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>

7 files changed, 140 insertions, 71 deletions

diff --git a/core/fpdfapi/font/cpdf_tounicodemap.cpp b/core/fpdfapi/font/cpdf_tounicodemap.cpp
index 8989f0be37..30bf0317ee 100644
--- a/core/fpdfapi/font/cpdf_tounicodemap.cpp
+++ b/core/fpdfapi/font/cpdf_tounicodemap.cpp
@@ -77,15 +77,14 @@ static CFX_WideString StringDataAdd(CFX_WideString str) {
   for (int i = len - 1; i >= 0; --i) {
     wchar_t ch = str[i] + value;
     if (ch < str[i]) {
-      ret.Insert(0, 0);
+      ret.InsertAtFront(0);
     } else {
-      ret.Insert(0, ch);
+      ret.InsertAtFront(ch);
       value = 0;
     }
   }
-  if (value) {
-    ret.Insert(0, value);
-  }
+  if (value)
+    ret.InsertAtFront(value);
   return ret;
 }
 
diff --git a/core/fxcrt/cfx_bytestring.cpp b/core/fxcrt/cfx_bytestring.cpp
index 5dcaf613a0..e031c87d2d 100644
--- a/core/fxcrt/cfx_bytestring.cpp
+++ b/core/fxcrt/cfx_bytestring.cpp
@@ -518,18 +518,18 @@ void CFX_ByteString::Format(const char* pFormat, ...) {
   va_end(argList);
 }
 
-FX_STRSIZE CFX_ByteString::Insert(FX_STRSIZE nIndex, char ch) {
-  FX_STRSIZE nNewLength = m_pData ? m_pData->m_nDataLength : 0;
-  nIndex = std::max(nIndex, 0);
-  nIndex = std::min(nIndex, nNewLength);
-  nNewLength++;
-
-  ReallocBeforeWrite(nNewLength);
-  memmove(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_ByteString::Insert(FX_STRSIZE index, char 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);
+  memmove(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_ByteString CFX_ByteString::Right(FX_STRSIZE nCount) const {
diff --git a/core/fxcrt/cfx_bytestring.h b/core/fxcrt/cfx_bytestring.h
index 8bd9f39fc0..df1b8309fc 100644
--- a/core/fxcrt/cfx_bytestring.h
+++ b/core/fxcrt/cfx_bytestring.h
@@ -118,6 +118,8 @@ class CFX_ByteString {
 
   void SetAt(FX_STRSIZE nIndex, char ch);
   FX_STRSIZE Insert(FX_STRSIZE index, char ch);
+  FX_STRSIZE InsertAtFront(char ch) { return Insert(0, ch); }
+  FX_STRSIZE InsertAtBack(char ch) { return Insert(GetLength(), ch); }
   FX_STRSIZE Delete(FX_STRSIZE index, FX_STRSIZE count = 1);
 
   void Format(const char* lpszFormat, ...);
diff --git a/core/fxcrt/cfx_bytestring_unittest.cpp b/core/fxcrt/cfx_bytestring_unittest.cpp
index 4379519046..89c8ac6060 100644
--- a/core/fxcrt/cfx_bytestring_unittest.cpp
+++ b/core/fxcrt/cfx_bytestring_unittest.cpp
@@ -387,32 +387,68 @@ TEST(fxcrt, ByteStringReplace) {
 
 TEST(fxcrt, ByteStringInsert) {
   CFX_ByteString fred("FRED");
-  fred.Insert(-1, 'X');
-  EXPECT_EQ("XFRED", fred);
-  fred.Insert(0, 'S');
-  EXPECT_EQ("SXFRED", fred);
-  fred.Insert(2, 'T');
-  EXPECT_EQ("SXTFRED", fred);
-  fred.Insert(5, 'U');
-  EXPECT_EQ("SXTFRUED", fred);
-  fred.Insert(8, 'V');
-  EXPECT_EQ("SXTFRUEDV", fred);
-  fred.Insert(12, 'P');
-  EXPECT_EQ("SXTFRUEDVP", fred);
+  EXPECT_EQ(4, fred.Insert(-1, 'X'));
+  EXPECT_EQ("FRED", fred);
+  EXPECT_EQ(5, fred.Insert(0, 'S'));
+  EXPECT_EQ("SFRED", fred);
+  EXPECT_EQ(6, fred.Insert(1, 'T'));
+  EXPECT_EQ("STFRED", fred);
+  EXPECT_EQ(7, fred.Insert(4, 'U'));
+  EXPECT_EQ("STFRUED", fred);
+  EXPECT_EQ(8, fred.Insert(7, 'V'));
+  EXPECT_EQ("STFRUEDV", fred);
+  EXPECT_EQ(8, fred.Insert(12, 'P'));
+  EXPECT_EQ("STFRUEDV", fred);
   {
     CFX_ByteString empty;
-    empty.Insert(-1, 'X');
-    EXPECT_EQ("X", empty);
+    EXPECT_EQ(0, empty.Insert(-1, 'X'));
+    EXPECT_NE("X", empty);
   }
   {
     CFX_ByteString empty;
-    empty.Insert(0, 'X');
+    EXPECT_EQ(1, empty.Insert(0, 'X'));
     EXPECT_EQ("X", empty);
   }
   {
     CFX_ByteString empty;
-    empty.Insert(5, 'X');
-    EXPECT_EQ("X", empty);
+    EXPECT_EQ(0, empty.Insert(5, 'X'));
+    EXPECT_NE("X", empty);
+  }
+}
+
+TEST(fxcrt, ByteStringInsertAtFrontAndInsertAtBack) {
+  {
+    CFX_ByteString empty;
+    EXPECT_EQ(1, empty.InsertAtFront('D'));
+    EXPECT_EQ("D", empty);
+    EXPECT_EQ(2, empty.InsertAtFront('E'));
+    EXPECT_EQ("ED", empty);
+    EXPECT_EQ(3, empty.InsertAtFront('R'));
+    EXPECT_EQ("RED", empty);
+    EXPECT_EQ(4, empty.InsertAtFront('F'));
+    EXPECT_EQ("FRED", empty);
+  }
+  {
+    CFX_ByteString empty;
+    EXPECT_EQ(1, empty.InsertAtBack('F'));
+    EXPECT_EQ("F", empty);
+    EXPECT_EQ(2, empty.InsertAtBack('R'));
+    EXPECT_EQ("FR", empty);
+    EXPECT_EQ(3, empty.InsertAtBack('E'));
+    EXPECT_EQ("FRE", empty);
+    EXPECT_EQ(4, empty.InsertAtBack('D'));
+    EXPECT_EQ("FRED", empty);
+  }
+  {
+    CFX_ByteString empty;
+    EXPECT_EQ(1, empty.InsertAtBack('E'));
+    EXPECT_EQ("E", empty);
+    EXPECT_EQ(2, empty.InsertAtFront('R'));
+    EXPECT_EQ("RE", empty);
+    EXPECT_EQ(3, empty.InsertAtBack('D'));
+    EXPECT_EQ("RED", empty);
+    EXPECT_EQ(4, empty.InsertAtFront('F'));
+    EXPECT_EQ("FRED", empty);
   }
 }
 
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 {
diff --git a/core/fxcrt/cfx_widestring.h b/core/fxcrt/cfx_widestring.h
index 02045c5c09..ccb1e752f7 100644
--- a/core/fxcrt/cfx_widestring.h
+++ b/core/fxcrt/cfx_widestring.h
@@ -120,6 +120,8 @@ class CFX_WideString {
   CFX_WideString Right(FX_STRSIZE count) const;
 
   FX_STRSIZE Insert(FX_STRSIZE index, wchar_t ch);
+  FX_STRSIZE InsertAtFront(wchar_t ch) { return Insert(0, ch); }
+  FX_STRSIZE InsertAtBack(wchar_t ch) { return Insert(GetLength(), ch); }
   FX_STRSIZE Delete(FX_STRSIZE index, FX_STRSIZE count = 1);
 
   void Format(const wchar_t* lpszFormat, ...);
diff --git a/core/fxcrt/cfx_widestring_unittest.cpp b/core/fxcrt/cfx_widestring_unittest.cpp
index b743a17fd1..a763f8abbd 100644
--- a/core/fxcrt/cfx_widestring_unittest.cpp
+++ b/core/fxcrt/cfx_widestring_unittest.cpp
@@ -347,38 +347,68 @@ TEST(fxcrt, WideStringReplace) {
 
 TEST(fxcrt, WideStringInsert) {
   CFX_WideString fred(L"FRED");
-  fred.Insert(-1, 'X');
-  EXPECT_EQ(L"XFRED", fred);
-
-  fred.Insert(0, 'S');
-  EXPECT_EQ(L"SXFRED", fred);
-
-  fred.Insert(2, 'T');
-  EXPECT_EQ(L"SXTFRED", fred);
-
-  fred.Insert(5, 'U');
-  EXPECT_EQ(L"SXTFRUED", fred);
-
-  fred.Insert(8, 'V');
-  EXPECT_EQ(L"SXTFRUEDV", fred);
-
-  fred.Insert(12, 'P');
-  EXPECT_EQ(L"SXTFRUEDVP", fred);
-
+  EXPECT_EQ(4, fred.Insert(-1, 'X'));
+  EXPECT_EQ(L"FRED", fred);
+  EXPECT_EQ(5, fred.Insert(0, 'S'));
+  EXPECT_EQ(L"SFRED", fred);
+  EXPECT_EQ(6, fred.Insert(1, 'T'));
+  EXPECT_EQ(L"STFRED", fred);
+  EXPECT_EQ(7, fred.Insert(4, 'U'));
+  EXPECT_EQ(L"STFRUED", fred);
+  EXPECT_EQ(8, fred.Insert(7, 'V'));
+  EXPECT_EQ(L"STFRUEDV", fred);
+  EXPECT_EQ(8, fred.Insert(12, 'P'));
+  EXPECT_EQ(L"STFRUEDV", fred);
   {
     CFX_WideString empty;
-    empty.Insert(-1, 'X');
-    EXPECT_EQ(L"X", empty);
+    EXPECT_EQ(0, empty.Insert(-1, 'X'));
+    EXPECT_NE(L"X", empty);
   }
   {
     CFX_WideString empty;
-    empty.Insert(0, 'X');
+    EXPECT_EQ(1, empty.Insert(0, 'X'));
     EXPECT_EQ(L"X", empty);
   }
   {
     CFX_WideString empty;
-    empty.Insert(5, 'X');
-    EXPECT_EQ(L"X", empty);
+    EXPECT_EQ(0, empty.Insert(5, 'X'));
+    EXPECT_NE(L"X", empty);
+  }
+}
+
+TEST(fxcrt, WideStringInsertAtFrontAndInsertAtBack) {
+  {
+    CFX_WideString empty;
+    EXPECT_EQ(1, empty.InsertAtFront('D'));
+    EXPECT_EQ(L"D", empty);
+    EXPECT_EQ(2, empty.InsertAtFront('E'));
+    EXPECT_EQ(L"ED", empty);
+    EXPECT_EQ(3, empty.InsertAtFront('R'));
+    EXPECT_EQ(L"RED", empty);
+    EXPECT_EQ(4, empty.InsertAtFront('F'));
+    EXPECT_EQ(L"FRED", empty);
+  }
+  {
+    CFX_WideString empty;
+    EXPECT_EQ(1, empty.InsertAtBack('F'));
+    EXPECT_EQ(L"F", empty);
+    EXPECT_EQ(2, empty.InsertAtBack('R'));
+    EXPECT_EQ(L"FR", empty);
+    EXPECT_EQ(3, empty.InsertAtBack('E'));
+    EXPECT_EQ(L"FRE", empty);
+    EXPECT_EQ(4, empty.InsertAtBack('D'));
+    EXPECT_EQ(L"FRED", empty);
+  }
+  {
+    CFX_WideString empty;
+    EXPECT_EQ(1, empty.InsertAtBack('E'));
+    EXPECT_EQ(L"E", empty);
+    EXPECT_EQ(2, empty.InsertAtFront('R'));
+    EXPECT_EQ(L"RE", empty);
+    EXPECT_EQ(3, empty.InsertAtBack('D'));
+    EXPECT_EQ(L"RED", empty);
+    EXPECT_EQ(4, empty.InsertAtFront('F'));
+    EXPECT_EQ(L"FRED", empty);
   }
 }
 
@@ -720,8 +750,8 @@ TEST(fxcrt, WideStringCOperatorSubscript) {
 TEST(fxcrt, WideStringCOperatorLT) {
   CFX_WideStringC empty;
   CFX_WideStringC a(L"a");
-  CFX_WideStringC abc(L"\x0110qq");  // Comes before despite endianness.
-  CFX_WideStringC def(L"\x1001qq");  // Comes after despite endianness.
+  CFX_WideStringC abc(L"\x0110qq");  // Comes InsertAtFront despite endianness.
+  CFX_WideStringC def(L"\x1001qq");  // Comes InsertAtBack despite endianness.
 
   EXPECT_FALSE(empty < empty);
   EXPECT_FALSE(a < a);