UDP support

Co-authored-by: Julien Salleyron <julien.salleyron@gmail.com>

pkg/udp/proxy.go

@@ -0,0 +1,56 @@
+package udp
+
+import (
+	"io"
+	"net"
+
+	"github.com/containous/traefik/v2/pkg/log"
+)
+
+// Proxy is a reverse-proxy implementation of the Handler interface.
+type Proxy struct {
+	// TODO: maybe optimize by pre-resolving it at proxy creation time
+	target string
+}
+
+// NewProxy creates a new Proxy
+func NewProxy(address string) (*Proxy, error) {
+	return &Proxy{target: address}, nil
+}
+
+// ServeUDP implements the Handler interface.
+func (p *Proxy) ServeUDP(conn *Conn) {
+	log.Debugf("Handling connection from %s", conn.rAddr)
+
+	// needed because of e.g. server.trackedConnection
+	defer conn.Close()
+
+	connBackend, err := net.Dial("udp", p.target)
+	if err != nil {
+		log.Errorf("Error while connecting to backend: %v", err)
+		return
+	}
+
+	// maybe not needed, but just in case
+	defer connBackend.Close()
+
+	errChan := make(chan error)
+	go p.connCopy(conn, connBackend, errChan)
+	go p.connCopy(connBackend, conn, errChan)
+
+	err = <-errChan
+	if err != nil {
+		log.WithoutContext().Errorf("Error while serving UDP: %v", err)
+	}
+
+	<-errChan
+}
+
+func (p Proxy) connCopy(dst io.WriteCloser, src io.Reader, errCh chan error) {
+	_, err := io.Copy(dst, src)
+	errCh <- err
+
+	if err := dst.Close(); err != nil {
+		log.WithoutContext().Debugf("Error while terminating connection: %v", err)
+	}
+}