feat(api): add i18n config snapshot

Co-Authored-By: Virgil <virgil@lethean.io>

api.go

@@ -63,6 +63,7 @@ type Engine struct {
 	expvarEnabled                  bool
 	ssePath                        string
 	graphql                        *graphqlConfig
+	i18nConfig                     I18nConfig
 }
 
 // New creates an Engine with the given options.

i18n.go

@@ -3,6 +3,7 @@
 package api
 
 import (
+	"slices"
 	"strings"
 
 	"github.com/gin-gonic/gin"
@@ -46,6 +47,23 @@ type I18nConfig struct {
 	Messages map[string]map[string]string
 }
 
+// I18nConfig returns the configured locale and message catalogue settings for
+// the engine.
+//
+// The result snapshots the Engine state at call time and clones slices/maps so
+// callers can safely reuse or modify the returned value.
+//
+// Example:
+//
+//	cfg := engine.I18nConfig()
+func (e *Engine) I18nConfig() I18nConfig {
+	if e == nil {
+		return I18nConfig{}
+	}
+
+	return cloneI18nConfig(e.i18nConfig)
+}
+
 // WithI18n adds Accept-Language header parsing and locale detection middleware.
 // The middleware uses golang.org/x/text/language for RFC 5646 language matching
 // with quality weighting support. The detected locale is stored in the Gin
@@ -77,9 +95,11 @@ func WithI18n(cfg ...I18nConfig) Option {
 				tags = append(tags, tag)
 			}
 		}
+		snapshot := cloneI18nConfig(config)
+		e.i18nConfig = snapshot
 		matcher := language.NewMatcher(tags)
 
-		e.middlewares = append(e.middlewares, i18nMiddleware(matcher, config))
+		e.middlewares = append(e.middlewares, i18nMiddleware(matcher, snapshot))
 	}
 }
 
@@ -197,3 +217,30 @@ func localeFallbacks(locale string) []string {
 
 	return fallbacks
 }
+
+func cloneI18nConfig(cfg I18nConfig) I18nConfig {
+	out := cfg
+	out.Supported = slices.Clone(cfg.Supported)
+	out.Messages = cloneI18nMessages(cfg.Messages)
+	return out
+}
+
+func cloneI18nMessages(messages map[string]map[string]string) map[string]map[string]string {
+	if len(messages) == 0 {
+		return nil
+	}
+
+	out := make(map[string]map[string]string, len(messages))
+	for locale, msgs := range messages {
+		if len(msgs) == 0 {
+			out[locale] = nil
+			continue
+		}
+		cloned := make(map[string]string, len(msgs))
+		for key, value := range msgs {
+			cloned[key] = value
+		}
+		out[locale] = cloned
+	}
+	return out
+}

i18n_test.go

@@ -6,6 +6,7 @@ import (
 	"encoding/json"
 	"net/http"
 	"net/http/httptest"
+	"slices"
 	"testing"
 
 	"github.com/gin-gonic/gin"
@@ -288,3 +289,85 @@ func TestWithI18n_Good_FallsBackToParentLocaleMessage(t *testing.T) {
 		t.Fatal("expected found=true")
 	}
 }
+
+func TestEngine_I18nConfig_Good_SnapshotsCurrentSettings(t *testing.T) {
+	e, _ := api.New(api.WithI18n(api.I18nConfig{
+		DefaultLocale: "en",
+		Supported:     []string{"en", "fr"},
+		Messages: map[string]map[string]string{
+			"en": {"greeting": "Hello"},
+			"fr": {"greeting": "Bonjour"},
+		},
+	}))
+
+	snap := e.I18nConfig()
+	if snap.DefaultLocale != "en" {
+		t.Fatalf("expected default locale en, got %q", snap.DefaultLocale)
+	}
+	if !slices.Equal(snap.Supported, []string{"en", "fr"}) {
+		t.Fatalf("expected supported locales [en fr], got %v", snap.Supported)
+	}
+	if snap.Messages["fr"]["greeting"] != "Bonjour" {
+		t.Fatalf("expected cloned French greeting, got %q", snap.Messages["fr"]["greeting"])
+	}
+}
+
+func TestEngine_I18nConfig_Good_ClonesMutableInputs(t *testing.T) {
+	supported := []string{"en", "fr"}
+	messages := map[string]map[string]string{
+		"en": {"greeting": "Hello"},
+		"fr": {"greeting": "Bonjour"},
+	}
+
+	e, _ := api.New(api.WithI18n(api.I18nConfig{
+		DefaultLocale: "en",
+		Supported:     supported,
+		Messages:      messages,
+	}))
+
+	supported[0] = "de"
+	messages["fr"]["greeting"] = "Salut"
+
+	snap := e.I18nConfig()
+	if !slices.Equal(snap.Supported, []string{"en", "fr"}) {
+		t.Fatalf("expected engine supported locales to be cloned, got %v", snap.Supported)
+	}
+	if snap.Messages["fr"]["greeting"] != "Bonjour" {
+		t.Fatalf("expected engine message catalogue to be cloned, got %q", snap.Messages["fr"]["greeting"])
+	}
+}
+
+func TestWithI18n_Good_SnapshotsMutableInputs(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	messages := map[string]map[string]string{
+		"en": {"greeting": "Hello"},
+		"fr": {"greeting": "Bonjour"},
+	}
+
+	e, _ := api.New(api.WithI18n(api.I18nConfig{
+		DefaultLocale: "en",
+		Supported:     []string{"en", "fr"},
+		Messages:      messages,
+	}))
+	e.Register(&i18nTestGroup{})
+
+	messages["fr"]["greeting"] = "Salut"
+
+	h := e.Handler()
+	w := httptest.NewRecorder()
+	req, _ := http.NewRequest(http.MethodGet, "/i18n/greeting", nil)
+	req.Header.Set("Accept-Language", "fr")
+	h.ServeHTTP(w, req)
+
+	if w.Code != http.StatusOK {
+		t.Fatalf("expected 200, got %d", w.Code)
+	}
+
+	var resp i18nMessageResponse
+	if err := json.Unmarshal(w.Body.Bytes(), &resp); err != nil {
+		t.Fatalf("unmarshal error: %v", err)
+	}
+	if resp.Data.Message != "Bonjour" {
+		t.Fatalf("expected cloned greeting %q, got %q", "Bonjour", resp.Data.Message)
+	}
+}