// Protocol Buffers - Google's data interchange format

// Copyright 2008 Google Inc.  All rights reserved.

// https://developers.google.com/protocol-buffers/

//

// Redistribution and use in source and binary forms, with or without

// modification, are permitted provided that the following conditions are

// met:

//

//     * Redistributions of source code must retain the above copyright

// notice, this list of conditions and the following disclaimer.

//     * Redistributions in binary form must reproduce the above

// copyright notice, this list of conditions and the following disclaimer

// in the documentation and/or other materials provided with the

// distribution.

//     * Neither the name of Google Inc. nor the names of its

// contributors may be used to endorse or promote products derived from

// this software without specific prior written permission.

//

// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS

// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT

// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR

// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT

// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,

// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT

// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,

// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY

// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT

// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE

// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

#ifndef GOOGLE_PROTOBUF_ARENASTRING_H__

#define GOOGLE_PROTOBUF_ARENASTRING_H__

#include <string>

#include <type_traits>

#include <utility>

#include <google/protobuf/stubs/logging.h>

#include <google/protobuf/stubs/common.h>

#include <google/protobuf/arena.h>

#include <google/protobuf/port.h>

#include <google/protobuf/port_def.inc>

#ifdef SWIG

#error "You cannot SWIG proto headers"

#endif

namespace google {

namespace protobuf {

namespace internal {

// 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 (PROTOBUF_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;

};

template <typename T>

class TaggedPtr {

 public:

  TaggedPtr() = default;

  explicit constexpr TaggedPtr(const std::string* ptr)

      : ptr_(const_cast<std::string*>(ptr)) {}

  void SetTagged(T* p) {

    Set(p);

    ptr_ = reinterpret_cast<void*>(as_int() | 1);

  }

  void Set(T* p) { ptr_ = p; }

  T* Get() const { return reinterpret_cast<T*>(as_int() & -2); }

  bool IsTagged() const { return as_int() & 1; }

  // Returned value is only safe to dereference if IsTagged() == false.

  // It is safe to compare.

  T* UnsafeGet() const { return static_cast<T*>(ptr_); }

  bool IsNull() { return ptr_ == nullptr; }

 private:

  uintptr_t as_int() const { return reinterpret_cast<uintptr_t>(ptr_); }

  void* ptr_;

};

static_assert(std::is_trivial<TaggedPtr<std::string>>::value,

              "TaggedPtr must be trivial");

// This class encapsulates a pointer to a std::string with or without a donated

// buffer, tagged by bottom bit. 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 object has different but similar code paths for when the default value is

// the empty string and when it is a non-empty string.

// The empty string is handled different throughout the library and there is a

// single global instance of it we can share.

//

// For fields with an empty string default value, there are three distinct

// states:

//

// - Pointer set to 'String' tag (LSB is 0), equal to

//   &GetEmptyStringAlreadyInited(): field is set to its default value. Points

//   to a true std::string*, but we do not own that std::string* (it's a

//   globally shared instance).

//

// - Pointer set to 'String' tag (LSB is 0), but not equal to the global empty

//   string: field points to a true std::string* instance that we own. This

//   instance is either on the heap or on the arena (i.e. registered on

//   free()/destructor-call list) as appropriate.

//

// - Pointer set to 'DonatedString' tag (LSB is 1): points to a std::string

//   instance with a buffer on the arena (arena != NULL, always, in this case).

//

// For fields with a non-empty string default value, there are three distinct

// states:

//

// - Pointer set to 'String' tag (LSB is 0), equal to `nullptr`:

//   Field is in "default" mode and does not point to any actual instance.

//   Methods that might need to create an instance of the object will pass a

//   `const LazyString&` for it.

//

// - Pointer set to 'String' tag (LSB is 0), but not equal to `nullptr`:

//   field points to a true std::string* instance that we own. This instance is

//   either on the heap or on the arena (i.e. registered on

//   free()/destructor-call list) as appropriate.

//

// - Pointer set to 'DonatedString' tag (LSB is 1): points to a std::string

//   instance with a buffer on the arena (arena != NULL, always, in this case).

//

// Generated code and reflection code both ensure that ptr_ is never null for

// fields with an empty default.

// Because ArenaStringPtr is used in oneof unions, its constructor is a NOP and

// so the field is always manually initialized via method calls.

//

// Side-note: why pass information about the default on every API call? Because

// we don't want to hold it in a member variable, or else this would go into

// every proto message instance. This would be a huge waste of space, since the

// default instance pointer is typically a global (static class field). We want

// the generated code to be as efficient as possible, and if we take

// the default value information as a parameter that's in practice taken from a

// static class field, and compare ptr_ to the default value, we end up with a

// single "cmp %reg, GLOBAL" in the resulting machine code. (Note that this also

// requires the String tag to be 0 so we can avoid the mask before comparing.)

struct PROTOBUF_EXPORT ArenaStringPtr {

  ArenaStringPtr() = default;

  explicit constexpr ArenaStringPtr(const std::string* default_value)

      : tagged_ptr_(default_value) {}

  // Some methods below are overloaded on a `default_value` and on tags.

  // The tagged overloads help reduce code size in the callers in generated

  // code, while the `default_value` overloads are useful from reflection.

  // By-value empty struct arguments are elided in the ABI.

  struct EmptyDefault {};

  struct NonEmptyDefault {};

  void Set(const std::string* default_value, ConstStringParam value,

           ::google::protobuf::Arena* arena);

  void Set(const std::string* default_value, std::string&& value,

           ::google::protobuf::Arena* arena);

  void Set(EmptyDefault, ConstStringParam value, ::google::protobuf::Arena* arena);

  void Set(EmptyDefault, std::string&& value, ::google::protobuf::Arena* arena);

  void Set(NonEmptyDefault, ConstStringParam value, ::google::protobuf::Arena* arena);

  void Set(NonEmptyDefault, std::string&& value, ::google::protobuf::Arena* arena);

  // Basic accessors.

  const std::string& Get() const PROTOBUF_ALWAYS_INLINE {

    // Unconditionally mask away the tag.

    return *tagged_ptr_.Get();

  }

  const std::string* GetPointer() const PROTOBUF_ALWAYS_INLINE {

    // Unconditionally mask away the tag.

    return tagged_ptr_.Get();

  }

  // For fields with an empty default value.

  std::string* Mutable(EmptyDefault, ::google::protobuf::Arena* arena);

  // For fields with a non-empty default value.

  std::string* Mutable(const LazyString& default_value, ::google::protobuf::Arena* arena);

  // 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 NULL. The

  // caller retains ownership. Clears this field back to NULL state. Used to

  // implement release_<field>() methods on generated classes.

  std::string* Release(const std::string* default_value,

                       ::google::protobuf::Arena* arena);

  std::string* ReleaseNonDefault(const std::string* default_value,

                                 ::google::protobuf::Arena* arena);

  // 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(const std::string* default_value, std::string* 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.

  inline void Swap(ArenaStringPtr* other, const std::string* default_value,

                   Arena* arena) PROTOBUF_ALWAYS_INLINE;

  // Frees storage (if not on an arena).

  void Destroy(const std::string* default_value, ::google::protobuf::Arena* arena);

  void Destroy(EmptyDefault, ::google::protobuf::Arena* arena);

  void Destroy(NonEmptyDefault, ::google::protobuf::Arena* arena);

  // 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 != NULL, 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);

  // 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 UnsafeSetDefault(const std::string* default_value);

  // Returns a mutable pointer, but doesn't initialize the string to the

  // default value.

  std::string* MutableNoArenaNoDefault(const std::string* default_value);

  // Get a mutable pointer with unspecified contents.

  // Similar to `MutableNoArenaNoDefault`, but also handles the arena case.

  // If the value was donated, the contents are discarded.

  std::string* MutableNoCopy(const std::string* default_value,

                             ::google::protobuf::Arena* arena);

  // Destroy the string. Assumes `arena == nullptr`.

  void DestroyNoArena(const std::string* default_value);

  // Internal setter used only at parse time to directly set a donated string

  // value.

  void UnsafeSetTaggedPointer(TaggedPtr<std::string> 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() PROTOBUF_RETURNS_NONNULL;

  inline bool IsDefault(const std::string* default_value) const {

    // Relies on the fact that kPtrTagString == 0, so if IsString(), ptr_ is the

    // actual std::string pointer (and if !IsString(), ptr_ will never be equal

    // to any aligned |default_value| pointer). The key is that we want to avoid

    // masking in the fastpath const-pointer Get() case for non-arena code.

    return tagged_ptr_.UnsafeGet() == default_value;

  }

 private:

  TaggedPtr<std::string> tagged_ptr_;

  bool IsDonatedString() const { return false; }

  // Slow paths.

  // MutableSlow requires that !IsString() || IsDefault

  // Variadic to support 0 args for EmptyDefault and 1 arg for LazyString.

  template <typename... Lazy>

  std::string* MutableSlow(::google::protobuf::Arena* arena, const Lazy&... lazy_default);

};

inline void ArenaStringPtr::UnsafeSetDefault(const std::string* value) {

  tagged_ptr_.Set(const_cast<std::string*>(value));

}

inline void ArenaStringPtr::Swap(ArenaStringPtr* other,

                                 const std::string* default_value,

                                 Arena* arena) {

#ifndef NDEBUG

  // For debug builds, we swap the contents of the string, rather than the

  // std::string instances themselves.  This invalidates previously taken const

  // references that are (per our documentation) invalidated by calling Swap()

  // on the message.

  //

  // If both strings are the default_value, swapping is uninteresting.

  // Otherwise, we use ArenaStringPtr::Mutable() to access the std::string, to

  // ensure that we do not try to mutate default_value itself.

  if (IsDefault(default_value) && other->IsDefault(default_value)) {

    return;

  }

  if (default_value == nullptr) {

    // If we have non-empty default, then `default_value` is null and we can't

    // call Mutable the same way. Just do the regular swap.

    std::swap(tagged_ptr_, other->tagged_ptr_);

  } else {

    std::string* this_ptr = Mutable(EmptyDefault{}, arena);

    std::string* other_ptr = other->Mutable(EmptyDefault{}, arena);

    this_ptr->swap(*other_ptr);

  }

#else

  std::swap(tagged_ptr_, other->tagged_ptr_);

#endif

}

inline void ArenaStringPtr::ClearNonDefaultToEmpty() {

  // Unconditionally mask away the tag.

  tagged_ptr_.Get()->clear();

}

inline std::string* ArenaStringPtr::MutableNoArenaNoDefault(

    const std::string* default_value) {

  // VERY IMPORTANT for performance and code size: this will reduce to a member

  // variable load, a pointer check (against |default_value|, in practice a

  // static global) and a branch to the slowpath (which calls operator new and

  // the ctor). DO NOT add any tagged-pointer operations here.

  if (IsDefault(default_value)) {

    std::string* new_string = new std::string();

    tagged_ptr_.Set(new_string);

    return new_string;

  } else {

    return UnsafeMutablePointer();

  }

}

inline void ArenaStringPtr::DestroyNoArena(const std::string* default_value) {

  if (!IsDefault(default_value)) {

    delete UnsafeMutablePointer();

  }

}

inline std::string* ArenaStringPtr::UnsafeMutablePointer() {

  GOOGLE_DCHECK(!tagged_ptr_.IsTagged());

  GOOGLE_DCHECK(tagged_ptr_.UnsafeGet() != nullptr);

  return tagged_ptr_.UnsafeGet();

}

}  // namespace internal

}  // namespace protobuf

}  // namespace google

#include <google/protobuf/port_undef.inc>

#endif  // GOOGLE_PROTOBUF_ARENASTRING_H__