add support unix socket for GRPC (#5943)

plugin/grpc/README.md

@@ -129,7 +129,15 @@ Or with multiple upstreams from the same provider
 }
 ~~~
 
+Forward requests to a local upstream listening on a Unix domain socket.
+
+~~~ corefile
+. {
+    grpc . unix:///path/to/grpc.sock
+}
+~~~
+
 ## Bugs
 
 The TLS config is global for the whole grpc proxy if you need a different `tls_servername` for
-different upstreams you're out of luck.
+different upstreams you're out of luck.

plugin/grpc/proxy_test.go

@@ -3,9 +3,15 @@ package grpc
 import (
 	"context"
 	"errors"
+	"net"
+	"os"
+	"path"
 	"testing"
 
+	"github.com/coredns/caddy"
 	"github.com/coredns/coredns/pb"
+	"github.com/coredns/coredns/plugin/pkg/dnstest"
+	"github.com/coredns/coredns/plugin/test"
 
 	"github.com/miekg/dns"
 	"google.golang.org/grpc"
@@ -64,3 +70,56 @@ type testServiceClient struct {
 func (m testServiceClient) Query(ctx context.Context, in *pb.DnsPacket, opts ...grpc.CallOption) (*pb.DnsPacket, error) {
 	return m.dnsPacket, m.err
 }
+
+func TestProxyUnix(t *testing.T) {
+	tdir, err := os.MkdirTemp("", "tmp*")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(tdir)
+
+	fd := path.Join(tdir, "test.grpc")
+	listener, err := net.Listen("unix", fd)
+	if err != nil {
+		t.Fatal("Failed to listen: ", err)
+	}
+	defer listener.Close()
+
+	server := grpc.NewServer()
+	pb.RegisterDnsServiceServer(server, &grpcDnsServiceServer{})
+
+	go server.Serve(listener)
+	defer server.Stop()
+
+	c := caddy.NewTestController("dns", "grpc . unix://"+fd)
+	g, err := parseGRPC(c)
+
+	if err != nil {
+		t.Errorf("Failed to create forwarder: %s", err)
+	}
+
+	m := new(dns.Msg)
+	m.SetQuestion("example.org.", dns.TypeA)
+	rec := dnstest.NewRecorder(&test.ResponseWriter{})
+
+	if _, err := g.ServeDNS(context.TODO(), rec, m); err != nil {
+		t.Fatal("Expected to receive reply, but didn't")
+	}
+	if x := rec.Msg.Answer[0].Header().Name; x != "example.org." {
+		t.Errorf("Expected %s, got %s", "example.org.", x)
+	}
+}
+
+type grpcDnsServiceServer struct {
+	pb.UnimplementedDnsServiceServer
+}
+
+func (*grpcDnsServiceServer) Query(ctx context.Context, in *pb.DnsPacket) (*pb.DnsPacket, error) {
+	msg := &dns.Msg{}
+	msg.Unpack(in.GetMsg())
+	answer := new(dns.Msg)
+	answer.Answer = append(answer.Answer, test.A("example.org. IN A 127.0.0.1"))
+	answer.SetRcode(msg, dns.RcodeSuccess)
+	buf, _ := answer.Pack()
+	return &pb.DnsPacket{Msg: buf}, nil
+}

plugin/grpc/setup_test.go

@@ -25,6 +25,7 @@ func TestSetup(t *testing.T) {
 		{"grpc . 127.0.0.1:8080", false, ".", nil, ""},
 		{"grpc . [::1]:53", false, ".", nil, ""},
 		{"grpc . [2003::1]:53", false, ".", nil, ""},
+		{"grpc . unix:///var/run/g.sock", false, ".", nil, ""},
 		// negative
 		{"grpc . a27.0.0.1", true, "", nil, "not an IP"},
 		{"grpc . 127.0.0.1 {\nblaatl\n}\n", true, "", nil, "unknown property"},

plugin/pkg/parse/host.go

@@ -33,6 +33,14 @@ func HostPortOrFile(s ...string) ([]string, error) {
 	var servers []string
 	for _, h := range s {
 		trans, host := Transport(h)
+		if len(host) == 0 {
+			return servers, fmt.Errorf("invalid address: %q", h)
+		}
+
+		if trans == transport.UNIX {
+			servers = append(servers, trans+"://"+host)
+			continue
+		}
 
 		addr, _, err := net.SplitHostPort(host)
 

plugin/pkg/parse/host_test.go

@@ -58,6 +58,16 @@ func TestHostPortOrFile(t *testing.T) {
 			"",
 			true,
 		},
+		{
+			"unix:///var/run/g.sock",
+			"unix:///var/run/g.sock",
+			false,
+		},
+		{
+			"unix://",
+			"",
+			true,
+		},
 	}
 
 	err := os.WriteFile("resolv.conf", []byte("nameserver 127.0.0.1\n"), 0600)

plugin/pkg/parse/transport.go

@@ -27,6 +27,9 @@ func Transport(s string) (trans string, addr string) {
 		s = s[len(transport.HTTPS+"://"):]
 
 		return transport.HTTPS, s
+	case strings.HasPrefix(s, transport.UNIX+"://"):
+		s = s[len(transport.UNIX+"://"):]
+		return transport.UNIX, s
 	}
 
 	return transport.DNS, s

plugin/pkg/transport/transport.go

@@ -6,6 +6,7 @@ const (
 	TLS   = "tls"
 	GRPC  = "grpc"
 	HTTPS = "https"
+	UNIX  = "unix"
 )
 
 // Port numbers for the various transports.