p2p/enr: updates for discovery v4 compatibility (#16679)

This applies spec changes from ethereum/EIPs#1049 and adds support for
pluggable identity schemes.

Some care has been taken to make the "v4" scheme standalone. It uses
public APIs only and could be moved out of package enr at any time.

A couple of minor changes were needed to make identity schemes work:

- The sequence number is now updated in Set instead of when signing.
- Record is now copy-safe, i.e. calling Set on a shallow copy doesn't
  modify the record it was copied from.

1 files changed, 36 insertions, 0 deletions

diff --git a/p2p/enr/idscheme_test.go b/p2p/enr/idscheme_test.go
new file mode 100644
index 000000000..d790e12f1
--- /dev/null
+++ b/p2p/enr/idscheme_test.go
@@ -0,0 +1,36 @@
+// Copyright 2018 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package enr
+
+import (
+	"crypto/ecdsa"
+	"math/big"
+	"testing"
+)
+
+// Checks that failure to sign leaves the record unmodified.
+func TestSignError(t *testing.T) {
+	invalidKey := &ecdsa.PrivateKey{D: new(big.Int), PublicKey: *pubkey}
+
+	var r Record
+	if err := SignV4(&r, invalidKey); err == nil {
+		t.Fatal("expected error from SignV4")
+	}
+	if len(r.pairs) > 0 {
+		t.Fatal("expected empty record, have", r.pairs)
+	}
+}