golang-inject

README

golang-inject

Tiny context-based dependency injection framework for Go.

Basic Example

This basic example contains three modules illustrating how to use the dependency framework in a project.

Config Module

package config

import (
	"context"

	"github.com/ibrt/golang-inject/injectz"
)

type contextKey int

const (
	cfgContextKey contextKey = iota
)

type Config struct {
	DatabaseURL string
}

func Initializer(ctx context.Context) (injectz.Injector, injectz.Releaser) {
	cfg := &Config{
		DatabaseURL: "...", // e.g. read from env var
	}
	return NewSingletonInjector(cfg), injectz.NewNoopReleaser()
}

func NewSingletonInjector(cfg *Config) injectz.Injector {
	return injectz.NewSingletonInjector(cfgContextKey, cfg)
}

func Get(ctx context.Context) *Config {
	return ctx.Value(cfgContextKey).(*Config)
}

Database Module

package database

import (
	"context"
	"database/sql"

	"project/modules/config"
	
	"github.com/ibrt/golang-inject/injectz"
)

type contextKey int

const (
	dbContextKey contextKey = iota
)

var (
	_ Database = &databaseImpl{}
)

type User struct {
	ID        string
	FirstName string
	LastName  string
}

type Database interface {
	GetUser(ctx context.Context, id string) (*User, error)
}

type databaseImpl struct {
	sqlDB *sql.DB
}

func (d *databaseImpl) GetUser(ctx context.Context, id string) (*User, error) {
	// e.g. run a query using d.sqlDB
	return &User{ID: id}, nil
}

func Initializer(ctx context.Context) (injectz.Injector, injectz.Releaser) {
	sqlDB, err := sql.Open("mysql", config.Get(ctx).DatabaseURL)
	if err != nil {
		panic(err)
	}

	db := &databaseImpl{
		sqlDB: sqlDB,
	}

	return NewSingletonInjector(db), injectz.NewCloseReleaser(sqlDB)
}

func NewSingletonInjector(db Database) injectz.Injector {
	return injectz.NewSingletonInjector(dbContextKey, db)
}

func Get(ctx context.Context) Database {
	return ctx.Value(dbContextKey).(Database)
}

Request ID Module

package request

import (
	"context"
	"math/rand"

	"github.com/ibrt/golang-inject/injectz"
)

type contextKey int

const (
	requestIDContextKey contextKey = iota
)

func Initializer(ctx context.Context) (injectz.Injector, injectz.Releaser) {
	injector := func(ctx context.Context) context.Context {
		return context.WithValue(ctx, requestIDContextKey, newID())
	}
	return injector, injectz.NewNoopReleaser()
}

func newID() string {
	const length = 8
	const chars = "abcdefghijklmnopqrstuvwxyz1234567890"
	b := make([]byte, length)
	_, _ = rand.Read(b)
	for i := 0; i < length; i++ {
		b[i] = chars[int(b[i])%len(chars)]
	}
	return string(b)
}

func Get(ctx context.Context) string {
	return ctx.Value(requestIDContextKey).(string)
}

Main

package main

import (
	"log"
	"net/http"

	"project/modules/config"
	"project/modules/database"
	"project/modules/request"
	
	"github.com/ibrt/golang-inject/injectz"
)

func main() {
	injector, releaser := injectz.Initialize(
		config.Initializer, 
		database.Initializer, 
		request.Initializer)
	defer releaser()

	middleware := injectz.NewMiddleware(injector)
	mux := http.NewServeMux()
	mux.Handle("/", middleware(http.HandlerFunc(handler)))
	_ = http.ListenAndServe(":3000", mux)
}

func handler(w http.ResponseWriter, r *http.Request) {
	// use the request ID module (note that the injector generates a new ID each time)
	requestID := request.Get(r.Context())
	log.Print(requestID, " ", r.URL.String())

	// use the database module
	user, err := database.Get(r.Context()).GetUser(r.Context(), "some-id")
	// ...

	_, _ = w.Write([]byte("response"))
}

Developers

Contributions are welcome, please check in on proposed implementation before sending a PR. You can validate your changes using the ./test.sh script.