wireguard: implement MarshalJSON for PrivateKey and PublicKey

Signed-off-by: Alejandro Mery <amery@jpi.io>

pkg/wireguard/keys.go

@@ -5,6 +5,7 @@ import (
 	"crypto/rand"
 	"encoding/base64"
 	"errors"
+	"fmt"
 
 	"golang.org/x/crypto/curve25519"
 )
@@ -50,6 +51,25 @@ func (pub PublicKey) String() string {
 	}
 }
 
+// MarshalJSON encodes the key for JSON, omiting empty.
+func (key PrivateKey) MarshalJSON() ([]byte, error) {
+	return encodeKeyJSON(key.String())
+}
+
+// MarshalJSON encodes the key for JSON, omiting empty.
+func (pub PublicKey) MarshalJSON() ([]byte, error) {
+	return encodeKeyJSON(pub.String())
+}
+
+func encodeKeyJSON(s string) ([]byte, error) {
+	var out []byte
+	if s != "" {
+		out = []byte(fmt.Sprintf("%q", s))
+	}
+
+	return out, nil
+}
+
 // IsZero tells if the key hasn't been set
 func (key PrivateKey) IsZero() bool {
 	var zero PrivateKey