feat: DNS over HTTPS resolver

extras/outbounds/dns_https.go

@@ -0,0 +1,84 @@
+package outbounds
+
+import (
+	"crypto/tls"
+	"net"
+	"net/http"
+	"time"
+
+	"github.com/babolivier/go-doh-client"
+)
+
+// dohResolver is a PluggableOutbound DNS resolver that resolves hostnames
+// using the user-provided DNS-over-HTTPS server.
+type dohResolver struct {
+	Resolver *doh.Resolver
+	Next     PluggableOutbound
+}
+
+func NewDoHResolver(host string, timeout time.Duration, sni string, insecure bool, next PluggableOutbound) PluggableOutbound {
+	tr := http.DefaultTransport.(*http.Transport).Clone()
+	tr.TLSClientConfig = &tls.Config{
+		ServerName:         sni,
+		InsecureSkipVerify: insecure,
+	}
+	return &dohResolver{
+		Resolver: &doh.Resolver{
+			Host:  host,
+			Class: doh.IN,
+			HTTPClient: &http.Client{
+				Transport: tr,
+				Timeout:   timeoutOrDefault(timeout),
+			},
+		},
+		Next: next,
+	}
+}
+
+func (r *dohResolver) resolve(reqAddr *AddrEx) {
+	if tryParseIP(reqAddr) {
+		// The host is already an IP address, we don't need to resolve it.
+		return
+	}
+	type lookupResult struct {
+		ip  net.IP
+		err error
+	}
+	ch4, ch6 := make(chan lookupResult, 1), make(chan lookupResult, 1)
+	go func() {
+		recs, _, err := r.Resolver.LookupA(reqAddr.Host)
+		var ip net.IP
+		if err == nil && len(recs) > 0 {
+			ip = net.ParseIP(recs[0].IP4).To4()
+		}
+		ch4 <- lookupResult{ip, err}
+	}()
+	go func() {
+		recs, _, err := r.Resolver.LookupAAAA(reqAddr.Host)
+		var ip net.IP
+		if err == nil && len(recs) > 0 {
+			ip = net.ParseIP(recs[0].IP6).To16()
+		}
+		ch6 <- lookupResult{ip, err}
+	}()
+	result4, result6 := <-ch4, <-ch6
+	reqAddr.ResolveInfo = &ResolveInfo{
+		IPv4: result4.ip,
+		IPv6: result6.ip,
+	}
+	if result4.err != nil {
+		reqAddr.ResolveInfo.Err = result4.err
+	} else if result6.err != nil {
+		reqAddr.ResolveInfo.Err = result6.err
+	}
+}
+
+func (r *dohResolver) TCP(reqAddr *AddrEx) (net.Conn, error) {
+	r.resolve(reqAddr)
+	return r.Next.TCP(reqAddr)
+}
+
+func (r *dohResolver) UDP(reqAddr *AddrEx) (UDPConn, error) {
+	r.resolve(reqAddr)
+	return r.Next.UDP(reqAddr)
+}