Ignore broken DecodeParms for stream with no filters

ChangeLog

@@ -1,5 +1,8 @@
 2013-07-07  Jay Berkenbilt  <ejb@ql.org>
 
+	* Ignore error case of a stream's decode parameters having invalid
+	length when there are no stream filters.
+
 	* qpdf: add --show-npages command-line option, which causes the
 	number of pages in the input file to be printed on a line by
 	itself.

TODO

@@ -17,6 +17,10 @@
  * Provide an option for QPDFWriter to preserve unreferenced objects
    when writing out a file.
 
+ * Look at all the exceptions and error conditions in QPDF_stream and
+   figure out which ones should be converted to warnings and treating
+   the stream as not filterable.
+
  * If possible, support user-pluggable stream filters.  This would
    enable external code to provide interpretation for filters that are
    missing from qpdf.

libqpdf/QPDF_Stream.cc

@@ -295,8 +295,13 @@ QPDF_Stream::filterable(std::vector<std::string>& filters,
         }
     }
 
-    if (decode_parms.size() != filters.size())
+    // Ignore /DecodeParms entirely if /Filters is empty.  At least
+    // one case of a file whose /DecodeParms was [ << >> ] when
+    // /Filters was empty has been seen in the wild.
+    if ((filters.size() != 0) && (decode_parms.size() != filters.size()))
     {
+        // We should just issue a warning and treat this as not
+        // filterable.
 	throw QPDFExc(qpdf_e_damaged_pdf, qpdf->getFilename(),
 		      "", this->offset,
 		      "stream /DecodeParms length is"

qpdf/qtest/qpdf.test

@@ -199,7 +199,7 @@ $td->runtest("remove page we don't have",
 show_ntests();
 # ----------
 $td->notify("--- Miscellaneous Tests ---");
-$n_tests += 66;
+$n_tests += 67;
 
 $td->runtest("qpdf version",
 	     {$td->COMMAND => "qpdf --version"},
@@ -522,6 +522,11 @@ $td->runtest("show number of pages",
                   "qpdf --show-npages 20-pages.pdf --password=user"},
              {$td->STRING => "20\n", $td->EXIT_STATUS => 0},
              $td->NORMALIZE_NEWLINES);
+$td->runtest("ignore broken decode parms with no filters",
+             {$td->COMMAND => "qpdf --check broken-decode-parms-no-filter.pdf"},
+             {$td->FILE => "broken-decode-parms-no-filter.out",
+              $td->EXIT_STATUS => 0},
+             $td->NORMALIZE_NEWLINES);
 
 show_ntests();
 # ----------

qpdf/qtest/qpdf/broken-decode-parms-no-filter.out

@@ -0,0 +1,6 @@
+checking broken-decode-parms-no-filter.pdf
+PDF Version: 1.3
+File is not encrypted
+File is not linearized
+No syntax or stream encoding errors found; the file may still contain
+errors that qpdf cannot detect

qpdf/qtest/qpdf/broken-decode-parms-no-filter.pdf

@@ -0,0 +1,102 @@
+%PDF-1.3
+%¿÷¢þ
+%QDF-1.0
+
+%% Original object ID: 1 0
+1 0 obj
+<<
+  /Pages 2 0 R
+  /Type /Catalog
+>>
+endobj
+
+%% Original object ID: 2 0
+2 0 obj
+<<
+  /Count 1
+  /Kids [
+    3 0 R
+  ]
+  /Type /Pages
+>>
+endobj
+
+%% Page 1
+%% Original object ID: 3 0
+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
+%% Original object ID: 4 0
+4 0 obj
+<<
+  /Length 5 0 R
+  /DecodeParms [ << >> ]
+>>
+stream
+BT
+  /F1 24 Tf
+  72 720 Td
+  (Potato) Tj
+ET
+endstream
+endobj
+
+5 0 obj
+44
+endobj
+
+%% Original object ID: 6 0
+6 0 obj
+<<
+  /BaseFont /Helvetica
+  /Encoding /WinAnsiEncoding
+  /Name /F1
+  /Subtype /Type1
+  /Type /Font
+>>
+endobj
+
+%% Original object ID: 5 0
+7 0 obj
+[
+  /PDF
+  /Text
+]
+endobj
+
+xref
+0 8
+0000000000 65535 f 
+0000000052 00000 n 
+0000000133 00000 n 
+0000000242 00000 n 
+0000000484 00000 n 
+0000000608 00000 n 
+0000000654 00000 n 
+0000000799 00000 n 
+trailer <<
+  /Root 1 0 R
+  /Size 8
+  /ID [<3ed0e583ae70f9665d727ef9c2780a19><3ed0e583ae70f9665d727ef9c2780a19>]
+>>
+startxref
+834
+%%EOF