From f34a73f8a6bae122ee14c2cc84068b3d711d0e30 Mon Sep 17 00:00:00 2001
From: James Hillyerd <james@hillyerd.com>
Date: Tue, 29 Oct 2013 20:40:47 -0700
Subject: [PATCH] Domain validator + tests (unwired)

---
 smtpd/utils.go      | 51 +++++++++++++++++++++++++++++++++++++++++++++
 smtpd/utils_test.go | 38 +++++++++++++++++++++++++++++++++
 2 files changed, 89 insertions(+)

diff --git a/smtpd/utils.go b/smtpd/utils.go
index e0d93a8..0e4c2e3 100644
--- a/smtpd/utils.go
+++ b/smtpd/utils.go
@@ -38,3 +38,54 @@ func JoinStringList(listOfStrings *list.List) string {
 	}
 	return strings.Join(s, ",")
 }
+
+// ValidateDomainPart returns true if the domain part complies to RFC3696, RFC1035
+func ValidateDomainPart(domain string) bool {
+	if len(domain) == 0 {
+		return false
+	}
+	if len(domain) > 255 {
+		return false
+	}
+	if domain[len(domain)-1] != '.' {
+		domain += "."
+	}
+	prev := '.'
+	labelLen := 0
+	hasLetters := false
+
+	for _, c := range domain {
+		switch {
+		case ('a' <= c && c <= 'z') || ('A' <= c && c <= 'Z') || c == '_':
+			// Must contain some of these to be a valid label
+			hasLetters = true
+			labelLen++
+		case '0' <= c && c <= '9':
+			labelLen++
+		case c == '-':
+			if prev == '.' {
+				// Cannot lead with hyphen
+				return false
+			}
+		case c == '.':
+			if prev == '.' || prev == '-' {
+				// Cannot end with hyphen or double-dot
+				return false
+			}
+			if labelLen > 63 {
+				return false
+			}
+			if !hasLetters {
+				return false
+			}
+			labelLen = 0
+			hasLetters = false
+		default:
+			// Unknown character
+			return false
+		}
+		prev = c
+	}
+
+	return true
+}
diff --git a/smtpd/utils_test.go b/smtpd/utils_test.go
index 0c2d198..cc30d8f 100644
--- a/smtpd/utils_test.go
+++ b/smtpd/utils_test.go
@@ -2,6 +2,7 @@ package smtpd
 
 import (
 	"github.com/stretchr/testify/assert"
+	"strings"
 	"testing"
 )
 
@@ -14,3 +15,40 @@ func TestParseMailboxName(t *testing.T) {
 func TestHashMailboxName(t *testing.T) {
 	assert.Equal(t, HashMailboxName("mail"), "1d6e1cf70ec6f9ab28d3ea4b27a49a77654d370e")
 }
+
+func TestValidateDomain(t *testing.T) {
+	assert.True(t, ValidateDomainPart("jhillyerd.github.com"),
+		"Simple domain failed")
+	assert.False(t, ValidateDomainPart(""), "Empty domain is not valid")
+	assert.False(t, ValidateDomainPart(strings.Repeat("a", 256)),
+		"Max domain length is 255")
+	assert.False(t, ValidateDomainPart(strings.Repeat("a", 64)+".com"),
+		"Max label length is 63")
+	assert.True(t, ValidateDomainPart(strings.Repeat("a", 63)+".com"),
+		"Should allow 63 char label")
+
+	var testTable = []struct {
+		input  string
+		expect bool
+		msg    string
+	}{
+		{"hostname", true, "Just a hostname is valid"},
+		{"github.com", true, "Two labels should be just fine"},
+		{"my-domain.com", true, "Hyphen is allowed mid-label"},
+		{"_domainkey.foo.com", true, "Underscores are allowed"},
+		{"bar.com.", true, "Must be able to end with a dot"},
+		{"ABC.6DBS.com", true, "Mixed case is OK"},
+		{"google..com", false, "Double dot not valid"},
+		{".foo.com", false, "Cannot start with a dot"},
+		{"mail.123.com", false, "Number only label not valid"},
+		{"google\r.com", false, "Special chars not allowed"},
+		{"foo.-bar.com", false, "Label cannot start with hyphen"},
+		{"foo-.bar.com", false, "Label cannot end with hyphen"},
+	}
+
+	for _, tt := range testTable {
+		if ValidateDomainPart(tt.input) != tt.expect {
+			t.Errorf("Expected %v for %q: %s", tt.expect, tt.input, tt.msg)
+		}
+	}
+}