ipn/localapi: fix validHost parsing logic

Signed-off-by: David Crawshaw <crawshaw@tailscale.com>

ipn/localapi/localapi_test.go

@@ -0,0 +1,34 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+package localapi
+
+import (
+	"testing"
+
+	"tailscale.com/client/tailscale/apitype"
+)
+
+func TestValidHost(t *testing.T) {
+	tests := []struct {
+		host  string
+		valid bool
+	}{
+		{"", true},
+		{apitype.LocalAPIHost, true},
+		{"localhost:9109", validLocalHost},
+		{"127.0.0.1:9110", validLocalHost},
+		{"[::1]:9111", validLocalHost},
+		{"100.100.100.100:41112", false},
+		{"10.0.0.1:41112", false},
+		{"37.16.9.210:41112", false},
+	}
+
+	for _, test := range tests {
+		t.Run(test.host, func(t *testing.T) {
+			if got := validHost(test.host); got != test.valid {
+				t.Errorf("validHost(%q)=%v, want %v", test.host, got, test.valid)
+			}
+		})
+	}
+}