bool udp_tracker_connection::on_connect_response(span<char const> buf)
	{
		// ignore packets smaller than 16 bytes
		if (buf.size() < 16) return false;

		restart_read_timeout();

		// skip header
		buf = buf.subspan(8);

		// reset transaction
		update_transaction_id();
		std::uint64_t const connection_id = aux::read_int64(buf);

		std::lock_guard<std::mutex> l(m_cache_mutex);
		connection_cache_entry& cce = m_connection_cache[m_target.address()];
		cce.connection_id = connection_id;
		cce.expires = aux::time_now() + seconds(m_man.settings().get_int(settings_pack::udp_tracker_token_expiry));

		if (0 == (tracker_req().kind & tracker_request::scrape_request))
			send_udp_announce();
		else if (0 != (tracker_req().kind & tracker_request::scrape_request))
			send_udp_scrape();
		return true;
	}

		void update(span<char const> data)
		{
			if (CryptHashData(m_hash, reinterpret_cast<BYTE const*>(data.data()), int(data.size()), 0) == false)
			{
				throw_ex<system_error>(error_code(GetLastError(), system_category()));
			}
		}

	int count_trailing_ones_hw(span<std::uint32_t const> buf)
	{
		auto const num = int(buf.size());
		std::uint32_t const* ptr = buf.data();

		TORRENT_ASSERT(num >= 0);
		TORRENT_ASSERT(ptr != nullptr);

		for (int i = num - 1; i >= 0; i--)
		{
			if (ptr[i] == 0xffffffff) continue;

#if TORRENT_HAS_BUILTIN_CTZ
			std::uint32_t const v = ~aux::network_to_host(ptr[i]);
			return (num - i - 1) * 32 + __builtin_ctz(v);
#elif defined _MSC_VER
			std::uint32_t const v = ~aux::network_to_host(ptr[i]);
			DWORD pos;
			_BitScanForward(&pos, v);
			return (num - i - 1) * 32 + pos;
#else
			TORRENT_ASSERT_FAIL();
			return -1;
#endif
		}

		return num * 32;
	}

		void random_bytes(span<char> buffer)
		{
#ifdef TORRENT_BUILD_SIMULATOR
			// simulator

			for (auto& b : buffer) b = char(random(0xff));

#elif TORRENT_USE_CRYPTOAPI
			// windows

			aux::crypt_gen_random(buffer);

#elif TORRENT_USE_DEV_RANDOM
			// /dev/random

			static dev_random dev;
			dev.read(buffer);

#elif defined TORRENT_USE_LIBCRYPTO
			// openssl

			int r = RAND_bytes(reinterpret_cast<unsigned char*>(buffer.data())
				, int(buffer.size()));
			if (r != 1) aux::throw_ex<system_error>(errors::no_entropy);
#else
			// fallback

			for (auto& b : buffer) b = char(random(0xff));
#endif
		}

	ImageFileInfo DetectImageFormat(span<uint8_t> data) {
		ImageFileInfo info;

		stbi__context ctx;
		stbi__start_mem(&ctx, &data[0], data.size_bytes());

		int comp;
		if (stbi__bmp_info(&ctx, &info.width, &info.height, &comp)) {
			info.hasAlpha = (comp == 4);
			info.format = ImageFileFormat::BMP;
			return info;
		}

		TjDecompressHandle handle;
		if (tjDecompressHeader(handle, &data[0], data.size_bytes(), &info.width, &info.height) == 0) {
			info.hasAlpha = false;
			info.format = ImageFileFormat::JPEG;
			return info;
		}

		if (DetectTga(data, info)) {
			return info;
		}

		// Not a very good heuristic
		if (data.size() == 256 * 256) {
			info.width = 256;
			info.height = 256;
			info.hasAlpha = true;
			info.format = ImageFileFormat::FNTART;
			return info;
		}

		return info;
	}

	void iterate_every_other_element(span<int, dynamic_range> av)
	{
		// pick every other element

		auto length = av.size() / 2;
#if _MSC_VER > 1800
		auto bounds = strided_bounds<1>({ length }, { 2 });
#else
		auto bounds = strided_bounds<1>(index<1>{ length }, index<1>{ 2 });
#endif
		strided_span<int, 1> strided(&av.data()[1], av.size() - 1, bounds);

		CHECK(strided.size() == length);
		CHECK(strided.bounds().index_bounds()[0] == length);
		for (auto i = 0; i < strided.size(); ++i)
		{
			CHECK(strided[i] == av[2 * i + 1]);
		}

		int idx = 0;
		for (auto num : strided)
		{
			CHECK(num == av[2 * idx + 1]);
			idx++;
		}
	}

bool CommObject::SendFrame(span<const std::uint8_t> frame)
{
    if (frame.size() > CommMaxFrameSize)
    {
        LOGF(LOG_LEVEL_ERROR, "Frame payload is too long. Allowed: %d, Requested: '%d'.", CommMaxFrameSize, frame.size());
        return false;
    }

    uint8_t cmd[ComPrefferedBufferSize];
    cmd[0] = TransmitterSendFrame;
    memcpy(cmd + 1, frame.data(), frame.size());
    uint8_t remainingBufferSize;

    const bool status = (this->_low.WriteRead(CommTransmitter,           //
                             span<const uint8_t>(cmd, 1 + frame.size()), //
                             span<uint8_t>(&remainingBufferSize, 1)      //
                             ) == I2CResult::OK);
    if (!status)
    {
        LOG(LOG_LEVEL_ERROR, "[comm] Failed to send frame");
    }

    if (remainingBufferSize == 0xff)
    {
        LOG(LOG_LEVEL_ERROR, "[comm] Frame was not accepted by the transmitter.");
    }

    return status && remainingBufferSize != 0xff;
}

 explicit
 enumerated_value_range(span<const T> v)
 noexcept
     : _begin(v.data())
     , _end(v.data()+v.size())
 {
     assert(_begin <= _end);
 }

	inline void crypt_gen_random(span<char> buffer)
	{
		static HCRYPTPROV provider = crypt_acquire_provider(PROV_RSA_FULL);
		if (!CryptGenRandom(provider, int(buffer.size())
			, reinterpret_cast<BYTE*>(buffer.data())))
		{
			throw_ex<system_error>(error_code(GetLastError(), system_category()));
		}
	}

	// allocate an uninitialized buffer of the specified size
	// and copy the initialization range into the start of the buffer
	buffer(std::size_t const size, span<char const> initialize)
		: buffer(size)
	{
		TORRENT_ASSERT(initialize.size() <= size);
		if (!initialize.empty())
		{
			std::memcpy(m_begin, initialize.data(), (std::min)(initialize.size(), size));
		}
	}

	allocation_slot stack_allocator::copy_buffer(span<char const> buf)
	{
		int const ret = int(m_storage.size());
		int const size = int(buf.size());
		if (size < 1) return {};
		m_storage.resize(ret + size);
		std::memcpy(&m_storage[ret], buf.data(), numeric_cast<std::size_t>(size));
		return allocation_slot(ret);
	}

	entry::entry(span<char const> v)
		: m_type(undefined_t)
	{
#if TORRENT_USE_ASSERTS
		m_type_queried = true;
#endif
		new(&data) string_type(v.data(), v.size());
		m_type = string_t;
	}

void GLVertexBuffer::upload(span<const byte> a_data)
{
	assert(GLStateBuffer::isBegun());
	assert(m_initialized);
	if (!a_data.empty())
	{
		glBindBuffer(GLenum(m_bufferType), m_id);
		glBufferData(GLenum(m_bufferType), a_data.length_bytes(), a_data.data(), GLenum(m_drawUsage));
	}
}

	entry bdecode(span<char const> buffer)
	{
		entry e;
		bool err = false;
		auto it = buffer.begin();
		detail::bdecode_recursive(it, buffer.end(), e, err, 0);
		TORRENT_ASSERT(e.m_type_queried == false);
		if (err) return entry();
		return e;
	}

void item::assign(entry v, span<char const> salt
	, sequence_number const seq
	, public_key const& pk, signature const& sig)
{

	m_pk = pk;
	m_sig = sig;
	m_salt.assign(salt.data(), salt.size());
	m_seq = seq;
	m_mutable = true;
	m_value = std::move(v);
}

	// this has to be thread safe and atomic. i.e. on posix systems it has to be
	// turned into a series of pread() calls
	std::int64_t file::readv(std::int64_t file_offset, span<iovec_t const> bufs
		, error_code& ec, open_mode_t flags)
	{
		if (m_file_handle == INVALID_HANDLE_VALUE)
		{
#ifdef TORRENT_WINDOWS
			ec = error_code(ERROR_INVALID_HANDLE, system_category());
#else
			ec = error_code(boost::system::errc::bad_file_descriptor, generic_category());
#endif
			return -1;
		}
		TORRENT_ASSERT((m_open_mode & open_mode::rw_mask) == open_mode::read_only
			|| (m_open_mode & open_mode::rw_mask) == open_mode::read_write);
		TORRENT_ASSERT(!bufs.empty());
		TORRENT_ASSERT(is_open());

#if TORRENT_USE_PREADV
		TORRENT_UNUSED(flags);
		std::int64_t ret = iov(&::preadv, native_handle(), file_offset, bufs, ec);
#else

		// there's no point in coalescing single buffer writes
		if (bufs.size() == 1)
		{
			flags &= ~open_mode::coalesce_buffers;
		}

		iovec_t tmp;
		span<iovec_t const> tmp_bufs = bufs;
		if (flags & open_mode::coalesce_buffers)
		{
			if (!coalesce_read_buffers(tmp_bufs, tmp))
				// ok, that failed, don't coalesce this read
				flags &= ~open_mode::coalesce_buffers;
		}

#if TORRENT_USE_PREAD
		std::int64_t ret = iov(&::pread, native_handle(), file_offset, tmp_bufs, ec);
#else
		std::int64_t ret = iov(&::read, native_handle(), file_offset, tmp_bufs, ec);
#endif

		if (flags & open_mode::coalesce_buffers)
			coalesce_read_buffers_end(bufs
				, tmp.data(), !ec);

#endif
		return ret;
	}

	std::unique_ptr<uint8_t[]> DecodeJpeg(const span<uint8_t> data) {
		TjDecompressHandle handle;

		int w, h;
		tjDecompressHeader(handle, &data[0], data.size_bytes(), &w, &h);

		std::unique_ptr<uint8_t[]> result(new uint8_t[w * h * 4]);
		auto status = tjDecompress2(handle, &data[0], data.size_bytes(), &result[0], w, w * 4, h, TJPF_BGRX, 0);
		if (status != 0) {
			throw TempleException("Unable to decompress jpeg image: {}",
			                      tjGetErrorStr());
		}
		return result;
	}

void item::assign(entry v, span<char const> salt
	, sequence_number const seq, public_key const& pk, secret_key const& sk)
{
	char buffer[1000];
	int bsize = bencode(buffer, v);
	TORRENT_ASSERT(bsize <= 1000);
	m_sig = sign_mutable_item(span<char const>(buffer, bsize)
		, salt, seq, pk, sk);
	m_salt.assign(salt.data(), salt.size());
	m_pk = pk;
	m_seq = seq;
	m_mutable = true;
	m_value = std::move(v);
}

	bool udp_tracker_connection::on_scrape_response(span<char const> buf)
	{
		using namespace libtorrent::aux;

		restart_read_timeout();
		int const action = aux::read_int32(buf);
		std::uint32_t const transaction = read_uint32(buf);

		if (transaction != m_transaction_id)
		{
			fail(error_code(errors::invalid_tracker_transaction_id));
			return false;
		}

		if (action == action_error)
		{
			fail(error_code(errors::tracker_failure), -1
				, std::string(buf.data(), buf.size()).c_str());
			return true;
		}

		if (action != action_scrape)
		{
			fail(error_code(errors::invalid_tracker_action));
			return true;
		}

		if (buf.size() < 12)
		{
			fail(error_code(errors::invalid_tracker_response_length));
			return true;
		}

		int const complete = aux::read_int32(buf);
		int const downloaded = aux::read_int32(buf);
		int const incomplete = aux::read_int32(buf);

		boost::shared_ptr<request_callback> cb = requester();
		if (!cb)
		{
			close();
			return true;
		}

		cb->tracker_scrape_response(tracker_req()
			, complete, incomplete, downloaded, -1);

		close();
		return true;
	}

		void random_bytes(span<char> buffer)
		{
#if TORRENT_USE_CRYPTOAPI
			HCRYPTPROV prov;

			if (!CryptAcquireContext(&prov, NULL, NULL
				, PROV_RSA_FULL, CRYPT_VERIFYCONTEXT))
			{
#ifndef BOOST_NO_EXCEPTIONS
				throw system_error(error_code(GetLastError(), system_category()));
#else
				std::terminate();
#endif
			}

			if (!CryptGenRandom(prov, int(buffer.size())
				, reinterpret_cast<BYTE*>(buffer.data())))
			{
				CryptReleaseContext(prov, 0);
#ifndef BOOST_NO_EXCEPTIONS
				throw system_error(error_code(GetLastError(), system_category()));
#else
				std::terminate();
#endif
			}

			CryptReleaseContext(prov, 0);
#elif defined TORRENT_USE_LIBCRYPTO
#ifdef TORRENT_MACOS_DEPRECATED_LIBCRYPTO
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wdeprecated-declarations"
#endif
			int r = RAND_bytes(reinterpret_cast<unsigned char*>(buffer.data())
				, int(buffer.size()));
			if (r != 1)
			{
#ifndef BOOST_NO_EXCEPTIONS
				throw system_error(error_code(int(::ERR_get_error()), system_category()));
#else
				std::terminate();
#endif
			}
#ifdef TORRENT_MACOS_DEPRECATED_LIBCRYPTO
#pragma clang diagnostic pop
#endif
#else
			for (auto& b : buffer) b = char(random(0xff));
#endif
		}