123 lines
4.1 KiB
C++
123 lines
4.1 KiB
C++
//-----------------------------------------------------------------------------
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// ___ __ _ _
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// / _ \__ _ _ __ ___ ___ / /(_)_ __ | | __
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// / /_)/ _` | '__/ __|/ _ \/ / | | '_ \| |/ /
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// / ___/ (_| | | \__ \ __/ /__| | | | | <
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// \/ \__,_|_| |___/\___\____/_|_| |_|_|\_\ .
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//
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//-----------------------------------------------------------------------------
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// Author: Kurt Sassenrath
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// Module: msgpack
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//
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// Token-based reader for unpacking MessagePack data. Ensure lifetime of the
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// MessagePack buffer exceeds the lifetime of parsed tokens.
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//
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// TBD: How best to handle arrays and maps.
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//
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// Copyright (c) 2023 Kurt Sassenrath.
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//
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// License TBD.
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//-----------------------------------------------------------------------------
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#ifndef msgpack_token_reader_8daff350a0b1a519
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#define msgpack_token_reader_8daff350a0b1a519
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#include "type.h"
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#include "../core/error.h"
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#include "../util/endianness.h"
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#include "../core/format.h"
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#include <tl/expected.hpp>
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namespace msgpack {
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namespace detail {
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constexpr inline decltype(auto) read(std::size_t size, auto& inp)
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noexcept {
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std::array<std::byte, token::word_size> value;
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be_to_host(inp, inp + size, std::begin(value));
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inp += size;
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return value;
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}
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template <format::type FormatType>
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constexpr inline decltype(auto) read_value(std::size_t size, auto& inp) {
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using value_type = typename token_traits<FormatType>::storage_type;
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return token{std::bit_cast<value_type>(read(size, inp))};
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}
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} // namespace detail
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class token_reader {
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public:
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constexpr token_reader(std::span<std::byte const> src) noexcept :
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data_(src), curr_{src.begin()}, end_(src.end()) {}
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constexpr auto remaining() noexcept {
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using dist_type = decltype(std::distance(curr_, end_));
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return std::max(dist_type(0), std::distance(curr_, end_));
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}
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// Read the next token. If the reader currently points to the end of the
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// byte buffer, then end_of_message is returned, and if there is still
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// some data present in the buffer, then incomplete_message is returned,
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// potentially hinting that further buffering is required.
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constexpr tl::expected<token, error> read_one() noexcept {
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if (curr_ >= end_) {
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return tl::make_unexpected(error::end_of_message);
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}
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// Enumerate the current byte first by switch statement, then by
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// fix types.
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long int size = 0;
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auto id = *curr_;
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++curr_;
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switch (id) {
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case format::uint8::marker:
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size = 1;
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case format::uint16::marker:
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size = 2;
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case format::uint32::marker:
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size = 3;
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case format::uint64::marker:
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size = 4;
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if (remaining() < size) {
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return tl::make_unexpected(error::incomplete_message);
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}
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return detail::read_value<format::type::unsigned_int>(size, curr_);
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case format::int8::marker:
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size = 1;
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case format::int16::marker:
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size = 2;
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case format::int32::marker:
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size = 3;
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case format::int64::marker:
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size = 4;
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if (remaining() < size) {
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return tl::make_unexpected(error::incomplete_message);
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}
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return detail::read_value<format::type::signed_int>(size, curr_);
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}
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return tl::make_unexpected(error::not_implemented);
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}
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// Read multiple tokens from the byte buffer. The number of tokens parsed
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// can be surmised from the returned span of tokens. If the reader
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// currently points to the end of the byte buffer, then
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// error::end_of_message is returned, and if there is not enough data to
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// fully parse a token, then incomplete_message is returned.
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constexpr tl::expected<std::span<token>, error> read_some(
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std::span<token> token_buffer) noexcept;
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private:
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std::span<std::byte const> data_;
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decltype(data_)::iterator curr_;
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decltype(data_)::iterator end_;
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};
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} // namespace msgpack
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#endif // msgpack_token_reader_8daff350a0b1a519
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