xl: PUT an empty dir on an existing prefix succeed (#6658)

This commit fixes a regression introduced in f187a16962
the regression returned AccessDenied when a client is trying to create an empty
directory on a existing prefix, though it should return 200 OK to be close as
much as possible to S3 specification.

cmd/object-api-putobject_test.go

@@ -159,6 +159,16 @@ func testObjectAPIPutObject(obj ObjectLayer, instanceType string, t TestErrHandl
 		// Test case 30
 		// valid data with X-Amz-Meta- meta
 		{bucket, object, data, map[string]string{"X-Amz-Meta-AppID": "a42"}, "", int64(len(data)), getMD5Hash(data), nil},
+
+		// Test case 31
+		// Put an empty object with a trailing slash
+		{bucket, "emptydir/", []byte{}, nil, "", 0, getMD5Hash([]byte{}), nil},
+		// Test case 32
+		// Put an object inside the empty directory
+		{bucket, "emptydir/" + object, data, nil, "", int64(len(data)), getMD5Hash(data), nil},
+		// Test case 33
+		// Put the empty object with a trailing slash again (refer to Test case 31), this needs to succeed
+		{bucket, "emptydir/", []byte{}, nil, "", 0, getMD5Hash([]byte{}), nil},
 	}
 
 	for i, testCase := range testCases {
@@ -171,7 +181,7 @@ func testObjectAPIPutObject(obj ObjectLayer, instanceType string, t TestErrHandl
 		}
 		// Failed as expected, but does it fail for the expected reason.
 		if actualErr != nil && actualErr != testCase.expectedError {
-			t.Errorf("Test %d: %s: Expected to fail with error \"%s\", but instead failed with error \"%s\" instead.", i+1, instanceType, testCase.expectedError.Error(), actualErr.Error())
+			t.Errorf("Test %d: %s: Expected to fail with error \"%v\", but instead failed with error \"%v\" instead.", i+1, instanceType, testCase.expectedError, actualErr)
 		}
 		// Test passes as expected, but the output values are verified for correctness here.
 		if actualErr == nil {

cmd/xl-v1-object.go

@@ -627,8 +627,9 @@ func (xl xlObjects) putObject(ctx context.Context, bucket string, object string,
 			return ObjectInfo{}, toObjectErr(err, bucket, object)
 		}
 
-		// Rename the successfully written temporary object to final location.
-		if _, err = rename(ctx, xl.getDisks(), minioMetaTmpBucket, tempObj, bucket, object, true, writeQuorum, nil); err != nil {
+		// Rename the successfully written temporary object to final location. Ignore errFileAccessDenied
+		// error because it means that the target object dir exists and we want to be close to S3 specification.
+		if _, err = rename(ctx, xl.getDisks(), minioMetaTmpBucket, tempObj, bucket, object, true, writeQuorum, []error{errFileAccessDenied}); err != nil {
 			return ObjectInfo{}, toObjectErr(err, bucket, object)
 		}