Issue #506: sort domain names in reverse dns notation

This patch fixes a behaviour where fabio routes to the wrong
backend when multiple glob matching routes are available since
the sorting of the host names was wrong.

Sorting DNS names requires reversing them before sorting since
they have their most significant part at the front.

Fixes #506

route/table.go

@@ -303,8 +303,38 @@ func (t Table) matchingHosts(req *http.Request) (hosts []string) {
 			hosts = append(hosts, pattern)
 		}
 	}
+
+	if len(hosts) < 2 {
+		return
+	}
+
+	// Issue 506: multiple glob patterns hosts in wrong order
+	//
+	// DNS names have their most specific part at the front. In order to sort
+	// them from most specific to least specific a lexicographic sort will
+	// return the wrong result since it sorts by host name. *.foo.com will come
+	// before *.a.foo.com even though the latter is more specific. To achieve
+	// the correct result we need to reverse the strings, sort them and then
+	// reverse them again.
+	for i, h := range hosts {
+		hosts[i] = Reverse(h)
+	}
 	sort.Sort(sort.Reverse(sort.StringSlice(hosts)))
-	return hosts
+	for i, h := range hosts {
+		hosts[i] = Reverse(h)
+	}
+	return
+}
+
+// Reverse returns its argument string reversed rune-wise left to right.
+//
+// taken from https://github.com/golang/example/blob/master/stringutil/reverse.go
+func Reverse(s string) string {
+	r := []rune(s)
+	for i, j := 0, len(r)-1; i < len(r)/2; i, j = i+1, j-1 {
+		r[i], r[j] = r[j], r[i]
+	}
+	return string(r)
 }
 
 // Lookup finds a target url based on the current matcher and picker
@@ -322,6 +352,9 @@ func (t Table) Lookup(req *http.Request, trace string, pick picker, match matche
 	// find matching hosts for the request
 	// and add "no host" as the fallback option
 	hosts := t.matchingHosts(req)
+	if trace != "" {
+		log.Printf("[TRACE] %s Matching hosts: %v", trace, hosts)
+	}
 	hosts = append(hosts, "")
 	for _, h := range hosts {
 		if target = t.lookup(h, req.URL.Path, trace, pick, match); target != nil {

route/table_test.go

@@ -569,7 +569,8 @@ func TestTableLookup(t *testing.T) {
 	route add svc z.abc.com/foo/ http://foo.com:3100
 	route add svc *.abc.com/ http://foo.com:4000
 	route add svc *.abc.com/foo/ http://foo.com:5000
-	route add svc *.def.abc.com/ http://foo.com:6000
+	route add svc *.aaa.abc.com/ http://foo.com:6000
+	route add svc *.bbb.abc.com/ http://foo.com:6100
 	route add svc xyz.com:80/ https://xyz.com
 	`
 
@@ -611,8 +612,10 @@ func TestTableLookup(t *testing.T) {
 		{&http.Request{Host: ".abc.com", URL: mustParse("/foo/")}, "http://foo.com:5000"},
 		{&http.Request{Host: "x.y.abc.com", URL: mustParse("/foo/")}, "http://foo.com:5000"},
 		{&http.Request{Host: "y.abc.com:80", URL: mustParse("/foo/")}, "http://foo.com:5000"},
-		{&http.Request{Host: "x.def.abc.com", URL: mustParse("/")}, "http://foo.com:6000"},
-		{&http.Request{Host: "x.def.abc.com", URL: mustParse("/foo")}, "http://foo.com:6000"},
+		{&http.Request{Host: "x.aaa.abc.com", URL: mustParse("/")}, "http://foo.com:6000"},
+		{&http.Request{Host: "x.aaa.abc.com", URL: mustParse("/foo")}, "http://foo.com:6000"},
+		{&http.Request{Host: "x.bbb.abc.com", URL: mustParse("/")}, "http://foo.com:6100"},
+		{&http.Request{Host: "x.bbb.abc.com", URL: mustParse("/foo")}, "http://foo.com:6100"},
 		{&http.Request{Host: "y.abc.com:443", URL: mustParse("/foo/"), TLS: &tls.ConnectionState{}}, "http://foo.com:5000"},
 
 		// exact match has precedence over glob match