Start all listeners when a given host resolves to multiple IPs. (#3145)

Default golang net.Listen only listens on the first IP when
host resolves to multiple IPs.

This change addresses a problem for example your ``/etc/hosts``
has entries as following

```
127.0.1.1  minio1

192.168.1.10 minio1
```

Trying to start minio as

```
minio server --address "minio1:9001" ~/Photos
```

Causes the minio server to be bound only to "127.0.1.1" which
is an incorrect behavior since we are generally interested in
`192.168.1.10` as well.

This patch addresses this issue if the hostname is resolvable
and gives back list of addresses associated with that hostname
we just bind on all of them as it is the expected behavior.

cmd/server-mux_test.go

@@ -31,11 +31,69 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"os"
+	"runtime"
 	"sync"
 	"testing"
 	"time"
 )
 
+// Tests initalizing listeners.
+func TestInitListeners(t *testing.T) {
+	testCases := []struct {
+		serverAddr string
+		shouldPass bool
+	}{
+		// Test 1 with ip and port.
+		{
+			serverAddr: "127.0.0.1:" + getFreePort(),
+			shouldPass: true,
+		},
+		// Test 2 only port.
+		{
+			serverAddr: ":" + getFreePort(),
+			shouldPass: true,
+		},
+		// Test 3 with no port error.
+		{
+			serverAddr: "127.0.0.1",
+			shouldPass: false,
+		},
+		// Test 4 with 'foobar' host not resolvable.
+		{
+			serverAddr: "foobar:9000",
+			shouldPass: false,
+		},
+	}
+	for i, testCase := range testCases {
+		listeners, err := initListeners(testCase.serverAddr, &tls.Config{})
+		if testCase.shouldPass {
+			if err != nil {
+				t.Fatalf("Test %d: Unable to initialize listeners %s", i+1, err)
+			}
+			for _, listener := range listeners {
+				if err = listener.Close(); err != nil {
+					t.Fatalf("Test %d: Unable to close listeners %s", i+1, err)
+				}
+			}
+		}
+		if err == nil && !testCase.shouldPass {
+			t.Fatalf("Test %d: Should fail but is successful", i+1)
+		}
+	}
+	// Windows doesn't have 'localhost' hostname.
+	if runtime.GOOS != "windows" {
+		listeners, err := initListeners("localhost:"+getFreePort(), &tls.Config{})
+		if err != nil {
+			t.Fatalf("Test 3: Unable to initialize listeners %s", err)
+		}
+		for _, listener := range listeners {
+			if err = listener.Close(); err != nil {
+				t.Fatalf("Test 3: Unable to close listeners %s", err)
+			}
+		}
+	}
+}
+
 func TestClose(t *testing.T) {
 	// Create ServerMux
 	m := NewServerMux("", nil)
@@ -43,6 +101,11 @@ func TestClose(t *testing.T) {
 	if err := m.Close(); err != nil {
 		t.Error("Server errored while trying to Close", err)
 	}
+
+	// Closing again should return an error.
+	if err := m.Close(); err.Error() != "Server has been closed" {
+		t.Error("Unexepcted error expected \"Server has been closed\", got", err)
+	}
 }
 
 func TestServerMux(t *testing.T) {
@@ -63,7 +126,7 @@ func TestServerMux(t *testing.T) {
 		Listener: ts.Listener,
 		config:   &tls.Config{},
 	}
-	m.listener = lm
+	m.listeners = []*ListenerMux{lm}
 
 	client := http.Client{}
 	res, err := client.Get(ts.URL)
@@ -116,7 +179,7 @@ func TestServerCloseBlocking(t *testing.T) {
 		Listener: ts.Listener,
 		config:   &tls.Config{},
 	}
-	m.listener = lm
+	m.listeners = []*ListenerMux{lm}
 
 	dial := func() net.Conn {
 		c, cerr := net.Dial("tcp", ts.Listener.Addr().String())
@@ -245,14 +308,23 @@ func TestListenAndServeTLS(t *testing.T) {
 			Timeout:   time.Millisecond * 10,
 			Transport: tr,
 		}
-		ok := false
-		for !ok {
+		okTLS := false
+		for !okTLS {
 			res, _ := client.Get("https://" + addr)
 			if res != nil && res.StatusCode == http.StatusOK {
-				ok = true
+				okTLS = true
 			}
 		}
 
+		okNoTLS := false
+		for !okNoTLS {
+			res, _ := client.Get("http://" + addr)
+			// Without TLS we expect a re-direction from http to https
+			// And also the request is not rejected.
+			if res != nil && res.StatusCode == http.StatusOK && res.Request.URL.Scheme == "https" {
+				okNoTLS = true
+			}
+		}
 		wg.Done()
 	}()