Generalise last commit to xref parsing and reconstruction

Tests use a modified dangling-bad-xref.pdf.

libqpdf/QPDF.cc

@@ -463,9 +463,8 @@ QPDF::fixDanglingReferences(bool force)
 size_t
 QPDF::getObjectCount()
 {
-    // This method returns the next available indirect object number. makeIndirectObject uses it for
-    // this purpose. After fixDanglingReferences is called, all objects in the xref table will also
-    // be in obj_cache.
+    // This method returns the highest used indirect object number. Calling this method will resolve
+    // all objects.
     return toS(m->objects.last_id());
 }
 

libqpdf/QPDF_objects.cc

@@ -171,18 +171,28 @@ Xref_table::initialize()
     initialized_ = true;
 }
 
-// Remove any dangling reference picked up while parsing the xref table.
+// Remove any dangling reference picked up while parsing or reconstructing the xref table from the
+// object table.
 void
 Xref_table::prepare_obj_table()
 {
     for (auto it = objects.table.begin(), end = objects.table.end(); it != end;) {
-        if (type(it->first, it->second.gen)) {
-            ++it;
-        } else {
+        if (it->second.unconfirmed && !type(it->first, it->second.gen)) {
             it->second.object->make_null();
             it = objects.table.erase(it);
+        } else {
+            it->second.unconfirmed = false;
+            ++it;
         }
     }
+    for (auto& [id_gen, obj]: objects.unconfirmed_objects) {
+        if (type(id_gen.first, id_gen.second)) {
+            objects.update_table(id_gen.first, id_gen.second, obj);
+        } else {
+            obj->make_null();
+        }
+    }
+    objects.unconfirmed_objects.clear();
 }
 
 void
@@ -204,6 +214,8 @@ Xref_table::reconstruct(QPDFExc& e)
     };
 
     reconstructed_ = true;
+    bool called_during_resolve_attempt = initialized_;
+    initialized_ = false;
 
     warn_damaged("file is damaged");
     qpdf.warn(e);
@@ -280,7 +292,7 @@ Xref_table::reconstruct(QPDFExc& e)
             if (item.type() != 1) {
                 continue;
             }
-            auto oh = objects.get(i, item.gen());
+            QPDFObjectHandle oh{objects.get_when_uncertain(i, item.gen())};
             try {
                 if (!oh.isStreamOfType("/XRef")) {
                     continue;
@@ -319,8 +331,11 @@ Xref_table::reconstruct(QPDFExc& e)
         throw damaged_pdf("unable to find objects while recovering damaged file");
     }
     check_warnings();
-    if (!initialized_) {
+    prepare_obj_table();
     initialized_ = true;
+    if (!called_during_resolve_attempt) {
+        // We can't do the checks because we may try to resolve the object that triggered the
+        // reconstruction.
         qpdf.getAllPages();
         check_warnings();
         if (qpdf.m->all_pages.empty()) {
@@ -1552,7 +1567,7 @@ QPDFObject*
 Objects::resolve(int id, int gen)
 {
     if (!unresolved(id, gen)) {
-        return get(id, gen).getObjectPtr();
+        return get_for_parser(id, gen, true).get();
     }
 
     auto og = QPDFObjGen(id, gen);
@@ -1835,6 +1850,9 @@ std::shared_ptr<QPDFObject>
 Objects::get_for_parser(int id, int gen, bool parse_pdf)
 {
     // This method is called by the parser and therefore must not resolve any objects.
+    if (!xref.initialized() && parse_pdf) {
+        return get_when_uncertain(id, gen);
+    }
     auto iter = table.find(id);
     if (iter != table.end() && iter->second.gen == gen) {
         return iter->second.object;
@@ -1843,7 +1861,7 @@ Objects::get_for_parser(int id, int gen, bool parse_pdf)
         // id in table, different gen
         return QPDF_Null::create();
     }
-    if (xref.type(id, gen) || !xref.initialized()) {
+    if (xref.type(id, gen)) {
         return table.insert({id, {gen, QPDF_Unresolved::create(&qpdf, QPDFObjGen(id, gen))}})
             .first->second.object;
     }
@@ -1869,7 +1887,9 @@ Objects::get_when_uncertain(int id, int gen)
         e.gen = gen;
         if (!xref.type(id, gen)) {
             e.unconfirmed = true;
-            return e.object = QPDF_Null::create(&qpdf, QPDFObjGen(id, gen));
+            return e.object = xref.initialized()
+                ? QPDF_Null::create(&qpdf, QPDFObjGen(id, gen))
+                : QPDF_Unresolved::create(&qpdf, QPDFObjGen(id, gen));
         } else {
             return e.object = QPDF_Unresolved::create(&qpdf, QPDFObjGen(id, gen));
         }
@@ -1889,7 +1909,8 @@ Objects::get_when_uncertain(int id, int gen)
     if (auto& j = unconfirmed_objects[{id, gen}]) {
         return j;
     } else {
-        return j = QPDF_Null::create(&qpdf, QPDFObjGen(id, gen));
+        return j = xref.initialized() ? QPDF_Null::create(&qpdf, QPDFObjGen(id, gen))
+                                      : QPDF_Unresolved::create(&qpdf, QPDFObjGen(id, gen));
     }
 }
 

qpdf/qtest/dangling-refs.test

@@ -14,7 +14,7 @@ cleanup();
 
 my $td = new TestDriver('dangling-refs');
 
-my @dangling = (qw(minimal dangling-refs dangling-bad-xref));
+my @dangling = (qw(minimal dangling-refs dangling-bad-xref dangling-multiple-gen-bad-xref));
 my $n_tests = 2 * scalar(@dangling);
 
 foreach my $f (@dangling)

qpdf/qtest/qpdf/dangling-multiple-gen-bad-xref-dangling.out

@@ -0,0 +1,15 @@
+WARNING: dangling-multiple-gen-bad-xref.pdf: file is damaged
+WARNING: dangling-multiple-gen-bad-xref.pdf (object 7 0, offset 10000): expected n n obj
+WARNING: dangling-multiple-gen-bad-xref.pdf: Attempting to reconstruct cross-reference table
+new object: 12 0 R
+all objects
+1 3 R
+2 3 R
+3 0 R
+4 0 R
+5 0 R
+6 0 R
+7 0 R
+11 0 R
+12 0 R
+test 53 done

qpdf/qtest/qpdf/dangling-multiple-gen-bad-xref.pdf

@@ -0,0 +1,118 @@
+%PDF-1.3
+%¿÷¢þ
+%QDF-1.0
+
+1 3 obj
+<<
+  /Pages 2 3 R
+  /Type /Catalog
+  /Dangling 8 0 R
+  /AlsoDangling [
+    9 0 R
+    <<
+      /yes 2 5 R
+      /no 10 0 R
+      /nope 8 0 R
+    >>
+  ]
+>>
+endobj
+
+2 3 obj
+<<
+  /Count 1
+  /Kids [
+    3 0 R
+  ]
+  /Type /Pages
+>>
+endobj
+
+%% Page 1
+3 0 obj
+<<
+  /Contents 4 0 R
+  /MediaBox [
+    0
+    0
+    612
+    792
+  ]
+  /Parent 2 0 R
+  /Resources <<
+    /Font <<
+      /F1 6 0 R
+    >>
+    /ProcSet 7 0 R
+  >>
+  /Type /Page
+>>
+endobj
+
+%% Contents for page 1
+4 0 obj
+<<
+  /Length 5 0 R
+>>
+stream
+BT
+  /F1 24 Tf
+  72 720 Td
+  (Potato) Tj
+ET
+endstream
+endobj
+
+5 0 obj
+44
+endobj
+
+6 0 obj
+<<
+  /BaseFont /Helvetica
+  /Encoding /WinAnsiEncoding
+  /Name /F1
+  /Subtype /Type1
+  /Type /Font
+>>
+endobj
+
+7 0 obj
+[
+  /PDF
+  /Text
+]
+endobj
+
+11 0 obj
+[
+  12 0 R
+  2 4 R
+  ]
+endobj
+
+xref
+0 8
+0000000000 65535 f 
+0000000025 00003 n 
+0000000195 00003 n 
+0000000277 00000 n 
+0000000492 00000 n 
+0000000591 00000 n 
+0000000610 00000 n 
+0000010000 00000 n 
+trailer <<
+  /Dangle [
+  1 0 R
+  1 6 R
+  2 6 R
+  2 0 R
+  4 6 R
+  ]
+  /Root 1 3 R
+  /Size 8
+  /ID [<7141a6cf32de469328cf0f51982b5f89><7141a6cf32de469328cf0f51982b5f89>]
+>>
+startxref
+803
+%%EOF