libcrosscoro/inc/coro/net/tcp_client.hpp

#pragma once

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

#include <chrono>
#include <memory>
#include <optional>
#include <string>
#include <variant>
#include <vector>

namespace coro
{
class io_scheduler;
} // namespace coro

namespace coro::net
{
class tcp_server;

class tcp_client
{
public:
    struct options
    {
        /// The  ip address to connect to.  Use a dns_resolver to turn hostnames into ip addresses.
        net::ip_address address{net::ip_address::from_string("127.0.0.1")};
        /// The port to connect to.
        uint16_t port{8080};
    };

    /**
     * Creates a new tcp client that can connect to an ip address + port.  By default the socket
     * created will be in non-blocking mode, meaning that any sending or receiving of data should
     * poll for event readiness prior.
     * @param scheduler The io scheduler to drive the tcp client.
     * @param opts See tcp_client::options for more information.
     */
    tcp_client(
        io_scheduler& scheduler,
        options       opts = options{.address = {net::ip_address::from_string("127.0.0.1")}, .port = 8080});
    tcp_client(const tcp_client&) = delete;
    tcp_client(tcp_client&&)      = default;
    auto operator=(const tcp_client&) noexcept -> tcp_client& = delete;
    auto operator=(tcp_client&&) noexcept -> tcp_client& = default;
    ~tcp_client()                                        = default;

    /**
     * @return The tcp socket this client is using.
     * @{
     **/
    auto socket() -> net::socket& { return m_socket; }
    auto socket() const -> const net::socket& { return m_socket; }
    /** @} */

    /**
     * Connects to the address+port with the given timeout.  Once connected calling this function
     * only returns the connected status, it will not reconnect.
     * @param timeout How long to wait for the connection to establish? Timeout of zero is indefinite.
     * @return The result status of trying to connect.
     */
    auto connect(std::chrono::milliseconds timeout = std::chrono::milliseconds{0}) -> coro::task<net::connect_status>;

    /**
     * Polls for the given operation on this client's tcp socket.  This should be done prior to
     * calling recv and after a send that doesn't send the entire buffer.
     * @param op The poll operation to perform, use read for incoming data and write for outgoing.
     * @param timeout The amount of time to wait for the poll event to be ready.  Use zero for infinte timeout.
     * @return The status result of th poll operation.  When poll_status::event is returned then the
     *         event operation is ready.
     */
    auto poll(coro::poll_op op, std::chrono::milliseconds timeout = std::chrono::milliseconds{0})
        -> coro::task<poll_status>
    {
        co_return co_await m_io_scheduler.poll(m_socket, op, timeout);
    }

    /**
     * Receives incoming data into the given buffer.  By default since all tcp client sockets are set
     * to non-blocking use co_await poll() to determine when data is ready to be received.
     * @param buffer Received bytes are written into this buffer up to the buffers size.
     * @return The status of the recv call and a span of the bytes recevied (if any).  The span of
     *         bytes will be a subspan or full span of the given input buffer.
     */
    template<concepts::mutable_buffer buffer_type>
    auto recv(buffer_type&& buffer) -> std::pair<recv_status, std::span<char>>
    {
        // If the user requested zero bytes, just return.
        if (buffer.empty())
        {
            return {recv_status::ok, std::span<char>{}};
        }

        auto bytes_recv = ::recv(m_socket.native_handle(), buffer.data(), buffer.size(), 0);
        if (bytes_recv > 0)
        {
            // Ok, we've recieved some data.
            return {recv_status::ok, std::span<char>{buffer.data(), static_cast<size_t>(bytes_recv)}};
        }
        else if (bytes_recv == 0)
        {
            // On TCP stream sockets 0 indicates the connection has been closed by the peer.
            return {recv_status::closed, std::span<char>{}};
        }
        else
        {
            // Report the error to the user.
            return {static_cast<recv_status>(errno), std::span<char>{}};
        }
    }

    /**
     * Sends outgoing data from the given buffer.  If a partial write occurs then use co_await poll()
     * to determine when the tcp client socket is ready to be written to again.  On partial writes
     * the status will be 'ok' and the span returned will be non-empty, it will contain the buffer
     * span data that was not written to the client's socket.
     * @param buffer The data to write on the tcp socket.
     * @return The status of the send call and a span of any remaining bytes not sent.  If all bytes
     *         were successfully sent the status will be 'ok' and the remaining span will be empty.
     */
    template<concepts::const_buffer buffer_type>
    auto send(const buffer_type& buffer) -> std::pair<send_status, std::span<const char>>
    {
        // If the user requested zero bytes, just return.
        if (buffer.empty())
        {
            return {send_status::ok, std::span<const char>{buffer.data(), buffer.size()}};
        }

        auto bytes_sent = ::send(m_socket.native_handle(), buffer.data(), buffer.size(), 0);
        if (bytes_sent >= 0)
        {
            // Some or all of the bytes were written.
            return {send_status::ok, std::span<const char>{buffer.data() + bytes_sent, buffer.size() - bytes_sent}};
        }
        else
        {
            // Due to the error none of the bytes were written.
            return {static_cast<send_status>(errno), std::span<const char>{buffer.data(), buffer.size()}};
        }
    }

private:
    /// The tcp_server creates already connected clients and provides a tcp socket pre-built.
    friend tcp_server;
    tcp_client(io_scheduler& scheduler, net::socket socket, options opts);

    /// The scheduler that will drive this tcp client.
    io_scheduler& m_io_scheduler;
    /// Options for what server to connect to.
    options m_options{};
    /// The tcp socket.
    net::socket m_socket{-1};
    /// Cache the status of the connect in the event the user calls connect() again.
    std::optional<net::connect_status> m_connect_status{std::nullopt};
};

} // namespace coro::net