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deluge/libtorrent/src/torrent_info.cpp

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/*
Copyright (c) 2003, Arvid Norberg
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/pch.hpp"
#include <ctime>
#include <iostream>
#include <fstream>
#include <iomanip>
#include <iterator>
#include <algorithm>
#include <set>
#ifdef _MSC_VER
#pragma warning(push, 1)
#endif
#include <boost/lexical_cast.hpp>
#include <boost/filesystem/path.hpp>
#include <boost/next_prior.hpp>
#include <boost/bind.hpp>
#ifdef _MSC_VER
#pragma warning(pop)
#endif
#include "libtorrent/torrent_info.hpp"
#include "libtorrent/bencode.hpp"
#include "libtorrent/hasher.hpp"
#include "libtorrent/entry.hpp"
namespace pt = boost::posix_time;
namespace gr = boost::gregorian;
using namespace libtorrent;
namespace
{
namespace fs = boost::filesystem;
void convert_to_utf8(std::string& str, unsigned char chr)
{
str += 0xc0 | ((chr & 0xff) >> 6);
str += 0x80 | (chr & 0x3f);
}
void verify_encoding(file_entry& target)
{
std::string tmp_path;
std::string file_path = target.path.string();
bool valid_encoding = true;
for (std::string::iterator i = file_path.begin()
, end(file_path.end()); i != end; ++i)
{
// valid ascii-character
if ((*i & 0x80) == 0)
{
tmp_path += *i;
continue;
}
if (std::distance(i, end) < 2)
{
convert_to_utf8(tmp_path, *i);
valid_encoding = false;
continue;
}
// valid 2-byte utf-8 character
if ((i[0] & 0xe0) == 0xc0
&& (i[1] & 0xc0) == 0x80)
{
tmp_path += i[0];
tmp_path += i[1];
i += 1;
continue;
}
if (std::distance(i, end) < 3)
{
convert_to_utf8(tmp_path, *i);
valid_encoding = false;
continue;
}
// valid 3-byte utf-8 character
if ((i[0] & 0xf0) == 0xe0
&& (i[1] & 0xc0) == 0x80
&& (i[2] & 0xc0) == 0x80)
{
tmp_path += i[0];
tmp_path += i[1];
tmp_path += i[2];
i += 2;
continue;
}
if (std::distance(i, end) < 4)
{
convert_to_utf8(tmp_path, *i);
valid_encoding = false;
continue;
}
// valid 4-byte utf-8 character
if ((i[0] & 0xf0) == 0xe0
&& (i[1] & 0xc0) == 0x80
&& (i[2] & 0xc0) == 0x80
&& (i[3] & 0xc0) == 0x80)
{
tmp_path += i[0];
tmp_path += i[1];
tmp_path += i[2];
tmp_path += i[3];
i += 3;
continue;
}
convert_to_utf8(tmp_path, *i);
valid_encoding = false;
}
// the encoding was not valid utf-8
// save the original encoding and replace the
// commonly used path with the correctly
// encoded string
if (!valid_encoding)
{
target.orig_path.reset(new fs::path(target.path));
target.path = tmp_path;
}
}
void extract_single_file(const entry& dict, file_entry& target
, std::string const& root_dir)
{
target.size = dict["length"].integer();
target.path = root_dir;
target.file_base = 0;
// prefer the name.utf-8
// because if it exists, it is more
// likely to be correctly encoded
const entry::list_type* list = 0;
if (entry const* p = dict.find_key("path.utf-8"))
{
list = &p->list();
}
else
{
list = &dict["path"].list();
}
for (entry::list_type::const_iterator i = list->begin();
i != list->end(); ++i)
{
if (i->string() != "..")
target.path /= i->string();
}
verify_encoding(target);
if (target.path.is_complete()) throw std::runtime_error("torrent contains "
"a file with an absolute path: '"
+ target.path.native_file_string() + "'");
}
void extract_files(const entry::list_type& list, std::vector<file_entry>& target
, std::string const& root_dir)
{
size_type offset = 0;
for (entry::list_type::const_iterator i = list.begin(); i != list.end(); ++i)
{
target.push_back(file_entry());
extract_single_file(*i, target.back(), root_dir);
target.back().offset = offset;
offset += target.back().size;
}
}
/*
void remove_dir(fs::path& p)
{
TORRENT_ASSERT(p.begin() != p.end());
path tmp;
for (path::iterator i = boost::next(p.begin()); i != p.end(); ++i)
tmp /= *i;
p = tmp;
}
*/
}
namespace libtorrent
{
// standard constructor that parses a torrent file
torrent_info::torrent_info(const entry& torrent_file)
: m_num_pieces(0)
, m_creation_date(pt::ptime(pt::not_a_date_time))
, m_multifile(false)
, m_private(false)
, m_extra_info(entry::dictionary_t)
#ifndef NDEBUG
, m_half_metadata(false)
#endif
{
try
{
read_torrent_info(torrent_file);
}
catch(type_error&)
{
throw invalid_torrent_file();
}
}
// constructor used for creating new torrents
// will not contain any hashes, comments, creation date
// just the necessary to use it with piece manager
// used for torrents with no metadata
torrent_info::torrent_info(sha1_hash const& info_hash)
: m_piece_length(0)
, m_total_size(0)
, m_num_pieces(0)
, m_info_hash(info_hash)
, m_name()
, m_creation_date(pt::second_clock::universal_time())
, m_multifile(false)
, m_private(false)
, m_extra_info(entry::dictionary_t)
#ifndef NDEBUG
, m_half_metadata(false)
#endif
{
}
torrent_info::torrent_info()
: m_piece_length(0)
, m_total_size(0)
, m_num_pieces(0)
, m_info_hash(0)
, m_name()
, m_creation_date(pt::second_clock::universal_time())
, m_multifile(false)
, m_private(false)
, m_extra_info(entry::dictionary_t)
#ifndef NDEBUG
, m_half_metadata(false)
#endif
{
}
torrent_info::~torrent_info()
{}
void torrent_info::swap(torrent_info& ti)
{
using std::swap;
m_urls.swap(ti.m_urls);
m_url_seeds.swap(ti.m_url_seeds);
swap(m_piece_length, ti.m_piece_length);
m_piece_hash.swap(ti.m_piece_hash);
m_files.swap(ti.m_files);
m_nodes.swap(ti.m_nodes);
swap(m_num_pieces, ti.m_num_pieces);
swap(m_info_hash, ti.m_info_hash);
m_name.swap(ti.m_name);
swap(m_creation_date, ti.m_creation_date);
m_comment.swap(ti.m_comment);
m_created_by.swap(ti.m_created_by);
swap(m_multifile, ti.m_multifile);
swap(m_private, ti.m_private);
m_extra_info.swap(ti.m_extra_info);
#ifndef NDEBUG
swap(m_half_metadata, ti.m_half_metadata);
#endif
}
void torrent_info::set_piece_size(int size)
{
// make sure the size is an even power of 2
#ifndef NDEBUG
for (int i = 0; i < 32; ++i)
{
if (size & (1 << i))
{
TORRENT_ASSERT((size & ~(1 << i)) == 0);
break;
}
}
#endif
TORRENT_ASSERT(!m_half_metadata);
m_piece_length = size;
m_num_pieces = static_cast<int>(
(m_total_size + m_piece_length - 1) / m_piece_length);
int old_num_pieces = static_cast<int>(m_piece_hash.size());
m_piece_hash.resize(m_num_pieces);
for (int i = old_num_pieces; i < m_num_pieces; ++i)
{
m_piece_hash[i].clear();
}
}
void torrent_info::parse_info_section(entry const& info)
{
// encode the info-field in order to calculate it's sha1-hash
std::vector<char> buf;
bencode(std::back_inserter(buf), info);
hasher h;
h.update(&buf[0], (int)buf.size());
m_info_hash = h.final();
// extract piece length
m_piece_length = (int)info["piece length"].integer();
if (m_piece_length <= 0) throw std::runtime_error("invalid torrent. piece length <= 0");
// extract file name (or the directory name if it's a multifile libtorrent)
if (entry const* e = info.find_key("name.utf-8"))
{ m_name = e->string(); }
else
{ m_name = info["name"].string(); }
fs::path tmp = m_name;
if (tmp.is_complete())
{
m_name = tmp.leaf();
}
else if (tmp.has_branch_path())
{
fs::path p;
for (fs::path::iterator i = tmp.begin()
, end(tmp.end()); i != end; ++i)
{
if (*i == "." || *i == "..") continue;
p /= *i;
}
m_name = p.string();
}
if (m_name == ".." || m_name == ".")
throw std::runtime_error("invalid 'name' of torrent (possible exploit attempt)");
// extract file list
entry const* i = info.find_key("files");
if (i == 0)
{
// if there's no list of files, there has to be a length
// field.
file_entry e;
e.path = m_name;
e.offset = 0;
e.size = info["length"].integer();
m_files.push_back(e);
}
else
{
extract_files(i->list(), m_files, m_name);
m_multifile = true;
}
// calculate total size of all pieces
m_total_size = 0;
for (std::vector<file_entry>::iterator i = m_files.begin(); i != m_files.end(); ++i)
m_total_size += i->size;
// extract sha-1 hashes for all pieces
// we want this division to round upwards, that's why we have the
// extra addition
m_num_pieces = static_cast<int>((m_total_size + m_piece_length - 1) / m_piece_length);
m_piece_hash.resize(m_num_pieces);
const std::string& hash_string = info["pieces"].string();
if ((int)hash_string.length() != m_num_pieces * 20)
throw invalid_torrent_file();
for (int i = 0; i < m_num_pieces; ++i)
std::copy(
hash_string.begin() + i*20
, hash_string.begin() + (i+1)*20
, m_piece_hash[i].begin());
for (entry::dictionary_type::const_iterator i = info.dict().begin()
, end(info.dict().end()); i != end; ++i)
{
if (i->first == "pieces"
|| i->first == "piece length"
|| i->first == "length")
continue;
m_extra_info[i->first] = i->second;
}
if (entry const* priv = info.find_key("private"))
{
if (priv->type() != entry::int_t
|| priv->integer() != 0)
{
// this key exists and it's not 0.
// consider the torrent private
m_private = true;
}
}
#ifndef NDEBUG
std::vector<char> info_section_buf;
entry gen_info_section = create_info_metadata();
bencode(std::back_inserter(info_section_buf), gen_info_section);
TORRENT_ASSERT(hasher(&info_section_buf[0], info_section_buf.size()).final()
== m_info_hash);
#endif
}
// extracts information from a libtorrent file and fills in the structures in
// the torrent object
void torrent_info::read_torrent_info(const entry& torrent_file)
{
// extract the url of the tracker
if (entry const* i = torrent_file.find_key("announce-list"))
{
const entry::list_type& l = i->list();
for (entry::list_type::const_iterator j = l.begin(); j != l.end(); ++j)
{
const entry::list_type& ll = j->list();
for (entry::list_type::const_iterator k = ll.begin(); k != ll.end(); ++k)
{
announce_entry e(k->string());
e.tier = (int)std::distance(l.begin(), j);
m_urls.push_back(e);
}
}
if (m_urls.size() == 0)
{
// the announce-list is empty
// fall back to look for announce
m_urls.push_back(announce_entry(
torrent_file["announce"].string()));
}
// shuffle each tier
std::vector<announce_entry>::iterator start = m_urls.begin();
std::vector<announce_entry>::iterator stop;
int current_tier = m_urls.front().tier;
for (stop = m_urls.begin(); stop != m_urls.end(); ++stop)
{
if (stop->tier != current_tier)
{
std::random_shuffle(start, stop);
start = stop;
current_tier = stop->tier;
}
}
std::random_shuffle(start, stop);
}
else if (entry const* i = torrent_file.find_key("announce"))
{
m_urls.push_back(announce_entry(i->string()));
}
if (entry const* i = torrent_file.find_key("nodes"))
{
entry::list_type const& list = i->list();
for (entry::list_type::const_iterator i(list.begin())
, end(list.end()); i != end; ++i)
{
if (i->type() != entry::list_t) continue;
entry::list_type const& l = i->list();
entry::list_type::const_iterator iter = l.begin();
if (l.size() < 1) continue;
std::string const& hostname = iter->string();
++iter;
int port = 6881;
if (l.end() != iter) port = iter->integer();
m_nodes.push_back(std::make_pair(hostname, port));
}
}
// extract creation date
try
{
m_creation_date = pt::ptime(gr::date(1970, gr::Jan, 1))
+ pt::seconds(long(torrent_file["creation date"].integer()));
}
catch (type_error) {}
// if there are any url-seeds, extract them
try
{
entry const& url_seeds = torrent_file["url-list"];
if (url_seeds.type() == entry::string_t)
{
m_url_seeds.push_back(url_seeds.string());
}
else if (url_seeds.type() == entry::list_t)
{
entry::list_type const& l = url_seeds.list();
for (entry::list_type::const_iterator i = l.begin();
i != l.end(); ++i)
{
m_url_seeds.push_back(i->string());
}
}
}
catch (type_error&) {}
// extract comment
if (entry const* e = torrent_file.find_key("comment.utf-8"))
{ m_comment = e->string(); }
else if (entry const* e = torrent_file.find_key("comment"))
{ m_comment = e->string(); }
if (entry const* e = torrent_file.find_key("created by.utf-8"))
{ m_created_by = e->string(); }
else if (entry const* e = torrent_file.find_key("created by"))
{ m_created_by = e->string(); }
parse_info_section(torrent_file["info"]);
}
boost::optional<pt::ptime>
torrent_info::creation_date() const
{
if (m_creation_date != pt::ptime(gr::date(pt::not_a_date_time)))
{
return boost::optional<pt::ptime>(m_creation_date);
}
return boost::optional<pt::ptime>();
}
void torrent_info::add_tracker(std::string const& url, int tier)
{
announce_entry e(url);
e.tier = tier;
m_urls.push_back(e);
using boost::bind;
std::sort(m_urls.begin(), m_urls.end(), boost::bind<bool>(std::less<int>()
, bind(&announce_entry::tier, _1), bind(&announce_entry::tier, _2)));
}
void torrent_info::add_file(fs::path file, size_type size)
{
// TORRENT_ASSERT(file.begin() != file.end());
if (!file.has_branch_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(m_files.empty());
TORRENT_ASSERT(!m_multifile);
m_name = file.string();
}
else
{
#ifndef NDEBUG
if (!m_files.empty())
TORRENT_ASSERT(m_name == *file.begin());
#endif
m_multifile = true;
m_name = *file.begin();
}
file_entry e;
e.path = file;
e.size = size;
e.offset = m_files.empty() ? 0 : m_files.back().offset
+ m_files.back().size;
m_files.push_back(e);
m_total_size += size;
if (m_piece_length == 0)
m_piece_length = 256 * 1024;
m_num_pieces = static_cast<int>(
(m_total_size + m_piece_length - 1) / m_piece_length);
int old_num_pieces = static_cast<int>(m_piece_hash.size());
m_piece_hash.resize(m_num_pieces);
if (m_num_pieces > old_num_pieces)
std::for_each(m_piece_hash.begin() + old_num_pieces
, m_piece_hash.end(), boost::bind(&sha1_hash::clear, _1));
}
void torrent_info::add_url_seed(std::string const& url)
{
m_url_seeds.push_back(url);
}
void torrent_info::set_comment(char const* str)
{
m_comment = str;
}
void torrent_info::set_creator(char const* str)
{
m_created_by = str;
}
entry torrent_info::create_info_metadata() const
{
// you have to add files to the torrent first
TORRENT_ASSERT(!m_files.empty());
entry info(m_extra_info);
if (!info.find_key("name"))
info["name"] = m_name;
if (!m_multifile)
{
info["length"] = m_files.front().size;
}
else
{
if (!info.find_key("files"))
{
entry& files = info["files"];
for (std::vector<file_entry>::const_iterator i = m_files.begin();
i != m_files.end(); ++i)
{
files.list().push_back(entry());
entry& file_e = files.list().back();
file_e["length"] = i->size;
entry& path_e = file_e["path"];
fs::path const* file_path;
if (i->orig_path) file_path = &(*i->orig_path);
else file_path = &i->path;
TORRENT_ASSERT(file_path->has_branch_path());
TORRENT_ASSERT(*file_path->begin() == m_name);
for (fs::path::iterator j = boost::next(file_path->begin());
j != file_path->end(); ++j)
{
path_e.list().push_back(entry(*j));
}
}
}
}
info["piece length"] = piece_length();
entry& pieces = info["pieces"];
std::string& p = pieces.string();
for (std::vector<sha1_hash>::const_iterator i = m_piece_hash.begin();
i != m_piece_hash.end(); ++i)
{
p.append((char*)i->begin(), (char*)i->end());
}
return info;
}
entry torrent_info::create_torrent() const
{
TORRENT_ASSERT(m_piece_length > 0);
if (m_files.empty())
{
// TODO: throw something here
// throw
return entry();
}
entry dict;
if (m_private) dict["private"] = 1;
if (!m_urls.empty())
dict["announce"] = m_urls.front().url;
if (!m_nodes.empty())
{
entry& nodes = dict["nodes"];
entry::list_type& nodes_list = nodes.list();
for (nodes_t::const_iterator i = m_nodes.begin()
, end(m_nodes.end()); i != end; ++i)
{
entry::list_type node;
node.push_back(entry(i->first));
node.push_back(entry(i->second));
nodes_list.push_back(entry(node));
}
}
if (m_urls.size() > 1)
{
entry trackers(entry::list_t);
entry tier(entry::list_t);
int current_tier = m_urls.front().tier;
for (std::vector<announce_entry>::const_iterator i = m_urls.begin();
i != m_urls.end(); ++i)
{
if (i->tier != current_tier)
{
current_tier = i->tier;
trackers.list().push_back(tier);
tier.list().clear();
}
tier.list().push_back(entry(i->url));
}
trackers.list().push_back(tier);
dict["announce-list"] = trackers;
}
if (!m_comment.empty())
dict["comment"] = m_comment;
dict["creation date"] =
(m_creation_date - pt::ptime(gr::date(1970, gr::Jan, 1))).total_seconds();
if (!m_created_by.empty())
dict["created by"] = m_created_by;
if (!m_url_seeds.empty())
{
if (m_url_seeds.size() == 1)
{
dict["url-list"] = m_url_seeds.front();
}
else
{
entry& list = dict["url-list"];
for (std::vector<std::string>::const_iterator i
= m_url_seeds.begin(); i != m_url_seeds.end(); ++i)
{
list.list().push_back(entry(*i));
}
}
}
dict["info"] = create_info_metadata();
entry const& info_section = dict["info"];
std::vector<char> buf;
bencode(std::back_inserter(buf), info_section);
m_info_hash = hasher(&buf[0], buf.size()).final();
return dict;
}
void torrent_info::set_hash(int index, const sha1_hash& h)
{
TORRENT_ASSERT(index >= 0);
TORRENT_ASSERT(index < (int)m_piece_hash.size());
m_piece_hash[index] = h;
}
void torrent_info::convert_file_names()
{
TORRENT_ASSERT(false);
}
void torrent_info::seed_free()
{
std::vector<std::string>().swap(m_url_seeds);
nodes_t().swap(m_nodes);
std::vector<sha1_hash>().swap(m_piece_hash);
#ifndef NDEBUG
m_half_metadata = true;
#endif
}
// ------- start deprecation -------
void torrent_info::print(std::ostream& os) const
{
os << "trackers:\n";
for (std::vector<announce_entry>::const_iterator i = trackers().begin();
i != trackers().end(); ++i)
{
os << i->tier << ": " << i->url << "\n";
}
if (!m_comment.empty())
os << "comment: " << m_comment << "\n";
// if (m_creation_date != pt::ptime(gr::date(pt::not_a_date_time)))
// os << "creation date: " << to_simple_string(m_creation_date) << "\n";
os << "private: " << (m_private?"yes":"no") << "\n";
os << "number of pieces: " << num_pieces() << "\n";
os << "piece length: " << piece_length() << "\n";
os << "files:\n";
for (file_iterator i = begin_files(); i != end_files(); ++i)
os << " " << std::setw(11) << i->size << " " << i->path.string() << "\n";
}
// ------- end deprecation -------
size_type torrent_info::piece_size(int index) const
{
TORRENT_ASSERT(index >= 0 && index < num_pieces());
if (index == num_pieces()-1)
{
size_type size = total_size()
- (num_pieces() - 1) * piece_length();
TORRENT_ASSERT(size > 0);
TORRENT_ASSERT(size <= piece_length());
return size;
}
else
return piece_length();
}
void torrent_info::add_node(std::pair<std::string, int> const& node)
{
m_nodes.push_back(node);
}
bool torrent_info::remap_files(std::vector<file_entry> const& map)
{
size_type offset = 0;
m_remapped_files.resize(map.size());
for (int i = 0; i < int(map.size()); ++i)
{
file_entry& fe = m_remapped_files[i];
fe.path = map[i].path;
fe.offset = offset;
fe.size = map[i].size;
fe.file_base = map[i].file_base;
fe.orig_path.reset();
offset += fe.size;
}
if (offset != total_size())
{
m_remapped_files.clear();
return false;
}
#ifndef NDEBUG
std::vector<file_entry> map2(m_remapped_files);
std::sort(map2.begin(), map2.end()
, bind(&file_entry::file_base, _1) < bind(&file_entry::file_base, _2));
std::stable_sort(map2.begin(), map2.end()
, bind(&file_entry::path, _1) < bind(&file_entry::path, _2));
fs::path last_path;
size_type last_end = 0;
for (std::vector<file_entry>::iterator i = map2.begin(), end(map2.end());
i != end; ++i)
{
if (last_path == i->path)
{
assert(last_end <= i->file_base);
}
last_end = i->file_base + i->size;
last_path = i->path;
}
#endif
return true;
}
std::vector<file_slice> torrent_info::map_block(int piece, size_type offset
, int size, bool storage) const
{
TORRENT_ASSERT(num_files() > 0);
std::vector<file_slice> ret;
size_type start = piece * (size_type)m_piece_length + offset;
TORRENT_ASSERT(start + size <= m_total_size);
// find the file iterator and file offset
// TODO: make a vector that can map piece -> file index in O(1)
size_type file_offset = start;
std::vector<file_entry>::const_iterator file_iter;
int counter = 0;
for (file_iter = begin_files(storage);; ++counter, ++file_iter)
{
TORRENT_ASSERT(file_iter != end_files(storage));
if (file_offset < file_iter->size)
{
file_slice f;
f.file_index = counter;
f.offset = file_offset + file_iter->file_base;
f.size = (std::min)(file_iter->size - file_offset, (size_type)size);
size -= f.size;
file_offset += f.size;
ret.push_back(f);
}
TORRENT_ASSERT(size >= 0);
if (size <= 0) break;
file_offset -= file_iter->size;
}
return ret;
}
peer_request torrent_info::map_file(int file_index, size_type file_offset
, int size, bool storage) const
{
TORRENT_ASSERT(file_index < num_files(storage));
TORRENT_ASSERT(file_index >= 0);
size_type offset = file_offset + file_at(file_index, storage).offset;
peer_request ret;
ret.piece = offset / piece_length();
ret.start = offset - ret.piece * piece_length();
ret.length = size;
return ret;
}
}
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