Feature: add support for dns search domains (#2597)

config/config.go

@@ -69,6 +69,7 @@ type DNS struct {
 	FakeIPRange       *fakeip.Pool
 	Hosts             *trie.DomainTrie
 	NameServerPolicy  map[string]dns.NameServer
+	SearchDomains     []string
 }
 
 // FallbackFilter config
@@ -117,6 +118,7 @@ type RawDNS struct {
 	FakeIPFilter      []string          `yaml:"fake-ip-filter"`
 	DefaultNameserver []string          `yaml:"default-nameserver"`
 	NameServerPolicy  map[string]string `yaml:"nameserver-policy"`
+	SearchDomains     []string          `yaml:"search-domains"`
 }
 
 type RawFallbackFilter struct {
@@ -702,6 +704,18 @@ func parseDNS(rawCfg *RawConfig, hosts *trie.DomainTrie) (*DNS, error) {
 		dnsCfg.Hosts = hosts
 	}
 
+	if len(cfg.SearchDomains) != 0 {
+		for _, domain := range cfg.SearchDomains {
+			if strings.HasPrefix(domain, ".") || strings.HasSuffix(domain, ".") {
+				return nil, errors.New("search domains should not start or end with '.'")
+			}
+			if strings.Contains(domain, ":") {
+				return nil, errors.New("search domains are for ipv4 only and should not contain ports")
+			}
+		}
+		dnsCfg.SearchDomains = cfg.SearchDomains
+	}
+
 	return dnsCfg, nil
 }
 

dns/resolver.go

@@ -39,6 +39,7 @@ type Resolver struct {
 	group                 singleflight.Group
 	lruCache              *cache.LruCache
 	policy                *trie.DomainTrie
+	searchDomains         []string
 }
 
 // LookupIP request with TypeA and TypeAAAA, priority return TypeA
@@ -285,17 +286,34 @@ func (r *Resolver) lookupIP(ctx context.Context, host string, dnsType uint16) ([
 	query := &D.Msg{}
 	query.SetQuestion(D.Fqdn(host), dnsType)
 
-	msg, err := r.Exchange(query)
+	msg, err := r.ExchangeContext(ctx, query)
 	if err != nil {
 		return nil, err
 	}
 
 	ips := msgToIP(msg)
-	if len(ips) == 0 {
+	if len(ips) != 0 {
+		return ips, nil
+	} else if len(r.searchDomains) == 0 {
 		return nil, resolver.ErrIPNotFound
 	}
+
+	// query provided search domains serially
+	for _, domain := range r.searchDomains {
+		q := &D.Msg{}
+		q.SetQuestion(D.Fqdn(fmt.Sprintf("%s.%s", host, domain)), dnsType)
+		msg, err := r.ExchangeContext(ctx, q)
+		if err != nil {
+			return nil, err
+		}
+		ips := msgToIP(msg)
+		if len(ips) != 0 {
 			return ips, nil
 		}
+	}
+
+	return nil, resolver.ErrIPNotFound
+}
 
 func (r *Resolver) msgToDomain(msg *D.Msg) string {
 	if len(msg.Question) > 0 {
@@ -336,6 +354,7 @@ type Config struct {
 	Pool           *fakeip.Pool
 	Hosts          *trie.DomainTrie
 	Policy         map[string]NameServer
+	SearchDomains  []string
 }
 
 func NewResolver(config Config) *Resolver {
@@ -349,6 +368,7 @@ func NewResolver(config Config) *Resolver {
 		main:          transform(config.Main, defaultResolver),
 		lruCache:      cache.New(cache.WithSize(4096), cache.WithStale(true)),
 		hosts:         config.Hosts,
+		searchDomains: config.SearchDomains,
 	}
 
 	if len(config.Fallback) != 0 {

hub/executor/executor.go

@@ -131,6 +131,7 @@ func updateDNS(c *config.DNS) {
 		},
 		Default:       c.DefaultNameserver,
 		Policy:        c.NameServerPolicy,
+		SearchDomains: c.SearchDomains,
 	}
 
 	r := dns.NewResolver(cfg)