Allow half-closed connections

server.go

@@ -241,6 +241,29 @@ func (ln *Listener) serve() error {
 	}
 }
 
+type duplexCloser interface {
+	CloseRead() error
+	CloseWrite() error
+}
+
+type tlsCloser struct {
+	closer duplexCloser
+	tls    *tls.Conn
+}
+
+func (tc tlsCloser) CloseWrite() error {
+	tlsErr := tc.tls.CloseWrite()
+	err := tc.closer.CloseWrite()
+	if tlsErr != nil {
+		return tlsErr
+	}
+	return err
+}
+
+func (tc tlsCloser) CloseRead() error {
+	return tc.closer.CloseRead()
+}
+
 func (ln *Listener) handle(conn net.Conn) error {
 	defer conn.Close()
 	srv := ln.atomic.Load().(*listenerHandles).Server
@@ -280,7 +303,11 @@ func (ln *Listener) handle(conn net.Conn) error {
 		return err
 	}
 
-	return fe.handle(tlsConn, &tlsState)
+	closer := tlsCloser{
+		closer: conn.(duplexCloser),
+		tls:    tlsConn,
+	}
+	return fe.handle(tlsConn, closer, &tlsState)
 }
 
 func (ln *Listener) matchFrontend(serverName string) (*Frontend, error) {
@@ -311,7 +338,7 @@ type Frontend struct {
 	Protocols []string
 }
 
-func (fe *Frontend) handle(downstream net.Conn, tlsState *tls.ConnectionState) error {
+func (fe *Frontend) handle(downstream net.Conn, downstreamCloser duplexCloser, tlsState *tls.ConnectionState) error {
 	defer downstream.Close()
 
 	be := &fe.Backend
@@ -319,8 +346,14 @@ func (fe *Frontend) handle(downstream net.Conn, tlsState *tls.ConnectionState) e
 	if err != nil {
 		return fmt.Errorf("failed to dial backend: %v", err)
 	}
+	upstreamCloser := upstream.(duplexCloser)
 	if be.TLSConfig != nil {
-		upstream = tls.Client(upstream, be.TLSConfig)
+		upstreamTLS := tls.Client(upstream, be.TLSConfig)
+		upstream = upstreamTLS
+		upstreamCloser = tlsCloser{
+			closer: upstreamCloser,
+			tls: upstreamTLS,
+		}
 	}
 	defer upstream.Close()
 
@@ -348,10 +381,30 @@ func (fe *Frontend) handle(downstream net.Conn, tlsState *tls.ConnectionState) e
 		}
 	}
 
-	if err := duplexCopy(upstream, downstream); err != nil {
-		return fmt.Errorf("failed to copy bytes: %v", err)
+	done := make(chan error, 2)
+	go func() {
+		_, copyErr := io.Copy(upstream, downstream)
+		upstreamCloser.CloseWrite()
+		if copyErr != nil {
+			done <- fmt.Errorf("failed to copy from downstream to upstream: %v", copyErr)
+		} else {
+			done <- nil
 		}
-	return nil
+	}()
+	go func() {
+		_, copyErr := io.Copy(downstream, upstream)
+		downstreamCloser.CloseWrite()
+		if copyErr != nil {
+			done <- fmt.Errorf("failed to copy from upstream to downstream: %v", copyErr)
+		} else {
+			done <- nil
+		}
+	}()
+
+	if err := <-done; err != nil {
+		return err
+	}
+	return <-done
 }
 
 type Backend struct {
@@ -361,19 +414,6 @@ type Backend struct {
 	TLSConfig *tls.Config // nil if no TLS
 }
 
-func duplexCopy(a, b io.ReadWriter) error {
-	done := make(chan error, 2)
-	go func() {
-		_, err := io.Copy(a, b)
-		done <- err
-	}()
-	go func() {
-		_, err := io.Copy(b, a)
-		done <- err
-	}()
-	return <-done
-}
-
 func authorityTLV(name string) proxyproto.TLV {
 	return proxyproto.TLV{
 		Type:  proxyproto.PP2_TYPE_AUTHORITY,