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

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

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)))