text: // Copyright 2001, Google Inc.  All rights reserved.
  // Maintainer: mec@google.com (Michael Chastain)
  //
  // The following only applies to changes made to this file as part of YugaByte development.
  //
  // Portions Copyright (c) YugaByte, Inc.
  //
  // Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
  // in compliance with the License.  You may obtain a copy of the License at
  //
  // http://www.apache.org/licenses/LICENSE-2.0
  //
  // Unless required by applicable law or agreed to in writing, software distributed under the License
  // is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
  // or implied.  See the License for the specific language governing permissions and limitations
  // under the License.
  //
  // A StringPiece points to part or all of a string, Cord, double-quoted string
  // literal, or other string-like object.  A StringPiece does *not* own the
  // string to which it points.  A StringPiece is not null-terminated.
  //
  // You can use StringPiece as a function or method parameter.  A StringPiece
  // parameter can receive a double-quoted string literal argument, a "const
  // char*" argument, a string argument, or a StringPiece argument with no data
  // copying.  Systematic use of StringPiece for arguments reduces data
  // copies and strlen() calls.
  //
  // You may pass a StringPiece argument by value or const reference.
  // Passing by value generates slightly smaller code.
  //   void MyFunction(const StringPiece& arg);
  //   // Slightly better, but same lifetime requirements as const-ref parameter:
  //   void MyFunction(StringPiece arg);
  //
  // StringPiece is also suitable for local variables if you know that
  // the lifetime of the underlying object is longer than the lifetime
  // of your StringPiece variable.
  //
  // Beware of binding a StringPiece to a temporary:
  //   StringPiece sp = obj.MethodReturningString();  // BAD: lifetime problem
  //
  // This code is okay:
  //   string str = obj.MethodReturningString();  // str owns its contents
  //   StringPiece sp(str);  // GOOD, although you may not need sp at all
  //
  // StringPiece is sometimes a poor choice for a return value and usually a poor
  // choice for a data member.  If you do use a StringPiece this way, it is your
  // responsibility to ensure that the object pointed to by the StringPiece
  // outlives the StringPiece.
  //
  // A StringPiece may represent just part of a string; thus the name "Piece".
  // For example, when splitting a string, vector<StringPiece> is a natural data
  // type for the output.  For another example, a Cord is a non-contiguous,
  // potentially very long string-like object.  The Cord class has an interface
  // that iteratively provides StringPiece objects that point to the
  // successive pieces of a Cord object.
  //
  // A StringPiece is not null-terminated.  If you write code that scans a
  // StringPiece, you must check its length before reading any characters.
  // Common idioms that work on null-terminated strings do not work on
  // StringPiece objects.
  //
  // There are several ways to create a null StringPiece:
  //   StringPiece()
  //   StringPiece(NULL)
  //   StringPiece(NULL, 0)
  // For all of the above, sp.data() == NULL, sp.length() == 0,
  // and sp.empty() == true.  Also, if you create a StringPiece with
  // a non-NULL pointer then sp.data() != non-NULL.  Once created,
  // sp.data() will stay either NULL or not-NULL, except if you call
  // sp.clear() or sp.set().
  //
  // Thus, you can use StringPiece(NULL) to signal an out-of-band value
  // that is different from other StringPiece values.  This is similar
  // to the way that const char* p1 = NULL; is different from
  // const char* p2 = "";.
  //
  // There are many ways to create an empty StringPiece:
  //   StringPiece()
  //   StringPiece(NULL)
  //   StringPiece(NULL, 0)
  //   StringPiece("")
  //   StringPiece("", 0)
  //   StringPiece("abcdef", 0)
  //   StringPiece("abcdef"+6, 0)
  // For all of the above, sp.length() will be 0 and sp.empty() will be true.
  // For some empty StringPiece values, sp.data() will be NULL.
  // For some empty StringPiece values, sp.data() will not be NULL.
  //
  // Be careful not to confuse: null StringPiece and empty StringPiece.
  // The set of empty StringPieces properly includes the set of null StringPieces.
  // That is, every null StringPiece is an empty StringPiece,
  // but some non-null StringPieces are empty Stringpieces too.
  //
  // All empty StringPiece values compare equal to each other.
  // Even a null StringPieces compares equal to a non-null empty StringPiece:
  //  StringPiece() == StringPiece("", 0)
  //  StringPiece(NULL) == StringPiece("abc", 0)
  //  StringPiece(NULL, 0) == StringPiece("abcdef"+6, 0)
  //
  // Look carefully at this example:
  //   StringPiece("") == NULL
  // True or false?  TRUE, because StringPiece::operator== converts
  // the right-hand side from NULL to StringPiece(NULL),
  // and then compares two zero-length spans of characters.
  // However, we are working to make this example produce a compile error.
  //
  // Suppose you want to write:
  //   bool TestWhat?(StringPiece sp) { return sp == NULL; }  // BAD
  // Do not do that.  Write one of these instead:
  //   bool TestNull(StringPiece sp) { return sp.data() == NULL; }
  //   bool TestEmpty(StringPiece sp) { return sp.empty(); }
  // The intent of TestWhat? is unclear.  Did you mean TestNull or TestEmpty?
  // Right now, TestWhat? behaves likes TestEmpty.
  // We are working to make TestWhat? produce a compile error.
  // TestNull is good to test for an out-of-band signal.
  // TestEmpty is good to test for an empty StringPiece.
  //
  // Caveats (again):
  // (1) The lifetime of the pointed-to string (or piece of a string)
  //     must be longer than the lifetime of the StringPiece.
  // (2) There may or may not be a '\0' character after the end of
  //     StringPiece data.
  // (3) A null StringPiece is empty.
  //     An empty StringPiece may or may not be a null StringPiece.
  
  #ifndef STRINGS_STRINGPIECE_H_
  #define STRINGS_STRINGPIECE_H_
  
  
  #include <assert.h>
  #include <functional>
  #include <iosfwd>
  #include <limits>
  #include <stddef.h>
  #include <string.h>
  #include <string>
  
  #include "yb/gutil/integral_types.h"
  #include "yb/gutil/port.h"
  #include "yb/gutil/type_traits.h"
  #include "yb/gutil/strings/fastmem.h"
  #include "yb/gutil/hash/hash.h"
  
  class StringPiece {
   private:
    const char*   ptr_;
    int           length_;
  
   public:
    // We provide non-explicit singleton constructors so users can pass
    // in a "const char*" or a "string" wherever a "StringPiece" is
    // expected.
    //
    // Style guide exception granted:
    // http://goto/style-guide-exception-20978288
    StringPiece() : ptr_(NULL), length_(0) {}
    StringPiece(const char* str)  // NOLINT(runtime/explicit)
        : ptr_(str), length_(0) {
      if (str != NULL) {
        size_t length = strlen(str);
        assert(length <= static_cast<size_t>(std::numeric_limits<int>::max()));
        length_ = static_cast<int>(length);
      }
    }
    StringPiece(const std::string& str)  // NOLINT(runtime/explicit)
        : ptr_(str.data()), length_(0) {
      size_t length = str.size();
      assert(length <= static_cast<size_t>(std::numeric_limits<int>::max()));
      length_ = static_cast<int>(length);
    }
    StringPiece(const char* offset, int len) : ptr_(offset), length_(len) {
      assert(len >= 0);
    }
  
    // Substring of another StringPiece.
    // pos must be non-negative and <= x.length().
    StringPiece(StringPiece x, int pos);
    // Substring of another StringPiece.
    // pos must be non-negative and <= x.length().
    // len must be non-negative and will be pinned to at most x.length() - pos.
    StringPiece(StringPiece x, int pos, int len);
  
    // data() may return a pointer to a buffer with embedded NULs, and the
    // returned buffer may or may not be null terminated.  Therefore it is
    // typically a mistake to pass data() to a routine that expects a NUL
    // terminated string.
    const char* data() const { return ptr_; }
    int size() const { return length_; }
    int length() const { return length_; }
    bool empty() const { return length_ == 0; }
  
    void clear() {
      ptr_ = NULL;
      length_ = 0;
    }
  
    void set(const char* data, int len) {
      assert(len >= 0);
      ptr_ = data;
      length_ = len;
    }
  
    void set(const char* str) {
      ptr_ = str;
      if (str != NULL)
        length_ = static_cast<int>(strlen(str));
      else
        length_ = 0;
    }
    void set(const void* data, int len) {
      ptr_ = reinterpret_cast<const char*>(data);
      length_ = len;
    }
  
    char operator[](int i) const {
      assert(0 <= i);
      assert(i < length_);
      return ptr_[i];
    }
  
    void remove_prefix(int n) {
      assert(length_ >= n);
      ptr_ += n;
      length_ -= n;
    }
  
    void remove_suffix(int n) {
      assert(length_ >= n);
      length_ -= n;
    }
  
    // returns {-1, 0, 1}
    int compare(StringPiece x) const {
      const int min_size = length_ < x.length_ ? length_ : x.length_;
      int r = memcmp(ptr_, x.ptr_, min_size);
      if (r < 0) return -1;
      if (r > 0) return 1;
      if (length_ < x.length_) return -1;
      if (length_ > x.length_) return 1;
      return 0;
    }
  
    std::string as_string() const {
      return ToString();
    }
    // We also define ToString() here, since many other string-like
    // interfaces name the routine that converts to a C++ string
    // "ToString", and it's confusing to have the method that does that
    // for a StringPiece be called "as_string()".  We also leave the
    // "as_string()" method defined here for existing code.
    std::string ToString() const {
      if (ptr_ == NULL) return std::string();
      return std::string(data(), size());
    }
  
    void CopyToString(std::string* target) const;
    void AppendToString(std::string* target) const;
  
    bool starts_with(StringPiece x) const {
      return (length_ >= x.length_) && (memcmp(ptr_, x.ptr_, x.length_) == 0);
    }
  
    bool ends_with(StringPiece x) const {
      return ((length_ >= x.length_) &&
              (memcmp(ptr_ + (length_-x.length_), x.ptr_, x.length_) == 0));
    }
  
    // standard STL container boilerplate
    typedef char value_type;
    typedef const char* pointer;
    typedef const char& reference;
    typedef const char& const_reference;
    typedef size_t size_type;
    typedef ptrdiff_t difference_type;
    static const size_type npos;
    typedef const char* const_iterator;
    typedef const char* iterator;
    typedef std::reverse_iterator<const_iterator> const_reverse_iterator;
    typedef std::reverse_iterator<iterator> reverse_iterator;
    iterator begin() const { return ptr_; }
    iterator end() const { return ptr_ + length_; }
    const_reverse_iterator rbegin() const {
      return const_reverse_iterator(ptr_ + length_);
    }
    const_reverse_iterator rend() const {
      return const_reverse_iterator(ptr_);
    }
    // STLS says return size_type, but Google says return int
    int max_size() const { return length_; }
    int capacity() const { return length_; }
  
    // cpplint.py emits a false positive [build/include_what_you_use]
    int copy(char* buf, size_type n, size_type pos = 0) const;  // NOLINT
  
    bool contains(StringPiece s) const;
  
    int find(StringPiece s, size_type pos = 0) const;
    int find(char c, size_type pos = 0) const;
    int rfind(StringPiece s, size_type pos = npos) const;
    int rfind(char c, size_type pos = npos) const;
  
    int find_first_of(StringPiece s, size_type pos = 0) const;
    int find_first_of(char c, size_type pos = 0) const { return find(c, pos); }
    int find_first_not_of(StringPiece s, size_type pos = 0) const;
    int find_first_not_of(char c, size_type pos = 0) const;
    int find_last_of(StringPiece s, size_type pos = npos) const;
    int find_last_of(char c, size_type pos = npos) const { return rfind(c, pos); }
    int find_last_not_of(StringPiece s, size_type pos = npos) const;
    int find_last_not_of(char c, size_type pos = npos) const;
  
    StringPiece substr(size_type pos, size_type n = npos) const;
  };
  
  #ifndef SWIG
  DECLARE_POD(StringPiece);  // So vector<StringPiece> becomes really fast
  #endif
  
  // This large function is defined inline so that in a fairly common case where
  // one of the arguments is a literal, the compiler can elide a lot of the
  // following comparisons.
  inline bool operator==(StringPiece x, StringPiece y) {
    int len = x.size();
    if (len != y.size()) {
      return false;
    }
  
    return x.data() == y.data() || len <= 0 ||
        strings::memeq(x.data(), y.data(), len);
  }
  
  inline bool operator!=(StringPiece x, StringPiece y) {
    return !(x == y);
  }
  
  inline bool operator<(StringPiece x, StringPiece y) {
    const int min_size = x.size() < y.size() ? x.size() : y.size();
    const int r = memcmp(x.data(), y.data(), min_size);
    return (r < 0) || (r == 0 && x.size() < y.size());
  }
  
  inline bool operator>(StringPiece x, StringPiece y) {
    return y < x;
  }
  
  inline bool operator<=(StringPiece x, StringPiece y) {
    return !(x > y);
  }
  
  inline bool operator>=(StringPiece x, StringPiece y) {
    return !(x < y);
  }
  class StringPiece;
  template <class X> struct GoodFastHash;
  
  // ------------------------------------------------------------------
  // Functions used to create STL containers that use StringPiece
  //  Remember that a StringPiece's lifetime had better be less than
  //  that of the underlying string or char*.  If it is not, then you
  //  cannot safely store a StringPiece into an STL container
  // ------------------------------------------------------------------
  
  // SWIG doesn't know how to parse this stuff properly. Omit it.
  #ifndef SWIG
  
  namespace std {
  template<> struct hash<StringPiece> {
    size_t operator()(StringPiece s) const;
  };
  }  // namespace std
  
  
  // An implementation of GoodFastHash for StringPiece.  See
  // GoodFastHash values.
  template<> struct GoodFastHash<StringPiece> {
    size_t operator()(StringPiece s) const {
      return HashStringThoroughly(s.data(), s.size());
    }
    // Less than operator, for MSVC.
    bool operator()(const StringPiece& s1, const StringPiece& s2) const {
      return s1 < s2;
    }
    static const size_t bucket_size = 4;  // These are required by MSVC
    static const size_t min_buckets = 8;  // 4 and 8 are defaults.
  };
  #endif
  
  // allow StringPiece to be logged
  extern ostream& operator<<(ostream& o, StringPiece piece);
  
  
  #endif  // STRINGS_STRINGPIECE_H__
  