Mention about custom listener

Signed-off-by: Vishal Rana <vr@labstack.com>

echo.go

@@ -562,27 +562,30 @@ func (e *Echo) startTLS(address string) error {
 }
 
 // StartServer starts a custom http server.
-func (e *Echo) StartServer(s *http.Server) error {
+func (e *Echo) StartServer(s *http.Server) (err error) {
 	// Setup
 	e.colorer.SetOutput(e.Logger.Output())
 	s.Handler = e
 	s.ErrorLog = e.stdLogger
 
-	l, err := net.Listen("tcp", s.Addr)
-	if err != nil {
-		return err
-	}
 	if s.TLSConfig == nil {
 		if e.Listener == nil {
-			e.Listener = tcpKeepAliveListener{l.(*net.TCPListener)}
+			e.Listener, err = newListener(s.Addr)
+			if err != nil {
+				return err
+			}
 		}
-		e.colorer.Printf("⇛ http server started on %s\n", e.colorer.Green(s.Addr))
+		e.colorer.Printf("⇛ http server started on %s\n", e.colorer.Green(e.Listener.Addr()))
 		return s.Serve(e.Listener)
 	}
 	if e.TLSListener == nil {
-		e.TLSListener = tls.NewListener(tcpKeepAliveListener{l.(*net.TCPListener)}, s.TLSConfig)
+		l, err := newListener(s.Addr)
+		if err != nil {
+			return err
+		}
+		e.TLSListener = tls.NewListener(l, s.TLSConfig)
 	}
-	e.colorer.Printf("⇛ https server started on %s\n", e.colorer.Green(s.Addr))
+	e.colorer.Printf("⇛ https server started on %s\n", e.colorer.Green(e.TLSListener.Addr()))
 	return s.Serve(e.TLSListener)
 }
 
@@ -646,3 +649,11 @@ func (ln tcpKeepAliveListener) Accept() (c net.Conn, err error) {
 	tc.SetKeepAlivePeriod(3 * time.Minute)
 	return tc, nil
 }
+
+func newListener(address string) (*tcpKeepAliveListener, error) {
+	l, err := net.Listen("tcp", address)
+	if err != nil {
+		return nil, err
+	}
+	return &tcpKeepAliveListener{l.(*net.TCPListener)}, nil
+}

echo_test.go

@@ -11,6 +11,8 @@ import (
 
 	"errors"
 
+	"time"
+
 	"github.com/stretchr/testify/assert"
 )
 
@@ -391,6 +393,7 @@ func TestEchoStart(t *testing.T) {
 	go func() {
 		assert.NoError(t, e.Start(":0"))
 	}()
+	time.Sleep(200 * time.Millisecond)
 }
 
 func TestEchoStartTLS(t *testing.T) {
@@ -398,6 +401,7 @@ func TestEchoStartTLS(t *testing.T) {
 	go func() {
 		assert.NoError(t, e.StartTLS(":0", "_fixture/certs/cert.pem", "_fixture/certs/key.pem"))
 	}()
+	time.Sleep(200 * time.Millisecond)
 }
 
 func testMethod(t *testing.T, method, path string, e *Echo) {

website/content/guide/customization.md

@@ -52,6 +52,21 @@ s := &http.Server{
 e.Logger.Fatal(e.StartServer(s))
 ```
 
+## Custom Listener
+
+`Echo#*Listener` can be used to run a custom listener.
+
+*Example*
+
+```go
+l, err := net.Listen("tcp", ":1323")
+if err != nil {
+  e.Logger.Fatal(l)
+}
+e.Listener = l
+e.Logger.Fatal(e.Start(""))
+```
+
 ## Disable HTTP/2
 
 `Echo#DisableHTTP2` can be used disable HTTP/2 protocol.

website/content/guide/faq.md

@@ -51,3 +51,9 @@ Q: How to run Echo on a specific IP address?
 ```go
 e.Start("<ip>:<port>")
 ```
+
+Q: How to run Echo on a random port?
+
+```go
+e.Start(":0")
+```