Properly handle zero-sized fields in the PReg parser.

For zero-sized values, we'd previously pass NULL to std::copy, which is
not OK though if the number of elements to copy is 0. Avoid the copy
altogether and cover this situation in the unit test.

BUG=None
R=joaodasilva@chromium.org

Review URL: https://codereview.chromium.org/23704008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@223345 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/policy/preg_parser_win.cc

@@ -64,12 +64,13 @@ int NextChar(const uint8** cursor, const uint8* end) {
 // Reads a fixed-size field from a PReg file.
 bool ReadFieldBinary(const uint8** cursor,
                      const uint8* end,
-                     int size,
+                     uint32 size,
                      uint8* data) {
-  if (!size)
-    return false;
+  if (size == 0)
+    return true;
+
   const uint8* field_end = *cursor + size;
-  if (field_end > end)
+  if (field_end <= *cursor || field_end > end)
     return false;
   std::copy(*cursor, field_end, data);
   *cursor = field_end;

chrome/browser/policy/preg_parser_win_unittest.cc

@@ -43,8 +43,9 @@ testing::AssertionResult RegistryDictEquals(const RegistryDict& a,
     if (iter_value_a->first != iter_value_b->first ||
         !base::Value::Equals(iter_value_a->second, iter_value_b->second)) {
       return testing::AssertionFailure()
-          << "Value mismatch " << iter_value_a->first
-          << " vs. " << iter_value_b->first;
+          << "Value mismatch "
+          << iter_value_a->first << "=" << *iter_value_a->second
+          << " vs. " << iter_value_b->first << "=" << *iter_value_b->second;
     }
   }
 
@@ -108,6 +109,7 @@ TEST(PRegParserWinTest, TestParseFile) {
   expected.SetKey("RestoreOnStartupURLs", startup_urls.Pass());
   SetInteger(&expected, "ShowHomeButton", 1);
   SetString(&expected, "Snowman", "\xE2\x98\x83");
+  SetString(&expected, "Empty", "");
 
   EXPECT_TRUE(RegistryDictEquals(dict, expected));
 }