dnsname,tailcfg: add hostname sanitation logic to node display names (#1304)

Signed-off-by: Sonia Appasamy <sonia@tailscale.com>

util/dnsname/dnsname_test.go

@@ -4,7 +4,60 @@
 
 package dnsname
 
-import "testing"
+import (
+	"strings"
+	"testing"
+)
+
+func TestSanitizeLabel(t *testing.T) {
+	tests := []struct {
+		name string
+		in   string
+		want string
+	}{
+		{"empty", "", ""},
+		{"space", " ", ""},
+		{"upper", "OBERON", "oberon"},
+		{"mixed", "Avery's iPhone 4(SE)", "averys-iphone-4se"},
+		{"dotted", "mon.ipn.dev", "mon-ipn-dev"},
+		{"email", "admin@example.com", "admin-example-com"},
+		{"boudary", ".bound.ary.", "bound-ary"},
+		{"bad_trailing", "a-", "a"},
+		{"bad_leading", "-a", "a"},
+		{"bad_both", "-a-", "a"},
+		{
+			"overlong",
+			strings.Repeat("test.", 20),
+			"test-test-test-test-test-test-test-test-test-test-test-test-tes",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := SanitizeLabel(tt.in)
+			if got != tt.want {
+				t.Errorf("want %q; got %q", tt.want, got)
+			}
+		})
+	}
+}
+
+func TestTrimCommonSuffixes(t *testing.T) {
+	tests := []struct {
+		hostname string
+		want     string
+	}{
+		{"computer.local", "computer"},
+		{"computer.localdomain", "computer"},
+		{"computer.lan", "computer"},
+		{"computer.mynetwork", "computer.mynetwork"},
+	}
+	for _, tt := range tests {
+		got := TrimCommonSuffixes(tt.hostname)
+		if got != tt.want {
+			t.Errorf("TrimCommonSuffixes(%q) = %q; want %q", tt.hostname, got, tt.want)
+		}
+	}
+}
 
 func TestHasSuffix(t *testing.T) {
 	tests := []struct {
@@ -14,6 +67,7 @@ func TestHasSuffix(t *testing.T) {
 		{"foo.com", "com", true},
 		{"foo.com.", "com", true},
 		{"foo.com.", "com.", true},
+		{"foo.com", ".com", true},
 
 		{"", "", false},
 		{"foo.com.", "", false},
@@ -26,3 +80,25 @@ func TestHasSuffix(t *testing.T) {
 		}
 	}
 }
+
+func TestTrimSuffix(t *testing.T) {
+	tests := []struct {
+		name   string
+		suffix string
+		want   string
+	}{
+		{"foo.magicdnssuffix.", "magicdnssuffix", "foo"},
+		{"foo.magicdnssuffix", "magicdnssuffix", "foo"},
+		{"foo.magicdnssuffix", ".magicdnssuffix", "foo"},
+		{"foo.anothersuffix", "magicdnssuffix", "foo.anothersuffix"},
+		{"foo.anothersuffix.", "magicdnssuffix", "foo.anothersuffix"},
+		{"a.b.c.d", "c.d", "a.b"},
+		{"name.", "foo", "name"},
+	}
+	for _, tt := range tests {
+		got := TrimSuffix(tt.name, tt.suffix)
+		if got != tt.want {
+			t.Errorf("TrimSuffix(%q, %q) = %q; want %q", tt.name, tt.suffix, got, tt.want)
+		}
+	}
+}