fix SubdomainRedirect on loopbacks

fix: https://github.com/kataras/iris/issues/1584#issuecomment-674001454

context/context.go

@@ -904,9 +904,12 @@ func (ctx *Context) GetHeader(name string) string {
 }
 
 // GetDomain resolves and returns the server's domain.
-func (ctx *Context) GetDomain() string {
-	hostport := ctx.Host()
-	if host, _, err := net.SplitHostPort(hostport); err == nil {
+func GetDomain(hostport string) string {
+	host := hostport
+	if tmp, _, err := net.SplitHostPort(hostport); err == nil {
+		host = tmp
+	}
+
 	// has port.
 	switch host {
 	case "127.0.0.1", "0.0.0.0", "::1", "[::1]", "0:0:0:0:0:0:0:0", "0:0:0:0:0:0:0:1":
@@ -921,7 +924,9 @@ func (ctx *Context) GetDomain() string {
 	}
 }
 
-	return hostport
+// GetDomain resolves and returns the server's domain.
+func (ctx *Context) GetDomain() string {
+	return GetDomain(ctx.Host())
 }
 
 // IsAjax returns true if this request is an 'ajax request'( XMLHttpRequest)

core/netutil/addr.go

@@ -21,7 +21,8 @@ func init() {
 
 // IsLoopbackSubdomain checks if a string is a subdomain or a hostname.
 var IsLoopbackSubdomain = func(s string) bool {
-	if strings.HasPrefix(s, "127.0.0.1:") || s == "127.0.0.1" {
+	if strings.HasPrefix(s, "127.0.0.1:") || s == "127.0.0.1" ||
+		strings.HasPrefix(s, "0.0.0.0:") || s == "0.0.0.0" /* let's resolve that without regex (see below)*/ {
 		return true
 	}
 
@@ -34,6 +35,17 @@ var IsLoopbackSubdomain = func(s string) bool {
 	return valid
 }
 
+// GetLoopbackSubdomain returns the part of the loopback subdomain.
+func GetLoopbackSubdomain(s string) string {
+	if strings.HasPrefix(s, "127.0.0.1:") || s == "127.0.0.1" ||
+		strings.HasPrefix(s, "0.0.0.0:") || s == "0.0.0.0" /* let's resolve that without regex (see below)*/ {
+		return s
+	}
+
+	ss := loopbackSubRegex.FindString(s)
+	return ss
+}
+
 // IsLoopbackHost tries to catch the local addresses when a developer
 // navigates to a subdomain that its hostname differs from Application.Config.Addr.
 // Developer may want to override this function to return always false

core/router/router_subdomain_redirect_wrapper.go

@@ -112,6 +112,10 @@ func (s *subdomainRedirectWrapper) Wrapper(w http.ResponseWriter, r *http.Reques
 
 	host := context.GetHost(r)
 	root := s.root()
+	if loopback := netutil.GetLoopbackSubdomain(root); loopback != "" {
+		root = strings.Replace(root, loopback, context.GetDomain(host), 1)
+	}
+	// println("root: " + root)
 	hasSubdomain := host != root
 
 	if !hasSubdomain && !s.isFromRoot {