Clean segregated file share backends

share/ports.go

@@ -0,0 +1,72 @@
+package share
+
+import (
+	"fmt"
+	"net"
+	"os"
+	"syscall"
+
+	"github.com/pkg/errors"
+)
+
+func getNetworkSharePort(subsequent uint16) (uint16, error) {
+	return getClosestAvailPortWithSubsequent(9000, subsequent)
+}
+
+func getClosestAvailPortWithSubsequent(port uint16, subsequent uint16) (uint16, error) {
+	// We use 10 as port range
+	for i := port; i < 65535; i += subsequent {
+		ok, err := checkPortAvailable(i, subsequent)
+		if err != nil {
+			return 0, errors.Wrapf(err, "check port available (%v)", i)
+		}
+
+		if ok {
+			return i, nil
+		}
+	}
+
+	return 0, fmt.Errorf("no available port (with %v subsequent ones) found", subsequent)
+}
+
+func checkPortAvailable(port uint16, subsequent uint16) (bool, error) {
+	if port+subsequent < port {
+		return false, fmt.Errorf("subsequent ports exceed allowed port range")
+	}
+
+	if subsequent == 0 {
+		ln, err := net.Listen("tcp", ":"+fmt.Sprint(port))
+		if err != nil {
+			if opErr, ok := err.(*net.OpError); ok {
+				if sysErr, ok := opErr.Err.(*os.SyscallError); ok {
+					if sysErr.Err == syscall.EADDRINUSE {
+						// The port is in use.
+						return false, nil
+					}
+				}
+			}
+
+			return false, errors.Wrapf(err, "net listen (port %v)", port)
+		}
+
+		err = ln.Close()
+		if err != nil {
+			return false, errors.Wrap(err, "close ephemeral listener")
+		}
+
+		return true, nil
+	}
+
+	for i := uint16(0); i < subsequent; i++ {
+		ok, err := checkPortAvailable(port+i, 0)
+		if err != nil {
+			return false, errors.Wrapf(err, "check subsequent port available (base: %v, seq: %v)", port, i)
+		}
+
+		if !ok {
+			return false, nil
+		}
+	}
+
+	return true, nil
+}