dream: error-handling middleware (dream-catch) + status reason phrases + 15 tests

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

lib/dream/conformance.sh

@@ -30,6 +30,7 @@ MODULES=(
   "lib/dream/form.sx"
   "lib/dream/websocket.sx"
   "lib/dream/static.sx"
+  "lib/dream/error.sx"
   "lib/dream/run.sx"
   "lib/dream/demos/hello.sx"
   "lib/dream/demos/counter.sx"
@@ -47,6 +48,7 @@ SUITES=(
   "form        dream-fo-tests-run!  lib/dream/tests/form.sx"
   "websocket   dream-ws-tests-run!  lib/dream/tests/websocket.sx"
   "static      dream-st-tests-run!  lib/dream/tests/static.sx"
+  "error       dream-er-tests-run!  lib/dream/tests/error.sx"
   "run         dream-rn-tests-run!  lib/dream/tests/run.sx"
   "demos       dream-dm-tests-run!  lib/dream/tests/demos.sx"
 )

lib/dream/error.sx

@@ -0,0 +1,41 @@
+;; lib/dream/error.sx — Dream-on-SX status phrases + error-handling middleware.
+;; dream-catch wraps a handler and turns a raised error into a 500 response (or a
+;; custom page). Depends on types.sx.
+
+;; ── status reason phrases ──────────────────────────────────────────
+(define dr/status-texts {:206 "Partial Content" :202 "Accepted" :422 "Unprocessable Entity" :400 "Bad Request" :302 "Found" :204 "No Content" :502 "Bad Gateway" :429 "Too Many Requests" :301 "Moved Permanently" :415 "Unsupported Media Type" :405 "Method Not Allowed" :303 "See Other" :401 "Unauthorized" :304 "Not Modified" :503 "Service Unavailable" :404 "Not Found" :308 "Permanent Redirect" :504 "Gateway Timeout" :416 "Range Not Satisfiable" :500 "Internal Server Error" :307 "Temporary Redirect" :201 "Created" :501 "Not Implemented" :409 "Conflict" :200 "OK" :410 "Gone" :403 "Forbidden"})
+
+(define
+  dream-status-text
+  (fn (status) (or (get dr/status-texts (str status)) "Unknown")))
+(define
+  dream-status-line
+  (fn (status) (str status " " (dream-status-text status))))
+
+;; ── error-handling middleware ──────────────────────────────────────
+(define
+  dream-default-error-page
+  (fn
+    (req e)
+    (dream-html-status
+      500
+      (str "<h1>" (dream-status-line 500) "</h1>"))))
+
+(define
+  dream-catch-with
+  (fn
+    (on-error)
+    (fn
+      (next)
+      (fn (req) (guard (e (true (on-error req e))) (next req))))))
+
+(define dream-catch (dream-catch-with dream-default-error-page))
+
+;; a fallback handler that renders a status page for any code
+(define
+  dream-status-page
+  (fn
+    (status)
+    (dream-html-status
+      status
+      (str "<h1>" (dream-status-line status) "</h1>"))))

lib/dream/tests/error.sx

@@ -0,0 +1,90 @@
+;; lib/dream/tests/error.sx — status phrases + dream-catch.
+
+(define dream-er-pass 0)
+(define dream-er-fail 0)
+(define dream-er-fails (list))
+
+(define
+  dream-er-test
+  (fn
+    (name actual expected)
+    (if
+      (= actual expected)
+      (set! dream-er-pass (+ dream-er-pass 1))
+      (begin
+        (set! dream-er-fail (+ dream-er-fail 1))
+        (append! dream-er-fails {:name name :actual actual :expected expected})))))
+
+;; ── status phrases ─────────────────────────────────────────────────
+(dream-er-test "200 OK" (dream-status-text 200) "OK")
+(dream-er-test "404 Not Found" (dream-status-text 404) "Not Found")
+(dream-er-test
+  "405 phrase"
+  (dream-status-text 405)
+  "Method Not Allowed")
+(dream-er-test
+  "500 phrase"
+  (dream-status-text 500)
+  "Internal Server Error")
+(dream-er-test "unknown phrase" (dream-status-text 599) "Unknown")
+(dream-er-test "status line" (dream-status-line 404) "404 Not Found")
+(dream-er-test
+  "status page status"
+  (dream-status (dream-status-page 403))
+  403)
+(dream-er-test
+  "status page body"
+  (dream-resp-body (dream-status-page 403))
+  "<h1>403 Forbidden</h1>")
+
+;; ── dream-catch ────────────────────────────────────────────────────
+(define dream-er-boom (fn (req) (error "kaboom")))
+(define dream-er-ok (fn (req) (dream-text "fine")))
+
+(dream-er-test
+  "catch normal passes through"
+  (dream-resp-body
+    ((dream-catch dream-er-ok) (dream-request "GET" "/" {} "")))
+  "fine")
+(dream-er-test
+  "catch error -> 500"
+  (dream-status
+    ((dream-catch dream-er-boom) (dream-request "GET" "/" {} "")))
+  500)
+(dream-er-test
+  "catch 500 body"
+  (dream-resp-body
+    ((dream-catch dream-er-boom) (dream-request "GET" "/" {} "")))
+  "<h1>500 Internal Server Error</h1>")
+
+;; custom error page receives the error
+(define
+  dream-er-custom
+  (dream-catch-with (fn (req e) (dream-text (str "ERR:" e)))))
+(dream-er-test
+  "custom error page"
+  (dream-resp-body
+    ((dream-er-custom dream-er-boom) (dream-request "GET" "/" {} "")))
+  "ERR:kaboom")
+(dream-er-test
+  "custom passes normal through"
+  (dream-resp-body
+    ((dream-er-custom dream-er-ok) (dream-request "GET" "/" {} "")))
+  "fine")
+
+;; catch composes around a router
+(define
+  dream-er-app
+  (dream-catch
+    (dream-router
+      (list (dream-get "/boom" dream-er-boom) (dream-get "/ok" dream-er-ok)))))
+(dream-er-test
+  "router error caught"
+  (dream-status (dream-er-app (dream-request "GET" "/boom" {} "")))
+  500)
+(dream-er-test
+  "router ok intact"
+  (dream-resp-body (dream-er-app (dream-request "GET" "/ok" {} "")))
+  "fine")
+
+(define dream-er-tests-run! (fn () {:total (+ dream-er-pass dream-er-fail) :passed dream-er-pass :failed dream-er-fail :fails dream-er-fails}))