Crafter.Network/tests/ShouldConnectDualStack/main.cpp

//SPDX-License-Identifier: LGPL-3.0-only
//SPDX-FileCopyrightText: Copyright (C) 2026 Catcrafts®

// ClientTCP resolves a host for IPv4 and IPv6 alike and tries every address
// the name resolves to, in order, the way Python's socket.create_connection
// does. Before, it asked getaddrinfo for AF_INET only and kept the first
// answer, so a server listening on ::1 alone — a dev server on a recent Node
// binds `localhost` that way — could not be reached by name, while every
// Python client reached it.
//
// The listeners are raw sockets, so nothing here depends on ListenerTCP: one
// IPv6-only on ::1, one on 127.0.0.1. Skips (77) on a host without IPv6
// loopback.

#include <arpa/inet.h>
#include <netdb.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <unistd.h>
#include <cerrno>
#include <cstdlib>

import Crafter.Network;
import std;
using namespace Crafter;
using namespace std::chrono_literals;

namespace {

int failures = 0;

void Check(bool ok, std::string_view what) {
    std::println("{}  {}", ok ? "PASS" : "FAIL", what);
    if (!ok) ++failures;
}

// A socket listening on the loopback address of `family`, on a port the
// kernel picks; fd stays -1 when the host cannot open one.
struct LoopbackListener {
    int fd = -1;
    std::uint16_t port = 0;

    explicit LoopbackListener(int family) {
        fd = socket(family, SOCK_STREAM, 0);
        if (fd == -1) return;
        sockaddr_storage address {};
        socklen_t length = 0;
        if (family == AF_INET6) {
            // v6 only, or the socket would also take IPv4 connects and the
            // checks below would not tell the two apart.
            int only = 1;
            setsockopt(fd, IPPROTO_IPV6, IPV6_V6ONLY, &only, sizeof(only));
            auto* v6 = reinterpret_cast<sockaddr_in6*>(&address);
            v6->sin6_family = AF_INET6;
            v6->sin6_addr = in6addr_loopback;
            length = sizeof(sockaddr_in6);
        } else {
            auto* v4 = reinterpret_cast<sockaddr_in*>(&address);
            v4->sin_family = AF_INET;
            v4->sin_addr.s_addr = htonl(INADDR_LOOPBACK);
            length = sizeof(sockaddr_in);
        }
        if (bind(fd, reinterpret_cast<sockaddr*>(&address), length) != 0 || listen(fd, 8) != 0) {
            close(fd);
            fd = -1;
            return;
        }
        getsockname(fd, reinterpret_cast<sockaddr*>(&address), &length);
        port = family == AF_INET6 ? ntohs(reinterpret_cast<sockaddr_in6*>(&address)->sin6_port)
                                  : ntohs(reinterpret_cast<sockaddr_in*>(&address)->sin_port);
    }
    ~LoopbackListener() {
        if (fd != -1) close(fd);
    }
};

// The address family of the peer a connected client reached.
int PeerFamily(const ClientTCP& client) {
    sockaddr_storage address {};
    socklen_t length = sizeof(address);
    getpeername(client.socketid, reinterpret_cast<sockaddr*>(&address), &length);
    return address.ss_family;
}

// Whether `localhost` resolves to ::1 here; /etc/hosts decides.
bool LocalhostResolvesToIPv6() {
    addrinfo hints {};
    hints.ai_family = AF_INET6;
    hints.ai_socktype = SOCK_STREAM;
    addrinfo* resolved = nullptr;
    if (getaddrinfo("localhost", nullptr, &hints, &resolved) != 0) return false;
    freeaddrinfo(resolved);
    return true;
}

} // namespace

int main() {
    LoopbackListener v6(AF_INET6);
    if (v6.fd == -1) {
        std::println("SKIP  no IPv6 loopback on this host");
        return 77;
    }

    {
        ClientTCP client("::1", v6.port, 2s);
        Check(PeerFamily(client) == AF_INET6, "an IPv6 literal connects over IPv6");
    }

    if (LocalhostResolvesToIPv6()) {
        try {
            ClientTCP client("localhost", v6.port, 2s);
            Check(PeerFamily(client) == AF_INET6, "localhost reaches a server that listens on ::1 only");
        } catch (const std::exception& e) {
            Check(false, std::format("localhost reaches a server that listens on ::1 only (threw: {})", e.what()));
        }
    } else {
        std::println("SKIP  localhost does not resolve to ::1 on this host");
    }

    {
        // Whichever address the resolver ranks first, a refused one is not
        // the end: the next is tried.
        LoopbackListener v4(AF_INET);
        try {
            ClientTCP client("localhost", v4.port, 2s);
            Check(PeerFamily(client) == AF_INET, "localhost reaches a server that listens on 127.0.0.1 only");
        } catch (const std::exception& e) {
            Check(false, std::format("localhost reaches a server that listens on 127.0.0.1 only (threw: {})", e.what()));
        }
    }

    {
        std::uint16_t closedPort = 0;
        {
            LoopbackListener gone(AF_INET);
            closedPort = gone.port;
        }
        bool refused = false;
        try {
            ClientTCP client("localhost", closedPort, 2s);
        } catch (const SocketErrorException& e) {
            refused = e.phase == SocketPhase::Connect && e.code() == std::errc::connection_refused;
        } catch (const std::exception&) {
        }
        Check(refused, "when no address answers, the last failure is thrown, with its errno");
    }

    std::println("{}", failures == 0 ? "all checks passed" : "check(s) failed");
    return failures == 0 ? EXIT_SUCCESS : EXIT_FAILURE;
}