Move flags and utils to internal packages

internal/flags/ecdsa_curve.go

@@ -0,0 +1,66 @@
+/*
+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 (
+	"crypto/elliptic"
+	"fmt"
+	"sort"
+	"strings"
+)
+
+type ECDSACurve struct {
+	elliptic.Curve
+}
+
+var supportedECDSACurves = map[string]elliptic.Curve{
+	"p256": elliptic.P256(),
+	"p384": elliptic.P384(),
+	"p521": elliptic.P521(),
+}
+
+func (c *ECDSACurve) String() string {
+	if c.Curve == nil {
+		return ""
+	}
+	return strings.ToLower(strings.Replace(c.Curve.Params().Name, "-", "", 1))
+}
+
+func (c *ECDSACurve) Set(str string) error {
+	if v, ok := supportedECDSACurves[str]; ok {
+		*c = ECDSACurve{v}
+		return nil
+	}
+	return fmt.Errorf("unsupported curve '%s', should be one of: %s", str, strings.Join(ecdsaCurves(), ", "))
+}
+
+func (c *ECDSACurve) Type() string {
+	return "ecdsaCurve"
+}
+
+func (c *ECDSACurve) Description() string {
+	return fmt.Sprintf("SSH ECDSA public key curve (%s)", strings.Join(ecdsaCurves(), ", "))
+}
+
+func ecdsaCurves() []string {
+	keys := make([]string, 0, len(supportedECDSACurves))
+	for k := range supportedECDSACurves {
+		keys = append(keys, k)
+	}
+	sort.Strings(keys)
+	return keys
+}