all: update share module

The update bring new features and enhancements for DNS server.

*  add support to save and load caches to/from storage

   rescached now able to save and load caches to local storage upon
   restart.

   On POSIX, the caches is stored in /var/cache/rescached/rescached.gob,
   encoded using gob.

   Update #9

*  remove the fallback name servers (NS) from server options

   The original idea of fallback NS is to send the query to the one
   define in resolv.conf, instead of using the one defined by user in
   ServerOptions NameServers, when an error occured.

   But, most of error usually caused by network (disconnected, time out),
   so re-sending query to fallback NS does not have any effect if the
   network it self is not working.

   This changes remove the unnecessary and complex fallback NS from
   server.

*  do not cache truncated answer

   Previously only answer with non-zero response code is ignored.

   This changes ignore also answer where response header is truncated.

*  lib/dns: make the TCP forwarders as complementary of UDP

   The TCP forwarders only active when client send the DNS request as TCP.
   When the server receive that request it should also forward the request
   as TCP not as UDP to prevent the truncated response.

   Another use case for TCP is when the response is truncated, the client
   will send the query back through TCP connection.  The server should
   forward this request using TCP instead of UDP.

1 files changed, 53 insertions, 1 deletions

diff --git a/rescached.go b/rescached.go
index 6d6464f..c990b77 100644
--- a/rescached.go
+++ b/rescached.go
@@ -10,6 +10,7 @@ import (
 	"fmt"
 	"log"
 	"os"
+	"path/filepath"
 	"sync"
 
 	"github.com/shuLhan/share/lib/debug"
@@ -18,6 +19,11 @@ import (
 	libio "github.com/shuLhan/share/lib/io"
 )
 
+const (
+	cachesDir  = "/var/cache/rescached/"
+	cachesFile = "rescached.gob"
+)
+
 // Server implement caching DNS server.
 type Server struct {
 	fileConfig string
@@ -57,11 +63,31 @@ func New(fileConfig string) (srv *Server, err error) {
 // it.
 //
 func (srv *Server) Start() (err error) {
+	logp := "Start"
+
 	srv.dns, err = dns.NewServer(&srv.env.ServerOptions)
 	if err != nil {
 		return err
 	}
 
+	cachesPath := filepath.Join(cachesDir, cachesFile)
+
+	fcaches, err := os.Open(cachesPath)
+	if err == nil {
+		// Load stored caches from file.
+		answers, err := srv.dns.CachesLoad(fcaches)
+		if err != nil {
+			log.Printf("%s: %s", logp, err)
+		} else {
+			fmt.Printf("%s: %d caches loaded from %s\n", logp, len(answers), cachesPath)
+		}
+
+		err = fcaches.Close()
+		if err != nil {
+			log.Printf("%s: %s", logp, err)
+		}
+	}
+
 	systemHostsFile, err := dns.ParseHostsFile(dns.GetSystemHosts())
 	if err != nil {
 		return err
@@ -134,10 +160,36 @@ func (srv *Server) run() {
 // Stop the server.
 //
 func (srv *Server) Stop() {
+	logp := "Stop"
+
 	if srv.rcWatcher != nil {
 		srv.rcWatcher.Stop()
 	}
 	srv.dns.Stop()
+
+	cachesPath := filepath.Join(cachesDir, cachesFile)
+
+	// Stores caches to file for next start.
+	err := os.MkdirAll(cachesDir, 0700)
+	if err != nil {
+		log.Printf("%s: %s", logp, err)
+		return
+	}
+	fcaches, err := os.Create(cachesPath)
+	if err != nil {
+		log.Printf("%s: %s", logp, err)
+		return
+	}
+	n, err := srv.dns.CachesSave(fcaches)
+	if err != nil {
+		log.Printf("%s: %s", logp, err)
+		// fall-through for Close.
+	}
+	err = fcaches.Close()
+	if err != nil {
+		log.Printf("%s: %s", logp, err)
+	}
+	fmt.Printf("%s: %d caches stored to %s\n", logp, n, cachesPath)
 }
 
 func (srv *Server) watchResolvConf(ns *libio.NodeState) {
@@ -155,6 +207,6 @@ func (srv *Server) watchResolvConf(ns *libio.NodeState) {
 			break
 		}
 
-		srv.dns.RestartForwarders(srv.env.NameServers, srv.env.FallbackNS)
+		srv.dns.RestartForwarders(srv.env.NameServers)
 	}
 }