Bug fix: properly handle overridden compressed objects

When caching objects in an object stream, only cache objects that
still resolve to that stream.  See Changelog mod from this commit for
details.

ChangeLog

@@ -1,3 +1,13 @@
+2013-02-23  Jay Berkenbilt  <ejb@ql.org>
+
+	* Bug fix: properly handle overridden compressed objects.  When
+	caching objects from an object stream, only cache objects that,
+	based on the xref table, would actually be resolved into this
+	stream.  Prior to this fix, if an object stream A contained an
+	object B that was overridden by an appended section of the file,
+	qpdf would cache the old value of B if any non-overridden member
+	of A was accessed before B.  This commit fixes that bug.
+
 2013-01-31  Jay Berkenbilt  <ejb@ql.org>
 
 	* Do not remove libtool's .la file during the make install step.

libqpdf/QPDF.cc

@@ -1538,20 +1538,31 @@ QPDF::resolveObjectsInStream(int obj_stream_number)
 	offsets[num] = offset + first;
     }
 
+    // To avoid having to read the object stream multiple times, store
+    // all objects that would be found here in the cache.  Remember
+    // that some objects stored here might have been overridden by new
+    // objects appended to the file, so it is necessary to recheck the
+    // xref table and only cache what would actually be resolved here.
     for (std::map<int, int>::iterator iter = offsets.begin();
 	 iter != offsets.end(); ++iter)
     {
 	int obj = (*iter).first;
-	int offset = (*iter).second;
-	input->seek(offset, SEEK_SET);
-	QPDFObjectHandle oh = readObject(input, "", obj, 0, true);
-
-	// Store in cache
 	ObjGen og(obj, 0);
-
-	this->obj_cache[og] =
-	    ObjCache(QPDFObjectHandle::ObjAccessor::getObject(oh),
-		     end_before_space, end_after_space);
+        QPDFXRefEntry const& entry = this->xref_table[og];
+        if ((entry.getType() == 2) &&
+            (entry.getObjStreamNumber() == obj_stream_number))
+        {
+            int offset = (*iter).second;
+            input->seek(offset, SEEK_SET);
+            QPDFObjectHandle oh = readObject(input, "", obj, 0, true);
+            this->obj_cache[og] =
+                ObjCache(QPDFObjectHandle::ObjAccessor::getObject(oh),
+                         end_before_space, end_after_space);
+        }
+        else
+        {
+            QTC::TC("qpdf", "QPDF not caching overridden objstm object");
+        }
     }
 }
 

qpdf/qpdf.testcov

@@ -261,3 +261,4 @@ qpdf-c called qpdf_set_r5_encryption_parameters 0
 qpdf-c called qpdf_set_r6_encryption_parameters 0
 QPDFObjectHandle EOF in inline image 0
 QPDFObjectHandle inline image token 0
+QPDF not caching overridden objstm object 0

qpdf/qtest/qpdf.test

@@ -199,7 +199,7 @@ $td->runtest("remove page we don't have",
 show_ntests();
 # ----------
 $td->notify("--- Miscellaneous Tests ---");
-$n_tests += 60;
+$n_tests += 61;
 
 $td->runtest("qpdf version",
 	     {$td->COMMAND => "qpdf --version"},
@@ -484,6 +484,18 @@ $td->runtest("content stream errors",
               $td->EXIT_STATUS => 2},
              $td->NORMALIZE_NEWLINES);
 
+# The file override-compressed-object.pdf contains an object stream
+# with four strings in it.  The file is then appended.  The appended
+# section overrides one of the four strings with a string in another
+# object stream and another one in an uncompressed object.  The other
+# two strings are left alone.  The test case exercises that all four
+# objects have the correct value.
+$td->runtest("overridden compressed objects",
+             {$td->COMMAND => "test_driver 38 override-compressed-object.pdf"},
+             {$td->FILE => "override-compressed-object.out",
+              $td->EXIT_STATUS => 0},
+             $td->NORMALIZE_NEWLINES);
+
 show_ntests();
 # ----------
 $td->notify("--- Numeric range parsing tests ---");

qpdf/qtest/qpdf/override-compressed-object.out

@@ -0,0 +1,5 @@
+(orig-1)
+(override-2)
+(override-3)
+(orig-4)
+test 38 done

qpdf/test_driver.cc

@@ -1302,6 +1302,15 @@ void runtest(int n, char const* filename1, char const* arg2)
             QPDFObjectHandle::parseContentStream(contents, &cb);
         }
     }
+    else if (n == 38)
+    {
+        // Designed for override-compressed-object.pdf
+        QPDFObjectHandle qtest = pdf.getRoot().getKey("/QTest");
+        for (int i = 0; i < qtest.getArrayNItems(); ++i)
+        {
+            std::cout << qtest.getArrayItem(i).unparseResolved() << std::endl;
+        }
+    }
     else
     {
 	throw std::runtime_error(std::string("invalid test ") +