Allow Træfik to know if a Host rule is malformed

rules/rules.go

@@ -9,7 +9,6 @@ import (
 	"sort"
 	"strings"
 
-	"github.com/BurntSushi/ty/fun"
 	"github.com/containous/mux"
 	"github.com/containous/traefik/types"
 )
@@ -270,9 +269,11 @@ func (r *Rules) Parse(expression string) (*mux.Route, error) {
 // ParseDomains parses rules expressions and returns domains
 func (r *Rules) ParseDomains(expression string) ([]string, error) {
 	var domains []string
+	isHostRule := false
 
 	err := r.parseRules(expression, func(functionName string, function interface{}, arguments []string) error {
 		if functionName == "Host" {
+			isHostRule = true
 			domains = append(domains, arguments...)
 		}
 		return nil
@@ -281,5 +282,18 @@ func (r *Rules) ParseDomains(expression string) ([]string, error) {
 		return nil, fmt.Errorf("error parsing domains: %v", err)
 	}
 
-	return fun.Map(types.CanonicalDomain, domains).([]string), nil
+	var cleanDomains []string
+	for _, domain := range domains {
+		canonicalDomain := types.CanonicalDomain(domain)
+		if len(canonicalDomain) > 0 {
+			cleanDomains = append(cleanDomains, canonicalDomain)
+		}
+	}
+
+	// Return an error if an Host rule is detected but no domain are parsed
+	if isHostRule && len(cleanDomains) == 0 {
+		return nil, fmt.Errorf("unable to parse correctly the domains in the Host rule from %q", expression)
+	}
+
+	return cleanDomains, nil
 }