factor out confirmation codes into utils, change their format

irc/utils/confirmation.go

@@ -0,0 +1,22 @@
+// Copyright (c) 2020 Shivaram Lingamneni <slingamn@cs.stanford.edu>
+// released under the MIT license
+
+package utils
+
+import (
+	"crypto/sha256"
+	"encoding/binary"
+	"time"
+)
+
+// Deterministically generates a confirmation code for some destructive activity;
+// `name` is typically the name of the identity being destroyed (a channel being
+// unregistered, or the server being crashed) and `createdAt` means a different
+// value is required each time.
+func ConfirmationCode(name string, createdAt time.Time) (code string) {
+	buf := make([]byte, len(name)+8)
+	binary.BigEndian.PutUint64(buf, uint64(createdAt.UnixNano()))
+	copy(buf[8:], name[:])
+	out := sha256.Sum256(buf)
+	return B32Encoder.EncodeToString(out[:3])
+}

irc/utils/confirmation_test.go

@@ -0,0 +1,36 @@
+// Copyright (c) 2020 Shivaram Lingamneni <slingamn@cs.stanford.edu>
+// released under the MIT license
+
+package utils
+
+import (
+	"testing"
+	"time"
+)
+
+func easyParse(timestamp string) time.Time {
+	result, err := time.Parse("2006-01-02 15:04:05Z", timestamp)
+	if err != nil {
+		panic(err)
+	}
+	return result
+}
+
+func TestConfirmation(t *testing.T) {
+	set := make(map[string]struct{})
+
+	set[ConfirmationCode("#darwin", easyParse("2006-01-01 00:00:00Z"))] = struct{}{}
+	set[ConfirmationCode("#darwin", easyParse("2006-01-02 00:00:00Z"))] = struct{}{}
+	set[ConfirmationCode("#xelpers", easyParse("2006-01-01 00:00:00Z"))] = struct{}{}
+	set[ConfirmationCode("#xelpers", easyParse("2006-01-02 00:00:00Z"))] = struct{}{}
+
+	if len(set) != 4 {
+		t.Error("confirmation codes are not unique")
+	}
+
+	for code := range set {
+		if len(code) <= 2 || len(code) >= 8 {
+			t.Errorf("bad code: %s", code)
+		}
+	}
+}