Add checking of CNAME records.

LookupMX will perform this if the CNAME result has an MX record as well, but the spec states we should "start again" so we will do just that.
This allows fallback to A/AAAA records in a CNAME -> A configuration.

Loops are handled by the LookupCNAME method.

Author: tomtom5152

htmltest/check-link.go

@@ -5,12 +5,12 @@ import (
 	"github.com/wjdp/htmltest/issues"
 	"github.com/wjdp/htmltest/output"
 	"golang.org/x/net/html"
+	"net"
 	"net/http"
 	"net/url"
 	"os"
 	"path"
 	"strings"
-	"net"
 	"fmt"
 )
 
@@ -351,45 +351,68 @@ func (hT *HTMLTest) checkMailto(ref *htmldoc.Reference) {
 		return
 	}
 
-	// split off domain, check mx, fallback to A or AAAA if that fais
-	domain := strings.Split(ref.URL.Opaque, "@")[1]
-	_, err := net.LookupMX(domain)
+	// split off domain, check mx, fallback to A or AAAA if that fails
 	var dnserr *net.DNSError
 	var ok bool
-	if err != nil {
-		if dnserr, ok = err.(*net.DNSError); ok {
-			switch dnserr.Err {
-			case "no such host":
-				// current no MX records, but we should try again with A record
-				_, err := net.LookupHost(domain)
-				if dnserr, ok = err.(*net.DNSError); ok {
-					break
-				} else {
-					hT.issueStore.AddIssue(issues.Issue{
-						Level:     issues.LevelWarning,
-						Message:   "unable to perform LookupHost, unknown error",
-						Reference: ref,
-					})
-					return
-				}
-			}
-		} else {
+
+	domain := strings.Split(ref.URL.Opaque, "@")[1]
+
+	for domain != "" {
+		// if a simple MX lookup works, we are done, continue
+		if _, err := net.LookupMX(domain); err == nil {
+			break // success, time to exit
+		} else if dnserr, ok = err.(*net.DNSError); !ok || dnserr.Err != "no such host" {
+			// this isn't an error we are expecting to see here
 			hT.issueStore.AddIssue(issues.Issue{
 				Level:     issues.LevelWarning,
 				Message:   "unable to perform LookupMX, unknown error",
 				Reference: ref,
 			})
 			return
 		}
-	}
 
-	// check if we finally have a dnserr
-	if dnserr != nil {
-		hT.issueStore.AddIssue(issues.Issue{
-			Level:     issues.LevelError,
-			Message:   "email cannot be routed to domain, no MX/A/AAAA records",
-			Reference: ref,
-		})
+		// do we have to restart because of a CNAME
+		if cname, err := net.LookupCNAME(domain); err == nil && cname != domain {
+			// we have a valid CNAME, try with that. Loops return NXDOMAIN by default
+			domain = cname
+			continue
+
+		} else if dnserr, ok = err.(*net.DNSError); !ok || dnserr.Err != "no such host" {
+			// this isn't an error we are expecting to see here
+			hT.issueStore.AddIssue(issues.Issue{
+				Level:     issues.LevelWarning,
+				Message:   "unable to perform LookupCNAME, unknown error",
+				Reference: ref,
+			})
+			return
+		}
+
+		// an A or AAAA record here would be valid
+		if _, err := net.LookupHost(domain); err == nil {
+			break // its not ideal, but a valid A/AAAA record is acceptable for email
+		} else {
+			dnserr, ok = err.(*net.DNSError)
+			if !ok || dnserr.Err != "no such host" {
+				// we shouldn't see this here
+				hT.issueStore.AddIssue(issues.Issue{
+					Level:     issues.LevelWarning,
+					Message:   "unable to perform LookupHost, unknown error",
+					Reference: ref,
+				})
+				return
+			}
+
+			if dnserr.Err == "no such host" {
+				// represents NXDOMAIN or no records
+				hT.issueStore.AddIssue(issues.Issue{
+					Level:     issues.LevelError,
+					Message:   "email domain could not be resolved correctly",
+					Reference: ref,
+				})
+				return
+			}
+		}
+
 	}
 }
 

htmltest/check-link_test.go

@@ -390,11 +390,24 @@ func TestMailtoInvalidFormat(t *testing.T) {
 	tExpectIssue(t, hT, "contains an invalid email address", 1)
 }
 
+func TestMailtoInvalidCname(t *testing.T) {
+	// fails for invalid mailto links
+	hT := tTestFile("fixtures/links/invalid_mailto_cname.html")
+	tExpectIssueCount(t, hT, 0)
+}
+
+func TestMailtoInvalidCnameLoop(t *testing.T) {
+	// fails for invalid mailto links
+	hT := tTestFile("fixtures/links/invalid_mailto_cname_loop.html")
+	tExpectIssueCount(t, hT, 1)
+	tExpectIssue(t, hT, "email domain could not be resolved correctly", 1)
+}
+
 func TestMailtoInvalidNoRecords(t *testing.T) {
 	// fails for invalid mailto links
 	hT := tTestFile("fixtures/links/invalid_mailto_norecords.html")
 	tExpectIssueCount(t, hT, 1)
-	tExpectIssue(t, hT, "email cannot be routed to domain, no MX/A/AAAA records", 1)
+	tExpectIssue(t, hT, "email domain could not be resolved correctly", 1)
 }
 
 func TestMailtoInvalidAFallback(t *testing.T) {

htmltest/fixtures/links/invalid_mailto_cname.html

@@ -0,0 +1,10 @@
+<html>
+
+<body>
+
+<!-- www.golang.org CNAME golang.org - seems appropriate -->
+<a href="mailto:helloworld@cname_to_a_with_no_mx.dtaylor.uk">Meow me</a>
+
+</body>
+
+</html>

htmltest/fixtures/links/invalid_mailto_cname_loop.html

@@ -0,0 +1,10 @@
+<html>
+
+<body>
+
+<!-- www.golang.org CNAME golang.org - seems appropriate -->
+<a href="mailto:[email protected]">Meow me</a>
+
+</body>
+
+</html>