fix(studio): input that carries a point is scaled with a fitted page or refused

desktop/electron/src/browserviews.js

@@ -142,10 +142,11 @@ class BrowserViews {
       send: (method, params) => {
         if (method === "Emulation.setDeviceMetricsOverride") return this.emulate(entry, params);
         if (method === "Emulation.clearDeviceMetricsOverride") return this.emulate(entry, null);
-        // The page reads input in the viewport it was told it has; the view
-        // draws that viewport scaled, and a point meant for the page lands
-        // where the page is drawn only after the same scaling.
-        if (method === "Input.dispatchMouseEvent" && entry.scale !== 1) params = { ...params, x: params.x * entry.scale, y: params.y * entry.scale };
+        try {
+          params = scaleInput(method, params, entry.scale);
+        } catch (e) {
+          return Promise.reject(e);
+        }
         if (!method.startsWith("Input.")) return contents.debugger.sendCommand(method, params);
         entry.synthUntil = Date.now() + 250;
         return this.wake.run(() => contents.debugger.sendCommand(method, params));
@@ -482,6 +483,29 @@ function placement(panel, emulated) {
   return { at: { x, y, width, height }, scale };
 }
 
+// Input that carries a point. The page reads it in the viewport it was told it
+// has, the view draws that viewport scaled, and a point meant for the page lands
+// where it is drawn only after the same scaling. The mouse is measured to; the
+// rest are not, and a point that silently lands elsewhere is worse than a
+// refusal, so they are refused while the page is scaled.
+const POINTED_INPUT = new Set([
+  "Input.dispatchTouchEvent",
+  "Input.dispatchDragEvent",
+  "Input.emulateTouchFromMouseEvent",
+  "Input.synthesizeTapGesture",
+  "Input.synthesizeScrollGesture",
+  "Input.synthesizePinchGesture",
+]);
+
+function scaleInput(method, params, scale) {
+  if (scale === 1) return params;
+  if (method === "Input.dispatchMouseEvent") return { ...params, x: params.x * scale, y: params.y * scale };
+  if (POINTED_INPUT.has(method)) {
+    throw Object.assign(new Error(`${method} is not available while the page is scaled to fit the panel`), { code: "input_unscaled" });
+  }
+  return params;
+}
+
 function sameRect(a, b) {
   return !!a && a.x === b.x && a.y === b.y && a.width === b.width && a.height === b.height;
 }
@@ -490,4 +514,4 @@ function validRect(rect) {
   return rect && [rect.x, rect.y, rect.width, rect.height].every(Number.isFinite) && rect.width > 0 && rect.height > 0;
 }
 
-module.exports = { BrowserViews, AGENT_VIEWPORT, LEAVE_LIMIT_MS, placement };
+module.exports = { BrowserViews, AGENT_VIEWPORT, LEAVE_LIMIT_MS, placement, scaleInput };

desktop/electron/test/unit.mjs

@@ -2304,6 +2304,32 @@ test("a page given its own viewport is fitted whole into its panel, centred, and
   assert.deepEqual(placement({ x: 20, y: 20, width: 1400, height: 1000 }, { width: 1280, height: 900 }), { at: { x: 80, y: 70, width: 1280, height: 900 }, scale: 1 });
 });
 
+test("input that carries a point is scaled with the page or refused, never sent to the wrong place", () => {
+  const Module = require("node:module");
+  const load = Module._load;
+  Module._load = function (request, ...rest) {
+    if (request === "electron") return { WebContentsView: class {}, session: { fromPartition: () => ({}) } };
+    return load.call(this, request, ...rest);
+  };
+  let scaleInput;
+  try {
+    ({ scaleInput } = require("../src/browserviews.js"));
+  } finally {
+    Module._load = load;
+  }
+  const mouse = { type: "mousePressed", x: 1200, y: 800, button: "left" };
+  assert.equal(scaleInput("Input.dispatchMouseEvent", mouse, 1), mouse, "an unscaled page gets the point as it is");
+  assert.deepEqual(scaleInput("Input.dispatchMouseEvent", mouse, 0.5), { type: "mousePressed", x: 600, y: 400, button: "left" });
+  for (const method of ["Input.dispatchTouchEvent", "Input.dispatchDragEvent", "Input.emulateTouchFromMouseEvent", "Input.synthesizeTapGesture", "Input.synthesizeScrollGesture", "Input.synthesizePinchGesture"]) {
+    const params = { x: 10, y: 20, touchPoints: [{ x: 10, y: 20 }] };
+    assert.equal(scaleInput(method, params, 1), params, `${method} passes on an unscaled page`);
+    assert.throws(() => scaleInput(method, params, 0.5), { code: "input_unscaled" }, `${method} must not reach a scaled page unscaled`);
+  }
+  const key = { type: "keyDown", key: "a" };
+  assert.equal(scaleInput("Input.dispatchKeyEvent", key, 0.5), key, "keys carry no point");
+  assert.equal(scaleInput("Input.insertText", { text: "x" }, 0.5).text, "x");
+});
+
 test("rewind notice dismissal survives the desktop preference disk round trip", (t) => {
   const dir = fs.mkdtempSync(path.join(os.tmpdir(), "rewind-notice-prefs-"));
   const file = path.join(dir, "prefs.json");