dream: forms (urlencoded) + stateless signed CSRF + 26 tests

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

lib/dream/conformance.sh

@@ -27,6 +27,7 @@ MODULES=(
   "lib/dream/middleware.sx"
   "lib/dream/session.sx"
   "lib/dream/flash.sx"
+  "lib/dream/form.sx"
 )
 
 # Suites: NAME RUNNER-FN PATH
@@ -36,6 +37,7 @@ SUITES=(
   "middleware  dream-mw-tests-run!  lib/dream/tests/middleware.sx"
   "session     dream-ss-tests-run!  lib/dream/tests/session.sx"
   "flash       dream-fl-tests-run!  lib/dream/tests/flash.sx"
+  "form        dream-fo-tests-run!  lib/dream/tests/form.sx"
 )
 
 TMPFILE=$(mktemp); trap "rm -f $TMPFILE" EXIT

lib/dream/form.sx

@@ -0,0 +1,228 @@
+;; lib/dream/form.sx — Dream-on-SX forms + CSRF.
+;; Parses application/x-www-form-urlencoded bodies; CSRF tokens are stateless,
+;; signed, and session-scoped. The signing function is injectable (a pure-SX keyed
+;; hash by default — production should swap in a host HMAC). Depends on types.sx +
+;; session.sx. dream-form returns an Ok/Err result value.
+
+;; ── Result (Ok/Err) ────────────────────────────────────────────────
+(define dream-ok (fn (v) {:value v :result "ok"}))
+(define dream-err (fn (r) {:reason r :result "err"}))
+(define dream-ok? (fn (x) (= (get x :result) "ok")))
+(define dream-err? (fn (x) (= (get x :result) "err")))
+(define dream-ok-value (fn (x) (get x :value)))
+(define dream-err-reason (fn (x) (get x :reason)))
+
+;; ── percent decoding ───────────────────────────────────────────────
+(define
+  dr/hex-digit
+  (fn
+    (c)
+    (let
+      ((n (char-code c)))
+      (cond
+        ((and (>= n 48) (<= n 57)) (- n 48))
+        ((and (>= n 65) (<= n 70))
+          (+ 10 (- n 65)))
+        ((and (>= n 97) (<= n 102))
+          (+ 10 (- n 97)))
+        (else 0)))))
+
+(define
+  dr/url-decode-loop
+  (fn
+    (s i n acc)
+    (if
+      (>= i n)
+      acc
+      (let
+        ((c (char-at s i)))
+        (if
+          (and (= c "%") (< (+ i 2) n))
+          (dr/url-decode-loop
+            s
+            (+ i 3)
+            n
+            (str
+              acc
+              (char-from-code
+                (+
+                  (* 16 (dr/hex-digit (char-at s (+ i 1))))
+                  (dr/hex-digit (char-at s (+ i 2)))))))
+          (dr/url-decode-loop s (+ i 1) n (str acc c)))))))
+
+(define
+  dr/url-decode
+  (fn
+    (s)
+    (let
+      ((s2 (replace s "+" " ")))
+      (dr/url-decode-loop s2 0 (string-length s2) ""))))
+
+;; ── urlencoded body parsing ────────────────────────────────────────
+(define
+  dr/parse-form-body
+  (fn
+    (body)
+    (if
+      (= body "")
+      {}
+      (reduce
+        (fn
+          (acc pair)
+          (if
+            (= pair "")
+            acc
+            (let
+              ((j (index-of pair "=")))
+              (if
+                (< j 0)
+                (assoc acc (dr/url-decode pair) "")
+                (assoc
+                  acc
+                  (dr/url-decode (substr pair 0 j))
+                  (dr/url-decode (substr pair (+ j 1))))))))
+        {}
+        (split body "&")))))
+
+;; raw fields, no CSRF check
+(define dream-form-fields (fn (req) (dr/parse-form-body (dream-body req))))
+(define
+  dream-form-field
+  (fn (req name) (get (dream-form-fields req) name)))
+
+;; ── CSRF signing (injectable; pure-SX keyed hash default) ──────────
+(define
+  dr/poly-hash
+  (fn (s base seed) (dr/poly-loop s 0 (string-length s) seed base)))
+(define
+  dr/poly-loop
+  (fn
+    (s i n h base)
+    (if
+      (>= i n)
+      h
+      (dr/poly-loop
+        s
+        (+ i 1)
+        n
+        (mod (+ (* h base) (char-code (char-at s i))) 2147483647)
+        base))))
+
+;; NOTE: not cryptographic — adequate to demonstrate stateless CSRF; production
+;; should inject a real HMAC via dream-csrf-with.
+(define
+  dream-csrf-sign-default
+  (fn
+    (secret msg)
+    (let
+      ((m (str secret "|" msg)))
+      (str
+        (dr/poly-hash m 131 7)
+        "-"
+        (dr/poly-hash m 137 13)))))
+
+(define dream-csrf-field-name "dream.csrf")
+
+(define
+  dr/csrf-make-token
+  (fn (sign secret sid) (str sid "." (sign secret sid))))
+
+(define
+  dr/csrf-valid?
+  (fn
+    (sign secret sid token)
+    (if
+      (or (nil? token) (= token ""))
+      false
+      (let
+        ((dot (index-of token ".")))
+        (if
+          (< dot 0)
+          false
+          (let
+            ((tsid (substr token 0 dot))
+              (tsig (substr token (+ dot 1))))
+            (and (= tsid sid) (= tsig (sign secret sid)))))))))
+
+;; ── CSRF middleware: attach signing context (needs session upstream) ──
+(define
+  dream-csrf-with
+  (fn
+    (secret sign)
+    (fn (next) (fn (req) (next (assoc req :dream-csrf {:sign sign :sid (dream-session-id req) :secret secret}))))))
+
+(define
+  dream-csrf
+  (fn (secret) (dream-csrf-with secret dream-csrf-sign-default)))
+
+(define dr/csrf-of (fn (req) (get req :dream-csrf)))
+
+;; current token + hidden-input tag for templates
+(define
+  dream-csrf-token
+  (fn
+    (req)
+    (let
+      ((c (dr/csrf-of req)))
+      (dr/csrf-make-token (get c :sign) (get c :secret) (get c :sid)))))
+
+(define
+  dream-csrf-tag
+  (fn
+    (req)
+    (str
+      "<input type=\"hidden\" name=\""
+      dream-csrf-field-name
+      "\" value=\""
+      (dream-csrf-token req)
+      "\">")))
+
+;; ── dream-form: parse + verify CSRF -> Ok fields | Err reason ──────
+(define
+  dream-form
+  (fn
+    (req)
+    (let
+      ((c (dr/csrf-of req)))
+      (if
+        (nil? c)
+        (dream-err :csrf-context-missing)
+        (let
+          ((fields (dream-form-fields req)))
+          (if
+            (dr/csrf-valid?
+              (get c :sign)
+              (get c :secret)
+              (get c :sid)
+              (get fields dream-csrf-field-name))
+            (dream-ok fields)
+            (dream-err :csrf-token-invalid)))))))
+
+;; ── CSRF auto-rejecting middleware (unsafe methods need a valid token) ──
+(define
+  dr/csrf-safe-method?
+  (fn (m) (or (= m "GET") (= m "HEAD") (= m "OPTIONS"))))
+
+(define
+  dream-csrf-protect-with
+  (fn
+    (secret sign)
+    (fn
+      (next)
+      (fn
+        (req)
+        (let
+          ((req2 (assoc req :dream-csrf {:sign sign :sid (dream-session-id req) :secret secret})))
+          (if
+            (dr/csrf-safe-method? (dream-method req2))
+            (next req2)
+            (let
+              ((token (get (dream-form-fields req2) dream-csrf-field-name)))
+              (if
+                (dr/csrf-valid? sign secret (dream-session-id req2) token)
+                (next req2)
+                (dream-html-status 403 "CSRF token invalid")))))))))
+
+(define
+  dream-csrf-protect
+  (fn (secret) (dream-csrf-protect-with secret dream-csrf-sign-default)))

lib/dream/tests/form.sx

@@ -0,0 +1,181 @@
+;; lib/dream/tests/form.sx — urlencoded parsing, Ok/Err, CSRF accept/reject.
+
+(define dream-fo-pass 0)
+(define dream-fo-fail 0)
+(define dream-fo-fails (list))
+
+(define
+  dream-fo-test
+  (fn
+    (name actual expected)
+    (if
+      (= actual expected)
+      (set! dream-fo-pass (+ dream-fo-pass 1))
+      (begin
+        (set! dream-fo-fail (+ dream-fo-fail 1))
+        (append! dream-fo-fails {:name name :actual actual :expected expected})))))
+
+;; ── Result ─────────────────────────────────────────────────────────
+(dream-fo-test "ok? on ok" (dream-ok? (dream-ok 5)) true)
+(dream-fo-test "err? on ok" (dream-err? (dream-ok 5)) false)
+(dream-fo-test "ok value" (dream-ok-value (dream-ok {:a 1})) {:a 1})
+(dream-fo-test "err reason" (dream-err-reason (dream-err :bad)) "bad")
+
+;; ── urlencoded parsing ─────────────────────────────────────────────
+(define
+  dream-fo-req
+  (fn (body) (dream-request "POST" "/f" {:Content-Type "application/x-www-form-urlencoded"} body)))
+
+(dream-fo-test
+  "parse two fields"
+  (dream-form-fields (dream-fo-req "a=1&b=2"))
+  {:a "1" :b "2"})
+(dream-fo-test
+  "url-decoded value"
+  (dream-form-field (dream-fo-req "name=Ada+Lovelace") "name")
+  "Ada Lovelace")
+(dream-fo-test
+  "percent decode"
+  (dream-form-field (dream-fo-req "x=a%20b%21") "x")
+  "a b!")
+(dream-fo-test "empty body" (dream-form-fields (dream-fo-req "")) {})
+(dream-fo-test
+  "valueless key"
+  (dream-form-field (dream-fo-req "flag") "flag")
+  "")
+(dream-fo-test
+  "decoded key"
+  (dream-form-field (dream-fo-req "first%20name=x") "first name")
+  "x")
+
+;; ── CSRF sign + verify ─────────────────────────────────────────────
+(dream-fo-test
+  "sign deterministic"
+  (=
+    (dream-csrf-sign-default "secret" "s1")
+    (dream-csrf-sign-default "secret" "s1"))
+  true)
+(dream-fo-test
+  "sign secret-sensitive"
+  (=
+    (dream-csrf-sign-default "secret" "s1")
+    (dream-csrf-sign-default "other" "s1"))
+  false)
+(dream-fo-test
+  "sign session-sensitive"
+  (=
+    (dream-csrf-sign-default "secret" "s1")
+    (dream-csrf-sign-default "secret" "s2"))
+  false)
+(dream-fo-test
+  "token valid for own session"
+  (dr/csrf-valid?
+    dream-csrf-sign-default
+    "k"
+    "s1"
+    (dr/csrf-make-token dream-csrf-sign-default "k" "s1"))
+  true)
+(dream-fo-test
+  "token invalid for other session"
+  (dr/csrf-valid?
+    dream-csrf-sign-default
+    "k"
+    "s2"
+    (dr/csrf-make-token dream-csrf-sign-default "k" "s1"))
+  false)
+(dream-fo-test
+  "tampered token invalid"
+  (dr/csrf-valid? dream-csrf-sign-default "k" "s1" "s1.deadbeef")
+  false)
+(dream-fo-test
+  "empty token invalid"
+  (dr/csrf-valid? dream-csrf-sign-default "k" "s1" "")
+  false)
+(dream-fo-test
+  "nil token invalid"
+  (dr/csrf-valid? dream-csrf-sign-default "k" "s1" nil)
+  false)
+
+;; ── full stack: session -> csrf -> handler ─────────────────────────
+(define dream-fo-backend (dream-memory-sessions))
+(define dream-fo-sid (dream-fo-backend {:op "session/create"}))   ;; s1
+
+;; build a request already carrying the session cookie + csrf middleware applied
+(define
+  dream-fo-stack
+  (fn
+    (handler)
+    ((dream-sessions dream-fo-backend) ((dream-csrf "topsecret") handler))))
+
+;; a handler that emits its csrf tag
+(define
+  dream-fo-tag-out
+  (dream-resp-body
+    ((dream-fo-stack (fn (req) (dream-text (dream-csrf-tag req))))
+      (dream-request "GET" "/form" {:Cookie "dream.session=s1"} ""))))
+(dream-fo-test
+  "csrf-tag is hidden input"
+  (contains? dream-fo-tag-out "type=\"hidden\"")
+  true)
+(dream-fo-test
+  "csrf-tag names field"
+  (contains? dream-fo-tag-out "name=\"dream.csrf\"")
+  true)
+
+;; valid token (signed for s1) -> dream-form Ok
+(define
+  dream-fo-good-token
+  (dr/csrf-make-token dream-csrf-sign-default "topsecret" "s1"))
+(define
+  dream-fo-submit
+  (fn
+    (token)
+    ((dream-fo-stack (fn (req) (let ((r (dream-form req))) (if (dream-ok? r) (dream-text (str "ok:" (get (dream-ok-value r) "msg"))) (dream-text (str "err:" (dream-err-reason r)))))))
+      (dream-request
+        "POST"
+        "/form"
+        {:Cookie "dream.session=s1"}
+        (str "msg=hello&dream.csrf=" token)))))
+
+(dream-fo-test
+  "valid csrf -> Ok fields"
+  (dream-resp-body (dream-fo-submit dream-fo-good-token))
+  "ok:hello")
+(dream-fo-test
+  "bad csrf -> Err"
+  (dream-resp-body (dream-fo-submit "s1.wrong"))
+  "err:csrf-token-invalid")
+(dream-fo-test
+  "missing csrf -> Err"
+  (dream-resp-body (dream-fo-submit ""))
+  "err:csrf-token-invalid")
+
+;; ── csrf-protect middleware auto-rejects ───────────────────────────
+(define
+  dream-fo-protected
+  (fn
+    (handler)
+    ((dream-sessions dream-fo-backend)
+      ((dream-csrf-protect "topsecret") handler))))
+(define dream-fo-ph (dream-fo-protected (fn (req) (dream-text "reached"))))
+
+(dream-fo-test
+  "GET passes without token"
+  (dream-resp-body (dream-fo-ph (dream-request "GET" "/x" {:Cookie "dream.session=s1"} "")))
+  "reached")
+(dream-fo-test
+  "POST without token 403"
+  (dream-status (dream-fo-ph (dream-request "POST" "/x" {:Cookie "dream.session=s1"} "")))
+  403)
+(dream-fo-test
+  "POST with valid token reaches"
+  (dream-resp-body
+    (dream-fo-ph
+      (dream-request
+        "POST"
+        "/x"
+        {:Cookie "dream.session=s1"}
+        (str "dream.csrf=" dream-fo-good-token))))
+  "reached")
+
+(define dream-fo-tests-run! (fn () {:total (+ dream-fo-pass dream-fo-fail) :passed dream-fo-pass :failed dream-fo-fail :fails dream-fo-fails}))

plans/dream-on-sx.md

@@ -64,11 +64,11 @@ The five types: `request`, `response`, `handler = request -> response`, `middlew
       - `dream-flash-middleware` — single-request cookie store.
       - `dream-add-flash-message req category msg`.
       - `dream-flash-messages req` — returns list of `(category, msg)`.
-- [ ] **Forms + CSRF** in `lib/dream/form.sx`:
-      - `dream-form req` — returns `(Ok fields)` or `(Err :csrf-token-invalid)`.
-      - `dream-multipart req` — streaming multipart form data.
-      - CSRF middleware: stateless signed tokens, session-scoped.
-      - `dream-csrf-tag req` — returns hidden input fragment for SX templates.
+- [~] **Forms + CSRF** in `lib/dream/form.sx`:
+      - [x] `dream-form req` — returns `(Ok fields)` or `(Err :csrf-token-invalid)`.
+      - [ ] `dream-multipart req` — streaming multipart form data. *(next commit)*
+      - [x] CSRF middleware: stateless signed tokens, session-scoped.
+      - [x] `dream-csrf-tag req` — returns hidden input fragment for SX templates.
 - [ ] **WebSockets** in `lib/dream/websocket.sx`:
       - `dream-websocket handler` — upgrades request; handler `(fn (ws) ...)`.
       - `dream-send ws msg`, `dream-receive ws`, `dream-close ws`.
@@ -151,6 +151,19 @@ Confirm scope before starting; some of these may be addable as Dream-internal he
   PREVIOUS request's messages) / `dream-flash-of` (by category) / accessors. Cookie
   codec percent-escapes the `|`/`~`/`%` separators so categories/messages round-trip.
   Read-after-write verified across request boundaries incl. multi-category.
+- **2026-06-07 — Forms + CSRF (urlencoded)** (`lib/dream/form.sx`, 26 tests). Ok/Err
+  result values (`dream-ok`/`dream-err` + predicates/accessors). `dream-form-fields`
+  parses `application/x-www-form-urlencoded` with a full percent-decoder
+  (`%XX` via `char-from-code`, `+`→space). CSRF is stateless + signed + session-
+  scoped: token = `sid.signature`, verified by recomputing the signature and checking
+  the session id — no server storage. Signing is **injectable** (`dream-csrf-with`);
+  the default `dream-csrf-sign-default` is a pure-SX dual-base polynomial keyed hash
+  (NOT cryptographic — production should inject a host HMAC). `dream-csrf` attaches
+  context (needs the session middleware upstream for the sid); `dream-csrf-token` /
+  `dream-csrf-tag` (hidden input for templates); `dream-form` returns `Ok fields` or
+  `Err :csrf-token-invalid`; `dream-csrf-protect` auto-rejects unsafe methods (403)
+  lacking a valid token. Full session→csrf→form stack verified accept + reject.
+  Multipart deferred to the next commit.
 
 ## Blockers