
	}

	return payrollObj, nil
}

Abstraction and reflection are costly

Source: https://github.com/volatiletech/sqlboiler

Generating decorators

What can we generate?

func (ps PayrollServiceWithTrace) AddPayroll(...) error {
	ps.tracer.Start(...)
	defer ps.tracer.End(...)
	
	err := ps.base.AddPayroll(...)
	
	if err != nil {
		ps.tracer.RaiseError(err)
	}
	return err
}

func (ps PayrollServiceWithTrace) AddPayslip(...) error {
	ps.tracer.Start(...)
	defer ps.tracer.End(...)
	
	err := ps.base.AddPayslip(...)
	
	if err != nil {
		ps.tracer.RaiseError(err)
	}
	return err
}

Everyday life with generated code

because you will hit some issues

Commit generated code, and check it in CI

No need to generate code before build
Easy to spot unintended changes during code review
Easily reproducible builds

Makefile is where it begins

.PHONY: install
install:
  @printf "\nInstalling sqlboiler...\n"
  @go install -mod=readonly github.com/volatiletech/sqlboiler/v4@v4.15.0
  @go install -mod=readonly github.com/volatiletech/sqlboiler/v4/drivers/sqlboiler-psql@v4.15.0

  @printf "\nInstalling gowrap...\n"
  @go install -mod=readonly github.com/hexdigest/gowrap/cmd/gowrap@v1.3.2
  
  # ...

.PHONY: generate
generate: 
  @printf "Generating protos...\n"
  @buf generate --template gen/grpc/buf.gen.yaml

  @printf "Generating db models...\n"
  @sqlboiler --config db/sqlboiler.toml psql

  @printf "go generate...\n"
  @go generate ./...

  @$(MAKE) format