text: /*
  
  Copyright (c) 2003-2016, 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/aux_/disable_warnings_push.hpp"
  
  #ifdef __GNUC__
  #pragma GCC diagnostic push
  #pragma GCC diagnostic ignored "-Wunused-macros"
  #endif
  
  #ifdef __clang__
  #pragma clang diagnostic push
  #pragma clang diagnostic ignored "-Wunknown-pragmas"
  #pragma clang diagnostic ignored "-Wunused-macros"
  #pragma clang diagnostic ignored "-Wreserved-id-macro"
  #endif
  
  // these defines are just in case the system we're on needs them for 64 bit file
  // support
  #define _FILE_OFFSET_BITS 64
  #define _LARGE_FILES 1
  
  // on mingw this is necessary to enable 64-bit time_t, specifically used for
  // the stat struct. Without this, modification times returned by stat may be
  // incorrect and consistently fail resume data
  #ifndef __MINGW_USE_VC2005_COMPAT
  # define __MINGW_USE_VC2005_COMPAT
  #endif
  
  #ifdef __clang__
  #pragma clang diagnostic pop
  #endif
  
  #ifdef __GNUC__
  #pragma GCC diagnostic pop
  #endif
  
  #include "libtorrent/aux_/disable_warnings_pop.hpp"
  
  #include "libtorrent/config.hpp"
  #include "libtorrent/aux_/alloca.hpp"
  #include "libtorrent/aux_/path.hpp"
  #include "libtorrent/file.hpp" // for directory
  #include "libtorrent/string_util.hpp"
  #include "libtorrent/aux_/max_path.hpp" // for TORRENT_MAX_PATH
  #include <cstring>
  
  // for convert_to_wstring and convert_to_native
  #include "libtorrent/aux_/escape_string.hpp"
  #include "libtorrent/assert.hpp"
  #include "libtorrent/aux_/throw.hpp"
  
  #include "libtorrent/aux_/disable_warnings_push.hpp"
  
  #include <sys/stat.h>
  #include <climits> // for IOV_MAX
  
  #ifdef TORRENT_WINDOWS
  // windows part
  
  #include "libtorrent/utf8.hpp"
  #include "libtorrent/aux_/win_util.hpp"
  
  #ifndef WIN32_LEAN_AND_MEAN
  #define WIN32_LEAN_AND_MEAN
  #endif
  #include <windows.h>
  #include <winioctl.h>
  #ifndef TORRENT_MINGW
  #include <direct.h> // for _getcwd, _mkdir
  #else
  #include <dirent.h>
  #endif
  #include <sys/types.h>
  #else
  // posix part
  
  #include <unistd.h>
  #include <sys/types.h>
  #include <cerrno>
  #include <dirent.h>
  
  #ifdef TORRENT_LINUX
  // linux specifics
  
  #include <sys/ioctl.h>
  
  #elif defined __APPLE__ && defined __MACH__ && MAC_OS_X_VERSION_MIN_REQUIRED >= 1050
  // mac specifics
  
  #include <copyfile.h>
  
  #endif
  
  #endif // posix part
  
  #include "libtorrent/aux_/disable_warnings_pop.hpp"
  
  namespace libtorrent {
  
  	int bufs_size(span<iovec_t const> bufs)
  	{
  		std::size_t size = 0;
  		for (auto buf : bufs) size += buf.size();
  		return int(size);
  	}
  
  	std::string convert_from_native_path(char const* s) { return convert_from_native(s); }
  
  #if defined TORRENT_WINDOWS && TORRENT_USE_WSTRING
  	std::string convert_from_native_path(wchar_t const* s) { return convert_from_wstring(s); }
  #endif
  
  	template <typename T>
  	std::unique_ptr<T, decltype(&std::free)> make_free_holder(T* ptr)
  	{
  		return std::unique_ptr<T, decltype(&std::free)>(ptr, &std::free);
  	}
  
  #ifdef TORRENT_WINDOWS
  	time_t file_time_to_posix(FILETIME f)
  	{
  		const std::uint64_t posix_time_offset = 11644473600LL;
  		std::uint64_t ft = (std::uint64_t(f.dwHighDateTime) << 32)
  			| f.dwLowDateTime;
  
  		// windows filetime is specified in 100 nanoseconds resolution.
  		// convert to seconds
  		return time_t(ft / 10000000 - posix_time_offset);
  	}
  #endif
  
  	native_path_string convert_to_native_path_string(std::string const& path)
  	{
  #ifdef TORRENT_WINDOWS
  #if TORRENT_USE_UNC_PATHS
  		std::string prepared_path;
  		// UNC paths must be absolute
  		// network paths are already UNC paths
  		if (path.substr(0,2) == "\\\\")
  			prepared_path = path;
  		else
  		{
  			std::string sep_path { path };
  			std::replace(sep_path.begin(), sep_path.end(), '/', '\\');
  			prepared_path = "\\\\?\\" + (is_complete(sep_path) ? sep_path : combine_path(current_working_directory(), sep_path));
  		}
  #else
  		std::string prepared_path { path };
  		std::replace(prepared_path.begin(), prepared_path.end(), '/', '\\');
  #endif
  
  #if TORRENT_USE_WSTRING
  		return convert_to_wstring(prepared_path);
  #else
  		return convert_to_native(prepared_path);
  #endif
  #else // TORRENT_WINDOWS
  		return convert_to_native(path);
  #endif
  	}
  
  	void stat_file(std::string const& inf, file_status* s
  		, error_code& ec, int const flags)
  	{
  		ec.clear();
  		native_path_string f = convert_to_native_path_string(inf);
  #ifdef TORRENT_WINDOWS
  
  		TORRENT_UNUSED(flags);
  
  #if TORRENT_USE_WSTRING
  #define CreateFile_ CreateFileW
  #else
  #define CreateFile_ CreateFileA
  #endif
  
  		// in order to open a directory, we need the FILE_FLAG_BACKUP_SEMANTICS
  		HANDLE h = CreateFile_(f.c_str(), 0, FILE_SHARE_DELETE | FILE_SHARE_READ
  			| FILE_SHARE_WRITE, nullptr, OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS, nullptr);
  #undef CreateFile_
  		if (h == INVALID_HANDLE_VALUE)
  		{
  			ec.assign(GetLastError(), system_category());
  			TORRENT_ASSERT(ec);
  			return;
  		}
  
  		BY_HANDLE_FILE_INFORMATION data;
  		if (!GetFileInformationByHandle(h, &data))
  		{
  			ec.assign(GetLastError(), system_category());
  			TORRENT_ASSERT(ec);
  			CloseHandle(h);
  			return;
  		}
  
  		s->file_size = (std::uint64_t(data.nFileSizeHigh) << 32) | data.nFileSizeLow;
  		s->ctime = file_time_to_posix(data.ftCreationTime);
  		s->atime = file_time_to_posix(data.ftLastAccessTime);
  		s->mtime = file_time_to_posix(data.ftLastWriteTime);
  
  		s->mode = (data.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY)
  			? file_status::directory
  			: (data.dwFileAttributes & FILE_ATTRIBUTE_DEVICE)
  			? file_status::character_special : file_status::regular_file;
  		CloseHandle(h);
  #else
  
  		// posix version
  
  		struct stat ret;
  		int retval;
  		if (flags & dont_follow_links)
  			retval = ::lstat(f.c_str(), &ret);
  		else
  			retval = ::stat(f.c_str(), &ret);
  		if (retval < 0)
  		{
  			ec.assign(errno, system_category());
  			return;
  		}
  
  		s->file_size = ret.st_size;
  		s->atime = std::uint64_t(ret.st_atime);
  		s->mtime = std::uint64_t(ret.st_mtime);
  		s->ctime = std::uint64_t(ret.st_ctime);
  
  		s->mode = (S_ISREG(ret.st_mode) ? file_status::regular_file : 0)
  			| (S_ISDIR(ret.st_mode) ? file_status::directory : 0)
  			| (S_ISLNK(ret.st_mode) ? file_status::link : 0)
  			| (S_ISFIFO(ret.st_mode) ? file_status::fifo : 0)
  			| (S_ISCHR(ret.st_mode) ? file_status::character_special : 0)
  			| (S_ISBLK(ret.st_mode) ? file_status::block_special : 0)
  			| (S_ISSOCK(ret.st_mode) ? file_status::socket : 0);
  
  #endif // TORRENT_WINDOWS
  	}
  
  	void rename(std::string const& inf, std::string const& newf, error_code& ec)
  	{
  		ec.clear();
  
  		native_path_string f1 = convert_to_native_path_string(inf);
  		native_path_string f2 = convert_to_native_path_string(newf);
  
  #if TORRENT_USE_WSTRING && defined TORRENT_WINDOWS
  #define RenameFunction_ _wrename
  #else
  #define RenameFunction_ ::rename
  #endif
  
  		if (RenameFunction_(f1.c_str(), f2.c_str()) < 0)
  		{
  			ec.assign(errno, generic_category());
  		}
  #undef RenameFunction_
  	}
  
  	void create_directories(std::string const& f, error_code& ec)
  	{
  		ec.clear();
  		if (is_directory(f, ec)) return;
  		if (ec != boost::system::errc::no_such_file_or_directory)
  			return;
  		ec.clear();
  		if (is_root_path(f)) return;
  		if (has_parent_path(f))
  		{
  			create_directories(parent_path(f), ec);
  			if (ec) return;
  		}
  		create_directory(f, ec);
  	}
  
  	void create_directory(std::string const& f, error_code& ec)
  	{
  		ec.clear();
  
  		native_path_string n = convert_to_native_path_string(f);
  #ifdef TORRENT_WINDOWS
  #if TORRENT_USE_WSTRING
  #define CreateDirectory_ CreateDirectoryW
  #else
  #define CreateDirectory_ CreateDirectoryA
  #endif // TORRENT_USE_WSTRING
  
  		if (CreateDirectory_(n.c_str(), 0) == 0
  			&& GetLastError() != ERROR_ALREADY_EXISTS)
  			ec.assign(GetLastError(), system_category());
  #undef CreateDirectory_
  #else
  		int ret = ::mkdir(n.c_str(), 0777);
  		if (ret < 0 && errno != EEXIST)
  			ec.assign(errno, system_category());
  #endif
  	}
  
  	void hard_link(std::string const& file, std::string const& link
  		, error_code& ec)
  	{
  		native_path_string n_exist = convert_to_native_path_string(file);
  		native_path_string n_link = convert_to_native_path_string(link);
  #ifdef TORRENT_WINDOWS
  
  #if TORRENT_USE_WSTRING
  #define CreateHardLink_ CreateHardLinkW
  #else
  #define CreateHardLink_ CreateHardLinkA
  #endif
  		BOOL ret = CreateHardLink_(n_link.c_str(), n_exist.c_str(), nullptr);
  		if (ret)
  		{
  			ec.clear();
  			return;
  		}
  #undef CreateHardLink_
  		// something failed. Does the filesystem not support hard links?
  		// TODO: 3 find out what error code is reported when the filesystem
  		// does not support hard links.
  		DWORD const error = GetLastError();
  		if (error != ERROR_NOT_SUPPORTED && error != ERROR_ACCESS_DENIED)
  		{
  			// it's possible CreateHardLink will copy the file internally too,
  			// if the filesystem does not support it.
  			ec.assign(GetLastError(), system_category());
  			return;
  		}
  
  		// fall back to making a copy
  
  #else
  		// assume posix's link() function exists
  		int ret = ::link(n_exist.c_str(), n_link.c_str());
  
  		if (ret == 0)
  		{
  			ec.clear();
  			return;
  		}
  
  		// most errors are passed through, except for the ones that indicate that
  		// hard links are not supported and require a copy.
  		// TODO: 2 test this on a FAT volume to see what error we get!
  		if (errno != EMLINK || errno != EXDEV)
  		{
  			// some error happened, report up to the caller
  			ec.assign(errno, system_category());
  			return;
  		}
  
  		// fall back to making a copy
  
  #endif
  
  		// if we get here, we should copy the file
  		copy_file(file, link, ec);
  	}
  
  	bool is_directory(std::string const& f, error_code& ec)
  	{
  		ec.clear();
  		error_code e;
  		file_status s;
  		stat_file(f, &s, e);
  		if (!e && s.mode & file_status::directory) return true;
  		ec = e;
  		return false;
  	}
  
  	void recursive_copy(std::string const& old_path, std::string const& new_path, error_code& ec)
  	{
  		TORRENT_ASSERT(!ec);
  		if (is_directory(old_path, ec))
  		{
  			create_directory(new_path, ec);
  			if (ec) return;
  			for (directory i(old_path, ec); !i.done(); i.next(ec))
  			{
  				std::string f = i.file();
  				if (f == ".." || f == ".") continue;
  				recursive_copy(combine_path(old_path, f), combine_path(new_path, f), ec);
  				if (ec) return;
  			}
  		}
  		else if (!ec)
  		{
  			copy_file(old_path, new_path, ec);
  		}
  	}
  
  	void copy_file(std::string const& inf, std::string const& newf, error_code& ec)
  	{
  		ec.clear();
  		native_path_string f1 = convert_to_native_path_string(inf);
  		native_path_string f2 = convert_to_native_path_string(newf);
  
  #ifdef TORRENT_WINDOWS
  #if TORRENT_USE_WSTRING
  #define CopyFile_ CopyFileW
  #else
  #define CopyFile_ CopyFileA
  #endif
  
  		if (CopyFile_(f1.c_str(), f2.c_str(), false) == 0)
  			ec.assign(GetLastError(), system_category());
  #undef CopyFile_
  
  #elif defined __APPLE__ && defined __MACH__ && MAC_OS_X_VERSION_MIN_REQUIRED >= 1050
  		// this only works on 10.5
  		copyfile_state_t state = copyfile_state_alloc();
  		if (copyfile(f1.c_str(), f2.c_str(), state, COPYFILE_ALL) < 0)
  			ec.assign(errno, system_category());
  		copyfile_state_free(state);
  #else
  		int const infd = ::open(f1.c_str(), O_RDONLY);
  		if (infd < 0)
  		{
  			ec.assign(errno, system_category());
  			return;
  		}
  
  		// rely on default umask to filter x and w permissions
  		// for group and others
  		int const permissions = S_IRUSR | S_IWUSR
  			| S_IRGRP | S_IWGRP
  			| S_IROTH | S_IWOTH;
  
  		int const outfd = ::open(f2.c_str(), O_WRONLY | O_CREAT, permissions);
  		if (outfd < 0)
  		{
  			close(infd);
  			ec.assign(errno, system_category());
  			return;
  		}
  		char buffer[4096];
  		for (;;)
  		{
  			int const num_read = int(read(infd, buffer, sizeof(buffer)));
  			if (num_read == 0) break;
  			if (num_read < 0)
  			{
  				ec.assign(errno, system_category());
  				break;
  			}
  			int const num_written = int(write(outfd, buffer, std::size_t(num_read)));
  			if (num_written < num_read)
  			{
  				ec.assign(errno, system_category());
  				break;
  			}
  			if (num_read < int(sizeof(buffer))) break;
  		}
  		close(infd);
  		close(outfd);
  #endif // TORRENT_WINDOWS
  	}
  
  	void move_file(std::string const& inf, std::string const& newf, error_code& ec)
  	{
  		ec.clear();
  
  		file_status s;
  		stat_file(inf, &s, ec);
  		if (ec) return;
  
  		if (has_parent_path(newf))
  		{
  			create_directories(parent_path(newf), ec);
  			if (ec) return;
  		}
  
  		rename(inf, newf, ec);
  	}
  
  	std::string split_path(std::string const& f, bool only_first_part)
  	{
  		if (f.empty()) return f;
  
  		std::string ret;
  		char const* start = f.c_str();
  		char const* p = start;
  		while (*start != 0)
  		{
  			while (*p != '/'
  				&& *p != '\0'
  #if defined(TORRENT_WINDOWS) || defined(TORRENT_OS2)
  				&& *p != '\\'
  #endif
  				) ++p;
  			if (p - start > 0)
  			{
  				ret.append(start, aux::numeric_cast<std::size_t>(p - start));
  				if (only_first_part) return ret;
  				ret.append(1, '\0');
  			}
  			if (*p != 0) ++p;
  			start = p;
  		}
  		if (only_first_part) return ret;
  		ret.append(1, '\0');
  		return ret;
  	}
  
  	char const* next_path_element(char const* p)
  	{
  		p += strlen(p) + 1;
  		if (*p == 0) return nullptr;
  		return p;
  	}
  
  	std::string extension(std::string const& f)
  	{
  		for (int i = int(f.size()) - 1; i >= 0; --i)
  		{
  			std::size_t const idx = std::size_t(i);
  			if (f[idx] == '/') break;
  #ifdef TORRENT_WINDOWS
  			if (f[idx] == '\\') break;
  #endif
  			if (f[idx] != '.') continue;
  			return f.substr(idx);
  		}
  		return "";
  	}
  
  	std::string remove_extension(std::string const& f)
  	{
  		char const* slash = std::strrchr(f.c_str(), '/');
  #ifdef TORRENT_WINDOWS
  		slash = (std::max)((char const*)std::strrchr(f.c_str(), '\\'), slash);
  #endif
  		char const* ext = std::strrchr(f.c_str(), '.');
  		// if we don't have an extension, just return f
  		if (ext == nullptr || ext == &f[0] || (slash != nullptr && ext < slash)) return f;
  		return f.substr(0, aux::numeric_cast<std::size_t>(ext - &f[0]));
  	}
  
  	void replace_extension(std::string& f, std::string const& ext)
  	{
  		for (int i = int(f.size()) - 1; i >= 0; --i)
  		{
  			std::size_t const idx = std::size_t(i);
  			if (f[idx] == '/') break;
  #ifdef TORRENT_WINDOWS
  			if (f[idx] == '\\') break;
  #endif
  
  			if (f[idx] != '.') continue;
  
  			f.resize(idx);
  			break;
  		}
  		f += '.';
  		f += ext;
  	}
  
  	bool is_root_path(std::string const& f)
  	{
  		if (f.empty()) return false;
  
  #if defined(TORRENT_WINDOWS) || defined(TORRENT_OS2)
  		// match \\ form
  		if (f == "\\\\") return true;
  		int i = 0;
  		// match the xx:\ or xx:/ form
  		while (f[i] && is_alpha(f[i])) ++i;
  		if (i == int(f.size()-2) && f[i] == ':' && (f[i+1] == '\\' || f[i+1] == '/'))
  			return true;
  		// match network paths \\computer_name\ form
  		if (f.size() > 2 && f[0] == '\\' && f[1] == '\\')
  		{
  			// we don't care about the last character, since it's OK for it
  			// to be a slash or a back slash
  			bool found = false;
  			for (int j = 2; j < int(f.size()) - 1; ++j)
  			{
  				if (f[j] != '\\' && f[j] != '/') continue;
  				// there is a directory separator in here,
  				// i.e. this is not the root
  				found = true;
  				break;
  			}
  			if (!found) return true;
  		}
  #else
  		// as well as parent_path("/") should be "/".
  		if (f == "/") return true;
  #endif
  		return false;
  	}
  
  	bool has_parent_path(std::string const& f)
  	{
  		if (f.empty()) return false;
  		if (is_root_path(f)) return false;
  
  		int len = int(f.size()) - 1;
  		// if the last character is / or \ ignore it
  		if (f[std::size_t(len)] == '/' || f[std::size_t(len)] == '\\') --len;
  		while (len >= 0)
  		{
  			if (f[std::size_t(len)] == '/' || f[std::size_t(len)] == '\\')
  				break;
  			--len;
  		}
  
  		return len >= 0;
  	}
  
  	std::string parent_path(std::string const& f)
  	{
  		if (f.empty()) return f;
  
  #ifdef TORRENT_WINDOWS
  		if (f == "\\\\") return "";
  #endif
  		if (f == "/") return "";
  
  		int len = int(f.size());
  		// if the last character is / or \ ignore it
  		if (f[std::size_t(len - 1)] == '/' || f[std::size_t(len - 1)] == '\\') --len;
  		while (len > 0)
  		{
  			--len;
  			if (f[std::size_t(len)] == '/' || f[std::size_t(len)] == '\\')
  				break;
  		}
  
  		if (f[std::size_t(len)] == '/' || f[std::size_t(len)] == '\\') ++len;
  		return std::string(f.c_str(), std::size_t(len));
  	}
  
  	char const* filename_cstr(char const* f)
  	{
  		if (f == nullptr) return f;
  
  		char const* sep = std::strrchr(f, '/');
  #ifdef TORRENT_WINDOWS
  		char const* altsep = std::strrchr(f, '\\');
  		if (sep == 0 || altsep > sep) sep = altsep;
  #endif
  		if (sep == nullptr) return f;
  		return sep+1;
  	}
  
  	std::string filename(std::string const& f)
  	{
  		if (f.empty()) return "";
  		char const* first = f.c_str();
  		char const* sep = std::strrchr(first, '/');
  #if defined(TORRENT_WINDOWS) || defined(TORRENT_OS2)
  		char const* altsep = std::strrchr(first, '\\');
  		if (sep == 0 || altsep > sep) sep = altsep;
  #endif
  		if (sep == nullptr) return f;
  
  		if (sep - first == int(f.size()) - 1)
  		{
  			// if the last character is a / (or \)
  			// ignore it
  			int len = 0;
  			while (sep > first)
  			{
  				--sep;
  				if (*sep == '/'
  #if defined(TORRENT_WINDOWS) || defined(TORRENT_OS2)
  					|| *sep == '\\'
  #endif
  					)
  					return std::string(sep + 1, std::size_t(len));
  				++len;
  			}
  			return std::string(first, std::size_t(len));
  
  		}
  		return std::string(sep + 1);
  	}
  
  	void append_path(std::string& branch, string_view leaf)
  	{
  		TORRENT_ASSERT(!is_complete(leaf));
  		if (branch.empty() || branch == ".")
  		{
  			branch.assign(leaf.data(), leaf.size());
  			return;
  		}
  		if (leaf.size() == 0) return;
  
  #if defined(TORRENT_WINDOWS) || defined(TORRENT_OS2)
  #define TORRENT_SEPARATOR_CHAR '\\'
  		bool const need_sep = branch[branch.size()-1] != '\\'
  			&& branch[branch.size()-1] != '/';
  #else
  #define TORRENT_SEPARATOR_CHAR '/'
  		bool const need_sep = branch[branch.size()-1] != '/';
  #endif
  
  		if (need_sep) branch += TORRENT_SEPARATOR_CHAR;
  		branch.append(leaf.data(), leaf.size());
  	}
  
  	std::string combine_path(string_view lhs, string_view rhs)
  	{
  		TORRENT_ASSERT(!is_complete(rhs));
  		if (lhs.empty() || lhs == ".") return rhs.to_string();
  		if (rhs.empty() || rhs == ".") return lhs.to_string();
  
  #if defined(TORRENT_WINDOWS) || defined(TORRENT_OS2)
  #define TORRENT_SEPARATOR "\\"
  		bool const need_sep = lhs[lhs.size() - 1] != '\\' && lhs[lhs.size() - 1] != '/';
  #else
  #define TORRENT_SEPARATOR "/"
  		bool const need_sep = lhs[lhs.size() - 1] != '/';
  #endif
  		std::string ret;
  		std::size_t target_size = lhs.size() + rhs.size() + 2;
  		ret.resize(target_size);
  		target_size = aux::numeric_cast<std::size_t>(std::snprintf(&ret[0], target_size, "%*s%s%*s"
  			, int(lhs.size()), lhs.data()
  			, (need_sep ? TORRENT_SEPARATOR : "")
  			, int(rhs.size()), rhs.data()));
  		ret.resize(target_size);
  		return ret;
  	}
  
  	std::string current_working_directory()
  	{
  #if defined TORRENT_WINDOWS
  #if TORRENT_USE_WSTRING
  #define GetCurrentDir_ ::_wgetcwd
  #else
  #define GetCurrentDir_ ::_getcwd
  #endif // TORRENT_USE_WSTRING
  #else
  #define GetCurrentDir_ ::getcwd
  #endif
  		auto cwd = GetCurrentDir_(nullptr, 0);
  		if (cwd == nullptr)
  			aux::throw_ex<system_error>(error_code(errno, generic_category()));
  		auto holder = make_free_holder(cwd);
  		return convert_from_native_path(cwd);
  #undef GetCurrentDir_
  	}
  
  #if TORRENT_USE_UNC_PATHS
  	std::string canonicalize_path(string_view f)
  	{
  		std::string ret;
  		ret.resize(f.size());
  		char* write_cur = &ret[0];
  		char* last_write_sep = write_cur;
  
  		char const* read_cur = f.data();
  		char const* last_read_sep = read_cur;
  
  		// the last_*_sep pointers point to one past
  		// the last path separator encountered and is
  		// initialized to the first character in the path
  		for (int i = 0; i < int(f.size()); ++i)
  		{
  			if (*read_cur != '\\')
  			{
  				*write_cur++ = *read_cur++;
  				continue;
  			}
  			int element_len = int(read_cur - last_read_sep);
  			if (element_len == 1 && std::memcmp(last_read_sep, ".", 1) == 0)
  			{
  				--write_cur;
  				++read_cur;
  				last_read_sep = read_cur;
  				continue;
  			}
  			if (element_len == 2 && std::memcmp(last_read_sep, "..", 2) == 0)
  			{
  				// find the previous path separator
  				if (last_write_sep > &ret[0])
  				{
  					--last_write_sep;
  					while (last_write_sep > &ret[0]
  						&& last_write_sep[-1] != '\\')
  						--last_write_sep;
  				}
  				write_cur = last_write_sep;
  				// find the previous path separator
  				if (last_write_sep > &ret[0])
  				{
  					--last_write_sep;
  					while (last_write_sep > &ret[0]
  						&& last_write_sep[-1] != '\\')
  						--last_write_sep;
  				}
  				++read_cur;
  				last_read_sep = read_cur;
  				continue;
  			}
  			*write_cur++ = *read_cur++;
  			last_write_sep = write_cur;
  			last_read_sep = read_cur;
  		}
  		// terminate destination string
  		*write_cur = 0;
  		ret.resize(write_cur - &ret[0]);
  		return ret;
  	}
  #endif
  
  	std::int64_t file_size(std::string const& f)
  	{
  		error_code ec;
  		file_status s;
  		stat_file(f, &s, ec);
  		if (ec) return 0;
  		return s.file_size;
  	}
  
  	bool exists(std::string const& f, error_code& ec)
  	{
  		file_status s;
  		stat_file(f, &s, ec);
  		if (ec)
  		{
  			if (ec == boost::system::errc::no_such_file_or_directory)
  				ec.clear();
  			return false;
  		}
  		return true;
  	}
  
  	bool exists(std::string const& f)
  	{
  		error_code ec;
  		return exists(f, ec);
  	}
  
  	void remove(std::string const& inf, error_code& ec)
  	{
  		ec.clear();
  		native_path_string f = convert_to_native_path_string(inf);
  
  #ifdef TORRENT_WINDOWS
  		// windows does not allow trailing / or \ in
  		// the path when removing files
  		while (!f.empty() && (
  			f.back() == '/' ||
  			f.back() == '\\'
  			)) f.pop_back();
  #if TORRENT_USE_WSTRING
  #define DeleteFile_ DeleteFileW
  #define RemoveDirectory_ RemoveDirectoryW
  #else
  #define DeleteFile_ DeleteFileA
  #define RemoveDirectory_ RemoveDirectoryA
  #endif
  		if (DeleteFile_(f.c_str()) == 0)
  		{
  			if (GetLastError() == ERROR_ACCESS_DENIED)
  			{
  				if (RemoveDirectory_(f.c_str()) != 0)
  					return;
  			}
  			ec.assign(GetLastError(), system_category());
  			return;
  		}
  #undef DeleteFile_
  #undef RemoveDirectory_
  #else // TORRENT_WINDOWS
  		if (::remove(f.c_str()) < 0)
  		{
  			ec.assign(errno, system_category());
  			return;
  		}
  #endif // TORRENT_WINDOWS
  	}
  
  	void remove_all(std::string const& f, error_code& ec)
  	{
  		ec.clear();
  
  		file_status s;
  		stat_file(f, &s, ec);
  		if (ec) return;
  
  		if (s.mode & file_status::directory)
  		{
  			for (directory i(f, ec); !i.done(); i.next(ec))
  			{
  				if (ec) return;
  				std::string p = i.file();
  				if (p == "." || p == "..") continue;
  				remove_all(combine_path(f, p), ec);
  				if (ec) return;
  			}
  		}
  		remove(f, ec);
  	}
  
  	std::string complete(string_view f)
  	{
  		if (is_complete(f)) return f.to_string();
  		if (f == ".") return current_working_directory();
  		return combine_path(current_working_directory(), f);
  	}
  
  	bool is_complete(string_view f)
  	{
  		if (f.empty()) return false;
  #if defined(TORRENT_WINDOWS) || defined(TORRENT_OS2)
  		int i = 0;
  		// match the xx:\ or xx:/ form
  		while (f[i] && is_alpha(f[i])) ++i;
  		if (i < int(f.size()-1) && f[i] == ':' && (f[i+1] == '\\' || f[i+1] == '/'))
  			return true;
  
  		// match the \\ form
  		if (int(f.size()) >= 2 && f[0] == '\\' && f[1] == '\\')
  			return true;
  		return false;
  #else
  		if (f[0] == '/') return true;
  		return false;
  #endif
  	}
  }
  
  