Fix FQDN validation and add tests

network/netutils/cleandns.go

@@ -2,13 +2,57 @@ package netutils
 
 import (
 	"regexp"
+
+	"github.com/miekg/dns"
 )
 
 var (
-	cleanDomainRegex = regexp.MustCompile(`^((xn--)?[a-z0-9-_]{0,61}[a-z0-9]{1,1}\.)*(xn--)?([a-z0-9-]{1,61}|[a-z0-9-]{1,30}\.[a-z]{2,}\.)$`)
+	cleanDomainRegex = regexp.MustCompile(
+		`^` + // match beginning
+			`(` + // start subdomain group
+			`(xn--)?` + // idn prefix
+			`[a-z0-9_-]{1,63}` + // main chunk
+			`\.` + // ending with a dot
+			`)*` + // end subdomain group, allow any number of subdomains
+			`(xn--)?` + // TLD idn prefix
+			`[a-z0-9_-]{2,63}` + // TLD main chunk with at least two characters
+			`\.` + // ending with a dot
+			`$`, // match end
+	)
 )
 
 // IsValidFqdn returns whether the given string is a valid fqdn.
 func IsValidFqdn(fqdn string) bool {
-	return cleanDomainRegex.MatchString(fqdn)
+	// root zone
+	if fqdn == "." {
+		return true
+	}
+
+	// check max length
+	if len(fqdn) > 256 {
+		return false
+	}
+
+	// check with regex
+	if !cleanDomainRegex.MatchString(fqdn) {
+		return false
+	}
+
+	// check with miegk/dns
+
+	// IsFqdn checks if a domain name is fully qualified.
+	if !dns.IsFqdn(fqdn) {
+		return false
+	}
+
+	// IsDomainName checks if s is a valid domain name, it returns the number of
+	// labels and true, when a domain name is valid.  Note that non fully qualified
+	// domain name is considered valid, in this case the last label is counted in
+	// the number of labels.  When false is returned the number of labels is not
+	// defined.  Also note that this function is extremely liberal; almost any
+	// string is a valid domain name as the DNS is 8 bit protocol. It checks if each
+	// label fits in 63 characters and that the entire name will fit into the 255
+	// octet wire format limit.
+	_, ok := dns.IsDomainName(fqdn)
+	return ok
 }

network/netutils/cleandns_test.go

@@ -0,0 +1,43 @@
+package netutils
+
+import "testing"
+
+func testDomainValidity(t *testing.T, domain string, isValid bool) {
+	if IsValidFqdn(domain) != isValid {
+		t.Errorf("domain %s failed check: was valid=%v, expected valid=%v", domain, IsValidFqdn(domain), isValid)
+	}
+}
+
+func TestDNSValidation(t *testing.T) {
+	// valid
+	testDomainValidity(t, ".", true)
+	testDomainValidity(t, "at.", true)
+	testDomainValidity(t, "orf.at.", true)
+	testDomainValidity(t, "www.orf.at.", true)
+	testDomainValidity(t, "a.b.c.d.e.f.g.h.i.j.k.l.m.n.o.p.q.r.s.t.u.v.x.y.z.example.org.", true)
+	testDomainValidity(t, "a_a.com.", true)
+	testDomainValidity(t, "a-a.com.", true)
+	testDomainValidity(t, "a_a.com.", true)
+	testDomainValidity(t, "a-a.com.", true)
+	testDomainValidity(t, "xn--a.com.", true)
+	testDomainValidity(t, "xn--asdfasdfasdfasdfasdfasdfasdfasdfasdfasdfasdfasdfasdfasdfasd.com.", true)
+
+	// maybe valid
+	testDomainValidity(t, "-.com.", true)
+	testDomainValidity(t, "_.com.", true)
+	testDomainValidity(t, "a_.com.", true)
+	testDomainValidity(t, "a-.com.", true)
+	testDomainValidity(t, "_a.com.", true)
+	testDomainValidity(t, "-a.com.", true)
+
+	// invalid
+	testDomainValidity(t, ".com.", false)
+	testDomainValidity(t, ".com.", false)
+	testDomainValidity(t, "xn--asdfasdfasdfasdfasdfasdfasdfasdfasdfasdfasdfasdfasdfasdfasdf.com.", false)
+	testDomainValidity(t, "asdfasdfasdfasdfasdfasdfasdfasdfasdfasdfasdfasdfasdfasdfasdfasdf.com.", false)
+	testDomainValidity(t, "asdfasdfasdfasdfasdfasdfasdfasdfasdfasdfasdfasdfasdfasdfasdfasdf.com.", false)
+	testDomainValidity(t, "asdf.asdf.asdf.asdf.asdf.asdf.asdf.asdf.asdf.asdf.asdf.asdf.asdf.asdf.asdf.asdf.asdf.asdf.asdf.asdf.asdf.asdf.asdf.asdf.asdf.asdf.asdf.asdf.asdf.asdf.asdf.asdf.asdf.asdf.asdf.asdf.asdf.asdf.asdf.asdf.asdf.asdf.asdf.asdf.asdf.asdf.asdf.asdf.asdf.asdf.as.com.", false)
+
+	// real world examples
+	testDomainValidity(t, "iuqerfsodp9ifjaposdfjhgosurijfaewrwergwea.com.", true)
+}