Remove single param Mid() method from string classes

This support is being removed from CFX_ByteString, CFX_ByteStringC,
CFX_WideString, and CFX_WideStringC. This standardizes all of these
classes to only have one Mid method that takes in 2 params, offset and
count. Count now must be positive. The old behaviour of calculating
the length for the user if -1 is passed in for the count has been
removed. This work is in preperation for converting these classes to
not accept negative lengths anywhere and thus make the underlying size
type unsigned.

BUG=pdfium:828

Change-Id: I5f15e7b7b00b264231817f143e2da88ee6f69e7b
Reviewed-on: https://pdfium-review.googlesource.com/9430
Reviewed-by: (OOO Jul 28 - Aug 8) dsinclair <dsinclair@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Ryan Harrison <rharrison@chromium.org>

21 files changed, 91 insertions, 76 deletions

diff --git a/core/fpdfapi/font/cpdf_simplefont.cpp b/core/fpdfapi/font/cpdf_simplefont.cpp
index a6c3ba0547..8c8520f0c4 100644
--- a/core/fpdfapi/font/cpdf_simplefont.cpp
+++ b/core/fpdfapi/font/cpdf_simplefont.cpp
@@ -130,7 +130,7 @@ bool CPDF_SimpleFont::LoadCommon() {
   }
   if (m_pFontFile) {
     if (m_BaseFont.GetLength() > 8 && m_BaseFont[7] == '+')
-      m_BaseFont = m_BaseFont.Mid(8);
+      m_BaseFont = m_BaseFont.Mid(8, m_BaseFont.GetLength() - 8);
   } else {
     LoadSubstFont();
   }
diff --git a/core/fpdfapi/page/cpdf_streamcontentparser.cpp b/core/fpdfapi/page/cpdf_streamcontentparser.cpp
index e00dbc54fd..5f571aa8d6 100644
--- a/core/fpdfapi/page/cpdf_streamcontentparser.cpp
+++ b/core/fpdfapi/page/cpdf_streamcontentparser.cpp
@@ -619,7 +619,8 @@ void CPDF_StreamContentParser::Handle_BeginImage() {
     if (type != CPDF_StreamParser::Name) {
       break;
     }
-    CFX_ByteString key(m_pSyntax->GetWord().Mid(1));
+    auto word = m_pSyntax->GetWord();
+    CFX_ByteString key(word.Mid(1, word.GetLength() - 1));
     auto pObj = m_pSyntax->ReadNextObject(false, false, 0);
     if (!key.IsEmpty()) {
       uint32_t dwObjNum = pObj ? pObj->GetObjNum() : 0;
@@ -1185,7 +1186,7 @@ CPDF_ColorSpace* CPDF_StreamContentParser::FindColorSpace(
   }
   if (name == "DeviceGray" || name == "DeviceCMYK" || name == "DeviceRGB") {
     CFX_ByteString defname = "Default";
-    defname += name.Mid(7);
+    defname += name.Mid(7, name.GetLength() - 7);
     CPDF_Object* pDefObj = FindResourceObj("ColorSpace", defname);
     if (!pDefObj) {
       if (name == "DeviceGray") {
@@ -1522,9 +1523,11 @@ uint32_t CPDF_StreamContentParser::Parse(const uint8_t* pData,
       case CPDF_StreamParser::Number:
         AddNumberParam(syntax.GetWord());
         break;
-      case CPDF_StreamParser::Name:
-        AddNameParam(syntax.GetWord().Mid(1));
+      case CPDF_StreamParser::Name: {
+        auto word = syntax.GetWord();
+        AddNameParam(word.Mid(1, word.GetLength() - 1));
         break;
+      }
       default:
         AddObjectParam(syntax.GetObject());
     }
diff --git a/core/fpdfdoc/cpvt_generateap.cpp b/core/fpdfdoc/cpvt_generateap.cpp
index eb874b3352..83c1f65587 100644
--- a/core/fpdfdoc/cpvt_generateap.cpp
+++ b/core/fpdfdoc/cpvt_generateap.cpp
@@ -65,15 +65,17 @@ bool GenerateWidgetAP(CPDF_Document* pDoc,
   if (!pDRFontDict)
     return false;
 
-  CPDF_Dictionary* pFontDict = pDRFontDict->GetDictFor(sFontName.Mid(1));
+  CPDF_Dictionary* pFontDict =
+      pDRFontDict->GetDictFor(sFontName.Mid(1, sFontName.GetLength() - 1));
   if (!pFontDict) {
     pFontDict = pDoc->NewIndirect<CPDF_Dictionary>();
     pFontDict->SetNewFor<CPDF_Name>("Type", "Font");
     pFontDict->SetNewFor<CPDF_Name>("Subtype", "Type1");
     pFontDict->SetNewFor<CPDF_Name>("BaseFont", "Helvetica");
     pFontDict->SetNewFor<CPDF_Name>("Encoding", "WinAnsiEncoding");
-    pDRFontDict->SetNewFor<CPDF_Reference>(sFontName.Mid(1), pDoc,
-                                           pFontDict->GetObjNum());
+    pDRFontDict->SetNewFor<CPDF_Reference>(
+        sFontName.Mid(1, sFontName.GetLength() - 1), pDoc,
+        pFontDict->GetObjNum());
   }
   CPDF_Font* pDefFont = pDoc->LoadFont(pFontDict);
   if (!pDefFont)
diff --git a/core/fxcrt/cfx_bytestring.cpp b/core/fxcrt/cfx_bytestring.cpp
index c88ad51ab3..e7e55de8e3 100644
--- a/core/fxcrt/cfx_bytestring.cpp
+++ b/core/fxcrt/cfx_bytestring.cpp
@@ -121,6 +121,7 @@ static_assert(sizeof(CFX_ByteString) <= sizeof(char*),
               "Strings must not require more space than pointers");
 
 CFX_ByteString::CFX_ByteString(const char* pStr, FX_STRSIZE nLen) {
+  ASSERT(nLen >= 0);
   if (nLen < 0)
     nLen = pStr ? FXSYS_strlen(pStr) : 0;
 
@@ -129,6 +130,7 @@ CFX_ByteString::CFX_ByteString(const char* pStr, FX_STRSIZE nLen) {
 }
 
 CFX_ByteString::CFX_ByteString(const uint8_t* pStr, FX_STRSIZE nLen) {
+  ASSERT(nLen >= 0);
   if (nLen > 0) {
     m_pData.Reset(
         StringData::Create(reinterpret_cast<const char*>(pStr), nLen));
@@ -456,14 +458,8 @@ void CFX_ByteString::Concat(const char* pSrcData, FX_STRSIZE nSrcLen) {
   m_pData.Swap(pNewData);
 }
 
-CFX_ByteString CFX_ByteString::Mid(FX_STRSIZE nFirst) const {
-  if (!m_pData)
-    return CFX_ByteString();
-
-  return Mid(nFirst, m_pData->m_nDataLength - nFirst);
-}
-
 CFX_ByteString CFX_ByteString::Mid(FX_STRSIZE nFirst, FX_STRSIZE nCount) const {
+  ASSERT(nCount >= 0);
   if (!m_pData)
     return CFX_ByteString();
 
diff --git a/core/fxcrt/cfx_bytestring.h b/core/fxcrt/cfx_bytestring.h
index abf8ac80c8..519cee39d4 100644
--- a/core/fxcrt/cfx_bytestring.h
+++ b/core/fxcrt/cfx_bytestring.h
@@ -124,7 +124,6 @@ class CFX_ByteString {
   char* GetBuffer(FX_STRSIZE len);
   void ReleaseBuffer(FX_STRSIZE len = -1);
 
-  CFX_ByteString Mid(FX_STRSIZE first) const;
   CFX_ByteString Mid(FX_STRSIZE first, FX_STRSIZE count) const;
   CFX_ByteString Left(FX_STRSIZE count) const;
   CFX_ByteString Right(FX_STRSIZE count) const;
diff --git a/core/fxcrt/cfx_bytestring_unittest.cpp b/core/fxcrt/cfx_bytestring_unittest.cpp
index f5d9413b7d..bcf6f7495e 100644
--- a/core/fxcrt/cfx_bytestring_unittest.cpp
+++ b/core/fxcrt/cfx_bytestring_unittest.cpp
@@ -440,10 +440,10 @@ TEST(fxcrt, ByteStringMid) {
   CFX_ByteString fred("FRED");
   EXPECT_EQ("", fred.Mid(0, 0));
   EXPECT_EQ("", fred.Mid(3, 0));
-  EXPECT_EQ("FRED", fred.Mid(0));
-  EXPECT_EQ("RED", fred.Mid(1));
-  EXPECT_EQ("ED", fred.Mid(2));
-  EXPECT_EQ("D", fred.Mid(3));
+  EXPECT_EQ("FRED", fred.Mid(0, 4));
+  EXPECT_EQ("RED", fred.Mid(1, 3));
+  EXPECT_EQ("ED", fred.Mid(2, 2));
+  EXPECT_EQ("D", fred.Mid(3, 1));
   EXPECT_EQ("F", fred.Mid(0, 1));
   EXPECT_EQ("R", fred.Mid(1, 1));
   EXPECT_EQ("E", fred.Mid(2, 1));
@@ -458,9 +458,6 @@ TEST(fxcrt, ByteStringMid) {
 
   CFX_ByteString empty;
   EXPECT_EQ("", empty.Mid(0, 0));
-  EXPECT_EQ("", empty.Mid(0));
-  EXPECT_EQ("", empty.Mid(1));
-  EXPECT_EQ("", empty.Mid(-1));
 }
 
 TEST(fxcrt, ByteStringLeft) {
diff --git a/core/fxcrt/cfx_string_c_template.h b/core/fxcrt/cfx_string_c_template.h
index cd3cd27e75..77f34f638e 100644
--- a/core/fxcrt/cfx_string_c_template.h
+++ b/core/fxcrt/cfx_string_c_template.h
@@ -130,29 +130,32 @@ class CFX_StringCTemplate {
     return found ? found - m_Ptr.Get() : -1;
   }
 
-  CFX_StringCTemplate Mid(FX_STRSIZE index, FX_STRSIZE count = -1) const {
-    index = std::max(0, index);
+  CFX_StringCTemplate Mid(FX_STRSIZE index, FX_STRSIZE count) const {
+    ASSERT(count >= 0);
     if (index > m_Length)
       return CFX_StringCTemplate();
 
-    if (count < 0 || count > m_Length - index)
-      count = m_Length - index;
+    index = pdfium::clamp(index, 0, m_Length);
+    count = pdfium::clamp(count, 0, m_Length - index);
+    if (count == 0)
+      return CFX_StringCTemplate();
 
     return CFX_StringCTemplate(m_Ptr.Get() + index, count);
   }
 
   CFX_StringCTemplate Left(FX_STRSIZE count) const {
-    if (count <= 0)
+    count = pdfium::clamp(count, 0, m_Length);
+    if (count == 0)
       return CFX_StringCTemplate();
 
-    return CFX_StringCTemplate(m_Ptr.Get(), std::min(count, m_Length));
+    return CFX_StringCTemplate(m_Ptr.Get(), count);
   }
 
   CFX_StringCTemplate Right(FX_STRSIZE count) const {
-    if (count <= 0)
+    count = pdfium::clamp(count, 0, m_Length);
+    if (count == 0)
       return CFX_StringCTemplate();
 
-    count = std::min(count, m_Length);
     return CFX_StringCTemplate(m_Ptr.Get() + m_Length - count, count);
   }
 
diff --git a/core/fxcrt/cfx_widestring.cpp b/core/fxcrt/cfx_widestring.cpp
index 6a4fbb9846..d7c1ef23ea 100644
--- a/core/fxcrt/cfx_widestring.cpp
+++ b/core/fxcrt/cfx_widestring.cpp
@@ -291,6 +291,7 @@ CFX_WideString::CFX_WideString(CFX_WideString&& other) noexcept {
 }
 
 CFX_WideString::CFX_WideString(const wchar_t* pStr, FX_STRSIZE nLen) {
+  ASSERT(nLen >= 0);
   if (nLen < 0)
     nLen = pStr ? FXSYS_wcslen(pStr) : 0;
 
@@ -605,14 +606,8 @@ CFX_ByteString CFX_WideString::UTF16LE_Encode() const {
   return result;
 }
 
-CFX_WideString CFX_WideString::Mid(FX_STRSIZE nFirst) const {
-  if (!m_pData)
-    return CFX_WideString();
-
-  return Mid(nFirst, m_pData->m_nDataLength - nFirst);
-}
-
 CFX_WideString CFX_WideString::Mid(FX_STRSIZE nFirst, FX_STRSIZE nCount) const {
+  ASSERT(nCount >= 0);
   if (!m_pData)
     return CFX_WideString();
 
diff --git a/core/fxcrt/cfx_widestring.h b/core/fxcrt/cfx_widestring.h
index 0e477bfc8b..938b1e7958 100644
--- a/core/fxcrt/cfx_widestring.h
+++ b/core/fxcrt/cfx_widestring.h
@@ -112,7 +112,6 @@ class CFX_WideString {
   int Compare(const CFX_WideString& str) const;
   int CompareNoCase(const wchar_t* str) const;
 
-  CFX_WideString Mid(FX_STRSIZE first) const;
   CFX_WideString Mid(FX_STRSIZE first, FX_STRSIZE count) const;
   CFX_WideString Left(FX_STRSIZE count) const;
   CFX_WideString Right(FX_STRSIZE count) const;
diff --git a/core/fxcrt/cfx_widestring_unittest.cpp b/core/fxcrt/cfx_widestring_unittest.cpp
index 4cd71d9997..1d6d110497 100644
--- a/core/fxcrt/cfx_widestring_unittest.cpp
+++ b/core/fxcrt/cfx_widestring_unittest.cpp
@@ -406,10 +406,10 @@ TEST(fxcrt, WideStringMid) {
   CFX_WideString fred(L"FRED");
   EXPECT_EQ(L"", fred.Mid(0, 0));
   EXPECT_EQ(L"", fred.Mid(3, 0));
-  EXPECT_EQ(L"FRED", fred.Mid(0));
-  EXPECT_EQ(L"RED", fred.Mid(1));
-  EXPECT_EQ(L"ED", fred.Mid(2));
-  EXPECT_EQ(L"D", fred.Mid(3));
+  EXPECT_EQ(L"FRED", fred.Mid(0, 4));
+  EXPECT_EQ(L"RED", fred.Mid(1, 3));
+  EXPECT_EQ(L"ED", fred.Mid(2, 2));
+  EXPECT_EQ(L"D", fred.Mid(3, 1));
   EXPECT_EQ(L"F", fred.Mid(0, 1));
   EXPECT_EQ(L"R", fred.Mid(1, 1));
   EXPECT_EQ(L"E", fred.Mid(2, 1));
@@ -424,9 +424,6 @@ TEST(fxcrt, WideStringMid) {
 
   CFX_WideString empty;
   EXPECT_EQ(L"", empty.Mid(0, 0));
-  EXPECT_EQ(L"", empty.Mid(0));
-  EXPECT_EQ(L"", empty.Mid(1));
-  EXPECT_EQ(L"", empty.Mid(-1));
 }
 
 TEST(fxcrt, WideStringLeft) {
diff --git a/core/fxcrt/xml/cxml_parser.cpp b/core/fxcrt/xml/cxml_parser.cpp
index a741d8409e..0166ea8490 100644
--- a/core/fxcrt/xml/cxml_parser.cpp
+++ b/core/fxcrt/xml/cxml_parser.cpp
@@ -87,7 +87,7 @@ void FX_XML_SplitQualifiedName(const CFX_ByteStringC& bsFullName,
     bsName = bsFullName;
   } else {
     bsSpace = bsFullName.Mid(0, iStart);
-    bsName = bsFullName.Mid(iStart + 1);
+    bsName = bsFullName.Mid(iStart + 1, bsFullName.GetLength() - (iStart + 1));
   }
 }
 
diff --git a/core/fxge/cfx_fontmapper.cpp b/core/fxge/cfx_fontmapper.cpp
index 5b4ceaac59..5c7b602fed 100644
--- a/core/fxge/cfx_fontmapper.cpp
+++ b/core/fxge/cfx_fontmapper.cpp
@@ -432,7 +432,7 @@ FXFT_Face CFX_FontMapper::FindSubstFont(const CFX_ByteString& name,
   CFX_ByteString SubstName = name;
   SubstName.Remove(' ');
   if (bTrueType && name[0] == '@')
-    SubstName = name.Mid(1);
+    SubstName = name.Mid(1, name.GetLength() - 1);
   PDF_GetStandardFontName(&SubstName);
   if (SubstName == "Symbol" && !bTrueType) {
     pSubstFont->m_Family = "Chrome Symbol";
@@ -453,7 +453,7 @@ FXFT_Face CFX_FontMapper::FindSubstFont(const CFX_ByteString& name,
   if (find >= 0) {
     family = SubstName.Left(find);
     PDF_GetStandardFontName(&family);
-    style = SubstName.Mid(find + 1);
+    style = SubstName.Mid(find + 1, SubstName.GetLength() - (find + 1));
     bHasComma = true;
   } else {
     family = SubstName;
@@ -480,7 +480,7 @@ FXFT_Face CFX_FontMapper::FindSubstFont(const CFX_ByteString& name,
     if (!bHasComma) {
       find = family.ReverseFind('-');
       if (find >= 0) {
-        style = family.Mid(find + 1);
+        style = family.Mid(find + 1, family.GetLength() - (find + 1));
         family = family.Left(find);
         bHasHyphen = true;
       }
diff --git a/fpdfsdk/formfiller/cba_fontmap.cpp b/fpdfsdk/formfiller/cba_fontmap.cpp
index 8bef264085..b195303800 100644
--- a/fpdfsdk/formfiller/cba_fontmap.cpp
+++ b/fpdfsdk/formfiller/cba_fontmap.cpp
@@ -220,7 +220,8 @@ CPDF_Font* CBA_FontMap::GetAnnotDefaultFont(CFX_ByteString* sAlias) {
   syntax.FindTagParamFromStart("Tf", 2);
 
   CFX_ByteString sFontName(syntax.GetWord());
-  *sAlias = PDF_NameDecode(sFontName).Mid(1);
+  CFX_ByteString sDecodedFontName = PDF_NameDecode(sFontName);
+  *sAlias = sDecodedFontName.Mid(1, sDecodedFontName.GetLength() - 1);
 
   CPDF_Dictionary* pFontDict = nullptr;
   if (CPDF_Dictionary* pAPDict = m_pAnnotDict->GetDictFor("AP")) {
diff --git a/fpdfsdk/javascript/PublicMethods.cpp b/fpdfsdk/javascript/PublicMethods.cpp
index bdae064cea..bf84b9cd91 100644
--- a/fpdfsdk/javascript/PublicMethods.cpp
+++ b/fpdfsdk/javascript/PublicMethods.cpp
@@ -983,7 +983,8 @@ bool CJS_PublicMethods::AFNumber_Keystroke(CJS_Runtime* pRuntime,
   CFX_WideString wprefix = wstrValue.Mid(0, pEvent->SelStart());
   CFX_WideString wpostfix;
   if (pEvent->SelEnd() < wstrValue.GetLength())
-    wpostfix = wstrValue.Mid(pEvent->SelEnd());
+    wpostfix = wstrValue.Mid(pEvent->SelEnd(),
+                             wstrValue.GetLength() - pEvent->SelEnd());
   val = wprefix + wstrChange + wpostfix;
   return true;
 }
diff --git a/xfa/fxfa/fm2js/cxfa_fm2jscontext.cpp b/xfa/fxfa/fm2js/cxfa_fm2jscontext.cpp
index 445d729668..1910e60e3e 100644
--- a/xfa/fxfa/fm2js/cxfa_fm2jscontext.cpp
+++ b/xfa/fxfa/fm2js/cxfa_fm2jscontext.cpp
@@ -1138,7 +1138,8 @@ void CXFA_FM2JSContext::IsoTime2Num(CFXJSE_Value* pThis,
   CXFA_Document* pDoc = pContext->GetDocument();
   CXFA_LocaleMgr* pMgr = pDoc->GetLocalMgr();
   CFX_ByteString szArgString = ValueToUTF8String(argOne.get());
-  szArgString = szArgString.Mid(szArgString.Find('T', 0) + 1);
+  FX_STRSIZE pos = szArgString.Find('T', 0);
+  szArgString = szArgString.Mid(pos + 1, szArgString.GetLength() - (pos + 1));
   if (szArgString.IsEmpty()) {
     args.GetReturnValue()->SetInteger(0);
     return;
@@ -3692,7 +3693,9 @@ void CXFA_FM2JSContext::Format(CFXJSE_Value* pThis,
         wsDatePattern += wsPattern.Left(iTChar) + L"} ";
 
         CFX_WideString wsTimePattern(L"time{");
-        wsTimePattern += wsPattern.Mid(iTChar + 1) + L"}";
+        wsTimePattern +=
+            wsPattern.Mid(iTChar + 1, wsPattern.GetLength() - (iTChar + 1)) +
+            L"}";
         wsPattern = wsDatePattern + wsTimePattern;
       } break;
       case XFA_VT_DATE: {
@@ -3877,7 +3880,10 @@ void CXFA_FM2JSContext::Parse(CFXJSE_Value* pThis,
     case XFA_VT_DATETIME: {
       FX_STRSIZE iTChar = wsPattern.Find(L'T');
       CFX_WideString wsDatePattern(L"date{" + wsPattern.Left(iTChar) + L"} ");
-      CFX_WideString wsTimePattern(L"time{" + wsPattern.Mid(iTChar + 1) + L"}");
+      CFX_WideString wsTimePattern(
+          L"time{" +
+          wsPattern.Mid(iTChar + 1, wsPattern.GetLength() - (iTChar + 1)) +
+          L"}");
       wsPattern = wsDatePattern + wsTimePattern;
       CXFA_LocaleValue localeValue(patternType, wsValue, wsPattern, pLocale,
                                    pMgr);
diff --git a/xfa/fxfa/fm2js/cxfa_fmexpression.cpp b/xfa/fxfa/fm2js/cxfa_fmexpression.cpp
index 7e6e0954aa..b201863b25 100644
--- a/xfa/fxfa/fm2js/cxfa_fmexpression.cpp
+++ b/xfa/fxfa/fm2js/cxfa_fmexpression.cpp
@@ -61,7 +61,8 @@ bool CXFA_FMFunctionDefinition::ToJavaScript(CFX_WideTextBuf& javascript) {
   }
   javascript << L"function ";
   if (m_wsName.GetAt(0) == L'!') {
-    CFX_WideString tempName = EXCLAMATION_IN_IDENTIFIER + m_wsName.Mid(1);
+    CFX_WideString tempName =
+        EXCLAMATION_IN_IDENTIFIER + m_wsName.Mid(1, m_wsName.GetLength() - 1);
     javascript << tempName;
   } else {
     javascript << m_wsName;
@@ -73,7 +74,8 @@ bool CXFA_FMFunctionDefinition::ToJavaScript(CFX_WideTextBuf& javascript) {
       javascript << L", ";
     if (identifier.GetAt(0) == L'!') {
       CFX_WideString tempIdentifier =
-          EXCLAMATION_IN_IDENTIFIER + identifier.Mid(1);
+          EXCLAMATION_IN_IDENTIFIER +
+          identifier.Mid(1, identifier.GetLength() - 1);
       javascript << tempIdentifier;
     } else {
       javascript << identifier;
@@ -127,7 +129,8 @@ bool CXFA_FMVarExpression::ToJavaScript(CFX_WideTextBuf& javascript) {
   javascript << L"var ";
   CFX_WideString tempName(m_wsName);
   if (m_wsName.GetAt(0) == L'!') {
-    tempName = EXCLAMATION_IN_IDENTIFIER + m_wsName.Mid(1);
+    tempName =
+        EXCLAMATION_IN_IDENTIFIER + m_wsName.Mid(1, m_wsName.GetLength() - 1);
   }
   javascript << tempName;
   javascript << L" = ";
@@ -150,7 +153,8 @@ bool CXFA_FMVarExpression::ToImpliedReturnJS(CFX_WideTextBuf& javascript) {
   javascript << L"var ";
   CFX_WideString tempName(m_wsName);
   if (m_wsName.GetAt(0) == L'!') {
-    tempName = EXCLAMATION_IN_IDENTIFIER + m_wsName.Mid(1);
+    tempName =
+        EXCLAMATION_IN_IDENTIFIER + m_wsName.Mid(1, m_wsName.GetLength() - 1);
   }
   javascript << tempName;
   javascript << L" = ";
@@ -456,7 +460,8 @@ bool CXFA_FMForExpression::ToJavaScript(CFX_WideTextBuf& javascript) {
   javascript << L"{\nvar ";
   CFX_WideString tempVariant;
   if (m_wsVariant.GetAt(0) == L'!') {
-    tempVariant = EXCLAMATION_IN_IDENTIFIER + m_wsVariant.Mid(1);
+    tempVariant = EXCLAMATION_IN_IDENTIFIER +
+                  m_wsVariant.Mid(1, m_wsVariant.GetLength() - 1);
     javascript << tempVariant;
   } else {
     tempVariant = m_wsVariant;
@@ -510,7 +515,8 @@ bool CXFA_FMForExpression::ToImpliedReturnJS(CFX_WideTextBuf& javascript) {
   javascript << L"{\nvar ";
   CFX_WideString tempVariant;
   if (m_wsVariant.GetAt(0) == L'!') {
-    tempVariant = EXCLAMATION_IN_IDENTIFIER + m_wsVariant.Mid(1);
+    tempVariant = EXCLAMATION_IN_IDENTIFIER +
+                  m_wsVariant.Mid(1, m_wsVariant.GetLength() - 1);
     javascript << tempVariant;
   } else {
     tempVariant = m_wsVariant;
@@ -576,7 +582,8 @@ bool CXFA_FMForeachExpression::ToJavaScript(CFX_WideTextBuf& javascript) {
   javascript << L"var ";
   if (m_wsIdentifier.GetAt(0) == L'!') {
     CFX_WideString tempIdentifier =
-        EXCLAMATION_IN_IDENTIFIER + m_wsIdentifier.Mid(1);
+        EXCLAMATION_IN_IDENTIFIER +
+        m_wsIdentifier.Mid(1, m_wsIdentifier.GetLength() - 1);
     javascript << tempIdentifier;
   } else {
     javascript << m_wsIdentifier;
@@ -607,7 +614,8 @@ bool CXFA_FMForeachExpression::ToJavaScript(CFX_WideTextBuf& javascript) {
   javascript << L".length)\n{\n";
   if (m_wsIdentifier.GetAt(0) == L'!') {
     CFX_WideString tempIdentifier =
-        EXCLAMATION_IN_IDENTIFIER + m_wsIdentifier.Mid(1);
+        EXCLAMATION_IN_IDENTIFIER +
+        m_wsIdentifier.Mid(1, m_wsIdentifier.GetLength() - 1);
     javascript << tempIdentifier;
   } else {
     javascript << m_wsIdentifier;
@@ -631,7 +639,8 @@ bool CXFA_FMForeachExpression::ToImpliedReturnJS(CFX_WideTextBuf& javascript) {
   javascript << L"var ";
   if (m_wsIdentifier.GetAt(0) == L'!') {
     CFX_WideString tempIdentifier =
-        EXCLAMATION_IN_IDENTIFIER + m_wsIdentifier.Mid(1);
+        EXCLAMATION_IN_IDENTIFIER +
+        m_wsIdentifier.Mid(1, m_wsIdentifier.GetLength() - 1);
     javascript << tempIdentifier;
   } else {
     javascript << m_wsIdentifier;
@@ -661,7 +670,8 @@ bool CXFA_FMForeachExpression::ToImpliedReturnJS(CFX_WideTextBuf& javascript) {
   javascript << L".length)\n{\n";
   if (m_wsIdentifier.GetAt(0) == L'!') {
     CFX_WideString tempIdentifier =
-        EXCLAMATION_IN_IDENTIFIER + m_wsIdentifier.Mid(1);
+        EXCLAMATION_IN_IDENTIFIER +
+        m_wsIdentifier.Mid(1, m_wsIdentifier.GetLength() - 1);
     javascript << tempIdentifier;
   } else {
     javascript << m_wsIdentifier;
diff --git a/xfa/fxfa/fm2js/cxfa_fmsimpleexpression.cpp b/xfa/fxfa/fm2js/cxfa_fmsimpleexpression.cpp
index 955b06fe93..1a3a125032 100644
--- a/xfa/fxfa/fm2js/cxfa_fmsimpleexpression.cpp
+++ b/xfa/fxfa/fm2js/cxfa_fmsimpleexpression.cpp
@@ -180,7 +180,8 @@ bool CXFA_FMIdentifierExpression::ToJavaScript(CFX_WideTextBuf& javascript) {
   } else if (tempStr == L"$template") {
     tempStr = L"xfa.template";
   } else if (tempStr[0] == L'!') {
-    tempStr = EXCLAMATION_IN_IDENTIFIER + tempStr.Mid(1);
+    tempStr =
+        EXCLAMATION_IN_IDENTIFIER + tempStr.Mid(1, tempStr.GetLength() - 1);
   }
   javascript << tempStr;
   return true;
diff --git a/xfa/fxfa/parser/cxfa_layoutpagemgr.cpp b/xfa/fxfa/parser/cxfa_layoutpagemgr.cpp
index a3f4ce9519..e3565835c3 100644
--- a/xfa/fxfa/parser/cxfa_layoutpagemgr.cpp
+++ b/xfa/fxfa/parser/cxfa_layoutpagemgr.cpp
@@ -162,7 +162,7 @@ CXFA_Node* ResolveBreakTarget(CXFA_Node* pPageSetRoot,
     if (wsExpr.GetAt(0) == '#') {
       CXFA_Node* pNode = pDocument->GetNodeByID(
           ToNode(pDocument->GetXFAObject(XFA_HASHCODE_Template)),
-          wsExpr.Mid(1).AsStringC());
+          wsExpr.Mid(1, wsExpr.GetLength() - 1).AsStringC());
       if (pNode)
         return pNode;
     } else if (bNewExprStyle) {
diff --git a/xfa/fxfa/parser/cxfa_measurement.cpp b/xfa/fxfa/parser/cxfa_measurement.cpp
index f161e49e49..50076583bb 100644
--- a/xfa/fxfa/parser/cxfa_measurement.cpp
+++ b/xfa/fxfa/parser/cxfa_measurement.cpp
@@ -40,7 +40,8 @@ void CXFA_Measurement::SetString(const CFX_WideStringC& wsMeasure) {
   int32_t iOffset = (wsMeasure.GetAt(0) == L'=') ? 1 : 0;
   float fValue = FXSYS_wcstof(wsMeasure.unterminated_c_str() + iOffset,
                               wsMeasure.GetLength() - iOffset, &iUsedLen);
-  XFA_UNIT eUnit = GetUnitFromString(wsMeasure.Mid(iOffset + iUsedLen));
+  XFA_UNIT eUnit = GetUnitFromString(wsMeasure.Mid(
+      iOffset + iUsedLen, wsMeasure.GetLength() - (iOffset + iUsedLen)));
   Set(fValue, eUnit);
 }
 
diff --git a/xfa/fxfa/parser/cxfa_node.cpp b/xfa/fxfa/parser/cxfa_node.cpp
index eac7ac04b0..1265988902 100644
--- a/xfa/fxfa/parser/cxfa_node.cpp
+++ b/xfa/fxfa/parser/cxfa_node.cpp
@@ -77,7 +77,7 @@ int32_t GetCount(CXFA_Node* pInstMgrNode) {
       CFX_WideStringC wsName = pNode->GetCData(XFA_ATTRIBUTE_Name);
       CFX_WideStringC wsInstName = pInstMgrNode->GetCData(XFA_ATTRIBUTE_Name);
       if (wsInstName.GetLength() < 1 || wsInstName.GetAt(0) != '_' ||
-          wsInstName.Mid(1) != wsName) {
+          wsInstName.Mid(1, wsInstName.GetLength() - 1) != wsName) {
         return iCount;
       }
       dwNameHash = pNode->GetNameHash();
@@ -198,7 +198,7 @@ CXFA_Node* GetItem(CXFA_Node* pInstMgrNode, int32_t iIndex) {
       CFX_WideStringC wsName = pNode->GetCData(XFA_ATTRIBUTE_Name);
       CFX_WideStringC wsInstName = pInstMgrNode->GetCData(XFA_ATTRIBUTE_Name);
       if (wsInstName.GetLength() < 1 || wsInstName.GetAt(0) != '_' ||
-          wsInstName.Mid(1) != wsName) {
+          wsInstName.Mid(1, wsInstName.GetLength() - 1) != wsName) {
         return nullptr;
       }
       dwNameHash = pNode->GetNameHash();
@@ -2737,7 +2737,7 @@ void CXFA_Node::Script_Subform_InstanceManager(CFXJSE_Value* pValue,
     if (pNode->GetElementType() == XFA_Element::InstanceManager) {
       CFX_WideStringC wsInstMgrName = pNode->GetCData(XFA_ATTRIBUTE_Name);
       if (wsInstMgrName.GetLength() >= 1 && wsInstMgrName.GetAt(0) == '_' &&
-          wsInstMgrName.Mid(1) == wsName) {
+          wsInstMgrName.Mid(1, wsInstMgrName.GetLength() - 1) == wsName) {
         pInstanceMgr = pNode;
       }
       break;
@@ -3162,9 +3162,10 @@ int32_t CXFA_Node::InstanceManager_SetInstances(int32_t iDesired) {
   }
   if (iDesired < iCount) {
     CFX_WideStringC wsInstManagerName = GetCData(XFA_ATTRIBUTE_Name);
-    CFX_WideString wsInstanceName =
-        CFX_WideString(wsInstManagerName.IsEmpty() ? wsInstManagerName
-                                                   : wsInstManagerName.Mid(1));
+    CFX_WideString wsInstanceName = CFX_WideString(
+        wsInstManagerName.IsEmpty()
+            ? wsInstManagerName
+            : wsInstManagerName.Mid(1, wsInstManagerName.GetLength() - 1));
     uint32_t dInstanceNameHash =
         FX_HashCode_GetW(wsInstanceName.AsStringC(), false);
     CXFA_Node* pPrevSibling =
@@ -4664,7 +4665,7 @@ CXFA_Node* CXFA_Node::GetInstanceMgrOfSubform() {
         CFX_WideStringC wsName = GetCData(XFA_ATTRIBUTE_Name);
         CFX_WideStringC wsInstName = pNode->GetCData(XFA_ATTRIBUTE_Name);
         if (wsInstName.GetLength() > 0 && wsInstName.GetAt(0) == '_' &&
-            wsInstName.Mid(1) == wsName) {
+            wsInstName.Mid(1, wsInstName.GetLength() - 1) == wsName) {
           pInstanceMgr = pNode;
         }
         break;
diff --git a/xfa/fxfa/parser/cxfa_widgetdata.cpp b/xfa/fxfa/parser/cxfa_widgetdata.cpp
index cbe0d14c91..1920e9f3fd 100644
--- a/xfa/fxfa/parser/cxfa_widgetdata.cpp
+++ b/xfa/fxfa/parser/cxfa_widgetdata.cpp
@@ -1323,7 +1323,10 @@ bool CXFA_WidgetData::GetBarcodeAttribute_WideNarrowRatio(float* val) {
     } else {
       int32_t fA, fB;
       fA = FXSYS_wtoi(wsWideNarrowRatio.Left(ptPos).c_str());
-      fB = FXSYS_wtoi(wsWideNarrowRatio.Mid(ptPos + 1).c_str());
+      fB = FXSYS_wtoi(
+          wsWideNarrowRatio
+              .Mid(ptPos + 1, wsWideNarrowRatio.GetLength() - (ptPos + 1))
+              .c_str());
       if (fB)
         fRatio = (float)fA / fB;
     }