Rewrite how string Insert() methods handle out of bound indices

The existing behaviour was to clamp the provided index to the valid
bounds. This would lead to programming errors being hidden, since
inserting would still do something even if the index calculation was
wrong. The behaviour of these methods has been changed to instead
early return when this occurs, returning the old length value. The
caller can check if the call to Insert actually did anything by
comparing the returned value to the length before calling insert.

All of the existing calls to Insert have been tested by running all of
the tests with asserts in the Insert method to check the index is in
bounds. Additionally the call sites have been manually inspected. The
majority of them are of the form Insert(0, foo) and the rest tend to
be in a loop advancing from 0 to length.

Convenience methods InsertAtFront/InsertAtBack have been added to
handle calling Insert when the intent is for the character to be added
to the beginning or end of the string. Existing call sites to Insert
that do this have been converted.

This work was originally being performed to check if there would be
any issues in these methods with making FX_STRSIZE unsigned.

BUG=pdfium:828

Change-Id: I60cee5ad45338aa8ed46569de7bcc78a76db18f7
Reviewed-on: https://pdfium-review.googlesource.com/9870
Commit-Queue: Ryan Harrison <rharrison@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>

1 files changed, 12 insertions, 12 deletions

diff --git a/core/fxcrt/cfx_widestring.cpp b/core/fxcrt/cfx_widestring.cpp
index b83752369b..6c079b354e 100644
--- a/core/fxcrt/cfx_widestring.cpp
+++ b/core/fxcrt/cfx_widestring.cpp
@@ -680,18 +680,18 @@ void CFX_WideString::Format(const wchar_t* pFormat, ...) {
   va_end(argList);
 }
 
-FX_STRSIZE CFX_WideString::Insert(FX_STRSIZE nIndex, wchar_t ch) {
-  FX_STRSIZE nNewLength = m_pData ? m_pData->m_nDataLength : 0;
-  nIndex = std::max(nIndex, 0);
-  nIndex = std::min(nIndex, nNewLength);
-  nNewLength++;
-
-  ReallocBeforeWrite(nNewLength);
-  wmemmove(m_pData->m_String + nIndex + 1, m_pData->m_String + nIndex,
-           nNewLength - nIndex);
-  m_pData->m_String[nIndex] = ch;
-  m_pData->m_nDataLength = nNewLength;
-  return nNewLength;
+FX_STRSIZE CFX_WideString::Insert(FX_STRSIZE index, wchar_t ch) {
+  const FX_STRSIZE cur_length = m_pData ? m_pData->m_nDataLength : 0;
+  if (index != pdfium::clamp(index, 0, cur_length))
+    return cur_length;
+
+  const FX_STRSIZE new_length = cur_length + 1;
+  ReallocBeforeWrite(new_length);
+  wmemmove(m_pData->m_String + index + 1, m_pData->m_String + index,
+           new_length - index);
+  m_pData->m_String[index] = ch;
+  m_pData->m_nDataLength = new_length;
+  return new_length;
 }
 
 CFX_WideString CFX_WideString::Right(FX_STRSIZE nCount) const {