*result = filename_;
  return OkStatus();
}

Status ModularWritableFile::Tell(int64_t* position) {
  if (ops_->tell == nullptr)
    return errors::Unimplemented(
        tensorflow::strings::StrCat("Tell() not implemented for ", filename_));

  UniquePtrTo_TF_Status plugin_status(TF_NewStatus(), TF_DeleteStatus);
  *position = ops_->tell(file_.get(), plugin_status.get());
  return StatusFromTF_Status(plugin_status.get());
}

  if (!status.ok())
    GTEST_SKIP() << "NewWritableFile() not supported: " << status;

  int64_t position;
  status = file->Tell(&position);
  EXPECT_PRED2(UnimplementedOrReturnsCode, status, Code::OK);
  if (!status.ok()) GTEST_SKIP() << "Tell() not supported: " << status;
  EXPECT_EQ(position, 0);

  const std::string test_data("asdf");
  status = file->Append(test_data);

  TF_EXPECT_OK(ReadCache(&cache, "", block_size, block_size, &out));
  EXPECT_EQ(out.size(), 1);
  // Now read the first block; this should yield an INTERNAL error because we
  // had already cached a partial block at a later position.
  Status status = ReadCache(&cache, "", 0, block_size, &out);
  EXPECT_EQ(status.code(), error::INTERNAL);
}

TEST(RamFileBlockCacheTest, LRU) {
  const size_t block_size = 16;
  std::list<size_t> calls;

      // block in the file, which does not extend all the way out to `offset`.
      std::stringstream os;
      os << "EOF at offset " << offset << " in file " << filename
         << " at position " << pos << " with data size " << data.size();
      TF_SetStatus(status, TF_OUT_OF_RANGE, std::move(os).str().c_str());
      return total_bytes_transferred;
    }
    auto begin = data.begin();
    if (offset > pos) {

      status, ::tensorflow::Env::Default()->DeleteFile(filename));
}

bool TF_StringStreamNext(TF_StringStream* list, const char** result) {
  if (list->position >= list->list->size()) {
    *result = nullptr;
    return false;
  }

  *result = list->list->at(list->position++).c_str();
  return true;
}

void TF_StringStreamDone(TF_StringStream* list) {
  delete list->list;
  delete list;
}

  // POSIX's `ftell` returns `long`, do a manual cast.
  int64_t position = int64_t{ftell(posix_file->handle)};
  if (position < 0)
    TF_SetStatusFromIOError(status, errno, posix_file->filename);
  else
    TF_SetStatus(status, TF_OK, "");

  return position;
}

static void Flush(const TF_WritableFile* file, TF_Status* status) {

  /// mu_.
  struct Block {
    /// The block data.
    std::vector<char> data;
    /// A list iterator pointing to the block's position in the LRU list.
    std::list<Key>::iterator lru_iterator;
    /// A list iterator pointing to the block's position in the LRA list.
    std::list<Key>::iterator lra_iterator;
    /// The timestamp (seconds since epoch) at which the block was cached.
    uint64_t timestamp;

  struct Entry {
    /// The timestamp (seconds) at which the entry was added to the cache.
    uint64_t timestamp;

    /// The entry's value.
    T value;

    /// A list iterator pointing to the entry's position in the LRU list.
    std::list<std::string>::iterator lru_iterator;
  };

  bool LookupLocked(const std::string& key, T* value)
      ABSL_EXCLUSIVE_LOCKS_REQUIRED(mu_) {
    auto it = cache_.find(key);

  Status Append(StringPiece data) override;
  Status Close() override;
  Status Flush() override;
  Status Sync() override;
  Status Name(StringPiece* result) const override;
  Status Tell(int64_t* position) override;

 private:
  std::string filename_;
  std::unique_ptr<TF_WritableFile> file_;
  const TF_WritableFileOps* ops_;  // not owned
  ModularWritableFile(const ModularWritableFile&) = delete;

  auto gcs_file = static_cast<GCSFile*>(file->plugin_file);
  int64_t position = int64_t(gcs_file->outfile.tellp());
  if (position == -1)
    TF_SetStatus(status, TF_INTERNAL,
                 "tellp on the internal temporary file failed");
  else
    TF_SetStatus(status, TF_OK, "");
  return position == -1
             ? -1
             : position + (gcs_file->offset == -1 ? 0 : gcs_file->offset);
}