core/impl/read_size.hpp

0001 //
0002 // Copyright (c) 2016-2019 Vinnie Falco (vinnie dot falco at gmail dot com)
0003 //
0004 // Distributed under the Boost Software License, Version 1.0. (See accompanying
0005 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
0006 //
0007 // Official repository: https://github.com/boostorg/beast
0008 //
0009
0010 #ifndef BOOST_BEAST_IMPL_READ_SIZE_HPP
0011 #define BOOST_BEAST_IMPL_READ_SIZE_HPP
0012
0013 #include <boost/asio/buffer.hpp>
0014 #include <boost/assert.hpp>
0015 #include <stdexcept>
0016 #include <type_traits>
0017
0018 namespace boost {
0019 namespace beast {
0020
0021 namespace detail {
0022
0023 template<class T, class = void>
0024 struct has_read_size_helper : std::false_type {};
0025
0026 template<class T>
0027 struct has_read_size_helper<T, decltype(
0028     read_size_helper(std::declval<T&>(), 512),
0029     (void)0)> : std::true_type
0030 {
0031 };
0032
0033 template<class DynamicBuffer>
0034 std::size_t
0035 read_size(DynamicBuffer& buffer,
0036     std::size_t max_size, std::true_type)
0037 {
0038     return read_size_helper(buffer, max_size);
0039 }
0040
0041 template<class DynamicBuffer>
0042 std::size_t
0043 read_size(DynamicBuffer& buffer,
0044     std::size_t max_size, std::false_type)
0045 {
0046     static_assert(
0047         net::is_dynamic_buffer<DynamicBuffer>::value,
0048         "DynamicBuffer type requirements not met");
0049     auto const size = buffer.size();
0050     auto const limit = buffer.max_size() - size;
0051     BOOST_ASSERT(size <= buffer.max_size());
0052     return std::min<std::size_t>(
0053         std::max<std::size_t>(512, buffer.capacity() - size),
0054         std::min<std::size_t>(max_size, limit));
0055 }
0056
0057 } // detail
0058
0059 template<class DynamicBuffer>
0060 std::size_t
0061 read_size(
0062     DynamicBuffer& buffer, std::size_t max_size)
0063 {
0064     return detail::read_size(buffer, max_size,
0065         detail::has_read_size_helper<DynamicBuffer>{});
0066 }
0067
0068 template<class DynamicBuffer>
0069 std::size_t
0070 read_size_or_throw(
0071     DynamicBuffer& buffer, std::size_t max_size)
0072 {
0073     auto const n = read_size(buffer, max_size);
0074     if(n == 0)
0075         BOOST_THROW_EXCEPTION(std::length_error{
0076             "buffer overflow"});
0077     return n;
0078 }
0079
0080 } // beast
0081 } // boost
0082
0083 #endif