Fix inability to send SSH keys over RPC

Gob is used by auto-generated RPC services to (de)serialize structures
used in method calls. Because ssh.PublicKey is an interface, gob is
unable to serialize it, unless its underlying concrete types are
registered using `gob.Register(anythingOfAforementionedType)`.

Change-Id: I0e28e5d58a2b69a6d726bb1ddb73e2f6d8e3f99e
Signed-off-by: Michal Sidor <m.sidor@samsung.com>

Author: Michal Sidor

rpc/dryad/clientmanager.go

@@ -25,6 +25,8 @@ import (
 	"net"
 
 	"git.tizen.org/tools/boruta"
+	// Needed for SSH public key serialization.
+	_ "git.tizen.org/tools/boruta/rpc/types"
 )
 
 // ClientManager defines API for managing client RPC calls to Dryad.

rpc/superviser/reception.go

@@ -28,6 +28,8 @@ import (
 	"net/rpc"
 
 	"git.tizen.org/tools/boruta"
+	// Needed for SSH public key serialization.
+	_ "git.tizen.org/tools/boruta/rpc/types"
 )
 
 type superviserReception struct {

rpc/types/init.go

@@ -0,0 +1,39 @@
+/*
+ *  Copyright (c) 2018 Samsung Electronics Co., Ltd All Rights Reserved
+ *
+ *  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 types contains gob registration of types needed for RPC
+// communication between dryad and supervisor.
+package types
+
+import (
+	"crypto/rsa"
+	"encoding/gob"
+
+	"golang.org/x/crypto/ed25519"
+	"golang.org/x/crypto/ssh"
+)
+
+func init() {
+	var rsaKey rsa.PublicKey
+	var ed25519Key ed25519.PublicKey
+	for _, foreignKey := range []interface{}{&rsaKey, ed25519Key} {
+		sshKey, err := ssh.NewPublicKey(foreignKey)
+		if err != nil {
+			panic("this should never happen: arbitrary ssh key preparation failed: " + err.Error())
+		}
+		gob.Register(sshKey)
+	}
+}