opera-proxy/dialer/resolver.go

package dialer

import (
	"context"
	"fmt"
	"net"
	"net/netip"
)

type LookupNetIPer interface {
	LookupNetIP(context.Context, string, string) ([]netip.Addr, error)
}

type ResolvingDialer struct {
	lookup LookupNetIPer
	next   ContextDialer
}

func NewResolvingDialer(lookup LookupNetIPer, next ContextDialer) *ResolvingDialer {
	return &ResolvingDialer{
		lookup: lookup,
		next:   next,
	}
}

func (d *ResolvingDialer) Dial(network, address string) (net.Conn, error) {
	return d.DialContext(context.Background(), network, address)
}

func (d *ResolvingDialer) DialContext(ctx context.Context, network, address string) (net.Conn, error) {
	host, port, err := net.SplitHostPort(address)
	if err != nil {
		return nil, fmt.Errorf("failed to extract host and port from %s: %w", address, err)
	}

	var resolveNetwork string
	switch network {
	case "udp4", "tcp4", "ip4":
		resolveNetwork = "ip4"
	case "udp6", "tcp6", "ip6":
		resolveNetwork = "ip6"
	case "udp", "tcp", "ip":
		resolveNetwork = "ip"
	default:
		return nil, fmt.Errorf("resolving dial %q: unsupported network %q", address, network)
	}
	resolved, err := d.lookup.LookupNetIP(ctx, resolveNetwork, host)
	if err != nil {
		return nil, fmt.Errorf("dial failed on address lookup: %w", err)
	}

	var conn net.Conn
	for _, ip := range resolved {
		conn, err = d.next.DialContext(ctx, network, net.JoinHostPort(ip.String(), port))
		if err == nil {
			return conn, nil
		}
	}

	return nil, fmt.Errorf("failed to dial %s: %w", address, err)
}