tailcfg: add Hostinfo.BasicallyEqual

Change-Id: I4fd82dea9bb3618f3a93d8b2d2486f3eabbbd915
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

tailcfg/tailcfg.go

@@ -571,12 +571,31 @@ func (h *Hostinfo) Equal(h2 *Hostinfo) bool {
 	if h == nil && h2 == nil {
 		return true
 	}
-	if (h == nil) != (h2 == nil) {
+	if h == nil || h2 == nil {
 		return false
 	}
 	return reflect.DeepEqual(h, h2)
 }
 
+// BasicallyEqual reports whether h and h2 are equal other than the
+// NetInfo DERP latency timing. (see NetInfo.BasicallyEqual).
+func (h *Hostinfo) BasicallyEqual(h2 *Hostinfo) bool {
+	if h == nil && h2 == nil {
+		return true
+	}
+	if h == nil || h2 == nil {
+		return false
+	}
+	a := *h
+	b := *h2
+	if !a.NetInfo.BasicallyEqual(b.NetInfo) {
+		return false
+	}
+	a.NetInfo = nil
+	b.NetInfo = nil
+	return a.Equal(&b)
+}
+
 // SignatureType specifies a scheme for signing RegisterRequest messages. It
 // specifies the crypto algorithms to use, the contents of what is signed, and
 // any other relevant details. Historically, requests were unsigned so the zero

tailcfg/tailcfg_test.go

@@ -190,6 +190,75 @@ func TestHostinfoEqual(t *testing.T) {
 	}
 }
 
+func TestHostinfoBasicallyEqual(t *testing.T) {
+	tests := []struct {
+		a, b *Hostinfo
+		want bool
+	}{
+		{
+			want: true,
+		},
+		{
+			a:    new(Hostinfo),
+			b:    new(Hostinfo),
+			want: true,
+		},
+		{
+			a: &Hostinfo{},
+			b: &Hostinfo{
+				NetInfo: &NetInfo{},
+			},
+			want: false, // one's nil, the other's not
+		},
+		{
+			a: &Hostinfo{
+				NetInfo: &NetInfo{},
+			},
+			b: &Hostinfo{
+				NetInfo: &NetInfo{},
+			},
+			want: true,
+		},
+		{
+			a: &Hostinfo{
+				NetInfo: &NetInfo{},
+			},
+			b: &Hostinfo{
+				NetInfo: &NetInfo{
+					DERPLatency: map[string]float64{ // ignored
+						"1": 1.0,
+						"2": 2.0,
+					},
+				},
+			},
+			want: true,
+		},
+		{
+			a: &Hostinfo{
+				NetInfo: &NetInfo{
+					PreferredDERP: 1,
+				},
+			},
+			b: &Hostinfo{
+				NetInfo: &NetInfo{
+					PreferredDERP: 2, // differs
+					DERPLatency: map[string]float64{ // ignored
+						"1": 1.0,
+						"2": 2.0,
+					},
+				},
+			},
+			want: false,
+		},
+	}
+	for i, tt := range tests {
+		got := tt.a.BasicallyEqual(tt.b)
+		if got != tt.want {
+			t.Errorf("%d. BasicallyEqual = %v; want %v", i, got, tt.want)
+		}
+	}
+}
+
 func TestNodeEqual(t *testing.T) {
 	nodeHandles := []string{
 		"ID", "StableID", "Name", "User", "Sharer",