feat(14.2.1-01): add optional surf LocaleResolver seam

Look up a backpack-published resolver so a compiled translate plugin can
strip an enabled URL prefix and write a validated locale onto context.

Co-authored-by: Cursor <cursoragent@cursor.com>

docs/architecture/request-lifecycle.md

@@ -35,13 +35,14 @@ In Go the same declaration is a `pact.HasRoutes` method. Paths use Go `http.Serv
 
 surf wraps every non-raw route in the same layers. From the outside in:
 
-1. CORS, only for the paths configured under `http.cors.paths`, including preflight requests.
+1. Optional locale-prefix rewrite, when a `surf.LocaleResolver` is published: an enabled locale as the first path segment is stripped so later layers and routing see the unprefixed path.
-2. Panic recovery. A panic becomes an opaque JSON 500 from [wire](../../modules/wire/README.md), and because the response is buffered until the handler returns, the client never receives half a body.
+2. CORS, only for the paths configured under `http.cors.paths`, including preflight requests.
-3. The request locale, taken from the `Accept-Language` header and stored in the context.
+3. Panic recovery. A panic becomes an opaque JSON 500 from [wire](../../modules/wire/README.md), and because the response is buffered until the handler returns, the client never receives half a body.
-4. The body limit: `http.body_limits.default_bytes`, or the route's own `body.limit:<bytes>`.
+4. The request locale, taken from the published `surf.LocaleResolver` when one exists, or from the `Accept-Language` header otherwise, and stored in the context.
-5. The route's middleware, in the order you listed them: group middleware first, then the route's own.
+5. The body limit: `http.body_limits.default_bytes`, or the route's own `body.limit:<bytes>`.
-6. The path constraints. A request whose parameter fails `pact.Router.Where` or `pact.Router.WhereIn` gets a 404 before your handler runs.
+6. The route's middleware, in the order you listed them: group middleware first, then the route's own.
-7. Your handler.
+7. The path constraints. A request whose parameter fails `pact.Router.Where` or `pact.Router.WhereIn` gets a 404 before your handler runs.
+8. Your handler.
 
 Raw groups, declared with `pact.Router.GroupRaw`, are for webhooks and file streams. They skip the default body limit, refuse house middleware, and a panic in them returns a bare 500.
 

docs/services/localization.md

@@ -75,7 +75,7 @@ for _, n := range []int{0, 1, 7} {
 
 ## The request locale
 
-The locale lives on the request context, not in a global. For every route, [surf](../../modules/surf/README.md) sets it from the `Accept-Language` header; the `locale.from-principal` middleware switches it to the signed-in user's preferred locale. Code reads it with `towel.Locale`, and code outside a request sets it with `towel.WithLocale`, as the example above does. A context without a locale uses `app.locale`.
+The locale lives on the request context, not in a global. For every route, [surf](../../modules/surf/README.md) looks up an optional `surf.LocaleResolver` published by a compiled plugin and writes that validated code with `towel.WithLocale`. When no resolver is published, surf sets the locale from the `Accept-Language` header and the `locale.from-principal` middleware can switch it to the signed-in user's preferred locale. Code reads it with `towel.Locale`, and code outside a request sets it with `towel.WithLocale`, as the example above does. A context without a locale uses `app.locale`.
 
 ## Strings for the admin
 

docs/services/routing.md

@@ -101,7 +101,7 @@ The framework registers these names:
 | `locale.from-principal` | Switches the request locale to the signed-in user's preferred locale. |
 | `backend` | The admin guard, when the admin is enabled. |
 
-Every route also gets, around its own middleware, JSON panic recovery, the request locale from `Accept-Language`, the body limit from `http.body_limits.default_bytes`, and CORS headers when its path matches `http.cors.paths`. The order is described in [Request lifecycle](../architecture/request-lifecycle.md).
+Every route also gets, around its own middleware, JSON panic recovery, the request locale from a published [`surf.LocaleResolver`](../../modules/surf/README.md) or from `Accept-Language` when none is published, the body limit from `http.body_limits.default_bytes`, and CORS headers when its path matches `http.cors.paths`. The order is described in [Request lifecycle](../architecture/request-lifecycle.md).
 
 `pact.Router.GroupRaw` declares a raw group for routes that must not be wrapped in the house JSON middleware, such as webhooks, file streams or the OAuth endpoints: the default body limit is skipped, and a panic returns a bare 500.
 

modules/surf/README.md

@@ -18,8 +18,9 @@ surf turns the routes that plugins declare through `pact.HasRoutes` into one `ht
 - Built-in middleware names: `throttle:<bucket>` or `throttle:<max>,<minutes>`, `body.limit:<bytes>`, `locale.from-principal`, plus `backend` (the admin guard) when the admin is enabled.
 - Fixed-window rate limiting (`surf.FixedWindowLimiter`): named buckets from plugins that implement `surf.BucketProvider`, or inline limits keyed by the signed-in user, or by client IP for guests. Rejected requests get a 429 with `Retry-After` and `X-RateLimit-*` headers. The in-process `surf.MemoryStore` sits behind the `surf.Store` interface.
 - Client IP resolution for limiter keys (`surf.ClientIP`) that only trusts `X-Forwarded-For` hops when the direct peer is inside a configured trusted proxy range (`surf.TrustedProxies`).
-- Every non-raw route runs inside JSON panic recovery (an opaque 500 via [wire](../wire/README.md)), gets the request locale from the `Accept-Language` header (see [towel](../towel/README.md)) and a request body cap. Responses are buffered until the handler returns, so a panic never leaves a half-written body.
+- Every non-raw route runs inside JSON panic recovery (an opaque 500 via [wire](../wire/README.md)), gets the request locale from a published `surf.LocaleResolver` when one exists or from the `Accept-Language` header otherwise (see [towel](../towel/README.md)), and a request body cap. Responses are buffered until the handler returns, so a panic never leaves a half-written body.
 - Path-scoped CORS configured with the same keys as Laravel's `config/cors.php` (`surf.CORSConfig`), including preflight handling. Every `OPTIONS` request on a CORS path is answered with 204 before routing, with the headers Laravel's `HandleCors` sends: `Cache-Control: no-cache, private` always and, on a preflight (an `Origin` and an `Access-Control-Request-Method`), the requested method (upper-cased) and headers echoed in `Access-Control-Allow-Methods` and `Access-Control-Allow-Headers` when `*` allows any, `Vary` on the request headers and PHP's default `Content-Type: text/html; charset=UTF-8`.
+- Optional `surf.LocaleResolver`: a compiled plugin publishes the interface through backpack; surf looks it up without importing the plugin. When present, it may strip an enabled locale prefix before routing and writes a validated code with `towel.WithLocale`. When absent, hosts keep the raw `Accept-Language` header and `surf.LocaleFromPrincipal` overlay.
 - `surf.LocaleFromPrincipal` switches the request locale to the signed-in user's preferred locale.
 - A read-only route table (`surf.Router.Routes`) and the `serve` and `route:list` commands.
 
@@ -118,6 +119,7 @@ The generated application `main` wires surf in with `surf.ServeCommand` and `sur
 | `surf.ClientIP` | Resolves the client IP, honouring trusted proxies. |
 | `surf.TrustedProxies` | Parses `http.trusted_proxies` into CIDR prefixes. |
 | `surf.CORSConfig` | CORS settings; `surf.LoadCORSConfig` reads them from config. |
+| `surf.LocaleResolver` | Optional backpack-published request locale; `Resolve` returns a validated code and `Rewrite` strips an enabled prefix before routing. |
 | `surf.LocaleFromPrincipal` | Middleware that applies the signed-in user's preferred locale. |
 | `surf.ServeCommand` | The `serve` console command. |
 | `surf.RouteListCommand` | The `route:list` console command. |

modules/surf/locale_resolver.go

@@ -0,0 +1,15 @@
+package surf
+
+import "net/http"
+
+// LocaleResolver is an optional backpack-published service that selects a
+// validated locale code for a request. When none is published, surf keeps
+// writing the raw Accept-Language header onto the request context.
+type LocaleResolver interface {
+	// Resolve returns a validated locale code for r. It may set cookies on w
+	// and must not store request locale on a process-wide variable.
+	Resolve(w http.ResponseWriter, r *http.Request) string
+	// Rewrite returns a request whose URL has a valid enabled locale prefix
+	// stripped so routing sees the unprefixed path, or r unchanged.
+	Rewrite(r *http.Request) *http.Request
+}

modules/surf/locale_resolver_test.go

@@ -0,0 +1,81 @@
+package surf
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"git.golem15.com/golem15/summercms/modules/backpack"
+	"git.golem15.com/golem15/summercms/modules/towel"
+)
+
+type stubLocaleResolver struct {
+	code      string
+	rewriteTo string
+}
+
+func (s stubLocaleResolver) Resolve(http.ResponseWriter, *http.Request) string {
+	return s.code
+}
+
+func (s stubLocaleResolver) Rewrite(r *http.Request) *http.Request {
+	if s.rewriteTo == "" {
+		return r
+	}
+	clone := r.Clone(r.Context())
+	clone.URL.Path = s.rewriteTo
+	return clone
+}
+
+func TestLocaleResolverWritesValidatedCodeAndStripsPrefix(t *testing.T) {
+	cfg := writeHTTPConfig(t, "body_limits:\n  default_bytes: 1024\n  upload_bytes: 1024\n")
+	app := backpack.New(cfg)
+	if err := app.Publish[LocaleResolver](stubLocaleResolver{code: "pl", rewriteTo: "/posts"}); err != nil {
+		t.Fatal(err)
+	}
+	r := New(nil)
+	r.app = app
+	r.defaultBytes = 1024
+	r.BindPlugin("acme.blog")
+	var gotPath, gotLoc string
+	var ok bool
+	r.Get("/posts", func(w http.ResponseWriter, req *http.Request) {
+		gotPath = req.URL.Path
+		gotLoc, ok = towel.Locale(req.Context())
+		w.WriteHeader(http.StatusNoContent)
+	})
+	h, err := r.compile()
+	if err != nil {
+		t.Fatal(err)
+	}
+	req := httptest.NewRequest(http.MethodGet, "/pl/posts", nil)
+	req.Header.Set("Accept-Language", "de")
+	h.ServeHTTP(httptest.NewRecorder(), req)
+	if gotPath != "/posts" {
+		t.Fatalf("path = %q, want /posts", gotPath)
+	}
+	if !ok || gotLoc != "pl" {
+		t.Fatalf("locale = %q ok=%t, want pl from resolver", gotLoc, ok)
+	}
+}
+
+func TestLocaleAbsentResolverKeepsAcceptLanguage(t *testing.T) {
+	r := New(nil)
+	r.BindPlugin("acme.blog")
+	var gotLoc string
+	var ok bool
+	r.Get("/posts", func(w http.ResponseWriter, req *http.Request) {
+		gotLoc, ok = towel.Locale(req.Context())
+		w.WriteHeader(http.StatusNoContent)
+	})
+	h, err := r.compile()
+	if err != nil {
+		t.Fatal(err)
+	}
+	req := httptest.NewRequest(http.MethodGet, "/posts", nil)
+	req.Header.Set("Accept-Language", "pl")
+	h.ServeHTTP(httptest.NewRecorder(), req)
+	if !ok || gotLoc != "pl" {
+		t.Fatalf("locale = %q ok=%t, want pl from Accept-Language", gotLoc, ok)
+	}
+}

modules/surf/router.go

@@ -59,6 +59,7 @@ type Router struct {
 	defaultBytes int64
 	uploadBytes  int64
 	built        map[string]pact.Middleware
+	app          *backpack.App
 }
 
 var (
@@ -375,7 +376,7 @@ func (r *Router) compile() (http.Handler, error) {
 	if err := registerOverlapFamilies(mux, r.routes, handlers, families); err != nil {
 		return nil, err
 	}
-	return pathScopedCORS(r.corsCfg, mux), nil
+	return r.stripLocalePrefix(pathScopedCORS(r.corsCfg, mux)), nil
 }
 
 // handleRoute registers a route, converting a ServeMux conflict panic into an error.
@@ -436,7 +437,7 @@ func (r *Router) wrap(rt route) (http.Handler, error) {
 	if limit > 0 {
 		h = bodyLimit(limit)(h)
 	}
-	h = locale(h)
+	h = r.locale(h)
 	if rt.raw {
 		h = recoverBare(h)
 	} else {
@@ -458,6 +459,7 @@ func Assemble(app *backpack.App, plugins []party.Plugin) (http.Handler, error) {
 // so callers (route:list) can inspect Routes() after a successful boot.
 func BuildRouter(app *backpack.App, plugins []party.Plugin) (*Router, error) {
 	r := New(corsOrigins(app))
+	r.app = app
 	trusted := TrustedProxies(nil)
 	if app != nil {
 		trusted = TrustedProxies(app.Config)
@@ -704,9 +706,27 @@ func (w *bufferedResponse) commit(dst http.ResponseWriter) {
 	_, _ = dst.Write(w.body.Bytes())
 }
 
-func locale(next http.Handler) http.Handler {
+func (r *Router) locale(next http.Handler) http.Handler {
-	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+	return http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
-		next.ServeHTTP(w, r.WithContext(towel.WithLocale(r.Context(), r.Header.Get("Accept-Language"))))
+		if r != nil && r.app != nil {
+			if resolver, ok := r.app.Lookup[LocaleResolver](); ok && resolver != nil {
+				code := resolver.Resolve(w, req)
+				next.ServeHTTP(w, req.WithContext(towel.WithLocale(req.Context(), code)))
+				return
+			}
+		}
+		next.ServeHTTP(w, req.WithContext(towel.WithLocale(req.Context(), req.Header.Get("Accept-Language"))))
+	})
+}
+
+func (r *Router) stripLocalePrefix(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
+		if r != nil && r.app != nil {
+			if resolver, ok := r.app.Lookup[LocaleResolver](); ok && resolver != nil {
+				req = resolver.Rewrite(req)
+			}
+		}
+		next.ServeHTTP(w, req)
 	})
 }