Add a TouchEventStreamValidator

content/common/input/touch_event_stream_validator.cc

Index: content/common/input/touch_event_stream_validator.cc
diff --git a/content/common/input/touch_event_stream_validator.cc b/content/common/input/touch_event_stream_validator.cc
new file mode 100644
index 0000000000000000000000000000000000000000..85bc469443315e516f26d4b362b75fdbd1146903
--- /dev/null
+++ b/content/common/input/touch_event_stream_validator.cc
@@ -0,0 +1,108 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "content/common/input/touch_event_stream_validator.h"
+
+#include "base/logging.h"
+#include "content/common/input/web_touch_event_traits.h"
+
+using blink::WebInputEvent;
+using blink::WebTouchEvent;
+using blink::WebTouchPoint;
+
+namespace content {
+namespace {
+
+const WebTouchPoint* FindTouchPoint(const WebTouchEvent& event, int id) {
+  for (unsigned i = 0; i < event.touchesLength; ++i) {
+    if (event.touches[i].id == id)
+      return &event.touches[i];
+  }
+  return NULL;
+}
+
+}  // namespace
+
+TouchEventStreamValidator::TouchEventStreamValidator() {
+}
+
+TouchEventStreamValidator::~TouchEventStreamValidator() {
+}
+
+bool TouchEventStreamValidator::Validate(const WebTouchEvent& event,
+                                         std::string* error_msg) {
+  DCHECK(error_msg);
+  error_msg->clear();
+
+  WebTouchEvent previous_event = previous_event_;
+  previous_event_ = event;
+
+  // Allow "hard" restarting of touch stream validation. This is necessary
+  // in cases where touch event forwarding ceases in response to the event ack
+  // or removal of touch handlers.
+  if (WebTouchEventTraits::IsTouchSequenceStart(event))
+    previous_event = WebTouchEvent();
+
+  // Unreleased points from the previous event should exist in the latest event.
+  for (unsigned i = 0; i < previous_event.touchesLength; ++i) {
+    const WebTouchPoint& previous_point = previous_event.touches[i];
+    if (previous_point.state == WebTouchPoint::StateCancelled ||
+        previous_point.state == WebTouchPoint::StateReleased)
+      continue;
+
+    const WebTouchPoint* point = FindTouchPoint(event, previous_point.id);
+    if (!point)
+      error_msg->append("Previously active touch point not in new event.\n");
+  }
+
+  for (unsigned i = 0; i < event.touchesLength; ++i) {
+    const WebTouchPoint& point = event.touches[i];
+    const WebTouchPoint* previous_point =
+        FindTouchPoint(previous_event, point.id);
+
+    // The point should exist in the previous event if it is not a new point.
+    if (!previous_point) {
+      if (point.state != WebTouchPoint::StatePressed)
+        error_msg->append("Active touch point not found in previous event.\n");
+    } else {
+      if (point.state == WebTouchPoint::StatePressed &&
+          previous_point->state != WebTouchPoint::StateCancelled &&
+          previous_point->state != WebTouchPoint::StateReleased) {
+        error_msg->append("Pressed touch point id already exists.\n");
+      }
+    }
+
+    switch (point.state) {
+      case WebTouchPoint::StateUndefined:
+        error_msg->append("Undefined WebTouchPoint state.\n");
+        break;
+
+      case WebTouchPoint::StateReleased:
+        if (event.type != WebInputEvent::TouchEnd)
+          error_msg->append("Released touch point outside touchend.\n");
+        break;
+
+      case WebTouchPoint::StatePressed:
+        if (event.type != WebInputEvent::TouchStart)
+          error_msg->append("Pressed touch point outside touchstart.\n");
+        break;
+
+      case WebTouchPoint::StateMoved:
+        if (event.type != WebInputEvent::TouchMove)
+          error_msg->append("Moved touch point outside touchmove.\n");
+        break;
+
+      case WebTouchPoint::StateStationary:
+        break;
+
+      case WebTouchPoint::StateCancelled:
+        if (event.type != WebInputEvent::TouchCancel)
+          error_msg->append("Cancelled touch point outside touchcancel.\n");
+        break;
+    }
+  }
+  return error_msg->empty();
+}
+
+}  // namespace content