CPDF_SyntaxParser::SearchWord() is always backwards and for whole-words

Change-Id: Ic31d9cda5e919a754162e14e69cb63671a3fe8b9
Reviewed-on: https://pdfium-review.googlesource.com/4794
Reviewed-by: dsinclair <dsinclair@chromium.org>
Commit-Queue: dsinclair <dsinclair@chromium.org>
Commit-Queue: Tom Sepez <tsepez@chromium.org>

4 files changed, 23 insertions, 66 deletions

diff --git a/core/fpdfapi/parser/cpdf_data_avail.cpp b/core/fpdfapi/parser/cpdf_data_avail.cpp
index 709874ef15..b13b982430 100644
--- a/core/fpdfapi/parser/cpdf_data_avail.cpp
+++ b/core/fpdfapi/parser/cpdf_data_avail.cpp
@@ -748,7 +748,6 @@ bool CPDF_DataAvail::IsLinearizedFile(uint8_t* pData, uint32_t dwLen) {
 bool CPDF_DataAvail::CheckEnd(DownloadHints* pHints) {
   uint32_t req_pos = (uint32_t)(m_dwFileLen > 1024 ? m_dwFileLen - 1024 : 0);
   uint32_t dwSize = (uint32_t)(m_dwFileLen - req_pos);
-
   if (!m_pFileAvail->IsDataAvail(req_pos, dwSize)) {
     pHints->AddSegment(req_pos, dwSize);
     return false;
@@ -761,12 +760,10 @@ bool CPDF_DataAvail::CheckEnd(DownloadHints* pHints) {
       buffer, static_cast<size_t>(dwSize), false);
   m_syntaxParser.InitParser(file, 0);
   m_syntaxParser.SetPos(dwSize - 1);
-
-  if (!m_syntaxParser.SearchWord("startxref", true, false, dwSize)) {
+  if (!m_syntaxParser.BackwardsSearchToWord("startxref", dwSize)) {
     m_docStatus = PDF_DATAAVAIL_LOADALLFILE;
     return true;
   }
-
   m_syntaxParser.GetNextWord(nullptr);
 
   bool bNumber;
diff --git a/core/fpdfapi/parser/cpdf_parser.cpp b/core/fpdfapi/parser/cpdf_parser.cpp
index fc98be5f6e..12ec81bc07 100644
--- a/core/fpdfapi/parser/cpdf_parser.cpp
+++ b/core/fpdfapi/parser/cpdf_parser.cpp
@@ -159,7 +159,7 @@ CPDF_Parser::Error CPDF_Parser::StartParse(
   m_pDocument = pDocument;
 
   bool bXRefRebuilt = false;
-  if (m_pSyntax->SearchWord("startxref", true, false, 4096)) {
+  if (m_pSyntax->BackwardsSearchToWord("startxref", 4096)) {
     m_SortedOffset.insert(m_pSyntax->GetPos());
     m_pSyntax->GetKeyword();
 
diff --git a/core/fpdfapi/parser/cpdf_syntax_parser.cpp b/core/fpdfapi/parser/cpdf_syntax_parser.cpp
index 45a5a8a709..e41736dd86 100644
--- a/core/fpdfapi/parser/cpdf_syntax_parser.cpp
+++ b/core/fpdfapi/parser/cpdf_syntax_parser.cpp
@@ -90,7 +90,7 @@ bool CPDF_SyntaxParser::GetNextChar(uint8_t& ch) {
   return true;
 }
 
-bool CPDF_SyntaxParser::GetCharAtBackward(FX_FILESIZE pos, uint8_t& ch) {
+bool CPDF_SyntaxParser::GetCharAtBackward(FX_FILESIZE pos, uint8_t* ch) {
   pos += m_HeaderOffset;
   if (pos >= m_FileLen)
     return false;
@@ -105,7 +105,7 @@ bool CPDF_SyntaxParser::GetCharAtBackward(FX_FILESIZE pos, uint8_t& ch) {
     if (!ReadChar(read_pos, read_size))
       return false;
   }
-  ch = m_pFileBuf[pos - m_BufOffset];
+  *ch = m_pFileBuf[pos - m_BufOffset];
   return true;
 }
 
@@ -814,74 +814,38 @@ bool CPDF_SyntaxParser::IsWholeWord(FX_FILESIZE startpos,
   return true;
 }
 
-// TODO(dsinclair): Split into a SearchWordForward and SearchWordBackwards
-// and drop the bool.
-bool CPDF_SyntaxParser::SearchWord(const CFX_ByteStringC& tag,
-                                   bool bWholeWord,
-                                   bool bForward,
-                                   FX_FILESIZE limit) {
+bool CPDF_SyntaxParser::BackwardsSearchToWord(const CFX_ByteStringC& tag,
+                                              FX_FILESIZE limit) {
   int32_t taglen = tag.GetLength();
   if (taglen == 0)
     return false;
 
   FX_FILESIZE pos = m_Pos;
-  int32_t offset = 0;
-  if (!bForward)
-    offset = taglen - 1;
-
-  const uint8_t* tag_data = tag.raw_str();
-  uint8_t byte;
+  int32_t offset = taglen - 1;
   while (1) {
-    if (bForward) {
-      if (limit && pos >= m_Pos + limit)
-        return false;
-
-      if (!GetCharAt(pos, byte))
-        return false;
-
-    } else {
-      if (limit && pos <= m_Pos - limit)
-        return false;
+    if (limit && pos <= m_Pos - limit)
+      return false;
 
-      if (!GetCharAtBackward(pos, byte))
-        return false;
-    }
+    uint8_t byte;
+    if (!GetCharAtBackward(pos, &byte))
+      return false;
 
-    if (byte == tag_data[offset]) {
-      if (bForward) {
-        offset++;
-        if (offset < taglen) {
-          pos++;
-          continue;
-        }
-      } else {
-        offset--;
-        if (offset >= 0) {
-          pos--;
-          continue;
-        }
+    if (byte == tag[offset]) {
+      offset--;
+      if (offset >= 0) {
+        pos--;
+        continue;
       }
-
-      FX_FILESIZE startpos = bForward ? pos - taglen + 1 : pos;
-      if (!bWholeWord || IsWholeWord(startpos, limit, tag, false)) {
-        m_Pos = startpos;
+      if (IsWholeWord(pos, limit, tag, false)) {
+        m_Pos = pos;
         return true;
       }
     }
-
-    if (bForward) {
-      offset = byte == tag_data[0] ? 1 : 0;
-      pos++;
-    } else {
-      offset = byte == tag_data[taglen - 1] ? taglen - 2 : taglen - 1;
-      pos--;
-    }
-
+    offset = byte == tag[taglen - 1] ? taglen - 2 : taglen - 1;
+    pos--;
     if (pos < 0)
       return false;
   }
-
-  return false;
 }
 
 FX_FILESIZE CPDF_SyntaxParser::FindTag(const CFX_ByteStringC& tag,
diff --git a/core/fpdfapi/parser/cpdf_syntax_parser.h b/core/fpdfapi/parser/cpdf_syntax_parser.h
index f9a9bd9a8a..4c5e252978 100644
--- a/core/fpdfapi/parser/cpdf_syntax_parser.h
+++ b/core/fpdfapi/parser/cpdf_syntax_parser.h
@@ -46,11 +46,7 @@ class CPDF_SyntaxParser {
   CFX_ByteString GetKeyword();
   void ToNextLine();
   void ToNextWord();
-  bool SearchWord(const CFX_ByteStringC& word,
-                  bool bWholeWord,
-                  bool bForward,
-                  FX_FILESIZE limit);
-
+  bool BackwardsSearchToWord(const CFX_ByteStringC& word, FX_FILESIZE limit);
   FX_FILESIZE FindTag(const CFX_ByteStringC& tag, FX_FILESIZE limit);
   void SetEncrypt(const CFX_RetainPtr<CPDF_CryptoHandler>& pCryptoHandler);
   bool ReadBlock(uint8_t* pBuf, uint32_t size);
@@ -68,7 +64,7 @@ class CPDF_SyntaxParser {
   uint32_t GetDirectNum();
   bool ReadChar(FX_FILESIZE read_pos, uint32_t read_size);
   bool GetNextChar(uint8_t& ch);
-  bool GetCharAtBackward(FX_FILESIZE pos, uint8_t& ch);
+  bool GetCharAtBackward(FX_FILESIZE pos, uint8_t* ch);
   void GetNextWordInternal(bool* bIsNumber);
   bool IsWholeWord(FX_FILESIZE startpos,
                    FX_FILESIZE limit,