accept Listen option in grpc server (#1201)

grpc.go

@@ -171,6 +171,17 @@ func (g *grpcServer) getGrpcOptions() []grpc.ServerOption {
 	return opts
 }
 
+func (g *grpcServer) getListener() net.Listener {
+	if g.opts.Context != nil {
+		if v := g.opts.Context.Value(netListener{}); v != nil {
+			if l, ok := v.(net.Listener); ok {
+				return l
+			}
+		}
+	}
+	return nil
+}
+
 func (g *grpcServer) handler(srv interface{}, stream grpc.ServerStream) error {
 	if g.wg != nil {
 		g.wg.Add(1)
@@ -788,10 +799,17 @@ func (g *grpcServer) Start() error {
 	config := g.Options()
 
 	// micro: config.Transport.Listen(config.Address)
-	ts, err := net.Listen("tcp", config.Address)
+	var ts net.Listener
+
+	if l := g.getListener(); l != nil {
+		ts = l
+	} else {
+		var err error
+		ts, err = net.Listen("tcp", config.Address)
 		if err != nil {
 			return err
 		}
+	}
 
 	log.Logf("Server [grpc] Listening on %s", ts.Addr().String())
 	g.Lock()

options.go

@@ -3,6 +3,7 @@ package grpc
 import (
 	"context"
 	"crypto/tls"
+	"net"
 
 	"github.com/micro/go-micro/v2/broker"
 	"github.com/micro/go-micro/v2/codec"
@@ -14,9 +15,10 @@ import (
 )
 
 type codecsKey struct{}
-type tlsAuth struct{}
-type maxMsgSizeKey struct{}
 type grpcOptions struct{}
+type netListener struct{}
+type maxMsgSizeKey struct{}
+type tlsAuth struct{}
 
 // gRPC Codec to be used to encode/decode requests for a given content type
 func Codec(contentType string, c encoding.Codec) server.Option {
@@ -43,6 +45,16 @@ func AuthTLS(t *tls.Config) server.Option {
 	}
 }
 
+// Listener specifies the net.Listener to use instead of the default
+func Listener(l net.Listener) server.Option {
+	return func(o *server.Options) {
+		if o.Context == nil {
+			o.Context = context.Background()
+		}
+		o.Context = context.WithValue(o.Context, netListener{}, l)
+	}
+}
+
 // Options to be used to configure gRPC options
 func Options(opts ...grpc.ServerOption) server.Option {
 	return func(o *server.Options) {