mcp/internal/index/builtins/README.md

Wiring Conventions

Forging a service is mostly wiring. Do it the same way every time.

This is not an Einherjar module — it is the canonical application shape that uses Einherjar modules. Apps live in their own repository with an internal/wire/ package that mirrors this template. The conventions here are distilled from production services built on Einherjar v1 (iron-dough-api, pei-api) and describe the one opinionated minimum a scaffolded app should have. You can hand-roll something else — but then it is yours to maintain, and it will not match what the rest of the ecosystem reads at a glance.

The opinionated minimum

Every scaffolded Einherjar application has, at minimum:

1. A clean main.go — nothing but .env autoload and a call to wire.Run().
2. An internal/wire/ package — one file per feature plus wire.go, which assembles everything.
3. An internal/config/config.go — one global Config that composes the framework's component configs, loaded from the environment with caarlos0/env.
4. A .env.example kept in lock-step with that config (see Config & .env.example).

Anything a developer freely chooses — how migrations run, how the first admin is seeded, an init-by-endpoint/webhook/email flow — is not part of this convention and is left to the app.

Project layout

cmd/<app>/main.go              one-line entrypoint: godotenv autoload + wire.Run()
internal/wire/wire.go          Run() — loads config, builds infra, registers feature hooks
internal/wire/<feature>.go     one file per feature, hosts a with<Feature> hook
internal/wire/middleware.go    authz, skipPublicPaths, skipMethodPath helpers
internal/config/config.go      global Config composing framework component configs
.env.example                   every env var the config reads, documented, in sync
internal/<feature>/dto/        request/response DTOs
internal/<feature>/handler/    HTTP handlers
internal/<feature>/repository/ data access
internal/<feature>/service/    domain logic

main.go

cmd/<app>/main.go contains nothing but the .env autoload and the call to wire.Run(). The blank import _ "github.com/joho/godotenv/autoload" is the standard, documented way to load a local .env — it never overrides variables already set in the real environment, and a missing file is not an error, so deployments (vars injected by the platform, no .env) are unaffected.

package main

import (
	"fmt"
	"os"

	_ "github.com/joho/godotenv/autoload"

	"myapp/internal/wire"
)

func main() {
	if err := wire.Run(); err != nil {
		fmt.Fprintln(os.Stderr, "fatal:", err)
		os.Exit(1)
	}
}

No config parsing, no component construction, no logging setup — all of that lives in internal/wire/. A main.go that builds anything itself is the single most common scaffolding mistake.

Config

internal/config/config.go is one Config struct that composes the framework's component configs as nested fields, alongside the app's own settings. caarlos0/env recurses into the nested fields, so each Einherjar component's EINHERJAR_* env tags load automatically next to the app-owned fields. App-owned fields use the APP_* prefix so they never collide with the framework's EINHERJAR_* namespace. There is exactly one Load().

package config

import (
	"time"

	"github.com/caarlos0/env/v11"

	"code.nochebuena.dev/einherjar/core/logz"
	"code.nochebuena.dev/einherjar/db-postgres"
	"code.nochebuena.dev/einherjar/web/server"
)

// JWTConfig is app-owned: the secret is handed to the signer in code, not consumed
// by a framework component, so it carries no EINHERJAR_ prefix.
type JWTConfig struct {
	Secret     string        `env:"APP_JWT_SECRET,required,notEmpty"`
	Issuer     string        `env:"APP_JWT_ISSUER"      envDefault:"myapp"`
	AccessTTL  time.Duration `env:"APP_JWT_ACCESS_TTL"  envDefault:"1h"`
	RefreshTTL time.Duration `env:"APP_JWT_REFRESH_TTL" envDefault:"168h"`
}

// Config is the fully-resolved startup configuration. Einherjar component configs
// are nested fields; caarlos0/env recurses into them, populating their
// EINHERJAR_SERVER_* / EINHERJAR_PG_* tags from the environment.
type Config struct {
	AppEnv      string   `env:"APP_ENV"          envDefault:"local"`
	CORSOrigins []string `env:"APP_CORS_ORIGINS" envSeparator:","`

	JWT JWTConfig

	// Framework component configs — composed verbatim. Their own EINHERJAR_* tags
	// load through this one env.Parse call.
	Log    logz.Config     // EINHERJAR_LOG_*
	Server server.Config   // EINHERJAR_SERVER_*
	PG     postgres.Config // EINHERJAR_PG_*
}

func Load() (Config, error) {
	var cfg Config
	if err := env.Parse(&cfg); err != nil {
		return Config{}, err
	}
	return cfg, nil
}

Never read framework env vars (EINHERJAR_*) with os.Getenv — compose the component's Config type and let caarlos0/env load it. A raw os.Getenv("EINHERJAR_PG_HOST") in application code is the mistake this convention removes.

Config & .env.example

Every environment variable the config package reads must also appear in .env.example at the repo root, documented. The two are kept in lock-step: when a feature introduces a new env var, the same change adds its env:"..." tag to config and a documented line to .env.example. This is not optional bookkeeping — it is what stops a long feature from shipping and then failing at boot because nobody knew which variables to set.

Two kinds of var, two ways to keep them honest:

• Framework component vars (EINHERJAR_*) — when you compose a new component later (e.g. cachevalkey.Config, minio.Config, smtp.Config), the MCP knows its real vars: call get_config_env("<module>") for the exact set (name, required, default) and add each to .env.example. The config.unknown-env-var rule rejects any EINHERJAR_* tag the framework doesn't declare, so a typo like EINHERJAR_PG_DATABASE is caught at validate_snippet time.
• App-owned vars (APP_*) — like APP_JWT_SECRET above: the framework can't know these, so keeping them in .env.example is your discipline, not something it can name-check.

After you compose a component, run check_env with the modules the app composes: it flags EINHERJAR_* names that don't exist, required vars you forgot to document, and vars set for a module you don't actually compose (dead vars). get_scaffold already emits a .env.example derived from these same tags, so the starting point is correct by construction.

# .env.example — copy to .env for local dev. Every var the app reads lives here.

# ── App ───────────────────────────────────────────────────────────────────
APP_ENV=local
APP_CORS_ORIGINS=*
APP_JWT_SECRET=change-me
APP_JWT_ISSUER=myapp

# ── Einherjar: logging (EINHERJAR_LOG_*) ──────────────────────────────────
# EINHERJAR_LOG_LEVEL=INFO
# EINHERJAR_LOG_JSON=false

# ── Einherjar: HTTP server (EINHERJAR_SERVER_*) ───────────────────────────
EINHERJAR_SERVER_HOST=0.0.0.0
EINHERJAR_SERVER_PORT=8080

# ── Einherjar: PostgreSQL (EINHERJAR_PG_*) ────────────────────────────────
EINHERJAR_PG_HOST=localhost
EINHERJAR_PG_PORT=5432
EINHERJAR_PG_USER=postgres
EINHERJAR_PG_PASSWORD=postgres
EINHERJAR_PG_NAME=myapp

To discover the full set for any component you compose, use get_config_env("<module>") rather than reading source by hand; every var it returns belongs in .env.example, and check_env confirms none are missing, misspelled, or dead.

wire.go — Run()

The application entry point. The order below is load-bearing: configuration first, observability second, infrastructure third, cross-cutting helpers fourth, then the launcher with every component appended, then feature hooks, then lc.Run().

package wire

import (
	"github.com/google/uuid"

	authjwt "code.nochebuena.dev/einherjar/auth-jwt"
	"code.nochebuena.dev/einherjar/auth/authmw"
	"code.nochebuena.dev/einherjar/auth/rbac"
	"code.nochebuena.dev/einherjar/core/launcher"
	"code.nochebuena.dev/einherjar/core/logz"
	"code.nochebuena.dev/einherjar/core/valid"
	"code.nochebuena.dev/einherjar/db-postgres"
	"code.nochebuena.dev/einherjar/web/mw"
	"code.nochebuena.dev/einherjar/web/server"

	"myapp/internal/config"
)

func Run() error {
	cfg, err := config.Load()
	if err != nil {
		return err
	}

	// logz.Config is composed in config, so EINHERJAR_LOG_LEVEL / _JSON load from
	// the environment; StaticArgs are set here (they carry no env tag).
	logCfg := cfg.Log
	logCfg.StaticArgs = []any{"service", "myapp", "env", cfg.AppEnv}
	logger := logz.New(logCfg)

	signer := authjwt.NewHMACSigner([]byte(cfg.JWT.Secret))

	publicPaths := []string{
		"/health",
		"/api/v1/auth/login",
		"/api/v1/auth/refresh",
	}

	db  := postgres.New(logger, cfg.PG)
	srv := server.New(logger, cfg.Server,
		server.WithMiddleware(
			mw.RequestID(uuid.NewString),
			mw.Recover(logger),
			mw.CORS(cfg.CORSOrigins),
			mw.RequestLogger(logger),
			authjwt.AuthMiddleware(logger, signer, publicPaths),
			authmw.EnrichmentMiddleware(logger, &claimsEnricher{}),
		),
	)

	v        := valid.New(valid.WithMessageProvider(valid.SpanishMessages))
	provider := rbac.NewClaimsPermissionProvider("masks", claimsFromCtx)

	lc := launcher.New(logger)
	lc.Append(db, srv)

	withHealth(lc, srv, logger, db)
	withUsers(lc, srv, db, logger, provider, v)
	// … one withFeature(...) call per feature in your domain.

	return lc.Run()
}

Feature hook

One file per feature in internal/wire/. The function signature is fixed: launcher.Launcher first, server.Server second when registering routes, deps last. The body is one call to lc.BeforeStart. Everything else — repository, service, handler construction, route registration — lives inside the closure.

package wire

import (
	"code.nochebuena.dev/einherjar/contracts/logging"
	"code.nochebuena.dev/einherjar/contracts/security"
	"code.nochebuena.dev/einherjar/core/launcher"
	"code.nochebuena.dev/einherjar/core/valid"
	"code.nochebuena.dev/einherjar/db-postgres"
	"code.nochebuena.dev/einherjar/web/server"

	"myapp/internal/domains"
	userhandler "myapp/internal/user/handler"
	userrepo    "myapp/internal/user/repository"
	usersvc     "myapp/internal/user/service"
)

func withUsers(
	lc       launcher.Launcher,
	srv      server.Server,
	db       postgres.Provider,
	logger   logging.Logger,
	provider security.PermissionProvider,
	v        valid.Validator,
) {
	lc.BeforeStart(func() error {
		repo := userrepo.New(db)
		uow  := postgres.NewUnitOfWork(logger, db)
		svc  := usersvc.New(repo, uow)
		h    := userhandler.New(svc, v)

		// Literal-segment routes register BEFORE parametrised siblings.
		srv.Put("/api/v1/users/me/password", h.ChangeOwnPassword)

		srv.With(authz(provider, domains.ResourceUsers, domains.GrantReadUser)).
			Get("/api/v1/users", h.ListUsers)
		srv.With(authz(provider, domains.ResourceUsers, domains.GrantCreateUser)).
			Post("/api/v1/users", h.CreateUser)
		srv.With(authz(provider, domains.ResourceUsers, domains.GrantUpdateUser)).
			Put("/api/v1/users/{user_id}", h.UpdateUser)

		return nil
	})
}

Route ordering

chi matches paths in registration order. Always register literal-segment routes before parametrised-segment routes that share the same prefix.

✅ Correct:

srv.Put("/api/v1/users/me/password", h.ChangeOwnPassword)
srv.Put("/api/v1/users/{user_id}",   h.UpdateUser)

❌ Wrong — chi binds me to {user_id} and the literal route is unreachable:

srv.Put("/api/v1/users/{user_id}",   h.UpdateUser)
srv.Put("/api/v1/users/me/password", h.ChangeOwnPassword)

Authorization

Every protected route registers with .With(authz(provider, resource, grant)):

srv.With(authz(provider, domains.ResourceUsers, domains.GrantReadUser)).
    Get("/api/v1/users", h.ListUsers)

Resource constants and grant bits live in internal/domains/. Routes that the caller owns (/me/...) intentionally skip authz — they are reachable to any authenticated user.

Middleware helpers

These belong in internal/wire/middleware.go and are used across every feature hook.

// authz returns a per-route authorization middleware that checks one bit.
func authz(p security.PermissionProvider, resource string, bit int) func(http.Handler) http.Handler {
	return authmw.AuthzMiddleware(nil, p, resource, security.Permission(bit))
}

// skipPublicPaths wraps mw so it is bypassed for any path that matches publicPaths.
// Use this for middleware that must not run on unauthenticated endpoints
// (e.g. EnrichmentMiddleware).
func skipPublicPaths(publicPaths []string, mw func(http.Handler) http.Handler) func(http.Handler) http.Handler {
	return func(next http.Handler) http.Handler {
		inner := mw(next)
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			for _, p := range publicPaths {
				if matched, _ := path.Match(p, r.URL.Path); matched {
					next.ServeHTTP(w, r)
					return
				}
			}
			inner.ServeHTTP(w, r)
		})
	}
}

// skipMethodPath bypasses mw only when BOTH method and path match. Use this to
// expose ONE method on an otherwise-authenticated path (e.g. GET /api/v1/config
// public while PUT is not). Adding such a path to publicPaths would silently
// strip identity from context on the protected methods, breaking authz().
func skipMethodPath(method, pathPattern string, mw func(http.Handler) http.Handler) func(http.Handler) http.Handler {
	return func(next http.Handler) http.Handler {
		inner := mw(next)
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			if r.Method == method {
				if matched, _ := path.Match(pathPattern, r.URL.Path); matched {
					next.ServeHTTP(w, r)
					return
				}
			}
			inner.ServeHTTP(w, r)
		})
	}
}

Adapters at the wire boundary

When a framework type does not match a service-layer port, write a small typed adapter in internal/wire/. Always compile-time assert with var _ TargetIface = (*adapter)(nil).

The framework intentionally exposes only Signer.Sign(claims) (string, error) — the framework gives you a signing primitive; the access/refresh strategy, claim layout, and response shape are application concerns. A "helper" that returned a fixed {access, refresh, type, expiresIn} struct would silently decide for every app whether refresh tokens exist, what fields to expose, and what casing to use. Those are wire-format choices the app owns.

import (
	"time"

	"github.com/golang-jwt/jwt/v5"
	"github.com/google/uuid"

	authjwt "code.nochebuena.dev/einherjar/auth-jwt"
)

type tokenSignerAdapter struct {
	signer authjwt.Signer
	cfg    authjwt.TokenConfig
}

var _ authsvc.TokenSigner = (*tokenSignerAdapter)(nil)

func (a *tokenSignerAdapter) IssueTokenPair(subject string, custom map[string]any) (authdto.TokenPairResponse, error) {
	now := time.Now()

	access := jwt.MapClaims{
		"sub": subject,
		"iss": a.cfg.Issuer,
		"iat": now.Unix(),
		"exp": now.Add(a.cfg.AccessTTL).Unix(),
	}
	for k, v := range custom {
		access[k] = v
	}
	accessToken, err := a.signer.Sign(access)
	if err != nil {
		return authdto.TokenPairResponse{}, err
	}

	refreshToken, err := a.signer.Sign(jwt.MapClaims{
		"sub": subject,
		"jti": uuid.NewString(),
		"iat": now.Unix(),
		"exp": now.Add(a.cfg.RefreshTTL).Unix(),
	})
	if err != nil {
		return authdto.TokenPairResponse{}, err
	}

	return authdto.TokenPairResponse{
		AccessToken:  accessToken,
		RefreshToken: refreshToken,
		TokenType:    "Bearer",
		ExpiresIn:    int(a.cfg.AccessTTL.Seconds()),
	}, nil
}