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

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

lib/dream/conformance.sh

@@ -24,12 +24,14 @@ VERBOSE="${1:-}"
 MODULES=(
   "lib/dream/types.sx"
   "lib/dream/router.sx"
+  "lib/dream/middleware.sx"
 )
 
 # Suites: NAME RUNNER-FN PATH
 SUITES=(
-  "types   dream-ty-tests-run!  lib/dream/tests/types.sx"
-  "router  dream-rt-tests-run!  lib/dream/tests/router.sx"
+  "types       dream-ty-tests-run!  lib/dream/tests/types.sx"
+  "router      dream-rt-tests-run!  lib/dream/tests/router.sx"
+  "middleware  dream-mw-tests-run!  lib/dream/tests/middleware.sx"
 )
 
 TMPFILE=$(mktemp); trap "rm -f $TMPFILE" EXIT

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))))))

lib/dream/tests/middleware.sx

@@ -0,0 +1,150 @@
+;; lib/dream/tests/middleware.sx — composition, logger, content-type sniffer.
+
+(define dream-mw-pass 0)
+(define dream-mw-fail 0)
+(define dream-mw-fails (list))
+
+(define
+  dream-mw-test
+  (fn
+    (name actual expected)
+    (if
+      (= actual expected)
+      (set! dream-mw-pass (+ dream-mw-pass 1))
+      (begin
+        (set! dream-mw-fail (+ dream-mw-fail 1))
+        (append! dream-mw-fails {:name name :actual actual :expected expected})))))
+
+(define dream-mw-req (dream-request "GET" "/p" {} ""))
+
+;; ── pipeline composition order ─────────────────────────────────────
+(define
+  dream-mw-wrap
+  (fn
+    (tag)
+    (fn
+      (next)
+      (fn
+        (req)
+        (dream-html (str tag "(" (dream-resp-body (next req)) ")"))))))
+(define dream-mw-h (fn (req) (dream-html "h")))
+
+(dream-mw-test
+  "pipeline empty is identity"
+  (dream-resp-body ((dream-pipeline (list) dream-mw-h) dream-mw-req))
+  "h")
+(dream-mw-test
+  "pipeline single"
+  (dream-resp-body
+    ((dream-pipeline (list (dream-mw-wrap "a")) dream-mw-h) dream-mw-req))
+  "a(h)")
+(dream-mw-test
+  "pipeline first is outermost"
+  (dream-resp-body
+    ((dream-pipeline (list (dream-mw-wrap "a") (dream-mw-wrap "b")) dream-mw-h)
+      dream-mw-req))
+  "a(b(h))")
+(dream-mw-test
+  "no-middleware is identity"
+  (dream-resp-body ((dream-no-middleware dream-mw-h) dream-mw-req))
+  "h")
+
+;; ── logger ─────────────────────────────────────────────────────────
+(define dream-mw-clock-n 0)
+(define
+  dream-mw-clock
+  (fn
+    ()
+    (begin
+      (set! dream-mw-clock-n (+ dream-mw-clock-n 1))
+      dream-mw-clock-n)))
+(define dream-mw-entries (list))
+(define dream-mw-sink (fn (e) (append! dream-mw-entries e)))
+(define
+  dream-mw-logged
+  ((dream-logger-with dream-mw-clock dream-mw-sink)
+    (fn (req) (dream-html-status 201 "ok"))))
+(define
+  dream-mw-lresp
+  (dream-mw-logged (dream-request "POST" "/log/path" {} "")))
+
+(dream-mw-test
+  "logger passes response through"
+  (dream-resp-body dream-mw-lresp)
+  "ok")
+(dream-mw-test "logger records one entry" (len dream-mw-entries) 1)
+(dream-mw-test
+  "logger entry method"
+  (get (first dream-mw-entries) :method)
+  "POST")
+(dream-mw-test
+  "logger entry path"
+  (get (first dream-mw-entries) :path)
+  "/log/path")
+(dream-mw-test
+  "logger entry status"
+  (get (first dream-mw-entries) :status)
+  201)
+(dream-mw-test
+  "logger entry elapsed"
+  (get (first dream-mw-entries) :elapsed)
+  1)
+(dream-mw-test
+  "log-line format"
+  (dream-log-line {:path "/x" :status 200 :method "GET" :elapsed 4})
+  "GET /x -> 200 (4ms)")
+
+;; ── content-type sniffer ───────────────────────────────────────────
+(define dream-mw-ct (fn (handler) (dream-content-type handler)))
+(define
+  dream-mw-sniff
+  (fn
+    (body)
+    (dream-resp-header
+      ((dream-content-type (fn (req) (dream-response 200 {} body)))
+        dream-mw-req)
+      "content-type")))
+
+(dream-mw-test
+  "sniff html"
+  (dream-mw-sniff "<p>hi</p>")
+  "text/html; charset=utf-8")
+(dream-mw-test
+  "sniff doctype"
+  (dream-mw-sniff "<!doctype html>")
+  "text/html; charset=utf-8")
+(dream-mw-test
+  "sniff json object"
+  (dream-mw-sniff "{\"a\":1}")
+  "application/json")
+(dream-mw-test "sniff json array" (dream-mw-sniff "[1,2]") "application/json")
+(dream-mw-test
+  "sniff plain text"
+  (dream-mw-sniff "just words")
+  "text/plain; charset=utf-8")
+(dream-mw-test
+  "sniff empty body"
+  (dream-mw-sniff "")
+  "text/plain; charset=utf-8")
+(dream-mw-test
+  "sniff does not override existing"
+  (dream-resp-header
+    ((dream-content-type (fn (req) (dream-json "{}"))) dream-mw-req)
+    "content-type")
+  "application/json")
+
+;; ── small middlewares ──────────────────────────────────────────────
+(dream-mw-test
+  "set-header attaches"
+  (dream-resp-header
+    (((dream-set-header "X-A" "1") dream-mw-h) dream-mw-req)
+    "x-a")
+  "1")
+(dream-mw-test
+  "tap-request rewrites"
+  (dream-resp-body
+    (((dream-tap-request (fn (req) (dream-set-body req "tapped"))) (fn (req) (dream-html (dream-body req))))
+      (dream-request "GET" "/" {} "orig")))
+  "tapped")
+
+(define dream-mw-tests-run! (fn () {:total (+ dream-mw-pass dream-mw-fail) :passed dream-mw-pass :failed dream-mw-fail :fails dream-mw-fails}))

plans/dream-on-sx.md

@@ -51,7 +51,7 @@ The five types: `request`, `response`, `handler = request -> response`, `middlew
       - `dream-router routes` — dispatch tree, returns handler; no match → 404.
       - Path param extraction: `:name` segments, `**` wildcard.
       - `dream-param req name` — retrieve matched path param.
-- [ ] **Middleware** in `lib/dream/middleware.sx`:
+- [x] **Middleware** in `lib/dream/middleware.sx`:
       - `dream-pipeline middlewares handler` — compose middleware left-to-right.
       - `dream-no-middleware` — identity.
       - Logger: `(dream-logger next req)` — logs method, path, status, timing.
@@ -121,6 +121,13 @@ Confirm scope before starting; some of these may be addable as Dream-internal he
   prefix and folds the middleware chain (`m1 @@ m2 @@ h`, first = outermost) onto each
   route's handler; nests correctly (inner mw innermost). Shared `dr/apply-middlewares`
   fold will back `dream-pipeline`.
+- **2026-06-07 — Middleware** (`lib/dream/middleware.sx`, 20 tests). `dream-pipeline`
+  (reuses `dr/apply-middlewares`), `dream-no-middleware` identity. `dream-logger-with
+  clock sink` is the testable core (records `{:method :path :status :elapsed}`);
+  `dream-logger` wires it to `(perform (:dream-clock))` / `(perform (:dream-log …))`;
+  `dream-log-line` formats one line. `dream-content-type` sniffs body (`<`→html,
+  `{`/`[`→json, else text) only when the handler left Content-Type unset. Bonus
+  `dream-set-header` and `dream-tap-request` combinators.
 
 ## Blockers