Add help IsValid* methods to string classeschromium/3198chromium/3197

The various string classes, CFX_ByteString, CFX_ByteStringC,
CFX_WideString, and CFX_WideStringC, have many conditionals that are
effectively determining if a value is a valid index or length. This CL
refactors the logic into one place per class, so it only needs to be
changed once if its behaviour needs to change. It also make the some
of the methods stricter on the inputs they will accept.

BUG=pdfium:828

Change-Id: Iadcdaa34a6d862a2804485770027179c89dc6956
Reviewed-on: https://pdfium-review.googlesource.com/12030
Commit-Queue: Ryan Harrison <rharrison@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>

1 files changed, 9 insertions, 1 deletions

diff --git a/core/fxcrt/cfx_bytestring.h b/core/fxcrt/cfx_bytestring.h
index 10675be7a5..a8a28169a5 100644
--- a/core/fxcrt/cfx_bytestring.h
+++ b/core/fxcrt/cfx_bytestring.h
@@ -84,6 +84,14 @@ class CFX_ByteString {
   }
   bool IsEmpty() const { return !GetLength(); }
 
+  bool IsValidIndex(FX_STRSIZE index) const {
+    return 0 <= index && index < GetLength();
+  }
+
+  bool IsValidLength(FX_STRSIZE length) const {
+    return 0 <= length && length <= GetLength();
+  }
+
   int Compare(const CFX_ByteStringC& str) const;
   bool EqualNoCase(const CFX_ByteStringC& str) const;
 
@@ -109,7 +117,7 @@ class CFX_ByteString {
   const CFX_ByteString& operator+=(const CFX_ByteStringC& bstrc);
 
   CharType operator[](const FX_STRSIZE index) const {
-    ASSERT(index >= 0 && index < GetLength());
+    ASSERT(IsValidIndex(index));
     return m_pData ? m_pData->m_String[index] : 0;
   }