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 // Protocol Buffers - Google's data interchange format
 // Copyright 2008 Google Inc.  All rights reserved.
 //
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file or at
 // https://developers.google.com/open-source/licenses/bsd
 
 #ifndef GOOGLE_PROTOBUF_ARENASTRING_H__
 #define GOOGLE_PROTOBUF_ARENASTRING_H__
 
 #include <algorithm>
 #include <cstdint>
 #include <string>
 #include <type_traits>
 #include <utility>
 
 #include "absl/log/absl_check.h"
 #include "absl/strings/string_view.h"
 #include "google/protobuf/arena.h"
 #include "google/protobuf/explicitly_constructed.h"
 #include "google/protobuf/port.h"
 
 // must be last:
 #include "google/protobuf/port_def.inc"
 
 #ifdef SWIG
 #error "You cannot SWIG proto headers"
 #endif
 
 
 namespace google {
 namespace protobuf {
 namespace internal {
 class EpsCopyInputStream;
 
 class SwapFieldHelper;
 
 // Lazy string instance to support string fields with non-empty default.
 // These are initialized on the first call to .get().
 class PROTOBUF_EXPORT LazyString {
  public:
   // We explicitly make LazyString an aggregate so that MSVC can do constant
   // initialization on it without marking it `constexpr`.
   // We do not want to use `constexpr` because it makes it harder to have extern
   // storage for it and causes library bloat.
   struct InitValue {
     const char* ptr;
     size_t size;
   };
   // We keep a union of the initialization value and the std::string to save on
   // space. We don't need the string array after Init() is done.
   union {
     mutable InitValue init_value_;
     alignas(std::string) mutable char string_buf_[sizeof(std::string)];
   };
   mutable std::atomic<const std::string*> inited_;
 
   const std::string& get() const {
     // This check generates less code than a call-once invocation.
     auto* res = inited_.load(std::memory_order_acquire);
     if (ABSL_PREDICT_FALSE(res == nullptr)) return Init();
     return *res;
   }
 
  private:
   // Initialize the string in `string_buf_`, update `inited_` and return it.
   // We return it here to avoid having to read it again in the inlined code.
   const std::string& Init() const;
 };
 
 class PROTOBUF_EXPORT TaggedStringPtr {
  public:
   // Bit flags qualifying string properties. We can use 2 bits as
   // ptr_ is guaranteed and enforced to be aligned on 4 byte boundaries.
   enum Flags {
     kArenaBit = 0x1,    // ptr is arena allocated
     kMutableBit = 0x2,  // ptr contents are fully mutable
     kMask = 0x3         // Bit mask
   };
 
   // Composed logical types
   enum Type {
     // Default strings are immutable and never owned.
     kDefault = 0,
 
     // Allocated strings are mutable and (as the name implies) owned.
     // A heap allocated string must be deleted.
     kAllocated = kMutableBit,
 
     // Mutable arena strings are strings where the string instance is owned
     // by the arena, but the string contents itself are owned by the string
     // instance. Mutable arena string instances need to be destroyed which is
     // typically done through a cleanup action added to the arena owning it.
     kMutableArena = kArenaBit | kMutableBit,
 
     // Fixed size arena strings are strings where both the string instance and
     // the string contents are fully owned by the arena. Fixed size arena
     // strings are a platform and c++ library specific customization. Fixed
     // size arena strings are immutable, with the exception of custom internal
     // updates to the content that fit inside the existing capacity.
     // Fixed size arena strings must never be deleted or destroyed.
     kFixedSizeArena = kArenaBit,
   };
 
   TaggedStringPtr() = default;
   explicit constexpr TaggedStringPtr(const GlobalEmptyString* ptr)
       : ptr_(const_cast<void*>(static_cast<const void*>(ptr))) {}
 
   // Sets the value to `p`, tagging the value as being a 'default' value.
   // See documentation for kDefault for more info.
   inline const std::string* SetDefault(const std::string* p) {
     return TagAs(kDefault, const_cast<std::string*>(p));
   }
 
   // Sets the value to `p`, tagging the value as a heap allocated value.
   // Allocated strings are mutable and (as the name implies) owned.
   // `p` must not be null
   inline std::string* SetAllocated(std::string* p) {
     return TagAs(kAllocated, p);
   }
 
   // Sets the value to `p`, tagging the value as a fixed size arena string.
   // See documentation for kFixedSizeArena for more info.
   // `p` must not be null
   inline std::string* SetFixedSizeArena(std::string* p) {
     return TagAs(kFixedSizeArena, p);
   }
 
   // Sets the value to `p`, tagging the value as a mutable arena string.
   // See documentation for kMutableArena for more info.
   // `p` must not be null
   inline std::string* SetMutableArena(std::string* p) {
     return TagAs(kMutableArena, p);
   }
 
   // Returns true if the contents of the current string are fully mutable.
   inline bool IsMutable() const { return as_int() & kMutableBit; }
 
   // Returns true if the current string is an immutable default value.
   inline bool IsDefault() const { return (as_int() & kMask) == kDefault; }
 
   // If the current string is a heap-allocated mutable value, returns a pointer
   // to it.  Returns nullptr otherwise.
   inline std::string* GetIfAllocated() const {
     auto allocated = as_int() ^ kAllocated;
     if (allocated & kMask) return nullptr;
 
     auto ptr = reinterpret_cast<std::string*>(allocated);
     PROTOBUF_ASSUME(ptr != nullptr);
     return ptr;
   }
 
   // Returns true if the current string is an arena allocated value.
   // This means it's either a mutable or fixed size arena string.
   inline bool IsArena() const { return as_int() & kArenaBit; }
 
   // Returns true if the current string is a fixed size arena allocated value.
   inline bool IsFixedSizeArena() const {
     return (as_int() & kMask) == kFixedSizeArena;
   }
 
   // Returns the contained string pointer.
   inline std::string* Get() const {
     return reinterpret_cast<std::string*>(as_int() & ~kMask);
   }
 
   // Returns true if the contained pointer is null, indicating some error.
   // The Null value is only used during parsing for temporary values.
   // A persisted ArenaStringPtr value is never null.
   inline bool IsNull() const { return ptr_ == nullptr; }
 
   // Returns a copy of this instance. In debug builds, the returned value may be
   // a forced copy regardless if the current instance is a compile time default.
   TaggedStringPtr Copy(Arena* arena) const;
 
   // Identical to the above `Copy` function except that in debug builds,
   // `default_value` can be used to substitute an empty default with a
   // hardened copy of the default value.
   TaggedStringPtr Copy(Arena* arena, const LazyString& default_value) const;
 
  private:
   static inline void assert_aligned(const void* p) {
     static_assert(kMask <= alignof(void*), "Pointer underaligned for bit mask");
     static_assert(kMask <= alignof(std::string),
                   "std::string underaligned for bit mask");
     ABSL_DCHECK_EQ(reinterpret_cast<uintptr_t>(p) & kMask, 0UL);
   }
 
   // Creates a heap or arena allocated copy of this instance.
   TaggedStringPtr ForceCopy(Arena* arena) const;
 
   inline std::string* TagAs(Type type, std::string* p) {
     ABSL_DCHECK(p != nullptr);
     assert_aligned(p);
     ptr_ = reinterpret_cast<void*>(reinterpret_cast<uintptr_t>(p) | type);
     return p;
   }
 
   uintptr_t as_int() const { return reinterpret_cast<uintptr_t>(ptr_); }
   void* ptr_;
 };
 
 static_assert(std::is_trivial<TaggedStringPtr>::value,
               "TaggedStringPtr must be trivial");
 
 // This class encapsulates a pointer to a std::string with or without arena
 // owned contents, tagged by the bottom bits of the string pointer. It is a
 // high-level wrapper that almost directly corresponds to the interface required
 // by string fields in generated code. It replaces the old std::string* pointer
 // in such cases.
 //
 // The string pointer is tagged to be either a default, externally owned value,
 // a mutable heap allocated value, or an arena allocated value. The object uses
 // a single global instance of an empty string that is used as the initial
 // default value. Fields that have empty default values directly use this global
 // default. Fields that have non empty default values are supported through
 // lazily initialized default values managed by the LazyString class.
 //
 // Generated code and reflection code both ensure that ptr_ is never null.
 // Because ArenaStringPtr is used in oneof unions, its constructor is a NOP and
 // the field is always manually initialized via method calls.
 //
 // See TaggedStringPtr for more information about the types of string values
 // being held, and the mutable and ownership invariants for each type.
 struct PROTOBUF_EXPORT ArenaStringPtr {
   // Default constructor, leaves current instance uninitialized (does nothing)
   ArenaStringPtr() = default;
 
   // Constexpr constructor, initializes to a constexpr, empty string value.
   constexpr ArenaStringPtr(const GlobalEmptyString* default_value,
                            ConstantInitialized)
       : tagged_ptr_(default_value) {}
 
   // Arena enabled constructor for strings without a default value.
   // Initializes this instance to a constexpr, empty string value, unless debug
   // hardening is enabled, in which case this instance will hold a forced copy.
   explicit ArenaStringPtr(Arena* arena)
       : tagged_ptr_(&fixed_address_empty_string) {
     if (DebugHardenForceCopyDefaultString()) {
       Set(absl::string_view(""), arena);
     }
   }
 
   // Arena enabled constructor for strings with a non-empty default value.
   // Initializes this instance to a constexpr, empty string value, unless debug
   // hardening is enabled, in which case this instance will be forced to hold a
   // forced copy of the value in `default_value`.
   ArenaStringPtr(Arena* arena, const LazyString& default_value)
       : tagged_ptr_(&fixed_address_empty_string) {
     if (DebugHardenForceCopyDefaultString()) {
       Set(absl::string_view(default_value.get()), arena);
     }
   }
 
   // Arena enabled copy constructor for strings without a default value.
   // This instance will be initialized with a copy of the value in `rhs`.
   // If `rhs` holds a default (empty) value, then this instance will also be
   // initialized with the default empty value, unless debug hardening is
   // enabled, in which case this instance will be forced to hold a copy of
   // an empty default value.
   ArenaStringPtr(Arena* arena, const ArenaStringPtr& rhs)
       : tagged_ptr_(rhs.tagged_ptr_.Copy(arena)) {}
 
   // Arena enabled copy constructor for strings with a non-empty default value.
   // This instance will be initialized with a copy of the value in `rhs`.
   // If `rhs` holds a default (empty) value, then this instance will also be
   // initialized with the default empty value, unless debug hardening is
   // enabled, in which case this instance will be forced to hold forced copy
   // of the value in `default_value`.
   ArenaStringPtr(Arena* arena, const ArenaStringPtr& rhs,
                  const LazyString& default_value)
       : tagged_ptr_(rhs.tagged_ptr_.Copy(arena, default_value)) {}
 
   // Called from generated code / reflection runtime only. Resets value to point
   // to a default string pointer, with the semantics that this ArenaStringPtr
   // does not own the pointed-to memory. Disregards initial value of ptr_ (so
   // this is the *ONLY* safe method to call after construction or when
   // reinitializing after becoming the active field in a oneof union).
   inline void InitDefault();
 
   // Similar to `InitDefault` except that it allows the default value to be
   // initialized to an externally owned string. This method is called from
   // parsing code. `str` must not be null and outlive this instance.
   inline void InitExternal(const std::string* str);
 
   // Called from generated code / reflection runtime only. Resets the value of
   // this instances to the heap allocated value in `str`. `str` must not be
   // null. Invokes `arena->Own(str)` to transfer ownership into the arena if
   // `arena` is not null, else, `str` will be owned by ArenaStringPtr. This
   // function should only be used to initialize a ArenaStringPtr or on an
   // instance known to not carry any heap allocated value.
   inline void InitAllocated(std::string* str, Arena* arena);
 
   void Set(absl::string_view value, Arena* arena);
   void Set(std::string&& value, Arena* arena);
   template <typename... OverloadDisambiguator>
   void Set(const std::string& value, Arena* arena);
   void Set(const char* s, Arena* arena);
   void Set(const char* s, size_t n, Arena* arena);
 
   void SetBytes(absl::string_view value, Arena* arena);
   void SetBytes(std::string&& value, Arena* arena);
   template <typename... OverloadDisambiguator>
   void SetBytes(const std::string& value, Arena* arena);
   void SetBytes(const char* s, Arena* arena);
   void SetBytes(const void* p, size_t n, Arena* arena);
 
   template <typename RefWrappedType>
   void Set(std::reference_wrapper<RefWrappedType> const_string_ref,
            ::google::protobuf::Arena* arena) {
     Set(const_string_ref.get(), arena);
   }
 
   // Returns a mutable std::string reference.
   // The version accepting a `LazyString` value is used in the generated code to
   // initialize mutable copies for fields with a non-empty default where the
   // default value is lazily initialized.
   std::string* Mutable(Arena* arena);
   std::string* Mutable(const LazyString& default_value, Arena* arena);
 
   // Gets a mutable pointer with unspecified contents.
   // This function is identical to Mutable(), except it is optimized for the
   // case where the caller is not interested in the current contents. For
   // example, if the current field is not mutable, it will re-initialize the
   // value with an empty string rather than a (non-empty) default value.
   // Likewise, if the current value is a fixed size arena string with contents,
   // it will be initialized into an empty mutable arena string.
   std::string* MutableNoCopy(Arena* arena);
 
   // Basic accessors.
   PROTOBUF_NDEBUG_INLINE const std::string& Get() const {
     // Unconditionally mask away the tag.
     return *tagged_ptr_.Get();
   }
 
   // Returns a pointer to the stored contents for this instance.
   // This method is for internal debugging and tracking purposes only.
   PROTOBUF_NDEBUG_INLINE const std::string* UnsafeGetPointer() const
       ABSL_ATTRIBUTE_RETURNS_NONNULL {
     return tagged_ptr_.Get();
   }
 
   // Release returns a std::string* instance that is heap-allocated and is not
   // Own()'d by any arena. If the field is not set, this returns nullptr. The
   // caller retains ownership. Clears this field back to the default state.
   // Used to implement release_<field>() methods on generated classes.
   [[nodiscard]] std::string* Release();
 
   // Takes a std::string that is heap-allocated, and takes ownership. The
   // std::string's destructor is registered with the arena. Used to implement
   // set_allocated_<field> in generated classes.
   void SetAllocated(std::string* value, Arena* arena);
 
   // Frees storage (if not on an arena).
   void Destroy();
 
   // Clears content, but keeps allocated std::string, to avoid the overhead of
   // heap operations. After this returns, the content (as seen by the user) will
   // always be the empty std::string. Assumes that |default_value| is an empty
   // std::string.
   void ClearToEmpty();
 
   // Clears content, assuming that the current value is not the empty
   // string default.
   void ClearNonDefaultToEmpty();
 
   // Clears content, but keeps allocated std::string if arena != nullptr, to
   // avoid the overhead of heap operations. After this returns, the content
   // (as seen by the user) will always be equal to |default_value|.
   void ClearToDefault(const LazyString& default_value, ::google::protobuf::Arena* arena);
 
   // Swaps internal pointers. Arena-safety semantics: this is guarded by the
   // logic in Swap()/UnsafeArenaSwap() at the message level, so this method is
   // 'unsafe' if called directly.
   PROTOBUF_NDEBUG_INLINE static void InternalSwap(ArenaStringPtr* rhs,
                                                   ArenaStringPtr* lhs,
                                                   Arena* arena);
 
   // Internal setter used only at parse time to directly set a donated string
   // value.
   void UnsafeSetTaggedPointer(TaggedStringPtr value) { tagged_ptr_ = value; }
   // Generated code only! An optimization, in certain cases the generated
   // code is certain we can obtain a std::string with no default checks and
   // tag tests.
   std::string* UnsafeMutablePointer() ABSL_ATTRIBUTE_RETURNS_NONNULL;
 
   // Returns true if this instances holds an immutable default value.
   inline bool IsDefault() const { return tagged_ptr_.IsDefault(); }
 
  private:
   template <typename... Args>
   inline std::string* NewString(Arena* arena, Args&&... args) {
     if (arena == nullptr) {
       auto* s = new std::string(std::forward<Args>(args)...);
       return tagged_ptr_.SetAllocated(s);
     } else {
       auto* s = Arena::Create<std::string>(arena, std::forward<Args>(args)...);
       return tagged_ptr_.SetMutableArena(s);
     }
   }
 
   TaggedStringPtr tagged_ptr_;
 
   bool IsFixedSizeArena() const { return false; }
 
   // Swaps tagged pointer without debug hardening. This is to allow python
   // protobuf to maintain pointer stability even in DEBUG builds.
   PROTOBUF_NDEBUG_INLINE static void UnsafeShallowSwap(ArenaStringPtr* rhs,
                                                        ArenaStringPtr* lhs) {
     std::swap(lhs->tagged_ptr_, rhs->tagged_ptr_);
   }
 
   friend class ::google::protobuf::internal::SwapFieldHelper;
   friend class TcParser;
 
   // Slow paths.
 
   // MutableSlow requires that !IsString() || IsDefault
   // Variadic to support 0 args for empty default and 1 arg for LazyString.
   template <typename... Lazy>
   std::string* MutableSlow(::google::protobuf::Arena* arena, const Lazy&... lazy_default);
 
   friend class EpsCopyInputStream;
 };
 
 inline TaggedStringPtr TaggedStringPtr::Copy(Arena* arena) const {
   if (DebugHardenForceCopyDefaultString()) {
     // Harden by forcing an allocated string value.
     return IsNull() ? *this : ForceCopy(arena);
   }
   return IsDefault() ? *this : ForceCopy(arena);
 }
 
 inline TaggedStringPtr TaggedStringPtr::Copy(
     Arena* arena, const LazyString& default_value) const {
   if (DebugHardenForceCopyDefaultString()) {
     // Harden by forcing an allocated string value.
     TaggedStringPtr hardened(*this);
     if (IsDefault()) {
       hardened.SetDefault(&default_value.get());
     }
     return hardened.ForceCopy(arena);
   }
   return IsDefault() ? *this : ForceCopy(arena);
 }
 
 inline void ArenaStringPtr::InitDefault() {
   tagged_ptr_ = TaggedStringPtr(&fixed_address_empty_string);
 }
 
 inline void ArenaStringPtr::InitExternal(const std::string* str) {
   tagged_ptr_.SetDefault(str);
 }
 
 inline void ArenaStringPtr::InitAllocated(std::string* str, Arena* arena) {
   if (arena != nullptr) {
     tagged_ptr_.SetMutableArena(str);
     arena->Own(str);
   } else {
     tagged_ptr_.SetAllocated(str);
   }
 }
 
 inline void ArenaStringPtr::Set(const char* s, Arena* arena) {
   Set(absl::string_view{s}, arena);
 }
 
 inline void ArenaStringPtr::Set(const char* s, size_t n, Arena* arena) {
   Set(absl::string_view{s, n}, arena);
 }
 
 inline void ArenaStringPtr::SetBytes(absl::string_view value, Arena* arena) {
   Set(value, arena);
 }
 
 template <>
 PROTOBUF_EXPORT void ArenaStringPtr::Set(const std::string& value,
                                          Arena* arena);
 
 template <>
 inline void ArenaStringPtr::SetBytes(const std::string& value, Arena* arena) {
   Set(value, arena);
 }
 
 inline void ArenaStringPtr::SetBytes(std::string&& value, Arena* arena) {
   Set(std::move(value), arena);
 }
 
 inline void ArenaStringPtr::SetBytes(const char* s, Arena* arena) {
   Set(s, arena);
 }
 
 inline void ArenaStringPtr::SetBytes(const void* p, size_t n, Arena* arena) {
   Set(absl::string_view{static_cast<const char*>(p), n}, arena);
 }
 
 PROTOBUF_NDEBUG_INLINE void ArenaStringPtr::InternalSwap(ArenaStringPtr* rhs,
                                                          ArenaStringPtr* lhs,
                                                          Arena* arena) {
   // Silence unused variable warnings in release buildls.
   (void)arena;
   std::swap(lhs->tagged_ptr_, rhs->tagged_ptr_);
   if (internal::DebugHardenForceCopyInSwap()) {
     for (auto* p : {lhs, rhs}) {
       if (p->IsDefault()) continue;
       std::string* old_value = p->tagged_ptr_.Get();
       std::string* new_value =
           p->IsFixedSizeArena()
               ? Arena::Create<std::string>(arena, *old_value)
               : Arena::Create<std::string>(arena, std::move(*old_value));
       if (arena == nullptr) {
         delete old_value;
         p->tagged_ptr_.SetAllocated(new_value);
       } else {
         p->tagged_ptr_.SetMutableArena(new_value);
       }
     }
   }
 }
 
 inline void ArenaStringPtr::ClearNonDefaultToEmpty() {
   // Unconditionally mask away the tag.
   ABSL_DCHECK(!tagged_ptr_.IsDefault());
   tagged_ptr_.Get()->clear();
 }
 
 inline std::string* ArenaStringPtr::UnsafeMutablePointer() {
   ABSL_DCHECK(tagged_ptr_.IsMutable());
   ABSL_DCHECK(tagged_ptr_.Get() != nullptr);
   return tagged_ptr_.Get();
 }
 
 
 }  // namespace internal
 }  // namespace protobuf
 }  // namespace google
 
 #include "google/protobuf/port_undef.inc"
 
 #endif  // GOOGLE_PROTOBUF_ARENASTRING_H__

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