limen/util/parse_buffer.h

#pragma once
#include <cstddef>
#include <cstdint>
#include <span>

// Bounds-checked sequential reader for byte streams. consume<T>() returns a
// typed pointer into the underlying buffer or nullptr on underflow. Used to
// walk packet headers in order without UB and without copies.
class parse_buffer {
    const uint8_t* m_data;
    size_t m_remaining;

public:
    parse_buffer(std::span<const uint8_t> data)
        : m_data(data.data()), m_remaining(data.size()) {}

    template <typename T>
    const T* consume() {
        if (m_remaining < sizeof(T)) return nullptr;
        auto* p = reinterpret_cast<const T*>(m_data);
        m_data += sizeof(T);
        m_remaining -= sizeof(T);
        return p;
    }

    bool skip(size_t len) {
        if (m_remaining < len) return false;
        m_data += len;
        m_remaining -= len;
        return true;
    }

    std::span<const uint8_t> remaining() const { return {m_data, m_remaining}; }
    size_t remaining_size() const { return m_remaining; }
};