dream: middleware pipeline + logger + content-type sniffer + 20 tests

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

lib/dream/middleware.sx

@@ -0,0 +1,92 @@
+;; lib/dream/middleware.sx — Dream-on-SX middleware.
+;; A middleware is handler->handler. Composition is plain function composition:
+;; m1 @@ m2 @@ handler = (m1 (m2 handler)). Depends on types.sx + router.sx
+;; (reuses dr/apply-middlewares for the fold).
+
+;; ── composition ────────────────────────────────────────────────────
+;; (dream-pipeline (list m1 m2 m3) handler) = (m1 (m2 (m3 handler))).
+(define
+  dream-pipeline
+  (fn (middlewares handler) (dr/apply-middlewares middlewares handler)))
+
+;; identity middleware
+(define dream-no-middleware (fn (next) next))
+
+;; ── logger ─────────────────────────────────────────────────────────
+;; Parameterised on a clock and a sink so it is testable without IO.
+;; sink receives {:method :path :status :elapsed}.
+(define
+  dream-logger-with
+  (fn
+    (clock sink)
+    (fn
+      (next)
+      (fn
+        (req)
+        (let
+          ((t0 (clock)))
+          (let ((resp (next req))) (begin (sink {:path (dream-path req) :status (dream-status resp) :method (dream-method req) :elapsed (- (clock) t0)}) resp)))))))
+
+;; default logger performs host effects for the clock and the log sink
+(define
+  dream-logger
+  (dream-logger-with
+    (fn () (perform (:dream-clock)))
+    (fn (entry) (perform (:dream-log entry)))))
+
+;; format a log entry as a one-line string (apache-ish)
+(define
+  dream-log-line
+  (fn
+    (entry)
+    (str
+      (get entry :method)
+      " "
+      (get entry :path)
+      " -> "
+      (get entry :status)
+      " ("
+      (get entry :elapsed)
+      "ms)")))
+
+;; ── content-type sniffer ───────────────────────────────────────────
+(define
+  dr/sniff-content-type
+  (fn
+    (body)
+    (cond
+      ((= body "") "text/plain; charset=utf-8")
+      ((starts-with? body "<") "text/html; charset=utf-8")
+      ((starts-with? body "{") "application/json")
+      ((starts-with? body "[") "application/json")
+      (else "text/plain; charset=utf-8"))))
+
+;; sets Content-Type from the body only when the handler left it unset
+(define
+  dream-content-type
+  (fn
+    (next)
+    (fn
+      (req)
+      (let
+        ((resp (next req)))
+        (if
+          (dream-resp-header resp "content-type")
+          resp
+          (dream-add-header
+            resp
+            "content-type"
+            (dr/sniff-content-type (dream-resp-body resp))))))))
+
+;; ── small reusable middlewares ─────────────────────────────────────
+;; always attach a response header
+(define
+  dream-set-header
+  (fn
+    (name val)
+    (fn (next) (fn (req) (dream-add-header (next req) name val)))))
+
+;; rewrite/observe the request before the handler sees it
+(define
+  dream-tap-request
+  (fn (f) (fn (next) (fn (req) (next (f req))))))