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// Copyright 2020 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "content/renderer/accessibility/ax_tree_snapshotter_impl.h"
#include "base/metrics/histogram_functions.h"
#include "content/renderer/render_frame_impl.h"
#include "third_party/blink/public/web/web_ax_context.h"
#include "third_party/blink/public/web/web_ax_object.h"
#include "third_party/blink/public/web/web_document.h"
#include "third_party/blink/public/web/web_frame.h"
#include "ui/accessibility/ax_tree_serializer.h"
#include "ui/accessibility/ax_tree_update.h"
using blink::WebAXContext;
using blink::WebAXObject;
using blink::WebDocument;
namespace content {
constexpr char kAXTreeSnapshotterErrorHistogramName[] =
"Accessibility.AXTreeSnapshotter.Snapshot.Error";
// These values are persisted to logs. Entries should not be renumbered and
// numeric values should never be reused.
enum class AXTreeSnapshotErrorReason {
kGenericSerializationError = 0,
kNoWebFrame = 1,
kNoActiveDocument = 2,
kNoExistingAXObjectCache = 3,
kMaxValue = kNoExistingAXObjectCache,
};
AXTreeSnapshotterImpl::AXTreeSnapshotterImpl(RenderFrameImpl* render_frame,
ui::AXMode ax_mode)
: render_frame_(render_frame) {
// Do not generate inline textboxes, which are expensive to create and just
// present extra noise to snapshot consumers.
ax_mode.set_mode(ui::AXMode::kInlineTextBoxes, false);
DCHECK(render_frame->GetWebFrame());
blink::WebDocument document_ = render_frame->GetWebFrame()->GetDocument();
context_ = std::make_unique<WebAXContext>(document_, ax_mode);
}
AXTreeSnapshotterImpl::~AXTreeSnapshotterImpl() = default;
void AXTreeSnapshotterImpl::Snapshot(size_t max_node_count,
base::TimeDelta timeout,
ui::AXTreeUpdate* response) {
base::UmaHistogramBoolean("Accessibility.AXTreeSnapshotter.Snapshot.Request",
true);
if (!render_frame_->GetWebFrame()) {
base::UmaHistogramEnumeration(kAXTreeSnapshotterErrorHistogramName,
AXTreeSnapshotErrorReason::kNoWebFrame);
return;
}
if (!context_->HasActiveDocument()) {
base::UmaHistogramEnumeration(kAXTreeSnapshotterErrorHistogramName,
AXTreeSnapshotErrorReason::kNoActiveDocument);
return;
}
if (!context_->HasAXObjectCache()) {
base::UmaHistogramEnumeration(
kAXTreeSnapshotterErrorHistogramName,
AXTreeSnapshotErrorReason::kNoExistingAXObjectCache);
// TODO(chrishtr): not clear why this can happen.
NOTREACHED_NORETURN();
}
if (context_->SerializeEntireTree(max_node_count, timeout, response)) {
return;
}
base::UmaHistogramEnumeration(
kAXTreeSnapshotterErrorHistogramName,
AXTreeSnapshotErrorReason::kGenericSerializationError);
// It failed again. Clear the response object because it might have errors.
*response = ui::AXTreeUpdate();
LOG(WARNING) << "Unable to serialize accessibility tree.";
// As a confidence check, node_id_to_clear and event_from should be
// uninitialized if this is a full tree snapshot. They'd only be set to
// something if this was indeed a partial update to the tree (which we don't
// want).
DCHECK_EQ(0, response->node_id_to_clear);
DCHECK_EQ(ax::mojom::EventFrom::kNone, response->event_from);
DCHECK_EQ(ax::mojom::Action::kNone, response->event_from_action);
}
} // namespace content
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