Adding Echo#ListenerNetwork as configuration

Now Echo could be configured to Listen on tcp supported networks of
net.Listen Go standard library (tcp, tcp4, tcp6)

echo.go

@@ -92,6 +92,7 @@ type (
 		Renderer         Renderer
 		Logger           Logger
 		IPExtractor      IPExtractor
+		ListenerNetwork  string
 	}
 
 	// Route contains a handler and information for matching against requests.
@@ -281,6 +282,7 @@ var (
 	ErrInvalidRedirectCode         = errors.New("invalid redirect status code")
 	ErrCookieNotFound              = errors.New("cookie not found")
 	ErrInvalidCertOrKeyType        = errors.New("invalid cert or key type, must be string or []byte")
+	ErrInvalidListenerNetwork      = errors.New("invalid listener network")
 )
 
 // Error handlers
@@ -305,6 +307,7 @@ func New() (e *Echo) {
 		Logger:          log.New("echo"),
 		colorer:         color.New(),
 		maxParam:        new(int),
+		ListenerNetwork: "tcp",
 	}
 	e.Server.Handler = e
 	e.TLSServer.Handler = e
@@ -712,7 +715,7 @@ func (e *Echo) StartServer(s *http.Server) (err error) {
 
 	if s.TLSConfig == nil {
 		if e.Listener == nil {
-			e.Listener, err = newListener(s.Addr)
+			e.Listener, err = newListener(s.Addr, e.ListenerNetwork)
 			if err != nil {
 				return err
 			}
@@ -723,7 +726,7 @@ func (e *Echo) StartServer(s *http.Server) (err error) {
 		return s.Serve(e.Listener)
 	}
 	if e.TLSListener == nil {
-		l, err := newListener(s.Addr)
+		l, err := newListener(s.Addr, e.ListenerNetwork)
 		if err != nil {
 			return err
 		}
@@ -752,7 +755,7 @@ func (e *Echo) StartH2CServer(address string, h2s *http2.Server) (err error) {
 	}
 
 	if e.Listener == nil {
-		e.Listener, err = newListener(s.Addr)
+		e.Listener, err = newListener(s.Addr, e.ListenerNetwork)
 		if err != nil {
 			return err
 		}
@@ -873,8 +876,11 @@ func (ln tcpKeepAliveListener) Accept() (c net.Conn, err error) {
 	return
 }
 
-func newListener(address string) (*tcpKeepAliveListener, error) {
-	l, err := net.Listen("tcp", address)
+func newListener(address, network string) (*tcpKeepAliveListener, error) {
+	if network != "tcp" && network != "tcp4" && network != "tcp6" {
+		return nil, ErrInvalidListenerNetwork
+	}
+	l, err := net.Listen(network, address)
 	if err != nil {
 		return nil, err
 	}

echo_test.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	stdContext "context"
 	"errors"
+	"fmt"
 	"io/ioutil"
 	"net/http"
 	"net/http/httptest"
@@ -609,3 +610,66 @@ func TestEchoShutdown(t *testing.T) {
 	err := <-errCh
 	assert.Equal(t, err.Error(), "http: Server closed")
 }
+
+var listenerNetworkTests = []struct {
+	test    string
+	network string
+	address string
+}{
+	{"tcp ipv4 address", "tcp", "127.0.0.1:1323"},
+	{"tcp ipv6 address", "tcp", "[::1]:1323"},
+	{"tcp4 ipv4 address", "tcp4", "127.0.0.1:1323"},
+	{"tcp6 ipv6 address", "tcp6", "[::1]:1323"},
+}
+
+func TestEchoListenerNetwork(t *testing.T) {
+	for _, tt := range listenerNetworkTests {
+		t.Run(tt.test, func(t *testing.T) {
+			e := New()
+			e.ListenerNetwork = tt.network
+
+			// HandlerFunc
+			e.GET("/ok", func(c Context) error {
+				return c.String(http.StatusOK, "OK")
+			})
+
+			errCh := make(chan error)
+
+			go func() {
+				errCh <- e.Start(tt.address)
+			}()
+
+			time.Sleep(200 * time.Millisecond)
+
+			if resp, err := http.Get(fmt.Sprintf("http://%s/ok", tt.address)); err == nil {
+				defer resp.Body.Close()
+				assert.Equal(t, http.StatusOK, resp.StatusCode)
+
+				if body, err := ioutil.ReadAll(resp.Body); err == nil {
+					assert.Equal(t, "OK", string(body))
+				} else {
+					assert.Fail(t, err.Error())
+				}
+
+			} else {
+				assert.Fail(t, err.Error())
+			}
+
+			if err := e.Close(); err != nil {
+				t.Fatal(err)
+			}
+		})
+	}
+}
+
+func TestEchoListenerNetworkInvalid(t *testing.T) {
+	e := New()
+	e.ListenerNetwork = "unix"
+
+	// HandlerFunc
+	e.GET("/ok", func(c Context) error {
+		return c.String(http.StatusOK, "OK")
+	})
+
+	assert.Equal(t, ErrInvalidListenerNetwork, e.Start(":1323"))
+}