Support creating empty directories. (#5049)

Every so often we get requirements for creating
directories/prefixes and we end up rejecting
such requirements. This PR implements this and
allows empty directories without any new file
addition to backend.

Existing lower APIs themselves are leveraged to provide
this behavior. Only FS backend supports this for
the time being as desired.

cmd/server_test.go

@@ -27,6 +27,7 @@ import (
 	"math/rand"
 	"net/http"
 	"net/url"
+	"os"
 	"reflect"
 	"strings"
 	"sync"
@@ -43,6 +44,7 @@ type TestSuiteCommon struct {
 	endPoint   string
 	accessKey  string
 	secretKey  string
+	configPath string
 	signer     signerType
 	secure     bool
 	transport  *http.Transport
@@ -56,7 +58,7 @@ type check struct {
 // Assert - checks if gotValue is same as expectedValue, if not fails the test.
 func (c *check) Assert(gotValue interface{}, expectedValue interface{}) {
 	if !reflect.DeepEqual(gotValue, expectedValue) {
-		c.Fatalf("Test %s: expected %v, got %v", c.testType, expectedValue, gotValue)
+		c.Fatalf("Test %s:%s expected %v, got %v", getSource(), c.testType, expectedValue, gotValue)
 	}
 }
 
@@ -74,7 +76,9 @@ func verifyError(c *check, response *http.Response, code, description string, st
 func runAllTests(suite *TestSuiteCommon, c *check) {
 	suite.SetUpSuite(c)
 	suite.TestBucketSQSNotificationWebHook(c)
-	suite.TestObjectDir(c)
+	if suite.serverType == "XL" {
+		suite.TestObjectDir(c)
+	}
 	suite.TestBucketSQSNotificationAMQP(c)
 	suite.TestBucketPolicy(c)
 	suite.TestDeleteBucket(c)
@@ -140,6 +144,9 @@ func TestServerSuite(t *testing.T) {
 // Setting up the test suite.
 // Starting the Test server with temporary FS backend.
 func (s *TestSuiteCommon) SetUpSuite(c *check) {
+	rootPath, err := newTestConfig("us-east-1")
+	c.Assert(err, nil)
+
 	if s.secure {
 		cert, key, err := generateTLSCertKey("127.0.0.1")
 		c.Assert(err, nil)
@@ -163,10 +170,12 @@ func (s *TestSuiteCommon) SetUpSuite(c *check) {
 	s.endPoint = s.testServer.Server.URL
 	s.accessKey = s.testServer.AccessKey
 	s.secretKey = s.testServer.SecretKey
+	s.configPath = rootPath
 }
 
 // Called implicitly by "gopkg.in/check.v1" after all tests are run.
 func (s *TestSuiteCommon) TearDownSuite(c *check) {
+	os.RemoveAll(s.configPath)
 	s.testServer.Stop()
 }