/*

Copyright (c) 2014-2020, Arvid Norberg

Copyright (c) 2016-2018, Alden Torres

Copyright (c) 2016-2017, Steven Siloti

Copyright (c) 2018, d-komarov

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.

*/

/*

  The part_file file format is an array of piece sized blocks with

  a simple header. For a given number of pieces, the header has a

  fixed size. The header size is rounded up to an even multiple of

  1024, in an attempt at improving disk I/O performance by aligning

  reads and writes to clusters on the drive. This is the file header

  format. All values are stored big endian on disk.

  // the size of the torrent (and can be used to calculate the size

  // of the file header)

  uint32_t num_pieces;

  // the number of bytes in each piece. This determines the size of

  // each slot in the part file. This is typically an even power of 2,

  // but it is not guaranteed to be.

  uint32_t piece_size;

  // this is an array specifying which slots a particular piece resides in,

  // A value of 0xffffffff (-1 if you will) means the piece is not in the part_file

  // Any other value means the piece resides in the slot with that index

  uint32_t piece[num_pieces];

  // unused, n is defined as the number to align the size of this

  // header to an even multiple of 1024 bytes.

  uint8_t padding[n];

*/

#include "libtorrent/part_file.hpp"

#include "libtorrent/io.hpp"

#include "libtorrent/assert.hpp"

#include "libtorrent/aux_/vector.hpp"

#include "libtorrent/aux_/path.hpp"

#include "libtorrent/aux_/storage_utils.hpp" // for iovec_t

#include <functional> // for std::function

#include <cstdint>

namespace {

  // round up to even kilobyte

  int round_up(int n)

  { return (n + 1023) & ~0x3ff; }

}

namespace libtorrent {

  part_file::part_file(std::string path, std::string name

    , int const num_pieces, int const piece_size)

    : m_path(std::move(path))

    , m_name(std::move(name))

    , m_max_pieces(num_pieces)

    , m_piece_size(piece_size)

    , m_header_size(round_up((2 + num_pieces) * 4))

  {

    TORRENT_ASSERT(num_pieces > 0);

    TORRENT_ASSERT(m_piece_size > 0);

    error_code ec;

    auto f = open_file(aux::open_mode::read_only, ec);

    if (ec) return;

    // parse header

    std::vector<char> header(static_cast<std::size_t>(m_header_size));

    int const n = int(aux::pread_all(f.fd(), header, 0, ec));

    if (ec) return;

    // we don't have a full header. consider the file empty

    if (n < m_header_size) return;

    using namespace libtorrent::aux;

    char* ptr = header.data();

    // we have a header. Parse it

    int const num_pieces_ = int(read_uint32(ptr));

    int const piece_size_ = int(read_uint32(ptr));

    // if there is a mismatch in number of pieces or piece size

    // consider the file empty and overwrite anything in there

    if (num_pieces != num_pieces_ || m_piece_size != piece_size_) return;

    // this is used to determine which slots are free, and how many

    // slots are allocated

    aux::vector<bool, slot_index_t> free_slots;

    free_slots.resize(num_pieces, true);

    for (piece_index_t i = piece_index_t(0); i < piece_index_t(num_pieces); ++i)

    {

      slot_index_t const slot(read_int32(ptr));

      if (static_cast<int>(slot) < 0) continue;

      // invalid part-file

      TORRENT_ASSERT(slot < slot_index_t(num_pieces));

      if (slot >= slot_index_t(num_pieces)) continue;

      if (slot >= m_num_allocated)

        m_num_allocated = next(slot);

      free_slots[slot] = false;

      m_piece_map[i] = slot;

    }

    // now, populate the free_list with the "holes"

    for (slot_index_t i(0); i < m_num_allocated; ++i)

    {

      if (free_slots[i]) m_free_slots.push_back(i);

    }

  }

  part_file::~part_file()

  {

    error_code ec;

    flush_metadata_impl(ec);

  }

  slot_index_t part_file::allocate_slot(piece_index_t const piece)

  {

    // the mutex is assumed to be held here, since this is a private function

    TORRENT_ASSERT(m_piece_map.find(piece) == m_piece_map.end());

    slot_index_t slot(-1);

    if (!m_free_slots.empty())

    {

      slot = m_free_slots.front();

      m_free_slots.erase(m_free_slots.begin());

    }

    else

    {

      slot = m_num_allocated;

      ++m_num_allocated;

    }

    m_piece_map[piece] = slot;

    m_dirty_metadata = true;

    return slot;

  }

  int part_file::write(span<char> buf, piece_index_t const piece

    , int const offset, error_code& ec)

  {

    TORRENT_ASSERT(offset >= 0);

    TORRENT_ASSERT(int(buf.size()) + offset <= m_piece_size);

    std::unique_lock<std::mutex> l(m_mutex);

    auto f = open_file(aux::open_mode::write | aux::open_mode::hidden, ec);

    if (ec) return -1;

    auto const i = m_piece_map.find(piece);

    slot_index_t const slot = (i == m_piece_map.end())

      ? allocate_slot(piece) : i->second;

    l.unlock();

    return int(aux::pwrite_all(f.fd(), buf, slot_offset(slot) + offset, ec));

  }

  int part_file::read(span<char> buf

    , piece_index_t const piece

    , int const offset, error_code& ec)

  {

    TORRENT_ASSERT(offset >= 0);

    TORRENT_ASSERT(int(buf.size()) + offset <= m_piece_size);

    std::unique_lock<std::mutex> l(m_mutex);

    auto const i = m_piece_map.find(piece);

    if (i == m_piece_map.end())

    {

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

      return -1;

    }

    slot_index_t const slot = i->second;

    l.unlock();

    auto f = open_file(aux::open_mode::read_only | aux::open_mode::hidden, ec);

    if (ec) return -1;

    return int(aux::pread_all(f.fd(), buf, slot_offset(slot) + offset, ec));

  }

  int part_file::hash(hasher& ph

    , std::ptrdiff_t const len

    , piece_index_t const piece

    , int const offset, error_code& ec)

  {

    return do_hash(ph, len, piece, offset, ec);

  }

  int part_file::hash2(hasher256& ph

    , std::ptrdiff_t const len

    , piece_index_t const piece

    , int const offset, error_code& ec)

  {

    return do_hash(ph, len, piece, offset, ec);

  }

  template <typename Hasher>

  int part_file::do_hash(Hasher& ph

    , std::ptrdiff_t const len

    , piece_index_t const piece

    , int const offset, error_code& ec)

  {

    TORRENT_ASSERT(offset >= 0);

    TORRENT_ASSERT(len >= 0);

    TORRENT_ASSERT(int(len) + offset <= m_piece_size);

    std::unique_lock<std::mutex> l(m_mutex);

    auto const i = m_piece_map.find(piece);

    if (i == m_piece_map.end())

    {

      ec = error_code(boost::system::errc::no_such_file_or_directory

        , boost::system::generic_category());

      return -1;

    }

    slot_index_t const slot = i->second;

    auto f = open_file(aux::open_mode::read_only | aux::open_mode::hidden, ec);

    if (ec) return -1;

    l.unlock();

    std::vector<char> buffer(static_cast<std::size_t>(len));

    std::int64_t const slot_offset = std::int64_t(m_header_size) + std::int64_t(static_cast<int>(slot)) * m_piece_size;

    int const ret = int(aux::pread_all(f.fd(), buffer, slot_offset + offset, ec));

    ph.update(buffer);

    return ret;

  }

Unexecuted instantiation: int libtorrent::part_file::do_hash<libtorrent::lcrypto::hasher>(libtorrent::lcrypto::hasher&, long, libtorrent::aux::strong_typedef<int, libtorrent::aux::piece_index_tag, void>, int, boost::system::error_code&)

Unexecuted instantiation: int libtorrent::part_file::do_hash<libtorrent::lcrypto::hasher256>(libtorrent::lcrypto::hasher256&, long, libtorrent::aux::strong_typedef<int, libtorrent::aux::piece_index_tag, void>, int, boost::system::error_code&)

  aux::file_handle part_file::open_file(aux::open_mode_t const mode, error_code& ec) try

  {

    std::string const fn = combine_path(m_path, m_name);

    try {

      return aux::file_handle(fn, 0, mode);

    }

    catch (storage_error const& e)

    {

      if ((mode & aux::open_mode::write)

        && e.ec == boost::system::errc::no_such_file_or_directory)

      {

        // this means the directory the file is in doesn't exist.

        // so create it

        ec.clear();

        create_directories(m_path, ec);

        if (ec) return {};

        return aux::file_handle(fn, 0, mode);

      }

      return {};

    }

  }

  catch (storage_error const& e)

  {

    ec = e.ec;

    return {};

  }

  void part_file::free_piece(piece_index_t const piece)

  {

    std::lock_guard<std::mutex> l(m_mutex);

    auto const i = m_piece_map.find(piece);

    if (i == m_piece_map.end()) return;

    // TODO: what do we do if someone is currently reading from the disk

    // from this piece? does it matter? Since we won't actively erase the

    // data from disk, but it may be overwritten soon, it's probably not that

    // big of a deal

    m_free_slots.push_back(i->second);

    m_piece_map.erase(i);

    m_dirty_metadata = true;

  }

  void part_file::move_partfile(std::string const& path, error_code& ec)

  {

    std::lock_guard<std::mutex> l(m_mutex);

    flush_metadata_impl(ec);

    if (ec) return;

    if (!m_piece_map.empty())

    {

      std::string old_path = combine_path(m_path, m_name);

      std::string new_path = combine_path(path, m_name);

      rename(old_path, new_path, ec);

      if (ec == boost::system::errc::no_such_file_or_directory)

        ec.clear();

      if (ec)

      {

        storage_error se;

        aux::copy_file(old_path, new_path, se);

        ec = se.ec;

        if (ec) return;

        remove(old_path, ec);

      }

    }

    m_path = path;

  }

  void part_file::export_file(std::function<void(std::int64_t, span<char>)> f

    , std::int64_t const offset, std::int64_t size, error_code& ec)

  {

    std::unique_lock<std::mutex> l(m_mutex);

    // there's nothing stored in the part_file. Nothing to do

    if (m_piece_map.empty()) return;

    piece_index_t piece(int(offset / m_piece_size));

    piece_index_t const end = piece_index_t(int(((offset + size) + m_piece_size - 1) / m_piece_size));

    std::unique_ptr<char[]> buf;

    std::int64_t piece_offset = offset - std::int64_t(static_cast<int>(piece))

      * m_piece_size;

    std::int64_t file_offset = 0;

    auto file = open_file(aux::open_mode::read_only, ec);

    if (ec) return;

    for (; piece < end; ++piece)

    {

      auto const i = m_piece_map.find(piece);

      int const block_to_copy = int(std::min(m_piece_size - piece_offset, size));

      if (i != m_piece_map.end())

      {

        slot_index_t const slot = i->second;

        if (!buf) buf.reset(new char[std::size_t(m_piece_size)]);

        // don't hold the lock during disk I/O

        l.unlock();

        span<char> v = {buf.get(), block_to_copy};

        auto bytes_read = aux::pread_all(file.fd(), v, slot_offset(slot) + piece_offset, ec);

        v = v.first(static_cast<std::ptrdiff_t>(bytes_read));

        if (ec || v.empty()) return;

        f(file_offset, {buf.get(), block_to_copy});

        // we're done with the disk I/O, grab the lock again to update

        // the slot map

        l.lock();

        if (block_to_copy == m_piece_size)

        {

          // since we released the lock, it's technically possible that

          // another thread removed this slot map entry, and invalidated

          // our iterator. Now that we hold the lock again, perform

          // another lookup to be sure.

          auto const j = m_piece_map.find(piece);

          if (j != m_piece_map.end())

          {

            // if the slot moved, that's really suspicious

            TORRENT_ASSERT(j->second == slot);

            m_free_slots.push_back(j->second);

            m_piece_map.erase(j);

            m_dirty_metadata = true;

          }

        }

      }

      file_offset += block_to_copy;

      piece_offset = 0;

      size -= block_to_copy;

    }

  }

  void part_file::flush_metadata(error_code& ec)

  {

    std::lock_guard<std::mutex> l(m_mutex);

    flush_metadata_impl(ec);

  }

  // TODO: instead of rebuilding the whole file header

  // and flushing it, update the slot entries as we go

  void part_file::flush_metadata_impl(error_code& ec)

  {

    // do we need to flush the metadata?

    if (m_dirty_metadata == false) return;

    if (m_piece_map.empty())

    {

      // if we don't have any pieces left in the

      // part file, remove it

      std::string const p = combine_path(m_path, m_name);

      remove(p, ec);

      if (ec == boost::system::errc::no_such_file_or_directory)

        ec.clear();

      return;

    }

    auto f = open_file(aux::open_mode::write | aux::open_mode::hidden, ec);

    if (ec) return;

    std::vector<char> header(static_cast<std::size_t>(m_header_size));

    using namespace libtorrent::aux;

    char* ptr = header.data();

    write_uint32(m_max_pieces, ptr);

    write_uint32(m_piece_size, ptr);

    for (piece_index_t piece(0); piece < piece_index_t(m_max_pieces); ++piece)

    {

      auto const i = m_piece_map.find(piece);

      slot_index_t const slot(i == m_piece_map.end()

        ? slot_index_t(-1) : i->second);

      write_int32(static_cast<int>(slot), ptr);

    }

    std::memset(ptr, 0, std::size_t(m_header_size - (ptr - header.data())));

    aux::pwrite_all(f.fd(), header, 0, ec);

    if (ec) return;

    m_dirty_metadata = false;

  }

}