fix(14-05): surf answers OPTIONS on CORS paths with Laravel's HandleCors headers

- every OPTIONS on a CORS path: 204 with Cache-Control no-cache, private
- a preflight echoes the requested method (upper-cased) and headers when * allows any, with Vary and PHP's default Content-Type, as recorded from PHP
- README and the routing docs describe the answer

modules/surf/README.md

@@ -19,7 +19,7 @@ surf turns the routes that plugins declare through `pact.HasRoutes` into one `ht
 - 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.
-- Path-scoped CORS configured with the same keys as Laravel's `config/cors.php` (`surf.CORSConfig`), including preflight handling.
+- 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`.
 - `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.
 

modules/surf/cors.go

@@ -94,13 +94,43 @@ func pathScopedCORS(cfg CORSConfig, next http.Handler) http.Handler {
 			}
 		}
 		if r.Method == http.MethodOptions {
-			w.WriteHeader(http.StatusNoContent)
+			writeOptions(w, r, allowed, allowAnyMethod, allowAnyHeader)
 			return
 		}
 		next.ServeHTTP(w, r)
 	})
 }
 
+// writeOptions answers an OPTIONS request on a CORS path with 204 and the
+// headers Laravel's HandleCors (fruitcake/php-cors) sends, so recorded PHP
+// preflights replay unchanged. Every answer carries Symfony's default
+// Cache-Control "no-cache, private". A preflight (an Origin and an
+// Access-Control-Request-Method) also carries the Content-Type PHP's SAPI
+// adds to a response that sets none ("text/html; charset=UTF-8") and Vary
+// on the two request headers; when any method or header is allowed, the
+// Allow-Methods and Allow-Headers values echo the requested method
+// (upper-cased) and headers, as php-cors does, instead of "*".
+func writeOptions(w http.ResponseWriter, r *http.Request, allowed, allowAnyMethod, allowAnyHeader bool) {
+	h := w.Header()
+	h.Set("Cache-Control", "no-cache, private")
+	method := r.Header.Get("Access-Control-Request-Method")
+	if r.Header.Get("Origin") != "" && method != "" {
+		h.Set("Content-Type", "text/html; charset=UTF-8")
+		h.Add("Vary", "Access-Control-Request-Method, Access-Control-Request-Headers")
+		if allowed && allowAnyMethod {
+			h.Set("Access-Control-Allow-Methods", strings.ToUpper(method))
+		}
+		if allowed && allowAnyHeader {
+			if requested := r.Header.Get("Access-Control-Request-Headers"); requested != "" {
+				h.Set("Access-Control-Allow-Headers", requested)
+			}
+		}
+	} else {
+		h.Add("Vary", "Access-Control-Request-Method")
+	}
+	w.WriteHeader(http.StatusNoContent)
+}
+
 func corsAllowOrigin(allowAny bool, origins map[string]struct{}, pats []*regexp.Regexp, origin string) (bool, string) {
 	if allowAny {
 		return true, "*"

modules/surf/cors_coverage_test.go

@@ -90,3 +90,75 @@ func TestCORSAllowOriginExactAndPattern(t *testing.T) {
 		}
 	})
 }
+
+// TestCORSOptionsMatchesLaravel pins the OPTIONS answers Laravel's
+// HandleCors gives (recorded from PHP for the feedback widget): a
+// preflight echoes the requested method and headers when any is allowed,
+// with PHP's default Content-Type and Symfony's Cache-Control; a plain
+// OPTIONS is a bare 204 with the Cache-Control.
+func TestCORSOptionsMatchesLaravel(t *testing.T) {
+	cfg := CORSConfig{
+		Paths:          []string{"_feedback/api/*"},
+		AllowedMethods: []string{"*"},
+		AllowedOrigins: []string{"*"},
+		AllowedHeaders: []string{"*"},
+	}
+	called := false
+	h := pathScopedCORS(cfg, http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { called = true }))
+
+	req := httptest.NewRequest(http.MethodOptions, "/_feedback/api/v1/wk_key/submit", nil)
+	req.Header.Set("Origin", "https://app.example.test")
+	req.Header.Set("Access-Control-Request-Method", "post")
+	req.Header.Set("Access-Control-Request-Headers", "content-type")
+	rec := httptest.NewRecorder()
+	h.ServeHTTP(rec, req)
+	want := map[string]string{
+		"Access-Control-Allow-Origin":  "*",
+		"Access-Control-Allow-Methods": "POST",
+		"Access-Control-Allow-Headers": "content-type",
+		"Cache-Control":                "no-cache, private",
+		"Content-Type":                 "text/html; charset=UTF-8",
+		"Vary":                         "Access-Control-Request-Method, Access-Control-Request-Headers",
+	}
+	if rec.Code != http.StatusNoContent || rec.Body.Len() != 0 {
+		t.Fatalf("preflight = %d %q", rec.Code, rec.Body.String())
+	}
+	for k, v := range want {
+		if got := rec.Header().Get(k); got != v {
+			t.Errorf("preflight %s = %q, want %q", k, got, v)
+		}
+	}
+
+	rec = httptest.NewRecorder()
+	h.ServeHTTP(rec, httptest.NewRequest(http.MethodOptions, "/_feedback/api/v1/anything/else", nil))
+	if rec.Code != http.StatusNoContent || rec.Body.Len() != 0 {
+		t.Fatalf("plain OPTIONS = %d %q", rec.Code, rec.Body.String())
+	}
+	if got := rec.Header().Get("Cache-Control"); got != "no-cache, private" {
+		t.Errorf("plain Cache-Control = %q", got)
+	}
+	if got := rec.Header().Get("Content-Type"); got != "" {
+		t.Errorf("plain Content-Type = %q", got)
+	}
+	if got := rec.Header().Get("Vary"); got != "Access-Control-Request-Method" {
+		t.Errorf("plain Vary = %q", got)
+	}
+	if called {
+		t.Fatal("an OPTIONS request reached the route handler")
+	}
+
+	// A listed method set is sent as configured, not echoed.
+	listed := pathScopedCORS(CORSConfig{Paths: []string{"api/*"}, AllowedMethods: []string{"GET", "POST"}, AllowedOrigins: []string{"*"}, AllowedHeaders: []string{"Authorization"}}, http.NotFoundHandler())
+	req = httptest.NewRequest(http.MethodOptions, "/api/items", nil)
+	req.Header.Set("Origin", "https://app.example.test")
+	req.Header.Set("Access-Control-Request-Method", "DELETE")
+	req.Header.Set("Access-Control-Request-Headers", "x-custom")
+	rec = httptest.NewRecorder()
+	listed.ServeHTTP(rec, req)
+	if got := rec.Header().Get("Access-Control-Allow-Methods"); got != "GET, POST" {
+		t.Errorf("listed methods = %q", got)
+	}
+	if got := rec.Header().Get("Access-Control-Allow-Headers"); got != "Authorization" {
+		t.Errorf("listed headers = %q", got)
+	}
+}