resolving dialer

dialer/resolver.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"fmt"
 	"io"
+	"net"
 	"net/netip"
 	"time"
 
@@ -50,3 +51,56 @@ func (r *Resolver) Close() error {
 	}
 	return res
 }
+
+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)
+}