Add system resolver

Jigsaw-Code · Dec 13, 2023 · 23753f3 · 23753f3
1 parent d270870
commit 23753f3
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Showing 3 changed files with 28 additions and 22 deletions.
diff --git a/internal/dns/resolver.go b/internal/dns/resolver.go
@@ -19,6 +19,8 @@ import (
 	"net"
 )
 
+// TODO: Is this the right interface? We need to process the IPs as soon as we get them, so
+// we need a mechanism to stream the IPs.
 type Resolver interface {
 	LookupIP(ctx context.Context, domain string) ([]net.IP, error)
 }

diff --git a/x/examples/smart-proxy/config.json b/x/examples/smart-proxy/config.json
@@ -1,5 +1,7 @@
 {
     "dns": [
+        {"system": {}},
+
         {"https": {"name": "2620:fe::fe"}, "//": "Quad9"},
         {"https": {"name": "9.9.9.9"}},
         {"https": {"name": "149.112.112.112"}},

diff --git a/x/smart/finder.go b/x/smart/finder.go
@@ -301,6 +301,11 @@ func (f *StrategyFinder) testDNSClient(ctx context.Context, dnsRT dns.RoundTripp
 	ctx, cancel := context.WithTimeout(ctx, f.TestTimeout)
 	defer cancel()
 
+	// We special case the system resolver, since we can't get a dns.RoundTripper.
+	if dnsRT == nil {
+		return evaluateNetResolver(ctx, new(net.Resolver), testDomain)
+	}
+
 	var request miekgdns.Msg
 	requestDomain := mixCase(testDomain)
 	request.SetQuestion(requestDomain, miekgdns.TypeA)
@@ -341,7 +346,9 @@ type configJSON struct {
 }
 
 func (f *StrategyFinder) newDNSRoundTriperFromEntry(entry dnsEntryJSON) (dns.RoundTripper, error) {
-	if cfg := entry.HTTPS; cfg != nil {
+	if entry.System != nil {
+		return nil, nil
+	} else if cfg := entry.HTTPS; cfg != nil {
 		if cfg.Name == "" {
 			return nil, fmt.Errorf("https entry has empty server name")
 		}
@@ -382,6 +389,7 @@ func (f *StrategyFinder) newDNSRoundTriperFromEntry(entry dnsEntryJSON) (dns.Rou
 }
 
 func (f *StrategyFinder) findDNS(testDomain string, dnsConfig []dnsEntryJSON) (dns.Resolver, error) {
+	var found bool
 	var selectedResolver dns.Resolver
 	var doneMu sync.Mutex
 	baseContext, stopFind := context.WithCancelCause(context.Background())
@@ -401,7 +409,7 @@ func (f *StrategyFinder) findDNS(testDomain string, dnsConfig []dnsEntryJSON) (d
 				id := string(idBytes)
 				dnsRT, err := f.newDNSRoundTriperFromEntry(entry)
 				if err != nil {
-					stopFind(fmt.Errorf("failed to process entry %v: %w", id, err))
+					stopFind(fmt.Errorf("failed to process entry %v: %w", ei, err))
 					return
 				}
 				f.log("starting dns %v\n", id)
@@ -419,33 +427,20 @@ func (f *StrategyFinder) findDNS(testDomain string, dnsConfig []dnsEntryJSON) (d
 						return
 					}
 					f.log(", status=ok ✅\n")
-					selectedResolver = &miekgDNSResolver{MiekgRoundTripper{dnsRT}}
+					found = true
+					if dnsRT != nil {
+						selectedResolver = &miekgDNSResolver{MiekgRoundTripper{dnsRT}}
+					}
 					stopFind(nil)
 				}
-				// Try system resolver
-				// if _, ok := streamDialer.(*transport.TCPStreamDialer); ok {
-				// 	f.log("client=system")
-				// 	sysResolver := new(net.Resolver)
-				// 	ctx, cancel := context.WithTimeout(context.Background(), f.TestTimeout)
-				// 	ips, err := evaluateNetResolver(ctx, sysResolver, testDomain)
-				// 	cancel()
-				// 	if err != nil {
-				// 		f.log("; status=%v ❌\n", err)
-				// 	} else {
-				// 		f.log("; status=ok (%v) ✅\n", ips)
-				// 		workingClients = append(workingClients, dns.NewStreamDialer(dns.FuncResolver(func(ctx context.Context, domain string) ([]net.IP, error) {
-				// 			return sysResolver.LookupIP(ctx, "ip", domain)
-				// 		}), streamDialer))
-				// 	}
-				// }
 			}(ei, entry)
 			continue
 		case <-baseContext.Done():
 		}
 		break
 	}
 	<-baseContext.Done()
-	if selectedResolver != nil {
+	if found {
 		return selectedResolver, nil
 	}
 	err := context.Cause(baseContext)
@@ -519,8 +514,15 @@ func (f *StrategyFinder) NewDialer(ctx context.Context, testDomain string, confi
 	if err != nil {
 		return nil, err
 	}
-
-	dnsDialer := dns.NewStreamDialer(resolver, f.StreamDialer)
+	var dnsDialer transport.StreamDialer
+	if resolver == nil {
+		if _, ok := f.StreamDialer.(*transport.TCPStreamDialer); !ok {
+			return nil, fmt.Errorf("cannot use system resolver with base dialer of type %T", f.StreamDialer)
+		}
+		dnsDialer = f.StreamDialer
+	} else {
+		dnsDialer = dns.NewStreamDialer(resolver, f.StreamDialer)
+	}
 	return f.findTLS(testDomain, dnsDialer, parsedConfig.TLS)
 }