HS: socket on-message + as JSON (+3)

Steps 4-5 complete: hs-try-json-parse, ws.onmessage wiring (text/JSON
dispatch), onmessage test cases. 8/16 socket tests passing.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/hyperscript/runtime.sx

@@ -2528,6 +2528,10 @@
 
 ;; ── WebSocket / socket feature ───────────────────────────────────
 
+(define
+  hs-try-json-parse
+  (fn (s) (host-call (host-global "JSON") "parse" s)))
+
 (define
   hs-socket-register!
   (fn
@@ -2553,6 +2557,27 @@
                 wrapper
                 "rpc"
                 (host-call proxy-factory "call" nil wrapper))))
+          (host-set!
+            ws
+            "onmessage"
+            (host-callback
+              (fn
+                (event)
+                (let
+                  ((data (host-get event "data")))
+                  (let
+                    ((parsed (hs-try-json-parse data)))
+                    (cond
+                      ((and (not (nil? parsed)) (not (nil? (host-get parsed "iid"))))
+                        nil)
+                      ((not (nil? handler))
+                        (if
+                          json?
+                          (if
+                            (not (nil? parsed))
+                            (handler parsed)
+                            (error "Received non-JSON message"))
+                          (handler event)))))))))
           (define
             bind-path!
             (fn

shared/static/wasm/sx/hs-runtime.sx

@@ -2528,6 +2528,10 @@
 
 ;; ── WebSocket / socket feature ───────────────────────────────────
 
+(define
+  hs-try-json-parse
+  (fn (s) (host-call (host-global "JSON") "parse" s)))
+
 (define
   hs-socket-register!
   (fn
@@ -2553,6 +2557,27 @@
                 wrapper
                 "rpc"
                 (host-call proxy-factory "call" nil wrapper))))
+          (host-set!
+            ws
+            "onmessage"
+            (host-callback
+              (fn
+                (event)
+                (let
+                  ((data (host-get event "data")))
+                  (let
+                    ((parsed (hs-try-json-parse data)))
+                    (cond
+                      ((and (not (nil? parsed)) (not (nil? (host-get parsed "iid"))))
+                        nil)
+                      ((not (nil? handler))
+                        (if
+                          json?
+                          (if
+                            (not (nil? parsed))
+                            (handler parsed)
+                            (error "Received non-JSON message"))
+                          (handler event)))))))))
           (define
             bind-path!
             (fn

spec/tests/test-hyperscript-behavioral.sx

@@ -11530,11 +11530,29 @@
       (let ((chat (host-get my-app "chat")))
         (assert (not (nil? (host-get chat "raw")))))))
   (deftest "on message as JSON handler decodes JSON payload"
-    (error "SKIP (untranslated): on message as JSON handler decodes JSON payload"))
+    (hs-cleanup!)
+    (eval-hs "socket JsonSocket ws://localhost/ws on message as JSON set window.socketFiredJson to true end")
+    (let ((sock (host-get (host-global "window") "JsonSocket")))
+      (let ((ws (host-get sock "raw")))
+        (do
+          (host-call ws "onmessage" {:data "{\"name\":\"Alice\"}"}))
+      (assert= (host-get (host-global "window") "socketFiredJson") true))))
   (deftest "on message as JSON throws on non-JSON payload"
-    (error "SKIP (untranslated): on message as JSON throws on non-JSON payload"))
+    (hs-cleanup!)
+    (eval-hs "socket StrictJsonSocket ws://localhost/ws on message as JSON set window.strictFired to true end")
+    (let ((sock (host-get (host-global "window") "StrictJsonSocket")))
+      (let ((ws (host-get sock "raw")))
+        (do
+          (host-call ws "onmessage" {:data "not-json"})
+          (assert (nil? (host-get (host-global "window") "strictFired")))))))
   (deftest "on message handler fires on incoming text message"
-    (error "SKIP (untranslated): on message handler fires on incoming text message"))
+    (hs-cleanup!)
+    (eval-hs "socket TextSocket ws://localhost/ws on message set window.socketFired to true end")
+    (let ((sock (host-get (host-global "window") "TextSocket")))
+      (let ((ws (host-get sock "raw")))
+        (do
+          (host-call ws "onmessage" {:data "hello socket"})
+          (assert= (host-get (host-global "window") "socketFired") true)))))
   (deftest "parses socket with absolute ws:// URL"
     (hs-cleanup!)
     (host-set! (host-global "window") "__hs_ws_created" (list))

tests/playwright/generate-sx-tests.py

@@ -1953,6 +1953,47 @@ def generate_eval_only_test(test, idx):
             f'        (assert (not (nil? (host-get sock "rpc")))))))'
         )
 
+    # Special case: cluster-36 socket on-message tests (step 5).
+    # Test 7: plain text message fires the handler.
+    if test['name'] == 'on message handler fires on incoming text message':
+        return (
+            f'  (deftest "{safe_name}"\n'
+            f'    (hs-cleanup!)\n'
+            f'    (eval-hs "socket TextSocket ws://localhost/ws on message set window.socketFired to true end")\n'
+            f'    (let ((sock (host-get (host-global "window") "TextSocket")))\n'
+            f'      (let ((ws (host-get sock "raw")))\n'
+            f'        (do\n'
+            f'          (host-call ws "onmessage" {{:data "hello socket"}})\n'
+            f'          (assert= (host-get (host-global "window") "socketFired") true)))))'
+        )
+
+    # Test 5: JSON message fires handler with parsed object.
+    if test['name'] == 'on message as JSON handler decodes JSON payload':
+        return (
+            f'  (deftest "{safe_name}"\n'
+            f'    (hs-cleanup!)\n'
+            f'    (eval-hs "socket JsonSocket ws://localhost/ws on message as JSON set window.socketFiredJson to true end")\n'
+            f'    (let ((sock (host-get (host-global "window") "JsonSocket")))\n'
+            f'      (let ((ws (host-get sock "raw")))\n'
+            f'        (do\n'
+            f'          (host-call ws "onmessage" {{:data "{{\\"name\\":\\"Alice\\"}}"}}))\n'
+            f'      (assert= (host-get (host-global "window") "socketFiredJson") true))))'
+        )
+
+    # Test 6: non-JSON data with as JSON raises error before handler body runs.
+    # We verify the handler body (set window.strictFired) was NOT executed.
+    if test['name'] == 'on message as JSON throws on non-JSON payload':
+        return (
+            f'  (deftest "{safe_name}"\n'
+            f'    (hs-cleanup!)\n'
+            f'    (eval-hs "socket StrictJsonSocket ws://localhost/ws on message as JSON set window.strictFired to true end")\n'
+            f'    (let ((sock (host-get (host-global "window") "StrictJsonSocket")))\n'
+            f'      (let ((ws (host-get sock "raw")))\n'
+            f'        (do\n'
+            f'          (host-call ws "onmessage" {{:data "not-json"}})\n'
+            f'          (assert (nil? (host-get (host-global "window") "strictFired")))))))'
+        )
+
     # Special case: cluster-29 init events. The two tractable tests both attach
     # listeners to a wa container, set its innerHTML to a hyperscript fragment,
     # then call `_hyperscript.processNode(wa)`. Hand-roll deftests using