node_file.cc

// Copyright Joyent, Inc. and other Node contributors.
//
// Permission is hereby granted, free of charge, to any person obtaining a
// copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to permit
// persons to whom the Software is furnished to do so, subject to the
// following conditions:
//
// The above copyright notice and this permission notice shall be included
// in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
// USE OR OTHER DEALINGS IN THE SOFTWARE.
#include "node_file.h"  // NOLINT(build/include_inline)
#include "node_file-inl.h"
#include "aliased_buffer.h"
#include "memory_tracker-inl.h"
#include "node_buffer.h"
#include "node_process.h"
#include "node_stat_watcher.h"
#include "util-inl.h"

#include "tracing/trace_event.h"

#include "req_wrap-inl.h"
#include "stream_base-inl.h"
#include "string_bytes.h"

#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <cstring>
#include <cerrno>
#include <climits>

#if defined(__MINGW32__) || defined(_MSC_VER)
# include <io.h>
#endif

#include <memory>

namespace node {

namespace fs {

using v8::Array;
using v8::BigInt;
using v8::Boolean;
using v8::Context;
using v8::EscapableHandleScope;
using v8::Function;
using v8::FunctionCallbackInfo;
using v8::FunctionTemplate;
using v8::HandleScope;
using v8::Int32;
using v8::Integer;
using v8::Isolate;
using v8::Local;
using v8::MaybeLocal;
using v8::Number;
using v8::Object;
using v8::ObjectTemplate;
using v8::Promise;
using v8::String;
using v8::Symbol;
using v8::Uint32;
using v8::Undefined;
using v8::Value;

#ifndef S_ISDIR
# define S_ISDIR(mode)  (((mode) & S_IFMT) == S_IFDIR)
#endif

#ifdef __POSIX__
constexpr char kPathSeparator = '/';
#else
const char* const kPathSeparator = "\\/";
#endif

std::string Basename(const std::string& str, const std::string& extension) {
  // Remove everything leading up to and including the final path separator.
  std::string::size_type pos = str.find_last_of(kPathSeparator);

  // Starting index for the resulting string
  std::size_t start_pos = 0;
  // String size to return
  std::size_t str_size = str.size();
  if (pos != std::string::npos) {
    start_pos = pos + 1;
    str_size -= start_pos;
  }

  // Strip away the extension, if any.
  if (str_size >= extension.size() &&
      str.compare(str.size() - extension.size(),
        extension.size(), extension) == 0) {
    str_size -= extension.size();
  }

  return str.substr(start_pos, str_size);
}

inline int64_t GetOffset(Local<Value> value) {
  return IsSafeJsInt(value) ? value.As<Integer>()->Value() : -1;
}

#define TRACE_NAME(name) "fs.sync." #name
#define GET_TRACE_ENABLED                                                  \
  (*TRACE_EVENT_API_GET_CATEGORY_GROUP_ENABLED                             \
  (TRACING_CATEGORY_NODE2(fs, sync)) != 0)
#define FS_SYNC_TRACE_BEGIN(syscall, ...)                                  \
  if (GET_TRACE_ENABLED)                                                   \
  TRACE_EVENT_BEGIN(TRACING_CATEGORY_NODE2(fs, sync), TRACE_NAME(syscall), \
  ##__VA_ARGS__);
#define FS_SYNC_TRACE_END(syscall, ...)                                    \
  if (GET_TRACE_ENABLED)                                                   \
  TRACE_EVENT_END(TRACING_CATEGORY_NODE2(fs, sync), TRACE_NAME(syscall),   \
  ##__VA_ARGS__);

// We sometimes need to convert a C++ lambda function to a raw C-style function.
// This is helpful, because ReqWrap::Dispatch() does not recognize lambda
// functions, and thus does not wrap them properly.
typedef void(*uv_fs_callback_t)(uv_fs_t*);


void FSContinuationData::MemoryInfo(MemoryTracker* tracker) const {
  tracker->TrackField("paths", paths_);
}

FileHandleReadWrap::~FileHandleReadWrap() = default;

FSReqBase::~FSReqBase() = default;

void FSReqBase::MemoryInfo(MemoryTracker* tracker) const {
  tracker->TrackField("continuation_data", continuation_data_);
}

// The FileHandle object wraps a file descriptor and will close it on garbage
// collection if necessary. If that happens, a process warning will be
// emitted (or a fatal exception will occur if the fd cannot be closed.)
FileHandle::FileHandle(BindingData* binding_data,
                       Local<Object> obj, int fd)
    : AsyncWrap(binding_data->env(), obj, AsyncWrap::PROVIDER_FILEHANDLE),
      StreamBase(env()),
      fd_(fd),
      binding_data_(binding_data) {
  MakeWeak();
  StreamBase::AttachToObject(GetObject());
}

FileHandle* FileHandle::New(BindingData* binding_data,
                            int fd, Local<Object> obj) {
  Environment* env = binding_data->env();
  if (obj.IsEmpty() && !env->fd_constructor_template()
                            ->NewInstance(env->context())
                            .ToLocal(&obj)) {
    return nullptr;
  }
  return new FileHandle(binding_data, obj, fd);
}

void FileHandle::New(const FunctionCallbackInfo<Value>& args) {
  BindingData* binding_data = Environment::GetBindingData<BindingData>(args);
  Environment* env = binding_data->env();
  CHECK(args.IsConstructCall());
  CHECK(args[0]->IsInt32());

  FileHandle* handle =
      FileHandle::New(binding_data, args[0].As<Int32>()->Value(), args.This());
  if (handle == nullptr) return;
  if (args[1]->IsNumber())
    handle->read_offset_ = args[1]->IntegerValue(env->context()).FromJust();
  if (args[2]->IsNumber())
    handle->read_length_ = args[2]->IntegerValue(env->context()).FromJust();
}

FileHandle::~FileHandle() {
  CHECK(!closing_);  // We should not be deleting while explicitly closing!
  Close();           // Close synchronously and emit warning
  CHECK(closed_);    // We have to be closed at the point
}

int FileHandle::DoWrite(WriteWrap* w,
                        uv_buf_t* bufs,
                        size_t count,
                        uv_stream_t* send_handle) {
  return UV_ENOSYS;  // Not implemented (yet).
}

void FileHandle::MemoryInfo(MemoryTracker* tracker) const {
  tracker->TrackField("current_read", current_read_);
}

FileHandle::TransferMode FileHandle::GetTransferMode() const {
  return reading_ || closing_ || closed_ ?
      TransferMode::kUntransferable : TransferMode::kTransferable;
}

std::unique_ptr<worker::TransferData> FileHandle::TransferForMessaging() {
  CHECK_NE(GetTransferMode(), TransferMode::kUntransferable);
  auto ret = std::make_unique<TransferData>(fd_);
  closed_ = true;
  return ret;
}

FileHandle::TransferData::TransferData(int fd) : fd_(fd) {}

FileHandle::TransferData::~TransferData() {
  if (fd_ > 0) {
    uv_fs_t close_req;
    CHECK_EQ(0, uv_fs_close(nullptr, &close_req, fd_, nullptr));
    uv_fs_req_cleanup(&close_req);
  }
}

BaseObjectPtr<BaseObject> FileHandle::TransferData::Deserialize(
    Environment* env,
    v8::Local<v8::Context> context,
    std::unique_ptr<worker::TransferData> self) {
  BindingData* bd = Environment::GetBindingData<BindingData>(context);
  if (bd == nullptr) return {};

  int fd = fd_;
  fd_ = -1;
  return BaseObjectPtr<BaseObject> { FileHandle::New(bd, fd) };
}

// Close the file descriptor if it hasn't already been closed. A process
// warning will be emitted using a SetImmediate to avoid calling back to
// JS during GC. If closing the fd fails at this point, a fatal exception
// will crash the process immediately.
inline void FileHandle::Close() {
  if (closed_) return;
  uv_fs_t req;
  int ret = uv_fs_close(env()->event_loop(), &req, fd_, nullptr);
  uv_fs_req_cleanup(&req);

  struct err_detail { int ret; int fd; };

  err_detail detail { ret, fd_ };

  AfterClose();

  if (ret < 0) {
    // Do not unref this
    env()->SetImmediate([detail](Environment* env) {
      char msg[70];
      snprintf(msg, arraysize(msg),
              "Closing file descriptor %d on garbage collection failed",
              detail.fd);
      // This exception will end up being fatal for the process because
      // it is being thrown from within the SetImmediate handler and
      // there is no JS stack to bubble it to. In other words, tearing
      // down the process is the only reasonable thing we can do here.
      HandleScope handle_scope(env->isolate());
      env->ThrowUVException(detail.ret, "close", msg);
    });
    return;
  }

  // If the close was successful, we still want to emit a process warning
  // to notify that the file descriptor was gc'd. We want to be noisy about
  // this because not explicitly closing the FileHandle is a bug.

  env()->SetImmediate([detail](Environment* env) {
    ProcessEmitWarning(env,
                       "Closing file descriptor %d on garbage collection",
                       detail.fd);
    if (env->filehandle_close_warning()) {
      env->set_filehandle_close_warning(false);
      ProcessEmitDeprecationWarning(
          env,
          "Closing a FileHandle object on garbage collection is deprecated. "
          "Please close FileHandle objects explicitly using "
          "FileHandle.prototype.close(). In the future, an error will be "
          "thrown if a file descriptor is closed during garbage collection.",
          "DEP0137").IsNothing();
    }
  }, CallbackFlags::kUnrefed);
}

void FileHandle::CloseReq::Resolve() {
  Isolate* isolate = env()->isolate();
  HandleScope scope(isolate);
  Context::Scope context_scope(env()->context());
  InternalCallbackScope callback_scope(this);
  Local<Promise> promise = promise_.Get(isolate);
  Local<Promise::Resolver> resolver = promise.As<Promise::Resolver>();
  resolver->Resolve(env()->context(), Undefined(isolate)).Check();
}

void FileHandle::CloseReq::Reject(Local<Value> reason) {
  Isolate* isolate = env()->isolate();
  HandleScope scope(isolate);
  Context::Scope context_scope(env()->context());
  InternalCallbackScope callback_scope(this);
  Local<Promise> promise = promise_.Get(isolate);
  Local<Promise::Resolver> resolver = promise.As<Promise::Resolver>();
  resolver->Reject(env()->context(), reason).Check();
}

FileHandle* FileHandle::CloseReq::file_handle() {
  Isolate* isolate = env()->isolate();
  HandleScope scope(isolate);
  Local<Value> val = ref_.Get(isolate);
  Local<Object> obj = val.As<Object>();
  return Unwrap<FileHandle>(obj);
}

FileHandle::CloseReq::CloseReq(Environment* env,
                               Local<Object> obj,
                               Local<Promise> promise,
                               Local<Value> ref)
  : ReqWrap(env, obj, AsyncWrap::PROVIDER_FILEHANDLECLOSEREQ) {
  promise_.Reset(env->isolate(), promise);
  ref_.Reset(env->isolate(), ref);
}

FileHandle::CloseReq::~CloseReq() {
  uv_fs_req_cleanup(req());
  promise_.Reset();
  ref_.Reset();
}

void FileHandle::CloseReq::MemoryInfo(MemoryTracker* tracker) const {
  tracker->TrackField("promise", promise_);
  tracker->TrackField("ref", ref_);
}



// Closes this FileHandle asynchronously and returns a Promise that will be
// resolved when the callback is invoked, or rejects with a UVException if
// there was a problem closing the fd. This is the preferred mechanism for
// closing the FD object even tho the object will attempt to close
// automatically on gc.
MaybeLocal<Promise> FileHandle::ClosePromise() {
  Isolate* isolate = env()->isolate();
  EscapableHandleScope scope(isolate);
  Local<Context> context = env()->context();
  auto maybe_resolver = Promise::Resolver::New(context);
  CHECK(!maybe_resolver.IsEmpty());
  Local<Promise::Resolver> resolver = maybe_resolver.ToLocalChecked();
  Local<Promise> promise = resolver.As<Promise>();
  CHECK(!reading_);
  if (!closed_ && !closing_) {
    closing_ = true;
    Local<Object> close_req_obj;
    if (!env()
             ->fdclose_constructor_template()
             ->NewInstance(env()->context())
             .ToLocal(&close_req_obj)) {
      return MaybeLocal<Promise>();
    }
    CloseReq* req = new CloseReq(env(), close_req_obj, promise, object());
    auto AfterClose = uv_fs_callback_t{[](uv_fs_t* req) {
      std::unique_ptr<CloseReq> close(CloseReq::from_req(req));
      CHECK_NOT_NULL(close);
      close->file_handle()->AfterClose();
      Isolate* isolate = close->env()->isolate();
      if (req->result < 0) {
        HandleScope handle_scope(isolate);
        close->Reject(
            UVException(isolate, static_cast<int>(req->result), "close"));
      } else {
        close->Resolve();
      }
    }};
    int ret = req->Dispatch(uv_fs_close, fd_, AfterClose);
    if (ret < 0) {
      req->Reject(UVException(isolate, ret, "close"));
      delete req;
    }
  } else {
    // Already closed. Just reject the promise immediately
    resolver->Reject(context, UVException(isolate, UV_EBADF, "close"))
        .Check();
  }
  return scope.Escape(promise);
}

void FileHandle::Close(const FunctionCallbackInfo<Value>& args) {
  FileHandle* fd;
  ASSIGN_OR_RETURN_UNWRAP(&fd, args.Holder());
  Local<Promise> ret;
  if (!fd->ClosePromise().ToLocal(&ret)) return;
  args.GetReturnValue().Set(ret);
}


void FileHandle::ReleaseFD(const FunctionCallbackInfo<Value>& args) {
  FileHandle* fd;
  ASSIGN_OR_RETURN_UNWRAP(&fd, args.Holder());
  // Just act as if this FileHandle has been closed.
  fd->AfterClose();
}


void FileHandle::AfterClose() {
  closing_ = false;
  closed_ = true;
  fd_ = -1;
  if (reading_ && !persistent().IsEmpty())
    EmitRead(UV_EOF);
}

void FileHandleReadWrap::MemoryInfo(MemoryTracker* tracker) const {
  tracker->TrackField("buffer", buffer_);
  tracker->TrackField("file_handle", this->file_handle_);
}

FileHandleReadWrap::FileHandleReadWrap(FileHandle* handle, Local<Object> obj)
  : ReqWrap(handle->env(), obj, AsyncWrap::PROVIDER_FSREQCALLBACK),
    file_handle_(handle) {}

int FileHandle::ReadStart() {
  if (!IsAlive() || IsClosing())
    return UV_EOF;

  reading_ = true;

  if (current_read_)
    return 0;

  BaseObjectPtr<FileHandleReadWrap> read_wrap;

  if (read_length_ == 0) {
    EmitRead(UV_EOF);
    return 0;
  }

  {
    // Create a new FileHandleReadWrap or re-use one.
    // Either way, we need these two scopes for AsyncReset() or otherwise
    // for creating the new instance.
    HandleScope handle_scope(env()->isolate());
    AsyncHooks::DefaultTriggerAsyncIdScope trigger_scope(this);

    auto& freelist = binding_data_->file_handle_read_wrap_freelist;
    if (freelist.size() > 0) {
      read_wrap = std::move(freelist.back());
      freelist.pop_back();
      // Use a fresh async resource.
      // Lifetime is ensured via AsyncWrap::resource_.
      Local<Object> resource = Object::New(env()->isolate());
      USE(resource->Set(
          env()->context(), env()->handle_string(), read_wrap->object()));
      read_wrap->AsyncReset(resource);
      read_wrap->file_handle_ = this;
    } else {
      Local<Object> wrap_obj;
      if (!env()
               ->filehandlereadwrap_template()
               ->NewInstance(env()->context())
               .ToLocal(&wrap_obj)) {
        return UV_EBUSY;
      }
      read_wrap = MakeDetachedBaseObject<FileHandleReadWrap>(this, wrap_obj);
    }
  }
  int64_t recommended_read = 65536;
  if (read_length_ >= 0 && read_length_ <= recommended_read)
    recommended_read = read_length_;

  read_wrap->buffer_ = EmitAlloc(recommended_read);

  current_read_ = std::move(read_wrap);

  current_read_->Dispatch(uv_fs_read,
                          fd_,
                          &current_read_->buffer_,
                          1,
                          read_offset_,
                          uv_fs_callback_t{[](uv_fs_t* req) {
    FileHandle* handle;
    {
      FileHandleReadWrap* req_wrap = FileHandleReadWrap::from_req(req);
      handle = req_wrap->file_handle_;
      CHECK_EQ(handle->current_read_.get(), req_wrap);
    }

    // ReadStart() checks whether current_read_ is set to determine whether
    // a read is in progress. Moving it into a local variable makes sure that
    // the ReadStart() call below doesn't think we're still actively reading.
    BaseObjectPtr<FileHandleReadWrap> read_wrap =
        std::move(handle->current_read_);

    ssize_t result = req->result;
    uv_buf_t buffer = read_wrap->buffer_;

    uv_fs_req_cleanup(req);

    // Push the read wrap back to the freelist, or let it be destroyed
    // once we’re exiting the current scope.
    constexpr size_t kWantedFreelistFill = 100;
    auto& freelist = handle->binding_data_->file_handle_read_wrap_freelist;
    if (freelist.size() < kWantedFreelistFill) {
      read_wrap->Reset();
      freelist.emplace_back(std::move(read_wrap));
    }

    if (result >= 0) {
      // Read at most as many bytes as we originally planned to.
      if (handle->read_length_ >= 0 && handle->read_length_ < result)
        result = handle->read_length_;

      // If we read data and we have an expected length, decrease it by
      // how much we have read.
      if (handle->read_length_ >= 0)
        handle->read_length_ -= result;

      // If we have an offset, increase it by how much we have read.
      if (handle->read_offset_ >= 0)
        handle->read_offset_ += result;
    }

    // Reading 0 bytes from a file always means EOF, or that we reached
    // the end of the requested range.
    if (result == 0)
      result = UV_EOF;

    handle->EmitRead(result, buffer);

    // Start over, if EmitRead() didn’t tell us to stop.
    if (handle->reading_)
      handle->ReadStart();
  }});

  return 0;
}

int FileHandle::ReadStop() {
  reading_ = false;
  return 0;
}

typedef SimpleShutdownWrap<ReqWrap<uv_fs_t>> FileHandleCloseWrap;

ShutdownWrap* FileHandle::CreateShutdownWrap(Local<Object> object) {
  return new FileHandleCloseWrap(this, object);
}

int FileHandle::DoShutdown(ShutdownWrap* req_wrap) {
  FileHandleCloseWrap* wrap = static_cast<FileHandleCloseWrap*>(req_wrap);
  closing_ = true;
  wrap->Dispatch(uv_fs_close, fd_, uv_fs_callback_t{[](uv_fs_t* req) {
    FileHandleCloseWrap* wrap = static_cast<FileHandleCloseWrap*>(
        FileHandleCloseWrap::from_req(req));
    FileHandle* handle = static_cast<FileHandle*>(wrap->stream());
    handle->AfterClose();

    int result = static_cast<int>(req->result);
    uv_fs_req_cleanup(req);
    wrap->Done(result);
  }});

  return 0;
}


void FSReqCallback::Reject(Local<Value> reject) {
  MakeCallback(env()->oncomplete_string(), 1, &reject);
}

void FSReqCallback::ResolveStat(const uv_stat_t* stat) {
  Resolve(FillGlobalStatsArray(binding_data(), use_bigint(), stat));
}

void FSReqCallback::Resolve(Local<Value> value) {
  Local<Value> argv[2] {
    Null(env()->isolate()),
    value
  };
  MakeCallback(env()->oncomplete_string(),
               value->IsUndefined() ? 1 : arraysize(argv),
               argv);
}

void FSReqCallback::SetReturnValue(const FunctionCallbackInfo<Value>& args) {
  args.GetReturnValue().SetUndefined();
}

void NewFSReqCallback(const FunctionCallbackInfo<Value>& args) {
  CHECK(args.IsConstructCall());
  BindingData* binding_data = Environment::GetBindingData<BindingData>(args);
  new FSReqCallback(binding_data, args.This(), args[0]->IsTrue());
}

FSReqAfterScope::FSReqAfterScope(FSReqBase* wrap, uv_fs_t* req)
    : wrap_(wrap),
      req_(req),
      handle_scope_(wrap->env()->isolate()),
      context_scope_(wrap->env()->context()) {
  CHECK_EQ(wrap_->req(), req);
}

FSReqAfterScope::~FSReqAfterScope() {
  Clear();
}

void FSReqAfterScope::Clear() {
  if (!wrap_) return;

  uv_fs_req_cleanup(wrap_->req());
  wrap_->Detach();
  wrap_.reset();
}

// TODO(joyeecheung): create a normal context object, and
// construct the actual errors in the JS land using the context.
// The context should include fds for some fs APIs, currently they are
// missing in the error messages. The path, dest, syscall, fd, .etc
// can be put into the context before the binding is even invoked,
// the only information that has to come from the C++ layer is the
// error number (and possibly the syscall for abstraction),
// which is also why the errors should have been constructed
// in JS for more flexibility.
void FSReqAfterScope::Reject(uv_fs_t* req) {
  BaseObjectPtr<FSReqBase> wrap { wrap_ };
  Local<Value> exception = UVException(wrap_->env()->isolate(),
                                       static_cast<int>(req->result),
                                       wrap_->syscall(),
                                       nullptr,
                                       req->path,
                                       wrap_->data());
  Clear();
  wrap->Reject(exception);
}

bool FSReqAfterScope::Proceed() {
  if (req_->result < 0) {
    Reject(req_);
    return false;
  }
  return true;
}

void AfterNoArgs(uv_fs_t* req) {
  FSReqBase* req_wrap = FSReqBase::from_req(req);
  FSReqAfterScope after(req_wrap, req);

  if (after.Proceed())
    req_wrap->Resolve(Undefined(req_wrap->env()->isolate()));
}

void AfterStat(uv_fs_t* req) {
  FSReqBase* req_wrap = FSReqBase::from_req(req);
  FSReqAfterScope after(req_wrap, req);

  if (after.Proceed()) {
    req_wrap->ResolveStat(&req->statbuf);
  }
}

void AfterInteger(uv_fs_t* req) {
  FSReqBase* req_wrap = FSReqBase::from_req(req);
  FSReqAfterScope after(req_wrap, req);

  int result = static_cast<int>(req->result);
  if (result >= 0 && req_wrap->is_plain_open())
    req_wrap->env()->AddUnmanagedFd(result);

  if (after.Proceed())
    req_wrap->Resolve(Integer::New(req_wrap->env()->isolate(), result));
}

void AfterOpenFileHandle(uv_fs_t* req) {
  FSReqBase* req_wrap = FSReqBase::from_req(req);
  FSReqAfterScope after(req_wrap, req);

  if (after.Proceed()) {
    FileHandle* fd = FileHandle::New(req_wrap->binding_data(),
                                     static_cast<int>(req->result));
    if (fd == nullptr) return;
    req_wrap->Resolve(fd->object());
  }
}

// Reverse the logic applied by path.toNamespacedPath() to create a
// namespace-prefixed path.
void FromNamespacedPath(std::string* path) {
#ifdef _WIN32
  if (path->compare(0, 8, "\\\\?\\UNC\\", 8) == 0) {
    *path = path->substr(8);
    path->insert(0, "\\\\");
  } else if (path->compare(0, 4, "\\\\?\\", 4) == 0) {
    *path = path->substr(4);
  }
#endif
}

void AfterMkdirp(uv_fs_t* req) {
  FSReqBase* req_wrap = FSReqBase::from_req(req);
  FSReqAfterScope after(req_wrap, req);

  MaybeLocal<Value> path;
  Local<Value> error;

  if (after.Proceed()) {
    if (!req_wrap->continuation_data()->first_path().empty()) {
      std::string first_path(req_wrap->continuation_data()->first_path());
      FromNamespacedPath(&first_path);
      path = StringBytes::Encode(req_wrap->env()->isolate(), first_path.c_str(),
                                 req_wrap->encoding(),
                                 &error);
      if (path.IsEmpty())
        req_wrap->Reject(error);
      else
        req_wrap->Resolve(path.ToLocalChecked());
    } else {
      req_wrap->Resolve(Undefined(req_wrap->env()->isolate()));
    }
  }
}

void AfterStringPath(uv_fs_t* req) {
  FSReqBase* req_wrap = FSReqBase::from_req(req);
  FSReqAfterScope after(req_wrap, req);

  MaybeLocal<Value> link;
  Local<Value> error;

  if (after.Proceed()) {
    link = StringBytes::Encode(req_wrap->env()->isolate(),
                               req->path,
                               req_wrap->encoding(),
                               &error);
    if (link.IsEmpty())
      req_wrap->Reject(error);
    else
      req_wrap->Resolve(link.ToLocalChecked());
  }
}

void AfterStringPtr(uv_fs_t* req) {
  FSReqBase* req_wrap = FSReqBase::from_req(req);
  FSReqAfterScope after(req_wrap, req);

  MaybeLocal<Value> link;
  Local<Value> error;

  if (after.Proceed()) {
    link = StringBytes::Encode(req_wrap->env()->isolate(),
                               static_cast<const char*>(req->ptr),
                               req_wrap->encoding(),
                               &error);
    if (link.IsEmpty())
      req_wrap->Reject(error);
    else
      req_wrap->Resolve(link.ToLocalChecked());
  }
}

void AfterScanDir(uv_fs_t* req) {
  FSReqBase* req_wrap = FSReqBase::from_req(req);
  FSReqAfterScope after(req_wrap, req);

  if (!after.Proceed()) {
    return;
  }
  Environment* env = req_wrap->env();
  Local<Value> error;
  int r;
  std::vector<Local<Value>> name_v;

  for (;;) {
    uv_dirent_t ent;

    r = uv_fs_scandir_next(req, &ent);
    if (r == UV_EOF)
      break;
    if (r != 0) {
      return req_wrap->Reject(UVException(
          env->isolate(), r, nullptr, req_wrap->syscall(), req->path));
    }

    MaybeLocal<Value> filename =
      StringBytes::Encode(env->isolate(),
          ent.name,
          req_wrap->encoding(),
          &error);
    if (filename.IsEmpty())
      return req_wrap->Reject(error);

    name_v.push_back(filename.ToLocalChecked());
  }

  req_wrap->Resolve(Array::New(env->isolate(), name_v.data(), name_v.size()));
}

void AfterScanDirWithTypes(uv_fs_t* req) {
  FSReqBase* req_wrap = FSReqBase::from_req(req);
  FSReqAfterScope after(req_wrap, req);

  if (!after.Proceed()) {
    return;
  }

  Environment* env = req_wrap->env();
  Isolate* isolate = env->isolate();
  Local<Value> error;
  int r;

  std::vector<Local<Value>> name_v;
  std::vector<Local<Value>> type_v;

  for (;;) {
    uv_dirent_t ent;

    r = uv_fs_scandir_next(req, &ent);
    if (r == UV_EOF)
      break;
    if (r != 0) {
      return req_wrap->Reject(
          UVException(isolate, r, nullptr, req_wrap->syscall(), req->path));
    }

    MaybeLocal<Value> filename =
      StringBytes::Encode(isolate,
          ent.name,
          req_wrap->encoding(),
          &error);
    if (filename.IsEmpty())
      return req_wrap->Reject(error);

    name_v.push_back(filename.ToLocalChecked());
    type_v.emplace_back(Integer::New(isolate, ent.type));
  }

  Local<Value> result[] = {
    Array::New(isolate, name_v.data(), name_v.size()),
    Array::New(isolate, type_v.data(), type_v.size())
  };
  req_wrap->Resolve(Array::New(isolate, result, arraysize(result)));
}

void Access(const FunctionCallbackInfo<Value>& args) {
  Environment* env = Environment::GetCurrent(args);
  Isolate* isolate = env->isolate();
  HandleScope scope(isolate);

  const int argc = args.Length();
  CHECK_GE(argc, 2);

  CHECK(args[1]->IsInt32());
  int mode = args[1].As<Int32>()->Value();

  BufferValue path(isolate, args[0]);
  CHECK_NOT_NULL(*path);

  FSReqBase* req_wrap_async = GetReqWrap(args, 2);
  if (req_wrap_async != nullptr) {  // access(path, mode, req)
    AsyncCall(env, req_wrap_async, args, "access", UTF8, AfterNoArgs,
              uv_fs_access, *path, mode);
  } else {  // access(path, mode, undefined, ctx)
    CHECK_EQ(argc, 4);
    FSReqWrapSync req_wrap_sync;
    FS_SYNC_TRACE_BEGIN(access);
    SyncCall(env, args[3], &req_wrap_sync, "access", uv_fs_access, *path, mode);
    FS_SYNC_TRACE_END(access);
  }
}


void Close(const FunctionCallbackInfo<Value>& args) {
  Environment* env = Environment::GetCurrent(args);

  const int argc = args.Length();
  CHECK_GE(argc, 2);

  CHECK(args[0]->IsInt32());
  int fd = args[0].As<Int32>()->Value();
  env->RemoveUnmanagedFd(fd);

  FSReqBase* req_wrap_async = GetReqWrap(args, 1);
  if (req_wrap_async != nullptr) {  // close(fd, req)
    AsyncCall(env, req_wrap_async, args, "close", UTF8, AfterNoArgs,
              uv_fs_close, fd);
  } else {  // close(fd, undefined, ctx)
    CHECK_EQ(argc, 3);
    FSReqWrapSync req_wrap_sync;
    FS_SYNC_TRACE_BEGIN(close);
    SyncCall(env, args[2], &req_wrap_sync, "close", uv_fs_close, fd);
    FS_SYNC_TRACE_END(close);
  }
}


// Used to speed up module loading. Returns an array [string, boolean]
static void InternalModuleReadJSON(const FunctionCallbackInfo<Value>& args) {
  Environment* env = Environment::GetCurrent(args);
  Isolate* isolate = env->isolate();
  uv_loop_t* loop = env->event_loop();

  CHECK(args[0]->IsString());
  node::Utf8Value path(isolate, args[0]);

  if (strlen(*path) != path.length()) {
    args.GetReturnValue().Set(Array::New(isolate));
    return;  // Contains a nul byte.
  }
  uv_fs_t open_req;
  const int fd = uv_fs_open(loop, &open_req, *path, O_RDONLY, 0, nullptr);
  uv_fs_req_cleanup(&open_req);

  if (fd < 0) {
    args.GetReturnValue().Set(Array::New(isolate));
    return;
  }

  auto defer_close = OnScopeLeave([fd, loop]() {
    uv_fs_t close_req;
    CHECK_EQ(0, uv_fs_close(loop, &close_req, fd, nullptr));
    uv_fs_req_cleanup(&close_req);
  });

  const size_t kBlockSize = 32 << 10;
  std::vector<char> chars;
  int64_t offset = 0;
  ssize_t numchars;
  do {
    const size_t start = chars.size();
    chars.resize(start + kBlockSize);

    uv_buf_t buf;
    buf.base = &chars[start];
    buf.len = kBlockSize;

    uv_fs_t read_req;
    numchars = uv_fs_read(loop, &read_req, fd, &buf, 1, offset, nullptr);
    uv_fs_req_cleanup(&read_req);

    if (numchars < 0) {
      args.GetReturnValue().Set(Array::New(isolate));
      return;
    }
    offset += numchars;
  } while (static_cast<size_t>(numchars) == kBlockSize);

  size_t start = 0;
  if (offset >= 3 && 0 == memcmp(&chars[0], "\xEF\xBB\xBF", 3)) {
    start = 3;  // Skip UTF-8 BOM.
  }

  const size_t size = offset - start;
  char* p = &chars[start];
  char* pe = &chars[size];
  char* pos[2];
  char** ppos = &pos[0];

  while (p < pe) {
    char c = *p++;
    if (c == '\\' && p < pe && *p == '"') p++;
    if (c != '"') continue;
    *ppos++ = p;
    if (ppos < &pos[2]) continue;
    ppos = &pos[0];

    char* s = &pos[0][0];
    char* se = &pos[1][-1];  // Exclude quote.
    size_t n = se - s;

    if (n == 4) {
      if (0 == memcmp(s, "main", 4)) break;
      if (0 == memcmp(s, "name", 4)) break;
      if (0 == memcmp(s, "type", 4)) break;
    } else if (n == 7) {
      if (0 == memcmp(s, "exports", 7)) break;
      if (0 == memcmp(s, "imports", 7)) break;
    }
  }


  Local<Value> return_value[] = {
    String::NewFromUtf8(isolate,
                        &chars[start],
                        v8::NewStringType::kNormal,
                        size).ToLocalChecked(),
    Boolean::New(isolate, p < pe ? true : false)
  };
  args.GetReturnValue().Set(
    Array::New(isolate, return_value, arraysize(return_value)));
}

// Used to speed up module loading.  Returns 0 if the path refers to
// a file, 1 when it's a directory or < 0 on error (usually -ENOENT.)
// The speedup comes from not creating thousands of Stat and Error objects.
static void InternalModuleStat(const FunctionCallbackInfo<Value>& args) {
  Environment* env = Environment::GetCurrent(args);

  CHECK(args[0]->IsString());
  node::Utf8Value path(env->isolate(), args[0]);

  uv_fs_t req;
  int rc = uv_fs_stat(env->event_loop(), &req, *path, nullptr);
  if (rc == 0) {
    const uv_stat_t* const s = static_cast<const uv_stat_t*>(req.ptr);
    rc = !!(s->st_mode & S_IFDIR);
  }
  uv_fs_req_cleanup(&req);

  args.GetReturnValue().Set(rc);
}

static void Stat(const FunctionCallbackInfo<Value>& args) {
  BindingData* binding_data = Environment::GetBindingData<BindingData>(args);
  Environment* env = binding_data->env();

  const int argc = args.Length();
  CHECK_GE(argc, 2);

  BufferValue path(env->isolate(), args[0]);
  CHECK_NOT_NULL(*path);

  bool use_bigint = args[1]->IsTrue();
  FSReqBase* req_wrap_async = GetReqWrap(args, 2, use_bigint);
  if (req_wrap_async != nullptr) {  // stat(path, use_bigint, req)
    AsyncCall(env, req_wrap_async, args, "stat", UTF8, AfterStat,
              uv_fs_stat, *path);
  } else {  // stat(path, use_bigint, undefined, ctx)
    CHECK_EQ(argc, 4);
    FSReqWrapSync req_wrap_sync;
    FS_SYNC_TRACE_BEGIN(stat);
    int err = SyncCall(env, args[3], &req_wrap_sync, "stat", uv_fs_stat, *path);
    FS_SYNC_TRACE_END(stat);
    if (err != 0) {
      return;  // error info is in ctx
    }

    Local<Value> arr = FillGlobalStatsArray(binding_data, use_bigint,
        static_cast<const uv_stat_t*>(req_wrap_sync.req.ptr));
    args.GetReturnValue().Set(arr);
  }
}

static void LStat(const FunctionCallbackInfo<Value>& args) {
  BindingData* binding_data = Environment::GetBindingData<BindingData>(args);
  Environment* env = binding_data->env();

  const int argc = args.Length();
  CHECK_GE(argc, 3);

  BufferValue path(env->isolate(), args[0]);
  CHECK_NOT_NULL(*path);

  bool use_bigint = args[1]->IsTrue();
  FSReqBase* req_wrap_async = GetReqWrap(args, 2, use_bigint);
  if (req_wrap_async != nullptr) {  // lstat(path, use_bigint, req)
    AsyncCall(env, req_wrap_async, args, "lstat", UTF8, AfterStat,
              uv_fs_lstat, *path);
  } else {  // lstat(path, use_bigint, undefined, ctx)
    CHECK_EQ(argc, 4);
    FSReqWrapSync req_wrap_sync;
    FS_SYNC_TRACE_BEGIN(lstat);
    int err = SyncCall(env, args[3], &req_wrap_sync, "lstat", uv_fs_lstat,
                       *path);
    FS_SYNC_TRACE_END(lstat);
    if (err != 0) {
      return;  // error info is in ctx
    }

    Local<Value> arr = FillGlobalStatsArray(binding_data, use_bigint,
        static_cast<const uv_stat_t*>(req_wrap_sync.req.ptr));
    args.GetReturnValue().Set(arr);
  }
}

static void FStat(const FunctionCallbackInfo<Value>& args) {
  BindingData* binding_data = Environment::GetBindingData<BindingData>(args);
  Environment* env = binding_data->env();

  const int argc = args.Length();
  CHECK_GE(argc, 2);

  CHECK(args[0]->IsInt32());
  int fd = args[0].As<Int32>()->Value();

  bool use_bigint = args[1]->IsTrue();
  FSReqBase* req_wrap_async = GetReqWrap(args, 2, use_bigint);
  if (req_wrap_async != nullptr) {  // fstat(fd, use_bigint, req)
    AsyncCall(env, req_wrap_async, args, "fstat", UTF8, AfterStat,
              uv_fs_fstat, fd);
  } else {  // fstat(fd, use_bigint, undefined, ctx)
    CHECK_EQ(argc, 4);
    FSReqWrapSync req_wrap_sync;
    FS_SYNC_TRACE_BEGIN(fstat);
    int err = SyncCall(env, args[3], &req_wrap_sync, "fstat", uv_fs_fstat, fd);
    FS_SYNC_TRACE_END(fstat);
    if (err != 0) {
      return;  // error info is in ctx
    }

    Local<Value> arr = FillGlobalStatsArray(binding_data, use_bigint,
        static_cast<const uv_stat_t*>(req_wrap_sync.req.ptr));
    args.GetReturnValue().Set(arr);
  }
}

static void Symlink(const FunctionCallbackInfo<Value>& args) {
  Environment* env = Environment::GetCurrent(args);
  Isolate* isolate = env->isolate();

  const int argc = args.Length();
  CHECK_GE(argc, 4);

  BufferValue target(isolate, args[0]);
  CHECK_NOT_NULL(*target);
  BufferValue path(isolate, args[1]);
  CHECK_NOT_NULL(*path);

  CHECK(args[2]->IsInt32());
  int flags = args[2].As<Int32>()->Value();

  FSReqBase* req_wrap_async = GetReqWrap(args, 3);
  if (req_wrap_async != nullptr) {  // symlink(target, path, flags, req)
    AsyncDestCall(env, req_wrap_async, args, "symlink", *path, path.length(),
                  UTF8, AfterNoArgs, uv_fs_symlink, *target, *path, flags);
  } else {  // symlink(target, path, flags, undefinec, ctx)
    CHECK_EQ(argc, 5);
    FSReqWrapSync req_wrap_sync;
    FS_SYNC_TRACE_BEGIN(symlink);
    SyncCall(env, args[4], &req_wrap_sync, "symlink",
             uv_fs_symlink, *target, *path, flags);
    FS_SYNC_TRACE_END(symlink);
  }
}

static void Link(const FunctionCallbackInfo<Value>& args) {
  Environment* env = Environment::GetCurrent(args);
  Isolate* isolate = env->isolate();

  const int argc = args.Length();
  CHECK_GE(argc, 3);

  BufferValue src(isolate, args[0]);
  CHECK_NOT_NULL(*src);

  BufferValue dest(isolate, args[1]);
  CHECK_NOT_NULL(*dest);

  FSReqBase* req_wrap_async = GetReqWrap(args, 2);
  if (req_wrap_async != nullptr) {  // link(src, dest, req)
    AsyncDestCall(env, req_wrap_async, args, "link", *dest, dest.length(), UTF8,
                  AfterNoArgs, uv_fs_link, *src, *dest);
  } else {  // link(src, dest)
    CHECK_EQ(argc, 4);
    FSReqWrapSync req_wrap_sync;
    FS_SYNC_TRACE_BEGIN(link);
    SyncCall(env, args[3], &req_wrap_sync, "link",
             uv_fs_link, *src, *dest);
    FS_SYNC_TRACE_END(link);
  }
}

static void ReadLink(const FunctionCallbackInfo<Value>& args) {
  Environment* env = Environment::GetCurrent(args);
  Isolate* isolate = env->isolate();

  const int argc = args.Length();
  CHECK_GE(argc, 3);

  BufferValue path(isolate, args[0]);
  CHECK_NOT_NULL(*path);

  const enum encoding encoding = ParseEncoding(isolate, args[1], UTF8);

  FSReqBase* req_wrap_async = GetReqWrap(args, 2);
  if (req_wrap_async != nullptr) {  // readlink(path, encoding, req)
    AsyncCall(env, req_wrap_async, args, "readlink", encoding, AfterStringPtr,
              uv_fs_readlink, *path);
  } else {
    CHECK_EQ(argc, 4);
    FSReqWrapSync req_wrap_sync;
    FS_SYNC_TRACE_BEGIN(readlink);
    int err = SyncCall(env, args[3], &req_wrap_sync, "readlink",
                       uv_fs_readlink, *path);
    FS_SYNC_TRACE_END(readlink);
    if (err < 0) {
      return;  // syscall failed, no need to continue, error info is in ctx
    }
    const char* link_path = static_cast<const char*>(req_wrap_sync.req.ptr);

    Local<Value> error;
    MaybeLocal<Value> rc = StringBytes::Encode(isolate,
                                               link_path,
                                               encoding,
                                               &error);
    if (rc.IsEmpty()) {
      Local<Object> ctx = args[3].As<Object>();
      ctx->Set(env->context(), env->error_string(), error).Check();
      return;
    }

    args.GetReturnValue().Set(rc.ToLocalChecked());
  }
}

static void Rename(const FunctionCallbackInfo<Value>& args) {
  Environment* env = Environment::GetCurrent(args);
  Isolate* isolate = env->isolate();

  const int argc = args.Length();
  CHECK_GE(argc, 3);

  BufferValue old_path(isolate, args[0]);
  CHECK_NOT_NULL(*old_path);
  BufferValue new_path(isolate, args[1]);
  CHECK_NOT_NULL(*new_path);

  FSReqBase* req_wrap_async = GetReqWrap(args, 2);
  if (req_wrap_async != nullptr) {
    AsyncDestCall(env, req_wrap_async, args, "rename", *new_path,
                  new_path.length(), UTF8, AfterNoArgs, uv_fs_rename,
                  *old_path, *new_path);
  } else {
    CHECK_EQ(argc, 4);
    FSReqWrapSync req_wrap_sync;
    FS_SYNC_TRACE_BEGIN(rename);
    SyncCall(env, args[3], &req_wrap_sync, "rename", uv_fs_rename,
             *old_path, *new_path);
    FS_SYNC_TRACE_END(rename);
  }
}

static void FTruncate(const FunctionCallbackInfo<Value>& args) {
  Environment* env = Environment::GetCurrent(args);

  const int argc = args.Length();
  CHECK_GE(argc, 3);

  CHECK(args[0]->IsInt32());
  const int fd = args[0].As<Int32>()->Value();

  CHECK(IsSafeJsInt(args[1]));
  const int64_t len = args[1].As<Integer>()->Value();

  FSReqBase* req_wrap_async = GetReqWrap(args, 2);
  if (req_wrap_async != nullptr) {
    AsyncCall(env, req_wrap_async, args, "ftruncate", UTF8, AfterNoArgs,
              uv_fs_ftruncate, fd, len);
  } else {
    CHECK_EQ(argc, 4);
    FSReqWrapSync req_wrap_sync;
    FS_SYNC_TRACE_BEGIN(ftruncate);
    SyncCall(env, args[3], &req_wrap_sync, "ftruncate", uv_fs_ftruncate, fd,
             len);
    FS_SYNC_TRACE_END(ftruncate);
  }
}

static void Fdatasync(const FunctionCallbackInfo<Value>& args) {
  Environment* env = Environment::GetCurrent(args);

  const int argc = args.Length();
  CHECK_GE(argc, 2);

  CHECK(args[0]->IsInt32());
  const int fd = args[0].As<Int32>()->Value();

  FSReqBase* req_wrap_async = GetReqWrap(args, 1);
  if (req_wrap_async != nullptr) {
    AsyncCall(env, req_wrap_async, args, "fdatasync", UTF8, AfterNoArgs,
              uv_fs_fdatasync, fd);
  } else {
    CHECK_EQ(argc, 3);
    FSReqWrapSync req_wrap_sync;
    FS_SYNC_TRACE_BEGIN(fdatasync);
    SyncCall(env, args[2], &req_wrap_sync, "fdatasync", uv_fs_fdatasync, fd);
    FS_SYNC_TRACE_END(fdatasync);
  }
}

static void Fsync(const FunctionCallbackInfo<Value>& args) {
  Environment* env = Environment::GetCurrent(args);

  const int argc = args.Length();
  CHECK_GE(argc, 2);

  CHECK(args[0]->IsInt32());
  const int fd = args[0].As<Int32>()->Value();

  FSReqBase* req_wrap_async = GetReqWrap(args, 1);
  if (req_wrap_async != nullptr) {
    AsyncCall(env, req_wrap_async, args, "fsync", UTF8, AfterNoArgs,
              uv_fs_fsync, fd);
  } else {
    CHECK_EQ(argc, 3);
    FSReqWrapSync req_wrap_sync;
    FS_SYNC_TRACE_BEGIN(fsync);
    SyncCall(env, args[2], &req_wrap_sync, "fsync", uv_fs_fsync, fd);
    FS_SYNC_TRACE_END(fsync);
  }
}

static void Unlink(const FunctionCallbackInfo<Value>& args) {
  Environment* env = Environment::GetCurrent(args);

  const int argc = args.Length();
  CHECK_GE(argc, 2);

  BufferValue path(env->isolate(), args[0]);
  CHECK_NOT_NULL(*path);

  FSReqBase* req_wrap_async = GetReqWrap(args, 1);
  if (req_wrap_async != nullptr) {
    AsyncCall(env, req_wrap_async, args, "unlink", UTF8, AfterNoArgs,
              uv_fs_unlink, *path);
  } else {
    CHECK_EQ(argc, 3);
    FSReqWrapSync req_wrap_sync;
    FS_SYNC_TRACE_BEGIN(unlink);
    SyncCall(env, args[2], &req_wrap_sync, "unlink", uv_fs_unlink, *path);
    FS_SYNC_TRACE_END(unlink);
  }
}

static void RMDir(const FunctionCallbackInfo<Value>& args) {
  Environment* env = Environment::GetCurrent(args);

  const int argc = args.Length();
  CHECK_GE(argc, 2);

  BufferValue path(env->isolate(), args[0]);
  CHECK_NOT_NULL(*path);

  FSReqBase* req_wrap_async = GetReqWrap(args, 1);  // rmdir(path, req)
  if (req_wrap_async != nullptr) {
    AsyncCall(env, req_wrap_async, args, "rmdir", UTF8, AfterNoArgs,
              uv_fs_rmdir, *path);
  } else {  // rmdir(path, undefined, ctx)
    CHECK_EQ(argc, 3);
    FSReqWrapSync req_wrap_sync;
    FS_SYNC_TRACE_BEGIN(rmdir);
    SyncCall(env, args[2], &req_wrap_sync, "rmdir",
             uv_fs_rmdir, *path);
    FS_SYNC_TRACE_END(rmdir);
  }
}

int MKDirpSync(uv_loop_t* loop,
               uv_fs_t* req,
               const std::string& path,
               int mode,
               uv_fs_cb cb) {
  FSReqWrapSync* req_wrap = ContainerOf(&FSReqWrapSync::req, req);

  // on the first iteration of algorithm, stash state information.
  if (req_wrap->continuation_data() == nullptr) {
    req_wrap->set_continuation_data(
        std::make_unique<FSContinuationData>(req, mode, cb));
    req_wrap->continuation_data()->PushPath(std::move(path));
  }

  while (req_wrap->continuation_data()->paths().size() > 0) {
    std::string next_path = req_wrap->continuation_data()->PopPath();
    int err = uv_fs_mkdir(loop, req, next_path.c_str(), mode, nullptr);
    while (true) {
      switch (err) {
        // Note: uv_fs_req_cleanup in terminal paths will be called by
        // ~FSReqWrapSync():
        case 0:
          req_wrap->continuation_data()->MaybeSetFirstPath(next_path);
          if (req_wrap->continuation_data()->paths().size() == 0) {
            return 0;
          }
          break;
        case UV_EACCES:
        case UV_ENOTDIR:
        case UV_EPERM: {
          return err;
        }
        case UV_ENOENT: {
          std::string dirname = next_path.substr(0,
                                        next_path.find_last_of(kPathSeparator));
          if (dirname != next_path) {
            req_wrap->continuation_data()->PushPath(std::move(next_path));
            req_wrap->continuation_data()->PushPath(std::move(dirname));
          } else if (req_wrap->continuation_data()->paths().size() == 0) {
            err = UV_EEXIST;
            continue;
          }
          break;
        }
        default:
          uv_fs_req_cleanup(req);
          int orig_err = err;
          err = uv_fs_stat(loop, req, next_path.c_str(), nullptr);
          if (err == 0 && !S_ISDIR(req->statbuf.st_mode)) {
            uv_fs_req_cleanup(req);
            if (orig_err == UV_EEXIST &&
              req_wrap->continuation_data()->paths().size() > 0) {
              return UV_ENOTDIR;
            }
            return UV_EEXIST;
          }
          if (err < 0) return err;
          break;
      }
      break;
    }
    uv_fs_req_cleanup(req);
  }

  return 0;
}

int MKDirpAsync(uv_loop_t* loop,
                uv_fs_t* req,
                const char* path,
                int mode,
                uv_fs_cb cb) {
  FSReqBase* req_wrap = FSReqBase::from_req(req);
  // on the first iteration of algorithm, stash state information.
  if (req_wrap->continuation_data() == nullptr) {
    req_wrap->set_continuation_data(
        std::make_unique<FSContinuationData>(req, mode, cb));
    req_wrap->continuation_data()->PushPath(std::move(path));
  }

  // on each iteration of algorithm, mkdir directory on top of stack.
  std::string next_path = req_wrap->continuation_data()->PopPath();
  int err = uv_fs_mkdir(loop, req, next_path.c_str(), mode,
                        uv_fs_callback_t{[](uv_fs_t* req) {
    FSReqBase* req_wrap = FSReqBase::from_req(req);
    Environment* env = req_wrap->env();
    uv_loop_t* loop = env->event_loop();
    std::string path = req->path;
    int err = static_cast<int>(req->result);

    while (true) {
      switch (err) {
        // Note: uv_fs_req_cleanup in terminal paths will be called by
        // FSReqAfterScope::~FSReqAfterScope()
        case 0: {
          if (req_wrap->continuation_data()->paths().size() == 0) {
            req_wrap->continuation_data()->MaybeSetFirstPath(path);
            req_wrap->continuation_data()->Done(0);
          } else {
            req_wrap->continuation_data()->MaybeSetFirstPath(path);
            uv_fs_req_cleanup(req);
            MKDirpAsync(loop, req, path.c_str(),
                        req_wrap->continuation_data()->mode(), nullptr);
          }
          break;
        }
        case UV_EACCES:
        case UV_ENOTDIR:
        case UV_EPERM: {
          req_wrap->continuation_data()->Done(err);
          break;
        }
        case UV_ENOENT: {
          std::string dirname = path.substr(0,
                                            path.find_last_of(kPathSeparator));
          if (dirname != path) {
            req_wrap->continuation_data()->PushPath(std::move(path));
            req_wrap->continuation_data()->PushPath(std::move(dirname));
          } else if (req_wrap->continuation_data()->paths().size() == 0) {
            err = UV_EEXIST;
            continue;
          }
          uv_fs_req_cleanup(req);
          MKDirpAsync(loop, req, path.c_str(),
                      req_wrap->continuation_data()->mode(), nullptr);
          break;
        }
        default:
          uv_fs_req_cleanup(req);
          // Stash err for use in the callback.
          req->data = reinterpret_cast<void*>(static_cast<intptr_t>(err));
          int err = uv_fs_stat(loop, req, path.c_str(),
                               uv_fs_callback_t{[](uv_fs_t* req) {
            FSReqBase* req_wrap = FSReqBase::from_req(req);
            int err = static_cast<int>(req->result);
            if (reinterpret_cast<intptr_t>(req->data) == UV_EEXIST &&
                  req_wrap->continuation_data()->paths().size() > 0) {
              if (err == 0 && S_ISDIR(req->statbuf.st_mode)) {
                Environment* env = req_wrap->env();
                uv_loop_t* loop = env->event_loop();
                std::string path = req->path;
                uv_fs_req_cleanup(req);
                MKDirpAsync(loop, req, path.c_str(),
                            req_wrap->continuation_data()->mode(), nullptr);
                return;
              }
              err = UV_ENOTDIR;
            }
            // verify that the path pointed to is actually a directory.
            if (err == 0 && !S_ISDIR(req->statbuf.st_mode)) err = UV_EEXIST;
            req_wrap->continuation_data()->Done(err);
          }});
          if (err < 0) req_wrap->continuation_data()->Done(err);
          break;
      }
      break;
    }
  }});

  return err;
}

int CallMKDirpSync(Environment* env, const FunctionCallbackInfo<Value>& args,
                   FSReqWrapSync* req_wrap, const char* path, int mode) {
  env->PrintSyncTrace();
  int err = MKDirpSync(env->event_loop(), &req_wrap->req, path, mode,
                       nullptr);
  if (err < 0) {
    v8::Local<v8::Context> context = env->context();
    v8::Local<v8::Object> ctx_obj = args[4].As<v8::Object>();
    v8::Isolate* isolate = env->isolate();
    ctx_obj->Set(context,
                 env->errno_string(),
                 v8::Integer::New(isolate, err)).Check();
    ctx_obj->Set(context,
                 env->syscall_string(),
                 OneByteString(isolate, "mkdir")).Check();
  }
  return err;
}

static void MKDir(const FunctionCallbackInfo<Value>& args) {
  Environment* env = Environment::GetCurrent(args);

  const int argc = args.Length();
  CHECK_GE(argc, 4);

  BufferValue path(env->isolate(), args[0]);
  CHECK_NOT_NULL(*path);

  CHECK(args[1]->IsInt32());
  const int mode = args[1].As<Int32>()->Value();

  CHECK(args[2]->IsBoolean());
  bool mkdirp = args[2]->IsTrue();

  FSReqBase* req_wrap_async = GetReqWrap(args, 3);
  if (req_wrap_async != nullptr) {  // mkdir(path, mode, req)
    AsyncCall(env, req_wrap_async, args, "mkdir", UTF8,
              mkdirp ? AfterMkdirp : AfterNoArgs,
              mkdirp ? MKDirpAsync : uv_fs_mkdir, *path, mode);
  } else {  // mkdir(path, mode, undefined, ctx)
    CHECK_EQ(argc, 5);
    FSReqWrapSync req_wrap_sync;
    FS_SYNC_TRACE_BEGIN(mkdir);
    if (mkdirp) {
      int err = CallMKDirpSync(env, args, &req_wrap_sync, *path, mode);
      if (err == 0 &&
          !req_wrap_sync.continuation_data()->first_path().empty()) {
        Local<Value> error;
        std::string first_path(req_wrap_sync.continuation_data()->first_path());
        FromNamespacedPath(&first_path);
        MaybeLocal<Value> path = StringBytes::Encode(env->isolate(),
                                                     first_path.c_str(),
                                                     UTF8, &error);
        if (path.IsEmpty()) {
          Local<Object> ctx = args[4].As<Object>();
          ctx->Set(env->context(), env->error_string(), error).Check();
          return;
        }
        args.GetReturnValue().Set(path.ToLocalChecked());
      }
    } else {
      SyncCall(env, args[4], &req_wrap_sync, "mkdir",
               uv_fs_mkdir, *path, mode);
    }
    FS_SYNC_TRACE_END(mkdir);
  }
}

static void RealPath(const FunctionCallbackInfo<Value>& args) {
  Environment* env = Environment::GetCurrent(args);
  Isolate* isolate = env->isolate();

  const int argc = args.Length();
  CHECK_GE(argc, 3);

  BufferValue path(isolate, args[0]);
  CHECK_NOT_NULL(*path);

  const enum encoding encoding = ParseEncoding(isolate, args[1], UTF8);

  FSReqBase* req_wrap_async = GetReqWrap(args, 2);
  if (req_wrap_async != nullptr) {  // realpath(path, encoding, req)
    AsyncCall(env, req_wrap_async, args, "realpath", encoding, AfterStringPtr,
              uv_fs_realpath, *path);
  } else {  // realpath(path, encoding, undefined, ctx)
    CHECK_EQ(argc, 4);
    FSReqWrapSync req_wrap_sync;
    FS_SYNC_TRACE_BEGIN(realpath);
    int err = SyncCall(env, args[3], &req_wrap_sync, "realpath",
                       uv_fs_realpath, *path);
    FS_SYNC_TRACE_END(realpath);
    if (err < 0) {
      return;  // syscall failed, no need to continue, error info is in ctx
    }

    const char* link_path = static_cast<const char*>(req_wrap_sync.req.ptr);

    Local<Value> error;
    MaybeLocal<Value> rc = StringBytes::Encode(isolate,
                                               link_path,
                                               encoding,
                                               &error);
    if (rc.IsEmpty()) {
      Local<Object> ctx = args[3].As<Object>();
      ctx->Set(env->context(), env->error_string(), error).Check();
      return;
    }

    args.GetReturnValue().Set(rc.ToLocalChecked());
  }
}

static void ReadDir(const FunctionCallbackInfo<Value>& args) {
  Environment* env = Environment::GetCurrent(args);
  Isolate* isolate = env->isolate();

  const int argc = args.Length();
  CHECK_GE(argc, 3);

  BufferValue path(isolate, args[0]);
  CHECK_NOT_NULL(*path);

  const enum encoding encoding = ParseEncoding(isolate, args[1], UTF8);

  bool with_types = args[2]->IsTrue();

  FSReqBase* req_wrap_async = GetReqWrap(args, 3);
  if (req_wrap_async != nullptr) {  // readdir(path, encoding, withTypes, req)
    if (with_types) {
      AsyncCall(env, req_wrap_async, args, "scandir", encoding,
                AfterScanDirWithTypes, uv_fs_scandir, *path, 0 /*flags*/);
    } else {
      AsyncCall(env, req_wrap_async, args, "scandir", encoding,
                AfterScanDir, uv_fs_scandir, *path, 0 /*flags*/);
    }
  } else {  // readdir(path, encoding, withTypes, undefined, ctx)
    CHECK_EQ(argc, 5);
    FSReqWrapSync req_wrap_sync;
    FS_SYNC_TRACE_BEGIN(readdir);
    int err = SyncCall(env, args[4], &req_wrap_sync, "scandir",
                       uv_fs_scandir, *path, 0 /*flags*/);
    FS_SYNC_TRACE_END(readdir);
    if (err < 0) {
      return;  // syscall failed, no need to continue, error info is in ctx
    }

    CHECK_GE(req_wrap_sync.req.result, 0);
    int r;
    std::vector<Local<Value>> name_v;
    std::vector<Local<Value>> type_v;

    for (;;) {
      uv_dirent_t ent;

      r = uv_fs_scandir_next(&(req_wrap_sync.req), &ent);
      if (r == UV_EOF)
        break;
      if (r != 0) {
        Local<Object> ctx = args[4].As<Object>();
        ctx->Set(env->context(), env->errno_string(),
                 Integer::New(isolate, r)).Check();
        ctx->Set(env->context(), env->syscall_string(),
                 OneByteString(isolate, "readdir")).Check();
        return;
      }

      Local<Value> error;
      MaybeLocal<Value> filename = StringBytes::Encode(isolate,
                                                       ent.name,
                                                       encoding,
                                                       &error);

      if (filename.IsEmpty()) {
        Local<Object> ctx = args[4].As<Object>();
        ctx->Set(env->context(), env->error_string(), error).Check();
        return;
      }

      name_v.push_back(filename.ToLocalChecked());

      if (with_types) {
        type_v.emplace_back(Integer::New(isolate, ent.type));
      }
    }


    Local<Array> names = Array::New(isolate, name_v.data(), name_v.size());
    if (with_types) {
      Local<Value> result[] = {
        names,
        Array::New(isolate, type_v.data(), type_v.size())
      };
      args.GetReturnValue().Set(Array::New(isolate, result, arraysize(result)));
    } else {
      args.GetReturnValue().Set(names);
    }
  }
}

static void Open(const FunctionCallbackInfo<Value>& args) {
  Environment* env = Environment::GetCurrent(args);

  const int argc = args.Length();
  CHECK_GE(argc, 3);

  BufferValue path(env->isolate(), args[0]);
  CHECK_NOT_NULL(*path);

  CHECK(args[1]->IsInt32());
  const int flags = args[1].As<Int32>()->Value();

  CHECK(args[2]->IsInt32());
  const int mode = args[2].As<Int32>()->Value();

  FSReqBase* req_wrap_async = GetReqWrap(args, 3);
  if (req_wrap_async != nullptr) {  // open(path, flags, mode, req)
    req_wrap_async->set_is_plain_open(true);
    AsyncCall(env, req_wrap_async, args, "open", UTF8, AfterInteger,
              uv_fs_open, *path, flags, mode);
  } else {  // open(path, flags, mode, undefined, ctx)
    CHECK_EQ(argc, 5);
    FSReqWrapSync req_wrap_sync;
    FS_SYNC_TRACE_BEGIN(open);
    int result = SyncCall(env, args[4], &req_wrap_sync, "open",
                          uv_fs_open, *path, flags, mode);
    FS_SYNC_TRACE_END(open);
    if (result >= 0) env->AddUnmanagedFd(result);
    args.GetReturnValue().Set(result);
  }
}

static void OpenFileHandle(const FunctionCallbackInfo<Value>& args) {
  BindingData* binding_data = Environment::GetBindingData<BindingData>(args);
  Environment* env = binding_data->env();
  Isolate* isolate = env->isolate();

  const int argc = args.Length();
  CHECK_GE(argc, 3);

  BufferValue path(isolate, args[0]);
  CHECK_NOT_NULL(*path);

  CHECK(args[1]->IsInt32());
  const int flags = args[1].As<Int32>()->Value();

  CHECK(args[2]->IsInt32());
  const int mode = args[2].As<Int32>()->Value();

  FSReqBase* req_wrap_async = GetReqWrap(args, 3);
  if (req_wrap_async != nullptr) {  // openFileHandle(path, flags, mode, req)
    AsyncCall(env, req_wrap_async, args, "open", UTF8, AfterOpenFileHandle,
              uv_fs_open, *path, flags, mode);
  } else {  // openFileHandle(path, flags, mode, undefined, ctx)
    CHECK_EQ(argc, 5);
    FSReqWrapSync req_wrap_sync;
    FS_SYNC_TRACE_BEGIN(open);
    int result = SyncCall(env, args[4], &req_wrap_sync, "open",
                          uv_fs_open, *path, flags, mode);
    FS_SYNC_TRACE_END(open);
    if (result < 0) {
      return;  // syscall failed, no need to continue, error info is in ctx
    }
    FileHandle* fd = FileHandle::New(binding_data, result);
    if (fd == nullptr) return;
    args.GetReturnValue().Set(fd->object());
  }
}

static void CopyFile(const FunctionCallbackInfo<Value>& args) {
  Environment* env = Environment::GetCurrent(args);
  Isolate* isolate = env->isolate();

  const int argc = args.Length();
  CHECK_GE(argc, 3);

  BufferValue src(isolate, args[0]);
  CHECK_NOT_NULL(*src);

  BufferValue dest(isolate, args[1]);
  CHECK_NOT_NULL(*dest);

  CHECK(args[2]->IsInt32());
  const int flags = args[2].As<Int32>()->Value();

  FSReqBase* req_wrap_async = GetReqWrap(args, 3);
  if (req_wrap_async != nullptr) {  // copyFile(src, dest, flags, req)
    AsyncDestCall(env, req_wrap_async, args, "copyfile",
                  *dest, dest.length(), UTF8, AfterNoArgs,
                  uv_fs_copyfile, *src, *dest, flags);
  } else {  // copyFile(src, dest, flags, undefined, ctx)
    CHECK_EQ(argc, 5);
    FSReqWrapSync req_wrap_sync;
    FS_SYNC_TRACE_BEGIN(copyfile);
    SyncCall(env, args[4], &req_wrap_sync, "copyfile",
             uv_fs_copyfile, *src, *dest, flags);
    FS_SYNC_TRACE_END(copyfile);
  }
}


// Wrapper for write(2).
//
// bytesWritten = write(fd, buffer, offset, length, position, callback)
// 0 fd        integer. file descriptor
// 1 buffer    the data to write
// 2 offset    where in the buffer to start from
// 3 length    how much to write
// 4 position  if integer, position to write at in the file.
//             if null, write from the current position
static void WriteBuffer(const FunctionCallbackInfo<Value>& args) {
  Environment* env = Environment::GetCurrent(args);

  const int argc = args.Length();
  CHECK_GE(argc, 4);

  CHECK(args[0]->IsInt32());
  const int fd = args[0].As<Int32>()->Value();

  CHECK(Buffer::HasInstance(args[1]));
  Local<Object> buffer_obj = args[1].As<Object>();
  char* buffer_data = Buffer::Data(buffer_obj);
  size_t buffer_length = Buffer::Length(buffer_obj);

  CHECK(IsSafeJsInt(args[2]));
  const int64_t off_64 = args[2].As<Integer>()->Value();
  CHECK_GE(off_64, 0);
  CHECK_LE(static_cast<uint64_t>(off_64), buffer_length);
  const size_t off = static_cast<size_t>(off_64);

  CHECK(IsSafeJsInt(args[3]));
  const size_t len = static_cast<size_t>(args[3].As<Integer>()->Value());
  CHECK(Buffer::IsWithinBounds(off, len, buffer_length));
  CHECK_LE(len, buffer_length);
  CHECK_GE(off + len, off);

  const int64_t pos = GetOffset(args[4]);

  char* buf = buffer_data + off;
  uv_buf_t uvbuf = uv_buf_init(buf, len);

  FSReqBase* req_wrap_async = GetReqWrap(args, 5);
  if (req_wrap_async != nullptr) {  // write(fd, buffer, off, len, pos, req)
    AsyncCall(env, req_wrap_async, args, "write", UTF8, AfterInteger,
              uv_fs_write, fd, &uvbuf, 1, pos);
  } else {  // write(fd, buffer, off, len, pos, undefined, ctx)
    CHECK_EQ(argc, 7);
    FSReqWrapSync req_wrap_sync;
    FS_SYNC_TRACE_BEGIN(write);
    int bytesWritten = SyncCall(env, args[6], &req_wrap_sync, "write",
                                uv_fs_write, fd, &uvbuf, 1, pos);
    FS_SYNC_TRACE_END(write, "bytesWritten", bytesWritten);
    args.GetReturnValue().Set(bytesWritten);
  }
}


// Wrapper for writev(2).
//
// bytesWritten = writev(fd, chunks, position, callback)
// 0 fd        integer. file descriptor
// 1 chunks    array of buffers to write
// 2 position  if integer, position to write at in the file.
//             if null, write from the current position
static void WriteBuffers(const FunctionCallbackInfo<Value>& args) {
  Environment* env = Environment::GetCurrent(args);

  const int argc = args.Length();
  CHECK_GE(argc, 3);

  CHECK(args[0]->IsInt32());
  const int fd = args[0].As<Int32>()->Value();

  CHECK(args[1]->IsArray());
  Local<Array> chunks = args[1].As<Array>();

  int64_t pos = GetOffset(args[2]);

  MaybeStackBuffer<uv_buf_t> iovs(chunks->Length());

  for (uint32_t i = 0; i < iovs.length(); i++) {
    Local<Value> chunk = chunks->Get(env->context(), i).ToLocalChecked();
    CHECK(Buffer::HasInstance(chunk));
    iovs[i] = uv_buf_init(Buffer::Data(chunk), Buffer::Length(chunk));
  }

  FSReqBase* req_wrap_async = GetReqWrap(args, 3);
  if (req_wrap_async != nullptr) {  // writeBuffers(fd, chunks, pos, req)
    AsyncCall(env, req_wrap_async, args, "write", UTF8, AfterInteger,
              uv_fs_write, fd, *iovs, iovs.length(), pos);
  } else {  // writeBuffers(fd, chunks, pos, undefined, ctx)
    CHECK_EQ(argc, 5);
    FSReqWrapSync req_wrap_sync;
    FS_SYNC_TRACE_BEGIN(write);
    int bytesWritten = SyncCall(env, args[4], &req_wrap_sync, "write",
                                uv_fs_write, fd, *iovs, iovs.length(), pos);
    FS_SYNC_TRACE_END(write, "bytesWritten", bytesWritten);
    args.GetReturnValue().Set(bytesWritten);
  }
}


// Wrapper for write(2).
//
// bytesWritten = write(fd, string, position, enc, callback)
// 0 fd        integer. file descriptor
// 1 string    non-buffer values are converted to strings
// 2 position  if integer, position to write at in the file.
//             if null, write from the current position
// 3 enc       encoding of string
static void WriteString(const FunctionCallbackInfo<Value>& args) {
  Environment* env = Environment::GetCurrent(args);
  Isolate* isolate = env->isolate();

  const int argc = args.Length();
  CHECK_GE(argc, 4);

  CHECK(args[0]->IsInt32());
  const int fd = args[0].As<Int32>()->Value();

  const int64_t pos = GetOffset(args[2]);

  const auto enc = ParseEncoding(isolate, args[3], UTF8);

  Local<Value> value = args[1];
  char* buf = nullptr;
  size_t len;

  FSReqBase* req_wrap_async = GetReqWrap(args, 4);
  const bool is_async = req_wrap_async != nullptr;

  // Avoid copying the string when it is externalized but only when:
  // 1. The target encoding is compatible with the string's encoding, and
  // 2. The write is synchronous, otherwise the string might get neutered
  //    while the request is in flight, and
  // 3. For UCS2, when the host system is little-endian.  Big-endian systems
  //    need to call StringBytes::Write() to ensure proper byte swapping.
  // The const_casts are conceptually sound: memory is read but not written.
  if (!is_async && value->IsString()) {
    auto string = value.As<String>();
    if ((enc == ASCII || enc == LATIN1) && string->IsExternalOneByte()) {
      auto ext = string->GetExternalOneByteStringResource();
      buf = const_cast<char*>(ext->data());
      len = ext->length();
    } else if (enc == UCS2 && IsLittleEndian() && string->IsExternalTwoByte()) {
      auto ext = string->GetExternalStringResource();
      buf = reinterpret_cast<char*>(const_cast<uint16_t*>(ext->data()));
      len = ext->length() * sizeof(*ext->data());
    }
  }

  if (is_async) {  // write(fd, string, pos, enc, req)
    CHECK_NOT_NULL(req_wrap_async);
    if (!StringBytes::StorageSize(isolate, value, enc).To(&len)) return;
    FSReqBase::FSReqBuffer& stack_buffer =
        req_wrap_async->Init("write", len, enc);
    // StorageSize may return too large a char, so correct the actual length
    // by the write size
    len = StringBytes::Write(isolate, *stack_buffer, len, args[1], enc);
    stack_buffer.SetLengthAndZeroTerminate(len);
    uv_buf_t uvbuf = uv_buf_init(*stack_buffer, len);
    int err = req_wrap_async->Dispatch(uv_fs_write,
                                       fd,
                                       &uvbuf,
                                       1,
                                       pos,
                                       AfterInteger);
    if (err < 0) {
      uv_fs_t* uv_req = req_wrap_async->req();
      uv_req->result = err;
      uv_req->path = nullptr;
      AfterInteger(uv_req);  // after may delete req_wrap_async if there is
                             // an error
    } else {
      req_wrap_async->SetReturnValue(args);
    }
  } else {  // write(fd, string, pos, enc, undefined, ctx)
    CHECK_EQ(argc, 6);
    FSReqWrapSync req_wrap_sync;
    FSReqBase::FSReqBuffer stack_buffer;
    if (buf == nullptr) {
      if (!StringBytes::StorageSize(isolate, value, enc).To(&len))
        return;
      stack_buffer.AllocateSufficientStorage(len + 1);
      // StorageSize may return too large a char, so correct the actual length
      // by the write size
      len = StringBytes::Write(isolate, *stack_buffer,
                               len, args[1], enc);
      stack_buffer.SetLengthAndZeroTerminate(len);
      buf = *stack_buffer;
    }
    uv_buf_t uvbuf = uv_buf_init(buf, len);
    FS_SYNC_TRACE_BEGIN(write);
    int bytesWritten = SyncCall(env, args[5], &req_wrap_sync, "write",
                                uv_fs_write, fd, &uvbuf, 1, pos);
    FS_SYNC_TRACE_END(write, "bytesWritten", bytesWritten);
    args.GetReturnValue().Set(bytesWritten);
  }
}


/*
 * Wrapper for read(2).
 *
 * bytesRead = fs.read(fd, buffer, offset, length, position)
 *
 * 0 fd        int32. file descriptor
 * 1 buffer    instance of Buffer
 * 2 offset    int64. offset to start reading into inside buffer
 * 3 length    int32. length to read
 * 4 position  int64. file position - -1 for current position
 */
static void Read(const FunctionCallbackInfo<Value>& args) {
  Environment* env = Environment::GetCurrent(args);

  const int argc = args.Length();
  CHECK_GE(argc, 5);

  CHECK(args[0]->IsInt32());
  const int fd = args[0].As<Int32>()->Value();

  CHECK(Buffer::HasInstance(args[1]));
  Local<Object> buffer_obj = args[1].As<Object>();
  char* buffer_data = Buffer::Data(buffer_obj);
  size_t buffer_length = Buffer::Length(buffer_obj);

  CHECK(IsSafeJsInt(args[2]));
  const int64_t off_64 = args[2].As<Integer>()->Value();
  CHECK_GE(off_64, 0);
  CHECK_LT(static_cast<uint64_t>(off_64), buffer_length);
  const size_t off = static_cast<size_t>(off_64);

  CHECK(args[3]->IsInt32());
  const size_t len = static_cast<size_t>(args[3].As<Int32>()->Value());
  CHECK(Buffer::IsWithinBounds(off, len, buffer_length));

  CHECK(IsSafeJsInt(args[4]) || args[4]->IsBigInt());
  const int64_t pos = args[4]->IsNumber() ?
                      args[4].As<Integer>()->Value() :
                      args[4].As<BigInt>()->Int64Value();

  char* buf = buffer_data + off;
  uv_buf_t uvbuf = uv_buf_init(buf, len);

  FSReqBase* req_wrap_async = GetReqWrap(args, 5);
  if (req_wrap_async != nullptr) {  // read(fd, buffer, offset, len, pos, req)
    AsyncCall(env, req_wrap_async, args, "read", UTF8, AfterInteger,
              uv_fs_read, fd, &uvbuf, 1, pos);
  } else {  // read(fd, buffer, offset, len, pos, undefined, ctx)
    CHECK_EQ(argc, 7);
    FSReqWrapSync req_wrap_sync;
    FS_SYNC_TRACE_BEGIN(read);
    const int bytesRead = SyncCall(env, args[6], &req_wrap_sync, "read",
                                   uv_fs_read, fd, &uvbuf, 1, pos);
    FS_SYNC_TRACE_END(read, "bytesRead", bytesRead);
    args.GetReturnValue().Set(bytesRead);
  }
}


// Wrapper for readv(2).
//
// bytesRead = fs.readv(fd, buffers[, position], callback)
// 0 fd        integer. file descriptor
// 1 buffers   array of buffers to read
// 2 position  if integer, position to read at in the file.
//             if null, read from the current position
static void ReadBuffers(const FunctionCallbackInfo<Value>& args) {
  Environment* env = Environment::GetCurrent(args);

  const int argc = args.Length();
  CHECK_GE(argc, 3);

  CHECK(args[0]->IsInt32());
  const int fd = args[0].As<Int32>()->Value();

  CHECK(args[1]->IsArray());
  Local<Array> buffers = args[1].As<Array>();

  int64_t pos = GetOffset(args[2]);  // -1 if not a valid JS int

  MaybeStackBuffer<uv_buf_t> iovs(buffers->Length());

  // Init uv buffers from ArrayBufferViews
  for (uint32_t i = 0; i < iovs.length(); i++) {
    Local<Value> buffer = buffers->Get(env->context(), i).ToLocalChecked();
    CHECK(Buffer::HasInstance(buffer));
    iovs[i] = uv_buf_init(Buffer::Data(buffer), Buffer::Length(buffer));
  }

  FSReqBase* req_wrap_async = GetReqWrap(args, 3);
  if (req_wrap_async != nullptr) {  // readBuffers(fd, buffers, pos, req)
    AsyncCall(env, req_wrap_async, args, "read", UTF8, AfterInteger,
              uv_fs_read, fd, *iovs, iovs.length(), pos);
  } else {  // readBuffers(fd, buffers, undefined, ctx)
    CHECK_EQ(argc, 5);
    FSReqWrapSync req_wrap_sync;
    FS_SYNC_TRACE_BEGIN(read);
    int bytesRead = SyncCall(env, /* ctx */ args[4], &req_wrap_sync, "read",
                             uv_fs_read, fd, *iovs, iovs.length(), pos);
    FS_SYNC_TRACE_END(read, "bytesRead", bytesRead);
    args.GetReturnValue().Set(bytesRead);
  }
}


/* fs.chmod(path, mode);
 * Wrapper for chmod(1) / EIO_CHMOD
 */
static void Chmod(const FunctionCallbackInfo<Value>& args) {
  Environment* env = Environment::GetCurrent(args);

  const int argc = args.Length();
  CHECK_GE(argc, 2);

  BufferValue path(env->isolate(), args[0]);
  CHECK_NOT_NULL(*path);

  CHECK(args[1]->IsInt32());
  int mode = args[1].As<Int32>()->Value();

  FSReqBase* req_wrap_async = GetReqWrap(args, 2);
  if (req_wrap_async != nullptr) {  // chmod(path, mode, req)
    AsyncCall(env, req_wrap_async, args, "chmod", UTF8, AfterNoArgs,
              uv_fs_chmod, *path, mode);
  } else {  // chmod(path, mode, undefined, ctx)
    CHECK_EQ(argc, 4);
    FSReqWrapSync req_wrap_sync;
    FS_SYNC_TRACE_BEGIN(chmod);
    SyncCall(env, args[3], &req_wrap_sync, "chmod",
             uv_fs_chmod, *path, mode);
    FS_SYNC_TRACE_END(chmod);
  }
}


/* fs.fchmod(fd, mode);
 * Wrapper for fchmod(1) / EIO_FCHMOD
 */
static void FChmod(const FunctionCallbackInfo<Value>& args) {
  Environment* env = Environment::GetCurrent(args);

  const int argc = args.Length();
  CHECK_GE(argc, 2);

  CHECK(args[0]->IsInt32());
  const int fd = args[0].As<Int32>()->Value();

  CHECK(args[1]->IsInt32());
  const int mode = args[1].As<Int32>()->Value();

  FSReqBase* req_wrap_async = GetReqWrap(args, 2);
  if (req_wrap_async != nullptr) {  // fchmod(fd, mode, req)
    AsyncCall(env, req_wrap_async, args, "fchmod", UTF8, AfterNoArgs,
              uv_fs_fchmod, fd, mode);
  } else {  // fchmod(fd, mode, undefined, ctx)
    CHECK_EQ(argc, 4);
    FSReqWrapSync req_wrap_sync;
    FS_SYNC_TRACE_BEGIN(fchmod);
    SyncCall(env, args[3], &req_wrap_sync, "fchmod",
             uv_fs_fchmod, fd, mode);
    FS_SYNC_TRACE_END(fchmod);
  }
}


/* fs.chown(path, uid, gid);
 * Wrapper for chown(1) / EIO_CHOWN
 */
static void Chown(const FunctionCallbackInfo<Value>& args) {
  Environment* env = Environment::GetCurrent(args);

  const int argc = args.Length();
  CHECK_GE(argc, 3);

  BufferValue path(env->isolate(), args[0]);
  CHECK_NOT_NULL(*path);

  CHECK(args[1]->IsUint32());
  const uv_uid_t uid = static_cast<uv_uid_t>(args[1].As<Uint32>()->Value());

  CHECK(args[2]->IsUint32());
  const uv_gid_t gid = static_cast<uv_gid_t>(args[2].As<Uint32>()->Value());

  FSReqBase* req_wrap_async = GetReqWrap(args, 3);
  if (req_wrap_async != nullptr) {  // chown(path, uid, gid, req)
    AsyncCall(env, req_wrap_async, args, "chown", UTF8, AfterNoArgs,
              uv_fs_chown, *path, uid, gid);
  } else {  // chown(path, uid, gid, undefined, ctx)
    CHECK_EQ(argc, 5);
    FSReqWrapSync req_wrap_sync;
    FS_SYNC_TRACE_BEGIN(chown);
    SyncCall(env, args[4], &req_wrap_sync, "chown",
             uv_fs_chown, *path, uid, gid);
    FS_SYNC_TRACE_END(chown);
  }
}


/* fs.fchown(fd, uid, gid);
 * Wrapper for fchown(1) / EIO_FCHOWN
 */
static void FChown(const FunctionCallbackInfo<Value>& args) {
  Environment* env = Environment::GetCurrent(args);

  const int argc = args.Length();
  CHECK_GE(argc, 3);

  CHECK(args[0]->IsInt32());
  const int fd = args[0].As<Int32>()->Value();

  CHECK(args[1]->IsUint32());
  const uv_uid_t uid = static_cast<uv_uid_t>(args[1].As<Uint32>()->Value());

  CHECK(args[2]->IsUint32());
  const uv_gid_t gid = static_cast<uv_gid_t>(args[2].As<Uint32>()->Value());

  FSReqBase* req_wrap_async = GetReqWrap(args, 3);
  if (req_wrap_async != nullptr) {  // fchown(fd, uid, gid, req)
    AsyncCall(env, req_wrap_async, args, "fchown", UTF8, AfterNoArgs,
              uv_fs_fchown, fd, uid, gid);
  } else {  // fchown(fd, uid, gid, undefined, ctx)
    CHECK_EQ(argc, 5);
    FSReqWrapSync req_wrap_sync;
    FS_SYNC_TRACE_BEGIN(fchown);
    SyncCall(env, args[4], &req_wrap_sync, "fchown",
             uv_fs_fchown, fd, uid, gid);
    FS_SYNC_TRACE_END(fchown);
  }
}


static void LChown(const FunctionCallbackInfo<Value>& args) {
  Environment* env = Environment::GetCurrent(args);

  const int argc = args.Length();
  CHECK_GE(argc, 3);

  BufferValue path(env->isolate(), args[0]);
  CHECK_NOT_NULL(*path);

  CHECK(args[1]->IsUint32());
  const uv_uid_t uid = static_cast<uv_uid_t>(args[1].As<Uint32>()->Value());

  CHECK(args[2]->IsUint32());
  const uv_gid_t gid = static_cast<uv_gid_t>(args[2].As<Uint32>()->Value());

  FSReqBase* req_wrap_async = GetReqWrap(args, 3);
  if (req_wrap_async != nullptr) {  // lchown(path, uid, gid, req)
    AsyncCall(env, req_wrap_async, args, "lchown", UTF8, AfterNoArgs,
              uv_fs_lchown, *path, uid, gid);
  } else {  // lchown(path, uid, gid, undefined, ctx)
    CHECK_EQ(argc, 5);
    FSReqWrapSync req_wrap_sync;
    FS_SYNC_TRACE_BEGIN(lchown);
    SyncCall(env, args[4], &req_wrap_sync, "lchown",
             uv_fs_lchown, *path, uid, gid);
    FS_SYNC_TRACE_END(lchown);
  }
}


static void UTimes(const FunctionCallbackInfo<Value>& args) {
  Environment* env = Environment::GetCurrent(args);

  const int argc = args.Length();
  CHECK_GE(argc, 3);

  BufferValue path(env->isolate(), args[0]);
  CHECK_NOT_NULL(*path);

  CHECK(args[1]->IsNumber());
  const double atime = args[1].As<Number>()->Value();

  CHECK(args[2]->IsNumber());
  const double mtime = args[2].As<Number>()->Value();

  FSReqBase* req_wrap_async = GetReqWrap(args, 3);
  if (req_wrap_async != nullptr) {  // utimes(path, atime, mtime, req)
    AsyncCall(env, req_wrap_async, args, "utime", UTF8, AfterNoArgs,
              uv_fs_utime, *path, atime, mtime);
  } else {  // utimes(path, atime, mtime, undefined, ctx)
    CHECK_EQ(argc, 5);
    FSReqWrapSync req_wrap_sync;
    FS_SYNC_TRACE_BEGIN(utimes);
    SyncCall(env, args[4], &req_wrap_sync, "utime",
             uv_fs_utime, *path, atime, mtime);
    FS_SYNC_TRACE_END(utimes);
  }
}

static void FUTimes(const FunctionCallbackInfo<Value>& args) {
  Environment* env = Environment::GetCurrent(args);

  const int argc = args.Length();
  CHECK_GE(argc, 3);

  CHECK(args[0]->IsInt32());
  const int fd = args[0].As<Int32>()->Value();

  CHECK(args[1]->IsNumber());
  const double atime = args[1].As<Number>()->Value();

  CHECK(args[2]->IsNumber());
  const double mtime = args[2].As<Number>()->Value();

  FSReqBase* req_wrap_async = GetReqWrap(args, 3);
  if (req_wrap_async != nullptr) {  // futimes(fd, atime, mtime, req)
    AsyncCall(env, req_wrap_async, args, "futime", UTF8, AfterNoArgs,
              uv_fs_futime, fd, atime, mtime);
  } else {  // futimes(fd, atime, mtime, undefined, ctx)
    CHECK_EQ(argc, 5);
    FSReqWrapSync req_wrap_sync;
    FS_SYNC_TRACE_BEGIN(futimes);
    SyncCall(env, args[4], &req_wrap_sync, "futime",
             uv_fs_futime, fd, atime, mtime);
    FS_SYNC_TRACE_END(futimes);
  }
}

static void LUTimes(const FunctionCallbackInfo<Value>& args) {
  Environment* env = Environment::GetCurrent(args);

  const int argc = args.Length();
  CHECK_GE(argc, 3);

  BufferValue path(env->isolate(), args[0]);
  CHECK_NOT_NULL(*path);

  CHECK(args[1]->IsNumber());
  const double atime = args[1].As<Number>()->Value();

  CHECK(args[2]->IsNumber());
  const double mtime = args[2].As<Number>()->Value();

  FSReqBase* req_wrap_async = GetReqWrap(args, 3);
  if (req_wrap_async != nullptr) {  // lutimes(path, atime, mtime, req)
    AsyncCall(env, req_wrap_async, args, "lutime", UTF8, AfterNoArgs,
              uv_fs_lutime, *path, atime, mtime);
  } else {  // lutimes(path, atime, mtime, undefined, ctx)
    CHECK_EQ(argc, 5);
    FSReqWrapSync req_wrap_sync;
    FS_SYNC_TRACE_BEGIN(lutimes);
    SyncCall(env, args[4], &req_wrap_sync, "lutime",
             uv_fs_lutime, *path, atime, mtime);
    FS_SYNC_TRACE_END(lutimes);
  }
}

static void Mkdtemp(const FunctionCallbackInfo<Value>& args) {
  Environment* env = Environment::GetCurrent(args);
  Isolate* isolate = env->isolate();

  const int argc = args.Length();
  CHECK_GE(argc, 2);

  BufferValue tmpl(isolate, args[0]);
  CHECK_NOT_NULL(*tmpl);

  const enum encoding encoding = ParseEncoding(isolate, args[1], UTF8);

  FSReqBase* req_wrap_async = GetReqWrap(args, 2);
  if (req_wrap_async != nullptr) {  // mkdtemp(tmpl, encoding, req)
    AsyncCall(env, req_wrap_async, args, "mkdtemp", encoding, AfterStringPath,
              uv_fs_mkdtemp, *tmpl);
  } else {  // mkdtemp(tmpl, encoding, undefined, ctx)
    CHECK_EQ(argc, 4);
    FSReqWrapSync req_wrap_sync;
    FS_SYNC_TRACE_BEGIN(mkdtemp);
    SyncCall(env, args[3], &req_wrap_sync, "mkdtemp",
             uv_fs_mkdtemp, *tmpl);
    FS_SYNC_TRACE_END(mkdtemp);
    const char* path = req_wrap_sync.req.path;

    Local<Value> error;
    MaybeLocal<Value> rc =
        StringBytes::Encode(isolate, path, encoding, &error);
    if (rc.IsEmpty()) {
      Local<Object> ctx = args[3].As<Object>();
      ctx->Set(env->context(), env->error_string(), error).Check();
      return;
    }
    args.GetReturnValue().Set(rc.ToLocalChecked());
  }
}

void BindingData::MemoryInfo(MemoryTracker* tracker) const {
  tracker->TrackField("stats_field_array", stats_field_array);
  tracker->TrackField("stats_field_bigint_array", stats_field_bigint_array);
  tracker->TrackField("file_handle_read_wrap_freelist",
                      file_handle_read_wrap_freelist);
}

// TODO(addaleax): Remove once we're on C++17.
constexpr FastStringKey BindingData::type_name;

void Initialize(Local<Object> target,
                Local<Value> unused,
                Local<Context> context,
                void* priv) {
  Environment* env = Environment::GetCurrent(context);
  Isolate* isolate = env->isolate();
  BindingData* const binding_data =
      env->AddBindingData<BindingData>(context, target);
  if (binding_data == nullptr) return;

  env->SetMethod(target, "access", Access);
  env->SetMethod(target, "close", Close);
  env->SetMethod(target, "open", Open);
  env->SetMethod(target, "openFileHandle", OpenFileHandle);
  env->SetMethod(target, "read", Read);
  env->SetMethod(target, "readBuffers", ReadBuffers);
  env->SetMethod(target, "fdatasync", Fdatasync);
  env->SetMethod(target, "fsync", Fsync);
  env->SetMethod(target, "rename", Rename);
  env->SetMethod(target, "ftruncate", FTruncate);
  env->SetMethod(target, "rmdir", RMDir);
  env->SetMethod(target, "mkdir", MKDir);
  env->SetMethod(target, "readdir", ReadDir);
  env->SetMethod(target, "internalModuleReadJSON", InternalModuleReadJSON);
  env->SetMethod(target, "internalModuleStat", InternalModuleStat);
  env->SetMethod(target, "stat", Stat);
  env->SetMethod(target, "lstat", LStat);
  env->SetMethod(target, "fstat", FStat);
  env->SetMethod(target, "link", Link);
  env->SetMethod(target, "symlink", Symlink);
  env->SetMethod(target, "readlink", ReadLink);
  env->SetMethod(target, "unlink", Unlink);
  env->SetMethod(target, "writeBuffer", WriteBuffer);
  env->SetMethod(target, "writeBuffers", WriteBuffers);
  env->SetMethod(target, "writeString", WriteString);
  env->SetMethod(target, "realpath", RealPath);
  env->SetMethod(target, "copyFile", CopyFile);

  env->SetMethod(target, "chmod", Chmod);
  env->SetMethod(target, "fchmod", FChmod);
  // env->SetMethod(target, "lchmod", LChmod);

  env->SetMethod(target, "chown", Chown);
  env->SetMethod(target, "fchown", FChown);
  env->SetMethod(target, "lchown", LChown);

  env->SetMethod(target, "utimes", UTimes);
  env->SetMethod(target, "futimes", FUTimes);
  env->SetMethod(target, "lutimes", LUTimes);

  env->SetMethod(target, "mkdtemp", Mkdtemp);

  target
      ->Set(context,
            FIXED_ONE_BYTE_STRING(isolate, "kFsStatsFieldsNumber"),
            Integer::New(
                isolate,
                static_cast<int32_t>(FsStatsOffset::kFsStatsFieldsNumber)))
      .Check();

  target->Set(context,
              FIXED_ONE_BYTE_STRING(isolate, "statValues"),
              binding_data->stats_field_array.GetJSArray()).Check();

  target->Set(context,
              FIXED_ONE_BYTE_STRING(isolate, "bigintStatValues"),
              binding_data->stats_field_bigint_array.GetJSArray()).Check();

  StatWatcher::Initialize(env, target);

  // Create FunctionTemplate for FSReqCallback
  Local<FunctionTemplate> fst = env->NewFunctionTemplate(NewFSReqCallback);
  fst->InstanceTemplate()->SetInternalFieldCount(
      FSReqBase::kInternalFieldCount);
  fst->Inherit(AsyncWrap::GetConstructorTemplate(env));
  env->SetConstructorFunction(target, "FSReqCallback", fst);

  // Create FunctionTemplate for FileHandleReadWrap. There’s no need
  // to do anything in the constructor, so we only store the instance template.
  Local<FunctionTemplate> fh_rw = FunctionTemplate::New(isolate);
  fh_rw->InstanceTemplate()->SetInternalFieldCount(
      FSReqBase::kInternalFieldCount);
  fh_rw->Inherit(AsyncWrap::GetConstructorTemplate(env));
  Local<String> fhWrapString =
      FIXED_ONE_BYTE_STRING(isolate, "FileHandleReqWrap");
  fh_rw->SetClassName(fhWrapString);
  env->set_filehandlereadwrap_template(
      fst->InstanceTemplate());

  // Create Function Template for FSReqPromise
  Local<FunctionTemplate> fpt = FunctionTemplate::New(isolate);
  fpt->Inherit(AsyncWrap::GetConstructorTemplate(env));
  Local<String> promiseString =
      FIXED_ONE_BYTE_STRING(isolate, "FSReqPromise");
  fpt->SetClassName(promiseString);
  Local<ObjectTemplate> fpo = fpt->InstanceTemplate();
  fpo->SetInternalFieldCount(FSReqBase::kInternalFieldCount);
  env->set_fsreqpromise_constructor_template(fpo);

  // Create FunctionTemplate for FileHandle
  Local<FunctionTemplate> fd = env->NewFunctionTemplate(FileHandle::New);
  fd->Inherit(AsyncWrap::GetConstructorTemplate(env));
  env->SetProtoMethod(fd, "close", FileHandle::Close);
  env->SetProtoMethod(fd, "releaseFD", FileHandle::ReleaseFD);
  Local<ObjectTemplate> fdt = fd->InstanceTemplate();
  fdt->SetInternalFieldCount(StreamBase::kInternalFieldCount);
  StreamBase::AddMethods(env, fd);
  env->SetConstructorFunction(target, "FileHandle", fd);
  env->set_fd_constructor_template(fdt);

  // Create FunctionTemplate for FileHandle::CloseReq
  Local<FunctionTemplate> fdclose = FunctionTemplate::New(isolate);
  fdclose->SetClassName(FIXED_ONE_BYTE_STRING(isolate,
                        "FileHandleCloseReq"));
  fdclose->Inherit(AsyncWrap::GetConstructorTemplate(env));
  Local<ObjectTemplate> fdcloset = fdclose->InstanceTemplate();
  fdcloset->SetInternalFieldCount(FSReqBase::kInternalFieldCount);
  env->set_fdclose_constructor_template(fdcloset);

  Local<Symbol> use_promises_symbol =
    Symbol::New(isolate,
                FIXED_ONE_BYTE_STRING(isolate, "use promises"));
  env->set_fs_use_promises_symbol(use_promises_symbol);
  target->Set(context,
              FIXED_ONE_BYTE_STRING(isolate, "kUsePromises"),
              use_promises_symbol).Check();
}

BindingData* FSReqBase::binding_data() {
  return binding_data_.get();
}
}  // namespace fs

}  // end namespace node

NODE_MODULE_CONTEXT_AWARE_INTERNAL(fs, node::fs::Initialize)