Fix overlay/underlay on page with no resources (fixes #527)

ChangeLog

@@ -1,3 +1,8 @@
+2021-11-03  Jay Berkenbilt  <ejb@ql.org>
+
+	* Bug fix: make overlay/underlay work on a page with no resource
+	dictionary. Fixes #527.
+
 2021-11-02  Jay Berkenbilt  <ejb@ql.org>
 
 	* Add QPDF::findPage to the public API. This is primarily to help

manual/qpdf-manual.xml

@@ -5080,6 +5080,12 @@ print "\n";
           that could occur when given bogus input.
          </para>
         </listitem>
+        <listitem>
+         <para>
+          Properly handle overlay/underlay on completely empty pages
+          (with no resource dictionary).
+         </para>
+        </listitem>
        </itemizedlist>
       </listitem>
       <listitem>

qpdf/qpdf.cc

@@ -5226,6 +5226,12 @@ static void do_under_overlay_for_page(
     std::string content;
     int min_suffix = 1;
     QPDFObjectHandle resources = dest_page.getAttribute("/Resources", true);
+    if (! resources.isDictionary())
+    {
+        QTC::TC("qpdf", "qpdf overlay page with no resources");
+        resources = QPDFObjectHandle::newDictionary();
+        dest_page.getObjectHandle().replaceKey("/Resources", resources);
+    }
     for (std::vector<int>::iterator iter = pagenos[pageno].begin();
          iter != pagenos[pageno].end(); ++iter)
     {
@@ -5257,7 +5263,11 @@ static void do_under_overlay_for_page(
         {
             resources.mergeResources(
                 QPDFObjectHandle::parse("<< /XObject << >> >>"));
-            resources.getKey("/XObject").replaceKey(name, fo[from_pageno]);
+            auto xobject = resources.getKey("/XObject");
+            if (xobject.isDictionary())
+            {
+                xobject.replaceKey(name, fo[from_pageno]);
+            }
             ++min_suffix;
             content += new_content;
         }

qpdf/qpdf.testcov

@@ -596,3 +596,4 @@ QPDFWriter preserve object streams 1
 QPDFWriter exclude from object stream 0
 check unclosed --pages 1
 QPDF_pages findPage not found 0
+qpdf overlay page with no resources 0

qpdf/qtest/qpdf.test

@@ -477,7 +477,7 @@ $td->runtest("compare files",
 show_ntests();
 # ----------
 $td->notify("--- Form XObject, underlay, overlay ---");
-$n_tests += 20;
+$n_tests += 22;
 
 $td->runtest("form xobject creation",
              {$td->COMMAND => "test_driver 55 fxo-red.pdf"},
@@ -550,6 +550,15 @@ $td->runtest("page operations on form xobject",
              {$td->FILE => "page-ops-on-form-xobject.out",
                   $td->EXIT_STATUS => 0},
              $td->NORMALIZE_NEWLINES);
+$td->runtest("overlay on page with no resources",
+             {$td->COMMAND =>
+                  "qpdf --deterministic-id page-with-no-resources.pdf" .
+                  " --overlay minimal.pdf -- a.pdf"},
+             {$td->STRING => "", $td->EXIT_STATUS => 0},
+             $td->NORMALIZE_NEWLINES);
+$td->runtest("check overlay with no resources output",
+             {$td->FILE => "a.pdf"},
+             {$td->FILE => "overlay-no-resources.pdf"});
 
 show_ntests();
 # ----------

qpdf/qtest/qpdf/page-with-no-resources.pdf

@@ -0,0 +1,21 @@
+%PDF-1.3
+%¿÷¢þ
+1 0 obj
+<< /Pages 2 0 R /Type /Catalog >>
+endobj
+2 0 obj
+<< /Count 1 /Kids [ 3 0 R ] /Type /Pages >>
+endobj
+3 0 obj
+<< /MediaBox [ 0.0 0.0 612 792 ] /Parent 2 0 R /Type /Page >>
+endobj
+xref
+0 4
+0000000000 65535 f 
+0000000015 00000 n 
+0000000064 00000 n 
+0000000123 00000 n 
+trailer << /Root 1 0 R /Size 4 /ID [<f47f51552a4f2e020e12a656e72ed64c><0c18b42478a35cdccff23c62f4c7b946>] >>
+startxref
+200
+%%EOF