DNS

Introduction

xpp::net::lookup_host() provides async hostname resolution, wrapping libx's xDnsResolve. Returns a vector of SocketAddr.

Example — .await()

#include <xpp/net/dns.h>

xpp::EventLoop loop;
xpp::WaitScope scope(loop);

auto addrs = xpp::net::lookup_host("example.com").await();
for (const auto &addr : addrs) {
    printf("%s\n", addr.to_string().c_str());
}

Example — co_await (C++20)

xpp::Promise<void> resolve_print(const char *hostname) {
    auto addrs = co_await xpp::net::lookup_host(hostname);
    for (const auto &addr : addrs) {
        printf("%s\n", addr.to_string().c_str());
    }
}

API Reference

Resolves to an empty vector on failure (hostname not found, DNS error, etc.).

How it works

lookup_host() uses adapt<vector<SocketAddr>, LookupHostAdapter>(). The adapter calls xDnsResolve in its constructor and xDnsCancel in its destructor. Dropping the Promise mid-query cancels the query safely.

Usage Examples

Resolve and connect — .await()

auto addrs = xpp::net::lookup_host("example.com").await();
if (!addrs.empty()) {
    auto conn = xpp::net::TcpStream::connect(addrs[0]).await();
}

Resolve and connect — co_await (C++20)

xpp::Promise<void> connect_to(const char *hostname) {
    auto addrs = co_await xpp::net::lookup_host(hostname);
    if (addrs.empty()) { printf("host not found\n"); co_return; }
    auto conn = co_await xpp::net::TcpStream::connect(addrs[0]);
}

Concurrent resolution — .await() with .then()

xpp::net::lookup_host("example.com").then([](std::vector<xpp::net::SocketAddr> addrs) {
    if (addrs.empty()) return xpp::resolve(xpp::net::TcpStream());
    return xpp::net::TcpStream::connect(addrs[0]);
}).await();

Concurrent multi-host resolution — co_await (C++20)

xpp::Promise<void> resolve_both() {
    auto a = xpp::net::lookup_host("example.com");
    auto b = xpp::net::lookup_host("example.org");
    auto pair = co_await xpp::all(std::move(a), std::move(b));
    printf("example.com: %zu addrs, example.org: %zu addrs\n",
           pair.first.size(), pair.second.size());
}

Implementation Notes

• Empty vector on error — libx's DNS callback provides xDnsResult with an error field. On error, the adapter resolves with an empty vector (not a rejection). Callers should check addrs.empty().