logging-middleware

Structure

As a code-generator first application, we have the following structure:

• cmd - The home of the code generator application to be invoked with go generate ...
• pkg - The layers of the application to parse an incoming file and validate to actual file generation
• example - The example with a couple of interfaces being middleware'd

How to use

Simply put, one can write a simple Foo interface with a common Middleware function type as type Middleware func(Foo)Foo

//go:generate go run middleware-generator Service SvcMiddleware tracer
package pkg

type Service interface {
	Foo(bar string) string
}

type SvcMiddleware func(Service) Service

What this will do is generate a new file alongside the target file prepended with logger_ and implements the given Service with a factory method called NewService. It's not necessary to call these types Service, but the types themselves must exist.

An example service that gets generated:

// Code generated by "logger-middleware Service SvcMiddleware tracer"; DO NOT EDIT.
// Copyright (c) 2022 Merit International Inc. All Rights Reserved

package example

import (
	"context"
	domain "github.com/gabizou/middleware-generator/example/domain"
	zipkingo "github.com/openzipkin/zipkin-go"
)

func NewServiceTracer(tracer zipkingo.Tracer) SvcMiddleware {
	return func(s Service) Service {
		return &tracerS{
			s:  s,
			tr: tracer,
		}
	}
}

type tracerS struct {
	tr zipkingo.Tracer
	s  Service
}

func (t *tracerS) Foo(ctx context.Context, bar string) domain.Merit {
	span, ctx := t.tr.StartSpanFromContext(ctx, "Foo")

	defer func() {
		span.Finish()
	}()

	return t.s.Foo(ctx, bar)
}

Technologies used

• golang.org/x/tools: Standard library tools to parse and resolve types of the source file
• golang.org/go/types: Standard library code for representing and interpreting the AST in go
• github.com/dave/jennifer: Code generation library to simplify actual AST -> source code