Always check all Kids nodes, in `Catalog.getPageDict`, to avoid getting stuck in an empty node further down in the Pages tree (issue 8088)

As discussed on IRC, we need to check all nodes at the *bottom* of the tree to ensure that we find the correct `Page` dict.
Furthermore, this patch also gets rid of the caching present in a previous version, since it's not clear if that really helps.

Note that this patch purposely adds an `eq` test, using a reduced test-case, so that we can be sure that the algorithm actually finds the correct `Page` dict for each `pageIndex`.

Fixes 8088.

src/core/obj.js

@@ -452,7 +452,6 @@ var Catalog = (function CatalogClosure() {
       var nodesToVisit = [this.catDict.getRaw('Pages')];
       var currentPageIndex = 0;
       var xref = this.xref;
-      var checkAllKids = false;
 
       function next() {
         while (nodesToVisit.length) {
@@ -476,16 +475,10 @@ var Catalog = (function CatalogClosure() {
           }
 
           // Must be a child page dictionary.
-          assert(
+          assert(isDict(currentNode),
-            isDict(currentNode),
+            'page dictionary kid reference points to wrong type of object');
-            'page dictionary kid reference points to wrong type of object'
+
-          );
           var count = currentNode.get('Count');
-          // If the current node doesn't have any children, avoid getting stuck
-          // in an empty node further down in the tree (see issue5644.pdf).
-          if (count === 0) {
-            checkAllKids = true;
-          }
           // Skip nodes where the page can't be.
           if (currentPageIndex + count <= pageIndex) {
             currentPageIndex += count;
@@ -494,21 +487,12 @@ var Catalog = (function CatalogClosure() {
 
           var kids = currentNode.get('Kids');
           assert(isArray(kids), 'page dictionary kids object is not an array');
-          if (!checkAllKids && count === kids.length) {
+
-            // Nodes that don't have the page have been skipped and this is the
+          // Always check all `Kids` nodes, to avoid getting stuck in an empty
-            // bottom of the tree which means the page requested must be a
+          // node further down in the tree (see issue5644.pdf, issue8088.pdf),
-            // descendant of this pages node. Ideally we would just resolve the
+          // and to ensure that we actually find the correct `Page` dict.
-            // promise with the page ref here, but there is the case where more
+          for (var last = kids.length - 1; last >= 0; last--) {
-            // pages nodes could link to single a page (see issue 3666 pdf). To
+            nodesToVisit.push(kids[last]);
-            // handle this push it back on the queue so if it is a pages node it
-            // will be descended into.
-            nodesToVisit = [kids[pageIndex - currentPageIndex]];
-            currentPageIndex = pageIndex;
-            continue;
-          } else {
-            for (var last = kids.length - 1; last >= 0; last--) {
-              nodesToVisit.push(kids[last]);
-            }
           }
         }
         capability.reject('Page index ' + pageIndex + ' not found.');

test/pdfs/.gitignore

@@ -46,6 +46,7 @@
 !issue7872.pdf
 !issue7901.pdf
 !issue8061.pdf
+!issue8088.pdf
 !bad-PageLabels.pdf
 !filled-background.pdf
 !ArabicCIDTrueType.pdf

test/pdfs/issue8088.pdf

@@ -0,0 +1,163 @@
+%PDF-1.7
+%âãÏÓ
+1 0 obj 
+<<
+/Parent 2 0 R
+/Resources 
+<<
+/Font 
+<<
+/F1 3 0 R
+>>
+>>
+/MediaBox [0 0 200 50]
+/Type /Page
+/Contents 4 0 R
+>>
+endobj 
+4 0 obj 
+<<
+/Length 50
+>>
+stream
+BT
+10 20 TD
+/F1 20 Tf
+(Issue 8088 - Page 2) Tj
+ET
+
+endstream 
+endobj 
+5 0 obj 
+<<
+/Parent 6 0 R
+/Resources 
+<<
+/Font 
+<<
+/F1 3 0 R
+>>
+>>
+/MediaBox [0 0 200 50]
+/Type /Page
+/Contents 7 0 R
+>>
+endobj 
+7 0 obj 
+<<
+/Length 50
+>>
+stream
+BT
+10 20 TD
+/F1 20 Tf
+(Issue 8088 - Page 3) Tj
+ET
+
+endstream 
+endobj 
+8 0 obj 
+<<
+/Parent 9 0 R
+/Kids []
+/Type /Pages
+/Count 0
+>>
+endobj 
+2 0 obj 
+<<
+/Parent 9 0 R
+/Kids [10 0 R 1 0 R]
+/Type /Pages
+/Count 2
+>>
+endobj 
+9 0 obj 
+<<
+/Parent 11 0 R
+/Kids [8 0 R 2 0 R]
+/Type /Pages
+/Count 2
+>>
+endobj 
+6 0 obj 
+<<
+/Parent 11 0 R
+/Kids [5 0 R]
+/Type /Pages
+/Count 1
+>>
+endobj 
+11 0 obj 
+<<
+/Kids [9 0 R 6 0 R]
+/Type /Pages
+/Count 3
+>>
+endobj 
+12 0 obj 
+<<
+/Pages 11 0 R
+/Type /Catalog
+>>
+endobj 
+10 0 obj 
+<<
+/Parent 2 0 R
+/Resources 
+<<
+/Font 
+<<
+/F1 3 0 R
+>>
+>>
+/MediaBox [0 0 200 50]
+/Type /Page
+/Contents 13 0 R
+>>
+endobj 
+13 0 obj 
+<<
+/Length 50
+>>
+stream
+BT
+10 20 TD
+/F1 20 Tf
+(Issue 8088 - Page 1) Tj
+ET
+
+endstream 
+endobj 
+3 0 obj 
+<<
+/BaseFont /Times-Roman
+/Subtype /Type1
+/Encoding /WinAnsiEncoding
+/Type /Font
+>>
+endobj xref
+0 14
+0000000000 65535 f 
+0000000015 00000 n 
+0000000547 00000 n 
+0000001135 00000 n 
+0000000144 00000 n 
+0000000247 00000 n 
+0000000707 00000 n 
+0000000376 00000 n 
+0000000479 00000 n 
+0000000627 00000 n 
+0000000900 00000 n 
+0000000781 00000 n 
+0000000847 00000 n 
+0000001031 00000 n 
+trailer
+
+<<
+/Root 12 0 R
+/Size 14
+>>
+startxref
+1235
+%%EOF

test/test_manifest.json

@@ -1318,6 +1318,15 @@
        "lastPage": 6,
        "type": "eq"
     },
+    {  "id": "issue8088",
+       "file": "pdfs/issue8088.pdf",
+       "md5": "5bbc33c7433799487518eb0d8094348c",
+       "rounds": 1,
+       "link": false,
+       "firstPage": 1,
+       "lastPage": 3,
+       "type": "eq"
+    },
     {  "id": "bug866395",
        "file": "pdfs/bug866395.pdf",
        "md5": "f03bc77e84637241980b09a0a220f575",