dream: static file serving — mime, etags, 304, ranges, traversal guard + 28 tests

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

lib/dream/conformance.sh

@@ -29,6 +29,7 @@ MODULES=(
   "lib/dream/flash.sx"
   "lib/dream/form.sx"
   "lib/dream/websocket.sx"
+  "lib/dream/static.sx"
 )
 
 # Suites: NAME RUNNER-FN PATH
@@ -40,6 +41,7 @@ SUITES=(
   "flash       dream-fl-tests-run!  lib/dream/tests/flash.sx"
   "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"
 )
 
 TMPFILE=$(mktemp); trap "rm -f $TMPFILE" EXIT

lib/dream/static.sx

@@ -0,0 +1,182 @@
+;; lib/dream/static.sx — Dream-on-SX static file serving.
+;; dream-static mounts at a ** route and serves files under a root: content-type by
+;; extension, ETags + If-None-Match (304), and Range requests (206). The filesystem
+;; is injectable: production reads via (perform op); tests pass an in-memory map.
+;; Depends on types.sx.
+
+;; ── filesystem backends ────────────────────────────────────────────
+;; An fs is (fn (op) result); op {:op "file/read" :path p} -> content | nil.
+(define dream-static-perform-fs (fn (op) (perform op)))
+
+;; in-memory fs over a {path -> content} dict (tests + demos)
+(define
+  dream-memory-fs
+  (fn
+    (files)
+    (fn
+      (op)
+      (if (= (get op :op) "file/read") (get files (get op :path)) nil))))
+
+;; ── content-type by extension ──────────────────────────────────────
+(define dr/mime-types {:js "application/javascript" :jpeg "image/jpeg" :css "text/css; charset=utf-8" :ico "image/x-icon" :mjs "application/javascript" :html "text/html; charset=utf-8" :pdf "application/pdf" :jpg "image/jpeg" :json "application/json" :htm "text/html; charset=utf-8" :wasm "application/wasm" :webp "image/webp" :gif "image/gif" :png "image/png" :svg "image/svg+xml" :md "text/markdown; charset=utf-8" :xml "application/xml" :sx "text/plain; charset=utf-8" :txt "text/plain; charset=utf-8"})
+
+(define
+  dr/ext-of
+  (fn
+    (path)
+    (let
+      ((segs (split path ".")))
+      (if
+        (> (len segs) 1)
+        (lower (nth segs (- (len segs) 1)))
+        ""))))
+
+(define
+  dream-content-type-for
+  (fn
+    (path)
+    (or (get dr/mime-types (dr/ext-of path)) "application/octet-stream")))
+
+;; ── ETag (weak content hash) ───────────────────────────────────────
+(define
+  dr/static-hash
+  (fn (s) (dr/static-hash-loop s 0 (string-length s) 7)))
+(define
+  dr/static-hash-loop
+  (fn
+    (s i n h)
+    (if
+      (>= i n)
+      h
+      (dr/static-hash-loop
+        s
+        (+ i 1)
+        n
+        (mod (+ (* h 131) (char-code (char-at s i))) 2147483647)))))
+(define
+  dr/etag-of
+  (fn
+    (content)
+    (str "\"" (dr/static-hash content) "-" (string-length content) "\"")))
+(define
+  dr/etag-match?
+  (fn (inm etag) (and (not (nil? inm)) (or (= inm "*") (= inm etag)))))
+
+;; ── path safety ────────────────────────────────────────────────────
+(define
+  dr/static-relpath
+  (fn
+    (req)
+    (or (dream-param req "**") (substr (dream-path req) 1))))
+(define
+  dr/unsafe-path?
+  (fn (rel) (or (contains? rel "..") (starts-with? rel "/")))) 
+(define
+  dr/path-join
+  (fn
+    (root rel)
+    (if (ends-with? root "/") (str root rel) (str root "/" rel))))
+
+;; ── range requests ─────────────────────────────────────────────────
+(define
+  dr/parse-range
+  (fn
+    (header total)
+    (let
+      ((eq (index-of header "=")))
+      (if
+        (< eq 0)
+        nil
+        (let
+          ((spec (substr header (+ eq 1))))
+          (let
+            ((dash (index-of spec "-")))
+            (if
+              (< dash 0)
+              nil
+              (let
+                ((s (substr spec 0 dash))
+                  (e (substr spec (+ dash 1))))
+                (let
+                  ((start (if (= s "") 0 (parse-int s)))
+                    (end (if (= e "") (- total 1) (parse-int e))))
+                  (if
+                    (or
+                      (< start 0)
+                      (>= start total)
+                      (> end (- total 1))
+                      (> start end))
+                    nil
+                    {:start start :end end}))))))))))
+
+(define
+  dr/serve-range
+  (fn
+    (req content etag ctype)
+    (let
+      ((total (string-length content)))
+      (let
+        ((r (dr/parse-range (dream-header req "range") total)))
+        (if
+          (nil? r)
+          (dream-add-header
+            (dream-response 416 {:content-type ctype} "")
+            "content-range"
+            (str "bytes */" total))
+          (let
+            ((start (get r :start)) (end (get r :end)))
+            (dream-add-header
+              (dream-add-header
+                (dream-response
+                  206
+                  {:content-type ctype}
+                  (substr content start (+ 1 (- end start))))
+                "content-range"
+                (str "bytes " start "-" end "/" total))
+              "etag"
+              etag)))))))
+
+;; ── serving ────────────────────────────────────────────────────────
+(define
+  dr/serve-file
+  (fn
+    (req content)
+    (let
+      ((rel (dr/static-relpath req)))
+      (let
+        ((etag (dr/etag-of content)) (ctype (dream-content-type-for rel)))
+        (cond
+          ((dr/etag-match? (dream-header req "if-none-match") etag)
+            (dream-add-header (dream-empty 304) "etag" etag))
+          ((dream-header req "range")
+            (dr/serve-range req content etag ctype))
+          (else
+            (dream-add-header
+              (dream-add-header
+                (dream-response 200 {:content-type ctype} content)
+                "etag"
+                etag)
+              "accept-ranges"
+              "bytes")))))))
+
+(define
+  dream-static-with
+  (fn
+    (root fs)
+    (fn
+      (req)
+      (let
+        ((rel (dr/static-relpath req)))
+        (if
+          (dr/unsafe-path? rel)
+          (dream-html-status 403 "Forbidden")
+          (let
+            ((content (fs {:path (dr/path-join root rel) :op "file/read"})))
+            (if
+              (nil? content)
+              (dream-not-found)
+              (dr/serve-file req content))))))))
+
+(define
+  dream-static
+  (fn (root) (dream-static-with root dream-static-perform-fs)))

lib/dream/tests/static.sx

@@ -0,0 +1,125 @@
+;; lib/dream/tests/static.sx — content types, etags, 304, ranges, traversal.
+
+(define dream-st-pass 0)
+(define dream-st-fail 0)
+(define dream-st-fails (list))
+
+(define
+  dream-st-test
+  (fn
+    (name actual expected)
+    (if
+      (= actual expected)
+      (set! dream-st-pass (+ dream-st-pass 1))
+      (begin
+        (set! dream-st-fail (+ dream-st-fail 1))
+        (append! dream-st-fails {:name name :actual actual :expected expected})))))
+
+;; ── content type + ext ─────────────────────────────────────────────
+(dream-st-test "ext css" (dr/ext-of "a/b/style.css") "css")
+(dream-st-test "ext multi-dot" (dr/ext-of "a.min.js") "js")
+(dream-st-test "ext none" (dr/ext-of "README") "")
+(dream-st-test
+  "ctype css"
+  (dream-content-type-for "x.css")
+  "text/css; charset=utf-8")
+(dream-st-test
+  "ctype html"
+  (dream-content-type-for "x.html")
+  "text/html; charset=utf-8")
+(dream-st-test "ctype png" (dream-content-type-for "x.png") "image/png")
+(dream-st-test
+  "ctype unknown"
+  (dream-content-type-for "x.bin")
+  "application/octet-stream")
+
+;; ── etag ───────────────────────────────────────────────────────────
+(dream-st-test
+  "etag deterministic"
+  (= (dr/etag-of "abc") (dr/etag-of "abc"))
+  true)
+(dream-st-test
+  "etag content-sensitive"
+  (= (dr/etag-of "abc") (dr/etag-of "abd"))
+  false)
+(dream-st-test
+  "etag length-sensitive"
+  (= (dr/etag-of "ab") (dr/etag-of "abc"))
+  false)
+
+;; ── serving via router mount ───────────────────────────────────────
+(define dream-st-files {:/srv/app.css "body{color:red}" :/srv/index.html "<h1>Hi</h1>"})
+(define dream-st-fs (dream-memory-fs dream-st-files))
+(define
+  dream-st-app
+  (dream-router
+    (list (dream-get "/static/**" (dream-static-with "/srv" dream-st-fs)))))
+(define
+  dream-st-get
+  (fn
+    (target headers)
+    (dream-st-app (dream-request "GET" target headers ""))))
+
+(define dream-st-css (dream-st-get "/static/app.css" {}))
+(dream-st-test "serve status 200" (dream-status dream-st-css) 200)
+(dream-st-test "serve body" (dream-resp-body dream-st-css) "body{color:red}")
+(dream-st-test
+  "serve content-type"
+  (dream-resp-header dream-st-css "content-type")
+  "text/css; charset=utf-8")
+(dream-st-test
+  "serve accept-ranges"
+  (dream-resp-header dream-st-css "accept-ranges")
+  "bytes")
+(dream-st-test
+  "serve has etag"
+  (not (nil? (dream-resp-header dream-st-css "etag")))
+  true)
+(dream-st-test
+  "missing file 404"
+  (dream-status (dream-st-get "/static/nope.txt" {}))
+  404)
+(dream-st-test
+  "traversal blocked 403"
+  (dream-status (dream-st-get "/static/../secret" {}))
+  403)
+
+;; ── conditional: If-None-Match -> 304 ──────────────────────────────
+(define dream-st-etag (dream-resp-header dream-st-css "etag"))
+(define dream-st-304 (dream-st-get "/static/app.css" {:If-None-Match dream-st-etag}))
+(dream-st-test "matching etag 304" (dream-status dream-st-304) 304)
+(dream-st-test "304 empty body" (dream-resp-body dream-st-304) "")
+(dream-st-test
+  "stale etag 200"
+  (dream-status (dream-st-get "/static/app.css" {:If-None-Match "\"stale\""}))
+  200)
+(dream-st-test
+  "star etag 304"
+  (dream-status (dream-st-get "/static/app.css" {:If-None-Match "*"}))
+  304)
+
+;; ── range requests ─────────────────────────────────────────────────
+(define dream-st-range (dream-st-get "/static/app.css" {:Range "bytes=0-3"}))
+(dream-st-test "range status 206" (dream-status dream-st-range) 206)
+(dream-st-test "range body slice" (dream-resp-body dream-st-range) "body")
+(dream-st-test
+  "range content-range"
+  (dream-resp-header dream-st-range "content-range")
+  "bytes 0-3/15")
+(define dream-st-open (dream-st-get "/static/app.css" {:Range "bytes=5-"}))
+(dream-st-test "open range body" (dream-resp-body dream-st-open) "color:red}")
+(dream-st-test
+  "open range header"
+  (dream-resp-header dream-st-open "content-range")
+  "bytes 5-14/15")
+(define dream-st-bad (dream-st-get "/static/app.css" {:Range "bytes=20-30"}))
+(dream-st-test
+  "unsatisfiable range 416"
+  (dream-status dream-st-bad)
+  416)
+(dream-st-test
+  "416 content-range"
+  (dream-resp-header dream-st-bad "content-range")
+  "bytes */15")
+
+(define dream-st-tests-run! (fn () {:total (+ dream-st-pass dream-st-fail) :passed dream-st-pass :failed dream-st-fail :fails dream-st-fails}))

plans/dream-on-sx.md

@@ -72,7 +72,7 @@ The five types: `request`, `response`, `handler = request -> response`, `middlew
 - [x] **WebSockets** in `lib/dream/websocket.sx`:
       - `dream-websocket handler` — upgrades request; handler `(fn (ws) ...)`.
       - `dream-send ws msg`, `dream-receive ws`, `dream-close ws`.
-- [ ] **Static files:** `dream-static root-path` — serves files, ETags, range requests.
+- [x] **Static files:** `dream-static root-path` — serves files, ETags, range requests.
 - [ ] **`dream-run`**: wires root handler into SX's `perform (:http-listen ...)`.
 - [ ] **Demos** in `lib/dream/demos/`:
       - `hello.ml` → `lib/dream/demos/hello.sx`: "Hello, World!" route.
@@ -182,6 +182,13 @@ Confirm scope before starting; some of these may be addable as Dream-internal he
   is `(perform op)`, tests use `dream-mock-ws` (in-memory inbox/outbox/closed via the
   cell pattern) with `dream-ws-sent` / `dream-ws-closed?` introspection and
   `dream-ws-run` to drive a handler. Echo loop + room broadcast verified.
+- **2026-06-07 — Static files** (`lib/dream/static.sx`, 28 tests). `dream-static root`
+  mounts at a `**` route and serves files: content-type by extension (mime map),
+  weak ETag (`"hash-length"`) with `If-None-Match` → 304 (incl. `*`), and `Range:
+  bytes=` requests → 206 with `Content-Range` (open-ended `bytes=N-` supported,
+  unsatisfiable → 416). `..`/absolute path traversal → 403; missing → 404; full
+  responses advertise `Accept-Ranges`. Filesystem is injectable —
+  `dream-static-perform-fs` (host) vs `dream-memory-fs` (in-memory map for tests).
 
 ## Blockers