Handle empty DecodeParams array for (fixes #331)

On read, ignore /DecodeParms when empty list; on write, delete it. Some files have been found that include an empty list for /DecodeParms, but this is not technically compliant with the spec, and the only sensible interpretation is to treat it as if there are no decode parameters.

Handle empty DecodeParams array for (fixes #331)
On read, ignore /DecodeParms when empty list; on write, delete it. Some files have been found that include an empty list for /DecodeParms, but this is not technically compliant with the spec, and the only sensible interpretation is to treat it as if there are no decode parameters.
Jay Berkenbilt
1 parent 74cc3440
Showing 5 changed files with 26 additions and 1 deletions
ChangeLog
libqpdf/QPDFWriter.cc
libqpdf/QPDF_Stream.cc
qpdf/qpdf.testcov
qpdf/qtest/qpdf.test
+2019-06-09  Jay Berkenbilt  <ejb@ql.org>
+
+	* When /DecodeParms is an empty list, ignore it on read and delete
+	it on write. Fixes #331.
+
 2019-05-18  Jay Berkenbilt  <ejb@ql.org>
 	* 8.4.2: release
@@ -1604,6 +1604,14 @@ QPDFWriter::unparseObject(QPDFObjectHandle object, int level,
             // Suppress /Length since we will write it manually
             object.removeKey("/Length");
+            // If /DecodeParms is an empty list, remove it.
+            if (object.getKey("/DecodeParms").isArray() &&
+                (0 == object.getKey("/DecodeParms").getArrayNItems()))
+            {
+                QTC::TC("qpdf", "QPDFWriter remove empty DecodeParms");
+                object.removeKey("/DecodeParms");
+            }
+
 	    if (flags & f_filtered)
             {
                 // We will supply our own filter and decode
@@ -391,6 +391,10 @@ QPDF_Stream::filterable(std::vector&lt;std::string&gt;&amp; filters,
     QPDFObjectHandle decode_obj = this->stream_dict.getKey("/DecodeParms");
     std::vector<QPDFObjectHandle> decode_parms;
+    if (decode_obj.isArray() && (decode_obj.getArrayNItems() == 0))
+    {
+        decode_obj = QPDFObjectHandle::newNull();
+    }
     if (decode_obj.isArray())
     {
         for (int i = 0; i < decode_obj.getArrayNItems(); ++i)
@@ -439,3 +439,4 @@ QPDFPageObjectHelper externalize inline image 0
 QPDFPageObjectHelper keep inline image 0
 qpdf image optimize colorspace 0
 qpdf image optimize bits per component 0
+QPDFWriter remove empty DecodeParms 0
@@ -847,7 +847,7 @@ $td-&gt;runtest(&quot;get stream data&quot;,
 show_ntests();
 # ----------
 $td->notify("--- Decode parameter problems ---");
-$n_tests += 4;
+$n_tests += 6;
 # Make sure we ignore decode parameters that we don't understand
 $td->runtest("unknown decode parameters",
@@ -870,6 +870,13 @@ $td-&gt;runtest(&quot;check file&quot;,
              {$td->FILE => "a.pdf"},
              {$td->FILE => "indirect-decode-parms-out.pdf"});
+$td->runtest("decode parameters empty list",
+             {$td->COMMAND => "qpdf --static-id empty-decode-parms.pdf a.pdf"},
+             {$td->STRING => "", $td->EXIT_STATUS => 0});
+$td->runtest("check file",
+             {$td->FILE => "a.pdf"},
+             {$td->FILE => "empty-decode-parms-out.pdf"});
+
 show_ntests();
 # ----------
 $td->notify("--- Cross reference streams ---");