From 9360c7cbdc93ca68fbad99f963e41eb492fd16e9 Mon Sep 17 00:00:00 2001
From: Jonas Jenwald <jonas.jenwald@gmail.com>
Date: Mon, 12 Apr 2021 08:52:35 +0200
Subject: [PATCH] Avoid unnecessary parsing, in `Page.GetStructTree`, when no
 structTree is available (PR 13221 follow-up)

It's obviously (a bit) more efficient to return early in `Page.getStructTree`, rather than trying to first "parse" an *empty* structTree-root.

*Somehow I didn't think of this yesterday, but this feels like a much better solution overall; sorry about the churn here!*
---
 src/core/document.js    |  8 +++++++-
 src/core/struct_tree.js |  4 ----
 src/core/worker.js      | 12 +++---------
 3 files changed, 10 insertions(+), 14 deletions(-)

diff --git a/src/core/document.js b/src/core/document.js
index 27cbede28..072ae3770 100644
--- a/src/core/document.js
+++ b/src/core/document.js
@@ -454,7 +454,13 @@ class Page {
     const structTreeRoot = await this.pdfManager.ensureCatalog(
       "structTreeRoot"
     );
-    return this.pdfManager.ensure(this, "_parseStructTree", [structTreeRoot]);
+    if (!structTreeRoot) {
+      return null;
+    }
+    const structTree = await this.pdfManager.ensure(this, "_parseStructTree", [
+      structTreeRoot,
+    ]);
+    return structTree.serializable;
   }
 
   /**
diff --git a/src/core/struct_tree.js b/src/core/struct_tree.js
index a07d99b96..41587d45c 100644
--- a/src/core/struct_tree.js
+++ b/src/core/struct_tree.js
@@ -328,10 +328,6 @@ class StructTreePage {
       }
       nodeToSerializable(child, root);
     }
-
-    if (root.children.length === 0) {
-      return null;
-    }
     return root;
   }
 }
diff --git a/src/core/worker.js b/src/core/worker.js
index fb81beb79..4cf69b769 100644
--- a/src/core/worker.js
+++ b/src/core/worker.js
@@ -743,15 +743,9 @@ class WorkerMessageHandler {
     });
 
     handler.on("GetStructTree", function wphGetStructTree(data) {
-      const pageIndex = data.pageIndex;
-      return pdfManager
-        .getPage(pageIndex)
-        .then(function (page) {
-          return pdfManager.ensure(page, "getStructTree");
-        })
-        .then(function (structTree) {
-          return structTree.serializable;
-        });
+      return pdfManager.getPage(data.pageIndex).then(function (page) {
+        return pdfManager.ensure(page, "getStructTree");
+      });
     });
 
     handler.on("FontFallback", function (data) {