package dns import ( "context" "crypto/tls" "fmt" "math/rand" "net" "strings" "github.com/Dreamacro/clash/component/dialer" "github.com/Dreamacro/clash/component/resolver" D "github.com/miekg/dns" ) type client struct { *D.Client r *Resolver port string host string iface string } func (c *client) Exchange(m *D.Msg) (*D.Msg, error) { return c.ExchangeContext(context.Background(), m) } func (c *client) ExchangeContext(ctx context.Context, m *D.Msg) (*D.Msg, error) { var ( ip net.IP err error ) if c.r == nil { // a default ip dns if ip = net.ParseIP(c.host); ip == nil { return nil, fmt.Errorf("dns %s not a valid ip", c.host) } } else { ips, err := resolver.LookupIPWithResolver(ctx, c.host, c.r) if err != nil { return nil, fmt.Errorf("use default dns resolve failed: %w", err) } else if len(ips) == 0 { return nil, fmt.Errorf("%w: %s", resolver.ErrIPNotFound, c.host) } ip = ips[rand.Intn(len(ips))] } network := "udp" if strings.HasPrefix(c.Client.Net, "tcp") { network = "tcp" } options := []dialer.Option{} if c.iface != "" { options = append(options, dialer.WithInterface(c.iface)) } conn, err := dialer.DialContext(ctx, network, net.JoinHostPort(ip.String(), c.port), options...) if err != nil { return nil, err } defer conn.Close() // miekg/dns ExchangeContext doesn't respond to context cancel. // this is a workaround type result struct { msg *D.Msg err error } ch := make(chan result, 1) go func() { if strings.HasSuffix(c.Client.Net, "tls") { conn = tls.Client(conn, c.Client.TLSConfig) } msg, _, err := c.Client.ExchangeWithConn(m, &D.Conn{ Conn: conn, UDPSize: c.Client.UDPSize, TsigSecret: c.Client.TsigSecret, TsigProvider: c.Client.TsigProvider, }) ch <- result{msg, err} }() select { case <-ctx.Done(): return nil, ctx.Err() case ret := <-ch: return ret.msg, ret.err } }