Move flags and utils to internal packages

internal/flags/rsa_key_bits.go

@@ -0,0 +1,55 @@
+/*
+Copyright 2020 The Flux CD contributors.
+
+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 flags
+
+import (
+	"fmt"
+	"strconv"
+	"strings"
+)
+
+var defaultRSAKeyBits = 2048
+
+type RSAKeyBits int
+
+func (b *RSAKeyBits) String() string {
+	return strconv.Itoa(int(*b))
+}
+
+func (b *RSAKeyBits) Set(str string) error {
+	if strings.TrimSpace(str) == "" {
+		*b = RSAKeyBits(defaultRSAKeyBits)
+		return nil
+	}
+	bits, err := strconv.Atoi(str)
+	if err != nil {
+		return err
+	}
+	if bits%8 != 0 {
+		return fmt.Errorf("RSA key bit size should be a multiples of 8")
+	}
+	*b = RSAKeyBits(bits)
+	return nil
+}
+
+func (b *RSAKeyBits) Type() string {
+	return "rsaKeyBits"
+}
+
+func (b *RSAKeyBits) Description() string {
+	return "SSH RSA public key bit size (multiplies of 8)"
+}