configurable dns search domains

Add a --dns-search parameter and a DnsSearch
configuration field for specifying dns search
domains.

Docker-DCO-1.1-Signed-off-by: Daniel Norberg <daniel.norberg@gmail.com> (github: danielnorberg)

opts/opts.go

@@ -136,3 +136,16 @@ func ValidateIp4Address(val string) (string, error) {
 	}
 	return "", fmt.Errorf("%s is not an ip4 address", val)
 }
+
+func ValidateDomain(val string) (string, error) {
+	alpha := regexp.MustCompile(`[a-zA-Z]`)
+	if alpha.FindString(val) == "" {
+		return "", fmt.Errorf("%s is not a valid domain", val)
+	}
+	re := regexp.MustCompile(`^(:?(:?[a-zA-Z0-9]|(:?[a-zA-Z0-9][a-zA-Z0-9\-]*[a-zA-Z0-9]))(:?\.(:?[a-zA-Z0-9]|(:?[a-zA-Z0-9][a-zA-Z0-9\-]*[a-zA-Z0-9])))*)\.?\s*$`)
+	var ns = re.FindSubmatch([]byte(val))
+	if len(ns) > 0 {
+		return string(ns[1]), nil
+	}
+	return "", fmt.Errorf("%s is not a valid domain", val)
+}

opts/opts_test.go

@@ -22,3 +22,57 @@ func TestValidateIP4(t *testing.T) {
 	}
 
 }
+
+func TestValidateDomain(t *testing.T) {
+	valid := []string{
+		`a`,
+		`a.`,
+		`1.foo`,
+		`17.foo`,
+		`foo.bar`,
+		`foo.bar.baz`,
+		`foo.bar.`,
+		`foo.bar.baz`,
+		`foo1.bar2`,
+		`foo1.bar2.baz`,
+		`1foo.2bar.`,
+		`1foo.2bar.baz`,
+		`foo-1.bar-2`,
+		`foo-1.bar-2.baz`,
+		`foo-1.bar-2.`,
+		`foo-1.bar-2.baz`,
+		`1-foo.2-bar`,
+		`1-foo.2-bar.baz`,
+		`1-foo.2-bar.`,
+		`1-foo.2-bar.baz`,
+	}
+
+	invalid := []string{
+		``,
+		`.`,
+		`17`,
+		`17.`,
+		`.17`,
+		`17-.`,
+		`17-.foo`,
+		`.foo`,
+		`foo-.bar`,
+		`-foo.bar`,
+		`foo.bar-`,
+		`foo.bar-.baz`,
+		`foo.-bar`,
+		`foo.-bar.baz`,
+	}
+
+	for _, domain := range valid {
+		if ret, err := ValidateDomain(domain); err != nil || ret == "" {
+			t.Fatalf("ValidateDomain(`"+domain+"`) got %s %s", ret, err)
+		}
+	}
+
+	for _, domain := range invalid {
+		if ret, err := ValidateDomain(domain); err == nil || ret != "" {
+			t.Fatalf("ValidateDomain(`"+domain+"`) got %s %s", ret, err)
+		}
+	}
+}