/*

Copyright (c) 2008-2022, Arvid Norberg

Copyright (c) 2009, Georg Rudoy

Copyright (c) 2016-2018, 2020, Alden Torres

Copyright (c) 2017-2019, Steven Siloti

Copyright (c) 2022, Konstantin Morozov

All rights reserved.

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 the author 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.

*/

#include "libtorrent/file_storage.hpp"

#include "libtorrent/string_util.hpp" // for allocate_string_copy

#include "libtorrent/utf8.hpp"

#include "libtorrent/index_range.hpp"

#include "libtorrent/aux_/path.hpp"

#include "libtorrent/aux_/numeric_cast.hpp"

#include "libtorrent/disk_interface.hpp" // for default_block_size

#include "libtorrent/aux_/merkle.hpp"

#include "libtorrent/aux_/throw.hpp"

#include "libtorrent/aux_/disable_warnings_push.hpp"

#include <boost/crc.hpp>

#include "libtorrent/aux_/disable_warnings_pop.hpp"

#include <cstdio>

#include <cinttypes>

#include <algorithm>

#include <functional>

#include <set>

#include <atomic>

#if defined(TORRENT_WINDOWS) || defined(TORRENT_OS2)

#define TORRENT_SEPARATOR '\\'

#else

#define TORRENT_SEPARATOR '/'

#endif

using namespace std::placeholders;

namespace libtorrent {

  constexpr file_flags_t file_storage::flag_pad_file;

  constexpr file_flags_t file_storage::flag_hidden;

  constexpr file_flags_t file_storage::flag_executable;

  constexpr file_flags_t file_storage::flag_symlink;

#if TORRENT_ABI_VERSION == 1

  constexpr file_flags_t file_storage::pad_file;

  constexpr file_flags_t file_storage::attribute_hidden;

  constexpr file_flags_t file_storage::attribute_executable;

  constexpr file_flags_t file_storage::attribute_symlink;

#endif

  file_storage::file_storage() = default;

  file_storage::~file_storage() = default;

  // even though this copy constructor and the copy assignment

  // operator are identical to what the compiler would have

  // generated, they are put here to explicitly make them part

  // of libtorrent and properly exported by the .dll.

  file_storage::file_storage(file_storage const&) = default;

  file_storage& file_storage::operator=(file_storage const&) & = default;

  file_storage::file_storage(file_storage&&) noexcept = default;

  file_storage& file_storage::operator=(file_storage&&) & = default;

  void file_storage::reserve(int num_files)

  {

    m_files.reserve(num_files);

  }

  int file_storage::piece_size(piece_index_t const index) const

  {

    TORRENT_ASSERT_PRECOND(index >= piece_index_t(0) && index < end_piece());

    if (index == last_piece())

    {

      std::int64_t const size_except_last

        = (num_pieces() - 1) * std::int64_t(piece_length());

      std::int64_t const size = total_size() - size_except_last;

      TORRENT_ASSERT(size > 0);

      TORRENT_ASSERT(size <= piece_length());

      return int(size);

    }

    else

      return piece_length();

  }

constexpr aux::path_index_t aux::file_entry::no_path;

constexpr aux::path_index_t aux::file_entry::path_is_absolute;

namespace {

  bool compare_file_offset(aux::file_entry const& lhs

    , aux::file_entry const& rhs)

  {

    return lhs.offset < rhs.offset;

  }

}

  int file_storage::piece_size2(piece_index_t const index) const

  {

    TORRENT_ASSERT_PRECOND(index >= piece_index_t{} && index < end_piece());

    TORRENT_ASSERT(max_file_offset / piece_length() > static_cast<int>(index));

    // find the file iterator and file offset

    aux::file_entry target;

    TORRENT_ASSERT(max_file_offset / piece_length() > static_cast<int>(index));

    target.offset = aux::numeric_cast<std::uint64_t>(std::int64_t(piece_length()) * static_cast<int>(index));

    TORRENT_ASSERT(!compare_file_offset(target, m_files.front()));

    auto const file_iter = std::upper_bound(

      m_files.begin(), m_files.end(), target, compare_file_offset);

    TORRENT_ASSERT(file_iter != m_files.begin());

    if (file_iter == m_files.end()) return piece_size(index);

    // this static cast is safe because the resulting value is capped by

    // piece_length(), which fits in an int

    return static_cast<int>(

      std::min(static_cast<std::uint64_t>(piece_length()), file_iter->offset - target.offset));

  }

  int file_storage::blocks_in_piece2(piece_index_t const index) const

  {

    // the number of default_block_size in a piece size, rounding up

    return (piece_size2(index) + default_block_size - 1) / default_block_size;

  }

  int file_storage::blocks_per_piece() const

  {

    return (m_piece_length + default_block_size - 1) / default_block_size;

  }

  // path is supposed to include the name of the torrent itself.

  // or an absolute path, to move a file outside of the download directory

  void file_storage::update_path_index(aux::file_entry& e

    , std::string const& path, bool const set_name)

  {

    if (is_complete(path))

    {

      TORRENT_ASSERT(set_name);

      e.set_name(path);

      e.path_index = aux::file_entry::path_is_absolute;

      return;

    }

    TORRENT_ASSERT(path[0] != '/');

    // split the string into the leaf filename

    // and the branch path

    string_view leaf;

    string_view branch_path;

    std::tie(branch_path, leaf) = rsplit_path(path);

    if (branch_path.empty())

    {

      if (set_name) e.set_name(leaf);

      e.path_index = aux::file_entry::no_path;

      return;

    }

    // if the path *does* contain the name of the torrent (as we expect)

    // strip it before adding it to m_paths

    if (lsplit_path(branch_path).first == m_name)

    {

      branch_path = lsplit_path(branch_path).second;

      // strip duplicate separators

      while (!branch_path.empty() && (branch_path.front() == TORRENT_SEPARATOR

#if defined(TORRENT_WINDOWS) || defined(TORRENT_OS2)

        || branch_path.front() == '/'

#endif

        ))

        branch_path.remove_prefix(1);

      e.no_root_dir = false;

    }

    else

    {

      e.no_root_dir = true;

    }

    e.path_index = get_or_add_path(branch_path);

    if (set_name) e.set_name(leaf);

  }

  aux::path_index_t file_storage::get_or_add_path(string_view const path)

  {

    // do we already have this path in the path list?

    auto const p = std::find(m_paths.rbegin(), m_paths.rend(), path);

    if (p == m_paths.rend())

    {

      // no, we don't. add it

      auto const ret = m_paths.end_index();

      TORRENT_ASSERT(path.size() == 0 || path[0] != '/');

      m_paths.emplace_back(path.data(), path.size());

      return ret;

    }

    else

    {

      // yes we do. use it

      return aux::path_index_t{aux::numeric_cast<std::uint32_t>(

        p.base() - m_paths.begin() - 1)};

    }

  }

#if TORRENT_ABI_VERSION == 1

  file_entry::file_entry(): offset(0), size(0)

    , mtime(0), pad_file(false), hidden_attribute(false)

    , executable_attribute(false)

    , symlink_attribute(false)

  {}

  file_entry::~file_entry() = default;

#endif // TORRENT_ABI_VERSION

namespace aux {

  file_entry::file_entry()

    : offset(0)

    , symlink_index(not_a_symlink)

    , no_root_dir(false)

    , size(0)

    , name_len(name_is_owned)

    , pad_file(false)

    , hidden_attribute(false)

    , executable_attribute(false)

    , symlink_attribute(false)

  {}

  file_entry::~file_entry()

  {

    if (name_len == name_is_owned) delete[] name;

  }

  file_entry::file_entry(file_entry const& fe)

    : offset(fe.offset)

    , symlink_index(fe.symlink_index)

    , no_root_dir(fe.no_root_dir)

    , size(fe.size)

    , name_len(fe.name_len)

    , pad_file(fe.pad_file)

    , hidden_attribute(fe.hidden_attribute)

    , executable_attribute(fe.executable_attribute)

    , symlink_attribute(fe.symlink_attribute)

    , root(fe.root)

    , path_index(fe.path_index)

  {

    bool const borrow = fe.name_len != name_is_owned;

    set_name(fe.filename(), borrow);

  }

  file_entry& file_entry::operator=(file_entry const& fe) &

  {

    if (&fe == this) return *this;

    offset = fe.offset;

    size = fe.size;

    path_index = fe.path_index;

    symlink_index = fe.symlink_index;

    pad_file = fe.pad_file;

    hidden_attribute = fe.hidden_attribute;

    executable_attribute = fe.executable_attribute;

    symlink_attribute = fe.symlink_attribute;

    no_root_dir = fe.no_root_dir;

    root = fe.root;

    // if the name is not owned, don't allocate memory, we can point into the

    // same metadata buffer

    bool const borrow = fe.name_len != name_is_owned;

    set_name(fe.filename(), borrow);

    return *this;

  }

  file_entry::file_entry(file_entry&& fe) noexcept

    : offset(fe.offset)

    , symlink_index(fe.symlink_index)

    , no_root_dir(fe.no_root_dir)

    , size(fe.size)

    , name_len(fe.name_len)

    , pad_file(fe.pad_file)

    , hidden_attribute(fe.hidden_attribute)

    , executable_attribute(fe.executable_attribute)

    , symlink_attribute(fe.symlink_attribute)

    , name(fe.name)

    , root(fe.root)

    , path_index(fe.path_index)

  {

    fe.name_len = 0;

    fe.name = nullptr;

  }

  file_entry& file_entry::operator=(file_entry&& fe) & noexcept

  {

    if (&fe == this) return *this;

    offset = fe.offset;

    size = fe.size;

    path_index = fe.path_index;

    symlink_index = fe.symlink_index;

    pad_file = fe.pad_file;

    hidden_attribute = fe.hidden_attribute;

    executable_attribute = fe.executable_attribute;

    symlink_attribute = fe.symlink_attribute;

    no_root_dir = fe.no_root_dir;

    if (name_len == name_is_owned) delete[] name;

    name = fe.name;

    root = fe.root;

    name_len = fe.name_len;

    fe.name_len = 0;

    fe.name = nullptr;

    return *this;

  }

  // if borrow_string is true, don't take ownership over n, just

  // point to it.

  // if borrow_string is false, n will be copied and owned by the

  // file_entry.

  void file_entry::set_name(string_view n, bool const borrow_string)

  {

    // free the current string, before assigning the new one

    if (name_len == name_is_owned) delete[] name;

    if (n.empty())

    {

      TORRENT_ASSERT(borrow_string == false);

      name = nullptr;

    }

    else if (borrow_string)

    {

      // we have limited space in the length field. truncate string

      // if it's too long

      if (n.size() >= name_is_owned) n = n.substr(name_is_owned - 1);

      name = n.data();

      name_len = aux::numeric_cast<std::uint64_t>(n.size());

    }

    else

    {

      name = allocate_string_copy(n);

      name_len = name_is_owned;

    }

  }

  string_view file_entry::filename() const

  {

    if (name_len != name_is_owned) return {name, std::size_t(name_len)};

    return name ? string_view(name) : string_view();

  }

} // aux namespace

#if TORRENT_ABI_VERSION == 1

  void file_storage::add_file_borrow(char const* filename, int filename_len

    , std::string const& path, std::int64_t file_size, file_flags_t file_flags

    , char const* filehash, std::int64_t mtime, string_view symlink_path)

  {

    TORRENT_ASSERT(filename_len >= 0);

    add_file_borrow({filename, std::size_t(filename_len)}, path, file_size

      , file_flags, filehash, mtime, symlink_path);

  }

  void file_storage::add_file(file_entry const& fe, char const* filehash)

  {

    file_flags_t flags = {};

    if (fe.pad_file) flags |= file_storage::flag_pad_file;

    if (fe.hidden_attribute) flags |= file_storage::flag_hidden;

    if (fe.executable_attribute) flags |= file_storage::flag_executable;

    if (fe.symlink_attribute) flags |= file_storage::flag_symlink;

    add_file_borrow({}, fe.path, fe.size, flags, filehash, fe.mtime

      , fe.symlink_path);

  }

#endif // TORRENT_ABI_VERSION

  void file_storage::rename_file(file_index_t const index

    , std::string const& new_filename)

  {

    TORRENT_ASSERT_PRECOND(index >= file_index_t(0) && index < end_file());

    update_path_index(m_files[index], new_filename);

  }

#if TORRENT_ABI_VERSION == 1

  file_storage::iterator file_storage::file_at_offset_deprecated(std::int64_t offset) const

  {

    // find the file iterator and file offset

    aux::file_entry target;

    TORRENT_ASSERT(offset <= max_file_offset);

    target.offset = aux::numeric_cast<std::uint64_t>(offset);

    TORRENT_ASSERT(!compare_file_offset(target, m_files.front()));

    auto file_iter = std::upper_bound(

      begin_deprecated(), end_deprecated(), target, compare_file_offset);

    TORRENT_ASSERT(file_iter != begin_deprecated());

    --file_iter;

    return file_iter;

  }

  file_storage::iterator file_storage::file_at_offset(std::int64_t offset) const

  {

    return file_at_offset_deprecated(offset);

  }

#endif

  file_index_t file_storage::file_index_at_offset(std::int64_t const offset) const

  {

    TORRENT_ASSERT_PRECOND(offset >= 0);

    TORRENT_ASSERT_PRECOND(offset < m_total_size);

    TORRENT_ASSERT(offset <= max_file_offset);

    // find the file iterator and file offset

    aux::file_entry target;

    target.offset = aux::numeric_cast<std::uint64_t>(offset);

    TORRENT_ASSERT(!compare_file_offset(target, m_files.front()));

    auto file_iter = std::upper_bound(

      m_files.begin(), m_files.end(), target, compare_file_offset);

    TORRENT_ASSERT(file_iter != m_files.begin());

    --file_iter;

    return file_index_t{int(file_iter - m_files.begin())};

  }

  file_index_t file_storage::file_index_at_piece(piece_index_t const piece) const

  {

    return file_index_at_offset(static_cast<int>(piece) * std::int64_t(piece_length()));

  }

  file_index_t file_storage::file_index_for_root(sha256_hash const& root_hash) const

  {

    // TODO: maybe it would be nice to have a better index here

    for (file_index_t const i : file_range())

    {

      if (root(i) == root_hash) return i;

    }

    return file_index_t{-1};

  }

  piece_index_t file_storage::piece_index_at_file(file_index_t f) const

  {

    return piece_index_t{aux::numeric_cast<int>(file_offset(f) / piece_length())};

  }

#if TORRENT_ABI_VERSION <= 2

  char const* file_storage::file_name_ptr(file_index_t const index) const

  {

    return m_files[index].name;

  }

  int file_storage::file_name_len(file_index_t const index) const

  {

    if (m_files[index].name_len == aux::file_entry::name_is_owned)

      return -1;

    return m_files[index].name_len;

  }

#endif

  std::vector<file_slice> file_storage::map_block(piece_index_t const piece

    , std::int64_t const offset, std::int64_t size) const

  {

    TORRENT_ASSERT_PRECOND(piece >= piece_index_t{0});

    TORRENT_ASSERT_PRECOND(piece < end_piece());

    TORRENT_ASSERT_PRECOND(num_files() > 0);

    TORRENT_ASSERT_PRECOND(size >= 0);

    std::vector<file_slice> ret;

    if (m_files.empty()) return ret;

    // find the file iterator and file offset

    aux::file_entry target;

    TORRENT_ASSERT(max_file_offset / m_piece_length > static_cast<int>(piece));

    target.offset = aux::numeric_cast<std::uint64_t>(static_cast<int>(piece) * std::int64_t(m_piece_length) + offset);

    TORRENT_ASSERT_PRECOND(std::int64_t(target.offset) <= m_total_size - size);

    TORRENT_ASSERT(!compare_file_offset(target, m_files.front()));

    // in case the size is past the end, fix it up

    if (std::int64_t(target.offset) > m_total_size - size)

      size = m_total_size - std::int64_t(target.offset);

    auto file_iter = std::upper_bound(

      m_files.begin(), m_files.end(), target, compare_file_offset);

    TORRENT_ASSERT(file_iter != m_files.begin());

    --file_iter;

    std::int64_t file_offset = target.offset - file_iter->offset;

    for (; size > 0; file_offset -= file_iter->size, ++file_iter)

    {

      TORRENT_ASSERT(file_iter != m_files.end());

      if (file_offset < std::int64_t(file_iter->size))

      {

        file_slice f{};

        f.file_index = file_index_t(int(file_iter - m_files.begin()));

        f.offset = file_offset;

        f.size = std::min(std::int64_t(file_iter->size) - file_offset, std::int64_t(size));

        TORRENT_ASSERT(f.size <= size);

        size -= f.size;

        file_offset += f.size;

        ret.push_back(f);

      }

      TORRENT_ASSERT(size >= 0);

    }

    return ret;

  }

#if TORRENT_ABI_VERSION == 1

  file_entry file_storage::at(int index) const

  {

    return at_deprecated(index);

  }

  aux::file_entry const& file_storage::internal_at(int const index) const

  {

    TORRENT_ASSERT(index >= 0);

    TORRENT_ASSERT(index < int(m_files.size()));

    return m_files[file_index_t(index)];

  }

  file_entry file_storage::at_deprecated(int index) const

  {

    TORRENT_ASSERT_PRECOND(index >= 0 && index < int(m_files.size()));

    file_entry ret;

    aux::file_entry const& ife = m_files[index];

    ret.path = file_path(index);

    ret.offset = ife.offset;

    ret.size = ife.size;

    ret.mtime = mtime(index);

    ret.pad_file = ife.pad_file;

    ret.hidden_attribute = ife.hidden_attribute;

    ret.executable_attribute = ife.executable_attribute;

    ret.symlink_attribute = ife.symlink_attribute;

    if (ife.symlink_index != aux::file_entry::not_a_symlink)

      ret.symlink_path = symlink(index);

    ret.filehash = hash(index);

    return ret;

  }

#endif // TORRENT_ABI_VERSION

  int file_storage::num_files() const noexcept

  { return int(m_files.size()); }

  // returns the index of the one-past-end file in the file storage

  file_index_t file_storage::end_file() const noexcept

  { return m_files.end_index(); }

  file_index_t file_storage::last_file() const noexcept

  { return --m_files.end_index(); }

  index_range<file_index_t> file_storage::file_range() const noexcept

  { return m_files.range(); }

  index_range<piece_index_t> file_storage::piece_range() const noexcept

  { return {piece_index_t{0}, end_piece()}; }

  peer_request file_storage::map_file(file_index_t const file_index

    , std::int64_t const file_offset, int const size) const

  {

    TORRENT_ASSERT_PRECOND(file_index < end_file());

    TORRENT_ASSERT(m_num_pieces >= 0);

    peer_request ret{};

    if (file_index >= end_file())

    {

      ret.piece = end_piece();

      ret.start = 0;

      ret.length = 0;

      return ret;

    }

    std::int64_t const offset = file_offset + this->file_offset(file_index);

    if (offset >= total_size())

    {

      ret.piece = end_piece();

      ret.start = 0;

      ret.length = 0;

    }

    else

    {

      ret.piece = piece_index_t(int(offset / piece_length()));

      ret.start = int(offset % piece_length());

      ret.length = size;

      if (offset + size > total_size())

        ret.length = int(total_size() - offset);

    }

    return ret;

  }

#ifndef BOOST_NO_EXCEPTIONS

  void file_storage::add_file(std::string const& path, std::int64_t const file_size

    , file_flags_t const file_flags, std::time_t const mtime, string_view const symlink_path

    , char const* root_hash)

  {

    error_code ec;

    add_file_borrow(ec, {}, path, file_size, file_flags, nullptr, mtime

      , symlink_path, root_hash);

    if (ec) aux::throw_ex<system_error>(ec);

  }

  void file_storage::add_file_borrow(string_view filename

    , std::string const& path, std::int64_t const file_size

    , file_flags_t const file_flags, char const* filehash

    , std::int64_t const mtime, string_view const symlink_path

    , char const* root_hash)

  {

    error_code ec;

    add_file_borrow(ec, filename, path, file_size

      , file_flags, filehash, mtime, symlink_path, root_hash);

    if (ec) aux::throw_ex<system_error>(ec);

  }

#endif // BOOST_NO_EXCEPTIONS

  void file_storage::add_file(error_code& ec, std::string const& path

    , std::int64_t const file_size, file_flags_t const file_flags, std::time_t const mtime

    , string_view symlink_path, char const* root_hash)

  {

    add_file_borrow(ec, {}, path, file_size, file_flags, nullptr, mtime

      , symlink_path, root_hash);

  }

  void file_storage::add_file_borrow(error_code& ec, string_view filename

    , std::string const& path, std::int64_t const file_size

    , file_flags_t const file_flags, char const* filehash

    , std::int64_t const mtime, string_view const symlink_path

    , char const* root_hash)

  {

    TORRENT_ASSERT_PRECOND(file_size >= 0);

    TORRENT_ASSERT_PRECOND(!is_complete(filename));

    if (file_size > max_file_size)

    {

      ec = make_error_code(boost::system::errc::file_too_large);

      return;

    }

    if (max_file_offset - m_total_size < file_size)

    {

      ec = make_error_code(errors::torrent_invalid_length);

      return;

    }

    if (!filename.empty())

    {

      if (filename.size() >= (1 << 12))

      {

        ec = make_error_code(boost::system::errc::filename_too_long);

        return;

      }

    }

    else if (lt::filename(path).size() >= (1 << 12))

    {

      ec = make_error_code(boost::system::errc::filename_too_long);

      return;

    }

    if (!has_parent_path(path))

    {

      // you have already added at least one file with a

      // path to the file (branch_path), which means that

      // all the other files need to be in the same top

      // directory as the first file.

      TORRENT_ASSERT_PRECOND(m_files.empty());

      m_name = path;

    }

    else

    {

      if (m_files.empty())

        m_name = lsplit_path(path).first.to_string();

    }

    // files without a root_hash are assumed to be v1, except symlinks. They

    // don't have a root hash and can be either v1 or v2

    if (symlink_path.empty() && file_size > 0)

    {

      bool const v2 = (root_hash != nullptr);

      // This condition is true of all files we've added so far have been

      // symlinks. i.e. this is the first "real" file we're adding.

      // or if m_total_size == 0, all files we've added so far have been

      // empty (which also are are v1/v2-ambigous)

      if (m_files.size() == m_symlinks.size() || m_total_size == 0)

      {

        m_v2 = v2;

      }

      else if (m_v2 != v2)

      {

        // you cannot mix v1 and v2 files when building torrent_storage. Either

        // all files are v1 or all files are v2

        ec = m_v2 ? make_error_code(errors::torrent_missing_pieces_root)

          : make_error_code(errors::torrent_inconsistent_files);

        return;

      }

    }

    m_files.emplace_back();

    aux::file_entry& e = m_files.back();

    // the last argument specified whether the function should also set

    // the filename. If it does, it will copy the leaf filename from path.

    // if filename is empty, we should copy it. If it isn't, we're borrowing

    // it and we can save the copy by setting it after this call to

    // update_path_index().

    update_path_index(e, path, filename.empty());

    // filename is allowed to be empty, in which case we just use path

    if (!filename.empty())

      e.set_name(filename, true);

    e.size = aux::numeric_cast<std::uint64_t>(file_size);

    e.offset = aux::numeric_cast<std::uint64_t>(m_total_size);

    e.pad_file = bool(file_flags & file_storage::flag_pad_file);

    e.hidden_attribute = bool(file_flags & file_storage::flag_hidden);

    e.executable_attribute = bool(file_flags & file_storage::flag_executable);

    e.symlink_attribute = bool(file_flags & file_storage::flag_symlink);

    e.root = root_hash;

    if (filehash)

    {

      if (m_file_hashes.size() < m_files.size()) m_file_hashes.resize(m_files.size());

      m_file_hashes[last_file()] = filehash;

    }

    if (!symlink_path.empty()

      && m_symlinks.size() < aux::file_entry::not_a_symlink - 1)

    {

      e.symlink_index = m_symlinks.size();

      m_symlinks.emplace_back(symlink_path.to_string());

    }

    else

    {

      e.symlink_attribute = false;

    }

    if (mtime)

    {

      if (m_mtime.size() < m_files.size()) m_mtime.resize(m_files.size());

      m_mtime[last_file()] = std::time_t(mtime);

    }

    m_total_size += e.size;

    // when making v2 torrents, pad the end of each file (if necessary) to

    // ensure it ends on a piece boundary.

    // we do this at the end of files rather in-front of files to conform to

    // the BEP52 reference implementation

    if (m_v2 && (m_total_size % piece_length()) != 0)

    {

      auto const pad_size = piece_length() - (m_total_size % piece_length());

      TORRENT_ASSERT(int(pad_size) != piece_length());

      TORRENT_ASSERT(int(pad_size) > 0);

      if (m_total_size > max_file_offset - pad_size)

      {

        ec = make_error_code(errors::torrent_invalid_length);

        return;

      }

      m_files.emplace_back();

      // e is invalid from here down!

      auto& pad = m_files.back();

      pad.size = static_cast<std::uint64_t>(pad_size);

      TORRENT_ASSERT(m_total_size <= max_file_offset);

      TORRENT_ASSERT(m_total_size > 0);

      pad.offset = static_cast<std::uint64_t>(m_total_size);

      pad.path_index = get_or_add_path(".pad");

      char name[30];

      std::snprintf(name, sizeof(name), "%" PRIu64

        , pad.size);

      pad.set_name(name);

      pad.pad_file = true;

      m_total_size += pad_size;

    }

  }

  // this is here for backwards compatibility with hybrid torrents created

  // with libtorrent 2.0.0-2.0.7, which would not add tail-padding

  void file_storage::remove_tail_padding()

  {

    file_index_t f = end_file();

    while (f > file_index_t{0})

    {

      --f;

      // empty files and symlinks are skipped

      if (file_size(f) == 0) continue;

      if (pad_file_at(f))

      {

        m_total_size -= file_size(f);

        m_files.erase(m_files.begin() + int(f));

        while (f < end_file())

        {

          m_files[f].offset = static_cast<std::uint64_t>(m_total_size);

          TORRENT_ASSERT(m_files[f].size == 0);

          ++f;

        }

      }

      // if the last non-empty file isn't a pad file, don't do anything

      return;

    }

    // nothing found

  }

  sha1_hash file_storage::hash(file_index_t const index) const

  {

    TORRENT_ASSERT_PRECOND(index >= file_index_t{} && index < end_file());

    if (index >= m_file_hashes.end_index()) return sha1_hash();

    return sha1_hash(m_file_hashes[index]);

  }

  sha256_hash file_storage::root(file_index_t const index) const

  {

    TORRENT_ASSERT_PRECOND(index >= file_index_t{} && index < end_file());

    if (m_files[index].root == nullptr) return sha256_hash();

    return sha256_hash(m_files[index].root);

  }

  char const* file_storage::root_ptr(file_index_t const index) const

  {

    TORRENT_ASSERT_PRECOND(index >= file_index_t{} && index < end_file());

    return m_files[index].root;

  }

  std::string file_storage::symlink(file_index_t const index) const

  {

    TORRENT_ASSERT_PRECOND(index >= file_index_t{} && index < end_file());

    aux::file_entry const& fe = m_files[index];

    if (fe.symlink_index == aux::file_entry::not_a_symlink)

      return {};

    TORRENT_ASSERT(fe.symlink_index < int(m_symlinks.size()));

    auto const& link = m_symlinks[fe.symlink_index];

    std::string ret;

    ret.reserve(m_name.size() + link.size() + 1);

    ret.assign(m_name);

    append_path(ret, link);

    return ret;

  }

  std::string const& file_storage::internal_symlink(file_index_t const index) const

  {

    TORRENT_ASSERT_PRECOND(index >= file_index_t{} && index < end_file());

    aux::file_entry const& fe = m_files[index];

    TORRENT_ASSERT(fe.symlink_index < int(m_symlinks.size()));

    return m_symlinks[fe.symlink_index];

  }

  std::time_t file_storage::mtime(file_index_t const index) const

  {

    TORRENT_ASSERT_PRECOND(index >= file_index_t{} && index < end_file());

    if (index >= m_mtime.end_index()) return 0;

    return m_mtime[index];

  }

namespace {

    template <class CRC>

    void process_string_lowercase(CRC& crc, string_view str)

    {

      for (char const c : str)

        crc.process_byte(to_lower(c) & 0xff);

    }

    template <class CRC>

    void process_path_lowercase(

      std::unordered_set<std::uint32_t>& table

      , CRC crc, string_view str)

    {

      if (str.empty()) return;

      for (char const c : str)

      {

        if (c == TORRENT_SEPARATOR)

          table.insert(crc.checksum());

        crc.process_byte(to_lower(c) & 0xff);

      }

      table.insert(crc.checksum());

    }

  }

  void file_storage::all_path_hashes(

    std::unordered_set<std::uint32_t>& table) const

  {

    boost::crc_optimal<32, 0x1EDC6F41, 0xFFFFFFFF, 0xFFFFFFFF, true, true> crc;

    if (!m_name.empty())

    {

      process_string_lowercase(crc, m_name);

      TORRENT_ASSERT(m_name[m_name.size() - 1] != TORRENT_SEPARATOR);

      crc.process_byte(TORRENT_SEPARATOR);

    }

    for (auto const& p : m_paths)

      process_path_lowercase(table, crc, p);

  }

  std::uint32_t file_storage::file_path_hash(file_index_t const index

    , std::string const& save_path) const

  {

    TORRENT_ASSERT_PRECOND(index >= file_index_t(0) && index < end_file());

    aux::file_entry const& fe = m_files[index];

    boost::crc_optimal<32, 0x1EDC6F41, 0xFFFFFFFF, 0xFFFFFFFF, true, true> crc;

    if (fe.path_index == aux::file_entry::path_is_absolute)

    {

      process_string_lowercase(crc, fe.filename());

    }

    else if (fe.path_index == aux::file_entry::no_path)

    {

      if (!save_path.empty())

      {

        process_string_lowercase(crc, save_path);

        TORRENT_ASSERT(save_path[save_path.size() - 1] != TORRENT_SEPARATOR);

        crc.process_byte(TORRENT_SEPARATOR);

      }

      process_string_lowercase(crc, fe.filename());

    }

    else if (fe.no_root_dir)

    {

      if (!save_path.empty())

      {

        process_string_lowercase(crc, save_path);

        TORRENT_ASSERT(save_path[save_path.size() - 1] != TORRENT_SEPARATOR);

        crc.process_byte(TORRENT_SEPARATOR);

      }

      std::string const& p = m_paths[fe.path_index];

      if (!p.empty())

      {

        process_string_lowercase(crc, p);

        TORRENT_ASSERT(p[p.size() - 1] != TORRENT_SEPARATOR);

        crc.process_byte(TORRENT_SEPARATOR);

      }

      process_string_lowercase(crc, fe.filename());

    }

    else

    {

      if (!save_path.empty())

      {

        process_string_lowercase(crc, save_path);

        TORRENT_ASSERT(save_path[save_path.size() - 1] != TORRENT_SEPARATOR);

        crc.process_byte(TORRENT_SEPARATOR);

      }

      process_string_lowercase(crc, m_name);

      TORRENT_ASSERT(m_name.size() > 0);

      TORRENT_ASSERT(m_name[m_name.size() - 1] != TORRENT_SEPARATOR);

      crc.process_byte(TORRENT_SEPARATOR);

      std::string const& p = m_paths[fe.path_index];

      if (!p.empty())

      {

        process_string_lowercase(crc, p);

        TORRENT_ASSERT(p.size() > 0);

        TORRENT_ASSERT(p[p.size() - 1] != TORRENT_SEPARATOR);

        crc.process_byte(TORRENT_SEPARATOR);

      }

      process_string_lowercase(crc, fe.filename());

    }