server: Move all the top level files into cmd folder. (#2490)

This change brings a change which was done for the 'mc'
package to allow for clean repo and have a cleaner
github drop in experience.

cmd/checkport.go

@@ -0,0 +1,48 @@
+/*
+ * Minio Cloud Storage, (C) 2016 Minio, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package cmd
+
+import (
+	"fmt"
+	"net"
+)
+
+// Make sure that none of the other processes are listening on the
+// specified port on any of the interfaces.
+//
+// On linux if a process is listening on 127.0.0.1:9000 then Listen()
+// on ":9000" fails with the error "port already in use".
+// However on Mac OSX Listen() on ":9000" falls back to the IPv6 address.
+// This causes confusion on Mac OSX that minio server is not reachable
+// on 127.0.0.1 even though minio server is running. So before we start
+// the minio server we make sure that the port is free on each tcp network.
+func checkPortAvailability(port int) error {
+	network := [3]string{"tcp", "tcp4", "tcp6"}
+	for _, n := range network {
+		l, err := net.Listen(n, fmt.Sprintf(":%d", port))
+		if err != nil {
+			return err
+		}
+
+		// look for error so we don't have dangling connection
+		if err = l.Close(); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}