libcrosscoro/inc/coro/net/udp_peer.hpp

#pragma once

#include "coro/concepts/buffer.hpp"
#include "coro/net/ip_address.hpp"
#include "coro/net/socket.hpp"
#include "coro/net/send_status.hpp"
#include "coro/net/recv_status.hpp"
#include "coro/task.hpp"
#include "coro/io_scheduler.hpp"

#include <chrono>
#include <variant>
#include <span>

namespace coro
{
class io_scheduler;
} // namespace coro

namespace coro::net
{

class udp_peer
{
public:
    struct info
    {
        /// The ip address of the peer.
        net::ip_address address{net::ip_address::from_string("127.0.0.1")};
        /// The port of the peer.
        uint16_t port{8080};

        auto operator<=>(const info& other) const = default;
    };

    /**
     * Creates a udp peer that can send packets but not receive them.  This udp peer will not explicitly
     * bind to a local ip+port.
     */
    explicit udp_peer(
        io_scheduler& scheduler,
        net::domain_t domain = net::domain_t::ipv4);

    /**
     * Creates a udp peer that can send and receive packets.  This peer will bind to the given ip_port.
     */
    explicit udp_peer(
        io_scheduler& scheduler,
        const info& bind_info);

    udp_peer(const udp_peer&) = delete;
    udp_peer(udp_peer&&)      = default;
    auto operator=(const udp_peer&) noexcept -> udp_peer& = delete;
    auto operator=(udp_peer&&) noexcept -> udp_peer& = default;
    ~udp_peer()                                        = default;

    /**
     * @param op The poll operation to perform on the udp socket.  Note that if this is a send only
     *           udp socket (did not bind) then polling for read will not work.
     * @param timeout The timeout for the poll operation to be ready.
     * @return The result status of the poll operation.
     */
    auto poll(
        poll_op op,
        std::chrono::milliseconds timeout = std::chrono::milliseconds{0}) -> coro::task<coro::poll_status>
    {
        co_return co_await m_io_scheduler.poll(m_socket, op, timeout);
    }

    /**
     * @param peer_info The peer to send the data to.
     * @param buffer The data to send.
     * @return The status of send call and a span view of any data that wasn't sent.  This data if
     *         un-sent will correspond to bytes at the end of the given buffer.
     */
    template<concepts::const_buffer buffer_type>
    auto sendto(
        const info& peer_info,
        const buffer_type& buffer) -> std::pair<send_status, std::span<const char>>
    {
        if(buffer.empty())
        {
            return {send_status::ok, std::span<const char>{}};
        }

        sockaddr_in peer{};
        peer.sin_family = static_cast<int>(peer_info.address.domain());
        peer.sin_port   = htons(peer_info.port);
        peer.sin_addr   = *reinterpret_cast<const in_addr*>(peer_info.address.data().data());

        socklen_t peer_len{sizeof(peer)};

        auto bytes_sent = ::sendto(
            m_socket.native_handle(),
            buffer.data(),
            buffer.size(),
            0,
            reinterpret_cast<sockaddr*>(&peer),
            peer_len);

        if(bytes_sent >= 0)
        {
            return {send_status::ok, std::span<const char>{buffer.data() + bytes_sent, buffer.size() - bytes_sent}};
        }
        else
        {
            return {static_cast<send_status>(errno), std::span<const char>{}};
        }
    }

    /**
     * @param buffer The buffer to receive data into.
     * @return The receive status, if ok then also the peer who sent the data and the data.
     *         The span view of the data will be set to the size of the received data, this will
     *         always start at the beggining of the buffer but depending on how large the data was
     *         it might not fill the entire buffer.
     */
    template<concepts::mutable_buffer buffer_type>
    auto recvfrom(
        buffer_type&& buffer) -> std::tuple<recv_status, udp_peer::info, std::span<char>>
    {
        // The user must bind locally to be able to receive packets.
        if(!m_bound)
        {
            return {recv_status::udp_not_bound, udp_peer::info{}, std::span<char>{}};
        }

        sockaddr_in peer{};
        socklen_t peer_len{sizeof(peer)};

        auto bytes_read = ::recvfrom(
            m_socket.native_handle(),
            buffer.data(),
            buffer.size(),
            0,
            reinterpret_cast<sockaddr*>(&peer),
            &peer_len);

        if(bytes_read < 0)
        {
            return {static_cast<recv_status>(errno), udp_peer::info{}, std::span<char>{}};
        }

        std::span<const uint8_t> ip_addr_view{
            reinterpret_cast<uint8_t*>(&peer.sin_addr.s_addr),
            sizeof(peer.sin_addr.s_addr),
        };

        return {
            recv_status::ok,
            udp_peer::info{
                .address = net::ip_address{ip_addr_view, static_cast<net::domain_t>(peer.sin_family)},
                .port = ntohs(peer.sin_port)
            },
            std::span<char>{buffer.data(), static_cast<size_t>(bytes_read)}
        };
    }

private:
    /// The scheduler that will drive this udp client.
    io_scheduler& m_io_scheduler;
    /// The udp socket.
    net::socket m_socket{-1};
    /// Did the user request this udp socket is bound locally to receive packets?
    bool m_bound{false};
};

} // namespace coro::net