XFA - Get each page asynchronously in order to avoid blocking the event loop (#14014)

src/core/document.js

@@ -787,7 +787,8 @@ class PDFDocument {
   get numPages() {
     let num = 0;
     if (this.xfaFactory) {
-      num = this.xfaFactory.numPages;
+      // num is a Promise.
+      num = this.xfaFactory.getNumPages();
     } else if (this.linearization) {
       num = this.linearization.numPages;
     } else {

src/core/xfa/factory.js

@@ -19,6 +19,7 @@ import {
   $nodeName,
   $text,
   $toHTML,
+  $toPages,
 } from "./xfa_object.js";
 import { Binder } from "./bind.js";
 import { DataHandler } from "./data.js";
@@ -45,9 +46,32 @@ class XFAFactory {
     return this.root && this.form;
   }
 
-  _createPages() {
+  /**
+   * In order to avoid to block the event loop, the conversion
+   * into pages is made asynchronously.
+   */
+  _createPagesHelper() {
+    const iterator = this.form[$toPages]();
+    return new Promise((resolve, reject) => {
+      const nextIteration = () => {
+        try {
+          const value = iterator.next();
+          if (value.done) {
+            resolve(value.value);
+          } else {
+            setTimeout(nextIteration, 0);
+          }
+        } catch (e) {
+          reject(e);
+        }
+      };
+      setTimeout(nextIteration, 0);
+    });
+  }
+
+  async _createPages() {
     try {
-      this.pages = this.form[$toHTML]();
+      this.pages = await this._createPagesHelper();
       this.dims = this.pages.children.map(c => {
         const { width, height } = c.attributes.style;
         return [0, 0, parseInt(width), parseInt(height)];
@@ -61,9 +85,9 @@ class XFAFactory {
     return this.dims[pageIndex];
   }
 
-  get numPages() {
+  async getNumPages() {
     if (!this.pages) {
-      this._createPages();
+      await this._createPages();
     }
     return this.dims.length;
   }
@@ -94,9 +118,9 @@ class XFAFactory {
     this.form[$globalData].fontFinder.add(fonts, reallyMissingFonts);
   }
 
-  getPages() {
+  async getPages() {
     if (!this.pages) {
-      this._createPages();
+      await this._createPages();
     }
     const pages = this.pages;
     this.pages = null;

src/core/xfa/template.js

@@ -55,6 +55,7 @@ import {
   $tabIndex,
   $text,
   $toHTML,
+  $toPages,
   $toStyle,
   $uid,
   ContentObject,
@@ -5395,7 +5396,12 @@ class Template extends XFAObject {
     return searchNode(this, container, expr, true, true);
   }
 
-  [$toHTML]() {
+  /**
+   * This function is a generator because the conversion into
+   * pages is done asynchronously and we want to save the state
+   * of the function where we were in the previous iteration.
+   */
+  *[$toPages]() {
     if (!this.subform.children.length) {
       return HTMLResult.success({
         name: "div",
@@ -5641,6 +5647,7 @@ class Template extends XFAObject {
         }
       }
       pageArea = targetPageArea || pageArea[$getNextPage]();
+      yield null;
     }
   }
 }

src/core/xfa/xfa_object.js

@@ -84,6 +84,7 @@ const $setSetAttributes = Symbol();
 const $setValue = Symbol();
 const $tabIndex = Symbol();
 const $text = Symbol();
+const $toPages = Symbol();
 const $toHTML = Symbol();
 const $toString = Symbol();
 const $toStyle = Symbol();
@@ -1137,6 +1138,7 @@ export {
   $tabIndex,
   $text,
   $toHTML,
+  $toPages,
   $toString,
   $toStyle,
   $uid,