ident: implement remote-part validation

This is mostly equivalent to email without IP addresses.

Signed-off-by: Yonah <contrib@gensokyo.uk>

ident/remote_test.go

@@ -0,0 +1,83 @@
+package ident_test
+
+import (
+	"bytes"
+	"strings"
+	"testing"
+
+	"git.gensokyo.uk/cofront/cof-spec/ident"
+)
+
+// mustNewRemote validates remote and returns its corresponding [ident.Remote].
+// If remote is invalid, mustNewRemote panics.
+func mustNewRemote(remote string) (r ident.Remote) {
+	if err := r.UnmarshalText([]byte(remote)); err != nil {
+		panic(err)
+	}
+	return
+}
+
+func TestRemote(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		name   string
+		remote string
+		err    error
+	}{
+		{"short", "", ident.ErrShortRemote},
+		{"long", strings.Repeat("\x00", 256), ident.ErrLongRemote},
+
+		{"short label", "test.label.short..empty", &ident.InvalidLabelError{
+			Data:   []byte{},
+			Label:  3,
+			Index:  -1,
+			Reason: ident.InvalidLabelShort,
+		}},
+
+		{"long label", "test.label.long." + strings.Repeat("\x00", 64), &ident.InvalidLabelError{
+			Data:   bytes.Repeat([]byte{0}, 64),
+			Label:  3,
+			Index:  63,
+			Reason: ident.InvalidLabelLong,
+		}},
+
+		{"ldh prefix", "test.prefix.-invalid-", &ident.InvalidLabelError{
+			Data:   []byte("-invalid-"),
+			Label:  2,
+			Index:  0,
+			Reason: ident.InvalidLabelLDH,
+		}},
+
+		{"ldh suffix", "test.suffix.invalid--", &ident.InvalidLabelError{
+			Data:   []byte("invalid--"),
+			Label:  2,
+			Index:  8,
+			Reason: ident.InvalidLabelLDH,
+		}},
+
+		{"ldh", "test.invalid:byte", &ident.InvalidLabelError{
+			Data:   []byte("invalid:byte"),
+			Label:  1,
+			Index:  7,
+			Reason: ident.InvalidLabelLDH,
+		}},
+
+		{"simple", "localhost", nil},
+		{"valid", "gensokyo.uk", nil},
+		{"full", "ABCDEFGHIJKLMNOPQRSTUVWXYZ." +
+			"abcdefghijklmnopqrstuvwxyz." +
+			"0123456789-9876543210", nil},
+	}
+
+	rtc := make(rTestCases[ident.Remote, *ident.Remote], len(testCases))
+	for i, tc := range testCases {
+		rtc[i].name = tc.name
+		if tc.err == nil {
+			rtc[i].ident = mustNewRemote(tc.remote)
+		}
+		rtc[i].want = []byte(tc.remote)
+		rtc[i].err = tc.err
+	}
+	rtc.run(t)
+}