Extend DbPath with RootLength function

include/leveldb/db_path.h

@@ -4,9 +4,6 @@
 #include <cstdint>
 #include <string>
 
-#include "leveldb/export.h"
-#include "leveldb/status.h"
-
 namespace leveldb {
 
 namespace path {
@@ -23,10 +20,9 @@ public:
   const std::string& Name() const { return path_; }
   const char* CName() const { return path_.c_str(); }
 
-  static bool IsDirectorySeparator(const char c);
-
   virtual bool IsAbsolute() const = 0;
   virtual bool IsRelative() const = 0;
+  virtual size_t RootLength() = 0;
 
   inline size_t Size() const { return path_.size(); }
   inline bool IsEmpty() const { return path_.empty(); }
@@ -38,9 +34,14 @@ protected:
 
   std::string path_;
 
+  static bool IsDirectorySeparator(const char c);
+
+  bool StartsWith(const std::string& value, bool ignore_case = false);
+
   virtual void Normalize() = 0;
 };
 
+// Win path
 class WindowsDbPath : public DbPath {
 public:
   explicit WindowsDbPath(const std::string& path) : DbPath(path) {
@@ -48,13 +49,19 @@ public:
   }
   ~WindowsDbPath() {}
 
-  static bool IsValidDriveChar(const char c);
-
   bool IsAbsolute() const override;
   bool IsRelative() const override;
 
+  size_t RootLength() override;
+
 protected:
+  static bool IsValidDriveChar(const char c);
+
   void Normalize() override;
+
+private:
+  const char* kExtendedPathPrefix = "\\\\?\\";
+  const char* kUncExtendedPathPrefix = "\\\\?\\UNC\\";
 };
 
 

util/db_path.cc

@@ -7,6 +7,17 @@ bool DbPath::IsDirectorySeparator(const char c) {
   return (c == DbPath::kDirectorySeparator || c == DbPath::kAltDirecttorySeparator);
 }
 
+bool DbPath::StartsWith(const std::string& value, bool ignore_case) {
+  if (value.size() > path_.size()) {
+    return false;
+  }
+  if (ignore_case) {
+    auto ignore_case_cmp_func = [](char a, char b) { return std::tolower(a) == std::tolower(b); };
+    return std::equal(value.begin(), value.end(), path_.begin(), ignore_case_cmp_func);
+  }
+  return std::equal(value.begin(), value.end(), path_.begin());
+}
+
 // Windows
 
 bool WindowsDbPath::IsAbsolute() const {
@@ -55,6 +66,45 @@ bool WindowsDbPath::IsValidDriveChar(const char c) {
   return drive_char >= 'A' && drive_char <= 'Z';
 }
 
+size_t WindowsDbPath::RootLength() {
+  size_t path_length = path_.size();
+  size_t root_length = 0;
+  size_t volume_separator_length = 2;
+  size_t unc_root_length = 2;
+
+  bool extended_syntax = StartsWith(kExtendedPathPrefix);
+  bool extended_unc_syntax = StartsWith(kUncExtendedPathPrefix);
+
+  if (extended_syntax) {
+    if (extended_unc_syntax) {
+      unc_root_length = std::strlen(kUncExtendedPathPrefix);
+    } 
+    else {
+      volume_separator_length += std::strlen(kExtendedPathPrefix);
+    }
+  }
+
+  if ((!extended_syntax || extended_unc_syntax) && path_length != 0 && IsDirectorySeparator(path_[0])) {
+    root_length = 1;
+
+    if (extended_unc_syntax || (path_length > 1 && IsDirectorySeparator(path_[1]))) {
+      root_length = unc_root_length;
+      int n = 2; // maximum separators to skip
+      while (root_length < path_length && (!IsDirectorySeparator(path_[root_length]) || --n > 0)) {
+        ++root_length;
+      }
+    }
+  } 
+  else if (path_length >= volume_separator_length && path_[volume_separator_length - 1] == kVolumeSeparatorChar) {
+    root_length = volume_separator_length;
+    if (path_length >= volume_separator_length && IsDirectorySeparator(path_[volume_separator_length])) {
+      ++root_length;
+    }
+  }
+
+  return root_length;
+}
+
 // Windows path
 
 DbPath* PathFactory::Create(const std::string& path) {