fix problem with lzw decoder when run without early code change, now that we actually have test input

git-svn-id: svn+q:///qpdf/trunk@646 71b93d88-0707-0410-a8cf-f5a4172ac649

6 files changed, 43 insertions, 9 deletions

diff --git a/ChangeLog b/ChangeLog
index f0b2711b..e327b7b3 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2009-02-19  Jay Berkenbilt  <ejb@ql.org>
+
+	* libqpdf/Pl_LZWDecoder.cc: correct logic error for previously
+	untested case of running the LZW decoder without the "early code
+	change" flag.  Thanks to a bug report from "Atom Smasher", I
+	finally was able to obtain an input stream compressed in this way.
+
 2009-02-15  Jay Berkenbilt  <ejb@ql.org>
 
 	* 2.0.3: release
diff --git a/libqpdf/Pl_LZWDecoder.cc b/libqpdf/Pl_LZWDecoder.cc
index e85531e9..95dcec37 100644
--- a/libqpdf/Pl_LZWDecoder.cc
+++ b/libqpdf/Pl_LZWDecoder.cc
@@ -199,7 +199,7 @@ Pl_LZWDecoder::handleCode(int code)
 		}
 	    }
 	    unsigned int last_idx = 258 + table_size;
-	    if (last_idx == 4095)
+	    if (last_idx + code_change_delta == 4096)
 	    {
 		throw QEXC::General("LZWDecoder: table full");
 	    }
diff --git a/libtests/lzw.cc b/libtests/lzw.cc
index 09ded352..034c0bb9 100644
--- a/libtests/lzw.cc
+++ b/libtests/lzw.cc
@@ -3,13 +3,18 @@
 #include <qpdf/Pl_StdioFile.hh>
 #include <iostream>
 #include <stdlib.h>
+#include <string.h>
 
-int main()
+int main(int argc, char* argv[])
 {
+    bool early_code_change = true;
+    if ((argc == 2) && (strcmp(argv[1], "--no-early-code-change") == 0))
+    {
+	early_code_change = false;
+    }
+
     Pl_StdioFile out("stdout", stdout);
-    // We don't exercise LZWDecoder with early code change false
-    // because we have no way to generate such an LZW stream.
-    Pl_LZWDecoder decode("decode", &out, true);
+    Pl_LZWDecoder decode("decode", &out, early_code_change);
 
     try
     {
diff --git a/libtests/qtest/lzw.test b/libtests/qtest/lzw.test
index abb412d4..649cd330 100644
--- a/libtests/qtest/lzw.test
+++ b/libtests/qtest/lzw.test
@@ -9,9 +9,31 @@ require TestDriver;
 
 my $td = new TestDriver('lzw');
 
-$td->runtest("decode",
-	     {$td->COMMAND => "lzw < lzw1.in"},
-	     {$td->FILE => "lzw1.out",
+cleanup();
+
+$td->runtest("decode: early code change",
+	     {$td->COMMAND => "lzw < lzw1.in > tmp"},
+	     {$td->STRING => "",
+	      $td->EXIT_STATUS => 0});
+
+$td->runtest("check output",
+	     {$td->FILE => "tmp"},
+	     {$td->FILE => "lzw1.out"});
+
+$td->runtest("decode: no early code change",
+	     {$td->COMMAND => "lzw --no-early-code-change < lzw2.in > tmp"},
+	     {$td->STRING => "",
 	      $td->EXIT_STATUS => 0});
 
-$td->report(1);
+$td->runtest("check output",
+	     {$td->FILE => "tmp"},
+	     {$td->FILE => "lzw2.out"});
+
+cleanup();
+
+$td->report(4);
+
+sub cleanup
+{
+    unlink "tmp";
+}
diff --git a/libtests/qtest/lzw/lzw2.in b/libtests/qtest/lzw/lzw2.in
new file mode 100644
index 00000000..5109c45a
--- /dev/null
+++ b/libtests/qtest/lzw/lzw2.in
diff --git a/libtests/qtest/lzw/lzw2.out b/libtests/qtest/lzw/lzw2.out
new file mode 100644
index 00000000..ab105031
--- /dev/null
+++ b/libtests/qtest/lzw/lzw2.out