dream: router 405 Method Not Allowed + Allow header + automatic HEAD + 9 tests

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/dream/router.sx

@@ -1,7 +1,9 @@
 ;; lib/dream/router.sx — Dream-on-SX routing.
 ;; Routes are dicts {:method :path :handler}; a router is a handler that
 ;; dispatches request -> response by method + path, extracting :name path
-;; params and binding a ** catch-all. No match -> 404. Depends on types.sx.
+;; params and binding a ** catch-all. No path match -> 404; path matches but
+;; method doesn't -> 405 + Allow. HEAD falls back to the GET handler with an
+;; empty body. Depends on types.sx.
 
 ;; ── route constructors (one per HTTP method) ───────────────────────
 (define dream-get (fn (path handler) (dream-route "GET" path handler)))
@@ -53,11 +55,25 @@
               (dr/match-segs (rest pat) (rest path) params))
             (else nil)))))))
 
+;; path-only match: returns params dict or nil
 (define
-  dr/method-match?
+  dr/route-params
+  (fn
+    (r req)
+    (dr/match-segs
+      (dr/segs (dream-route-path r))
+      (dr/segs (dream-path req))
+      {})))
+
+;; method acceptance: exact, ANY, or HEAD served by a GET route
+(define
+  dr/method-accepts?
   (fn
     (route-method req-method)
-    (or (= route-method "ANY") (= route-method req-method))))
+    (or
+      (= route-method "ANY")
+      (= route-method req-method)
+      (and (= req-method "HEAD") (= route-method "GET")))))
 
 ;; ── middleware pipeline (shared with middleware.sx) ────────────────
 ;; m1 @@ m2 @@ handler = (m1 (m2 handler)); first in list is outermost.
@@ -95,30 +111,55 @@
       (dr/flatten-routes routes))))
 
 ;; ── dispatch ───────────────────────────────────────────────────────
-(define
-  dr/try-route
-  (fn
-    (r req)
-    (if
-      (dr/method-match? (dream-route-method r) (dream-method req))
-      (let
-        ((params (dr/match-segs (dr/segs (dream-route-path r)) (dr/segs (dream-path req)) {})))
-        (if
-          (nil? params)
-          :no-match (dream-coerce-response
-            ((dream-route-handler r) (dream-with-params req params)))))
-      :no-match)))
-
+;; allowed = methods of routes whose PATH matched (for 405 + Allow).
 (define
   dr/dispatch
   (fn
-    (routes req)
+    (routes req allowed)
     (if
       (empty? routes)
-      (dream-not-found)
+      (if
+        (empty? allowed)
+        (dream-not-found)
+        (dream-method-not-allowed allowed))
       (let
-        ((res (dr/try-route (first routes) req)))
-        (if (= res :no-match) (dr/dispatch (rest routes) req) res)))))
+        ((r (first routes)))
+        (let
+          ((params (dr/route-params r req)))
+          (if
+            (nil? params)
+            (dr/dispatch (rest routes) req allowed)
+            (if
+              (dr/method-accepts? (dream-route-method r) (dream-method req))
+              (dr/run-route r req params)
+              (dr/dispatch
+                (rest routes)
+                req
+                (concat allowed (list (dream-route-method r)))))))))))
+
+;; run a matched route; blank the body for an auto-HEAD on a GET route
+(define
+  dr/run-route
+  (fn
+    (r req params)
+    (let
+      ((resp (dream-coerce-response ((dream-route-handler r) (dream-with-params req params)))))
+      (if
+        (and
+          (= (dream-method req) "HEAD")
+          (not (= (dream-route-method r) "HEAD")))
+        (dream-response (dream-status resp) (dream-headers resp) "")
+        resp))))
+
+;; 405 response with an Allow header listing the path's methods
+(define
+  dream-method-not-allowed
+  (fn
+    (allowed)
+    (dream-add-header
+      (dream-response 405 {:content-type "text/plain; charset=utf-8"} "Method Not Allowed")
+      "allow"
+      (join ", " allowed))))
 
 (define
   dream-router
@@ -126,4 +167,4 @@
     (routes)
     (let
       ((flat (dr/flatten-routes routes)))
-      (fn (req) (dr/dispatch flat req)))))
+      (fn (req) (dr/dispatch flat req (list))))))