fixup! proto: Implement Error for NotPrimaryMaster

Provide details in the error message.

go/neo/proto/proto-misc.go

-// Copyright (C) 2017-2021  Nexedi SA and Contributors.
+// Copyright (C) 2017-2023  Nexedi SA and Contributors.
 //                          Kirill Smelkov <kirr@nexedi.com>
 //
 // This program is free software: you can Use, Study, Modify and Redistribute
@@ -57,7 +57,15 @@ func (e *Error) Error() string {
 
 
 func (n *NotPrimaryMaster) Error() string {
-	return "not primary master"
+	s := "not primary master; primary: "
+	p := int(n.Primary)
+	if 0 <= p && p < len(n.KnownMasterList) {
+		s += n.KnownMasterList[p].String()
+	} else {
+		s += "?"
+	}
+	s += fmt.Sprintf(" ; known masters: %v", n.KnownMasterList)
+	return s
 }
 
 

go/neo/proto/proto-misc_test.go

+// Copyright (C) 2023  Nexedi SA and Contributors.
+//                     Kirill Smelkov <kirr@nexedi.com>
+//
+// This program is free software: you can Use, Study, Modify and Redistribute
+// it under the terms of the GNU General Public License version 3, or (at your
+// option) any later version, as published by the Free Software Foundation.
+//
+// You can also Link and Combine this program with other software covered by
+// the terms of any of the Free Software licenses or any of the Open Source
+// Initiative approved licenses and Convey the resulting work. Corresponding
+// source of such a combination shall include the source code for all other
+// software used.
+//
+// This program is distributed WITHOUT ANY WARRANTY; without even the implied
+// warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+//
+// See COPYING file for full licensing terms.
+// See https://www.nexedi.com/licensing for rationale and options.
+
+package proto
+
+import (
+	"testing"
+)
+
+
+func TestNotPrimaryMasterError(t *testing.T) {
+	var testv = []struct {
+		msg    *NotPrimaryMaster
+		estrok string
+	}{
+		{&NotPrimaryMaster{},
+			"not primary master; primary: ? ; known masters: []",
+		},
+
+		{&NotPrimaryMaster{1, nil},
+			"not primary master; primary: ? ; known masters: []",
+		},
+
+		{&NotPrimaryMaster{1, []struct{Address}{{Address{"α",111}}, {Address{"β",222}}, {Address{"γ",333}}}},
+			"not primary master; primary: β:222 ; known masters: [α:111 β:222 γ:333]",
+		},
+	}
+
+	for _, tt := range testv {
+		estr := tt.msg.Error()
+		if estr != tt.estrok {
+			t.Errorf("%v: invalid error:\nhave: %q\nwant: %q", tt.msg, estr, tt.estrok)
+		}
+	}
+}