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_widestring.h b/core/fxcrt/cfx_widestring.h
index a6d0eca044..242138853b 100644
--- a/core/fxcrt/cfx_widestring.h
+++ b/core/fxcrt/cfx_widestring.h
@@ -81,6 +81,14 @@ class CFX_WideString {
   }
   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();
+  }
+
   const CFX_WideString& operator=(const wchar_t* str);
   const CFX_WideString& operator=(const CFX_WideString& stringSrc);
   const CFX_WideString& operator=(const CFX_WideStringC& stringSrc);
@@ -103,7 +111,7 @@ class CFX_WideString {
   bool operator<(const CFX_WideString& str) const;
 
   CharType operator[](const FX_STRSIZE index) const {
-    ASSERT(index >= 0 && index < GetLength());
+    ASSERT(IsValidIndex(index));
     return m_pData ? m_pData->m_String[index] : 0;
   }