hosts: support dot prefix mapping key

pkg/hosts/hosts.go

@@ -2,6 +2,7 @@ package hosts
 
 import (
 	"net"
+	"strings"
 	"sync"
 
 	"github.com/go-gost/gost/pkg/logger"
@@ -61,24 +62,33 @@ func (h *Hosts) Map(ip net.IP, hostname string, aliases ...string) {
 
 // Lookup searches the IP address corresponds to the given network and host from the host table.
 // The network should be 'ip', 'ip4' or 'ip6', default network is 'ip'.
+// the host should be a hostname (example.org) or a hostname with dot prefix (.example.org).
 func (h *Hosts) Lookup(network, host string) (ips []net.IP, ok bool) {
-	if h == nil || host == "" {
-		return
+	m := h.lookup(host)
+	if m == nil {
+		m = h.lookup("." + host)
+	}
+	if m == nil {
+		s := host
+		for {
+			if index := strings.IndexByte(s, '.'); index > 0 {
+				m = h.lookup(s[index:])
+				s = s[index+1:]
+				if m == nil {
+					continue
+				}
+			}
+			break
+		}
 	}
 
-	v, ok := h.mappings.Load(host)
-	if !ok {
-		return
-	}
-	m, _ := v.(*hostMapping)
 	if m == nil {
 		return
 	}
 
 	// hostname alias
-	if host != m.Hostname {
-		v, _ = h.mappings.Load(m.Hostname)
-		m, _ = v.(*hostMapping)
+	if !strings.HasPrefix(m.Hostname, ".") && host != m.Hostname {
+		m = h.lookup(m.Hostname)
 		if m == nil {
 			return
 		}
@@ -107,3 +117,16 @@ func (h *Hosts) Lookup(network, host string) (ips []net.IP, ok bool) {
 
 	return
 }
+
+func (h *Hosts) lookup(host string) *hostMapping {
+	if h == nil || host == "" {
+		return nil
+	}
+
+	v, ok := h.mappings.Load(host)
+	if !ok {
+		return nil
+	}
+	m, _ := v.(*hostMapping)
+	return m
+}