fix missing trailers with retry

integration/fixtures/grpc/config_retry.toml

@@ -0,0 +1,34 @@
+[serversTransport]
+rootCAs = [ """{{ .CertContent }}""" ]
+
+[entryPoints]
+  [entryPoints.https]
+  address = ":4443"
+    [entryPoints.https.tls]
+     [entryPoints.https.tls.DefaultCertificate]
+     certFile = """{{ .CertContent }}"""
+     keyFile  = """{{ .KeyContent }}"""
+
+
+[api]
+
+[providers]
+   [providers.file]
+
+[routers]
+  [routers.router1]
+    rule = "Host(`127.0.0.1`)"
+    service = "service1"
+    middlewares = ["retryer"]
+
+[middlewares]
+  [middlewares.retryer.retry]
+    Attempts = 2
+
+[services]
+  [services.service1.loadbalancer]
+  [services.service1.loadbalancer.responseForwarding]
+     flushInterval="1ms"
+    [[services.service1.loadbalancer.servers]]
+      url = "https://127.0.0.1:{{ .GRPCServerPort }}"
+      weight = 1

integration/grpc_test.go

@@ -423,3 +423,45 @@ func (s *GRPCSuite) TestGRPCBufferWithFlushInterval(c *check.C) {
 	})
 	c.Assert(err, check.IsNil)
 }
+
+func (s *GRPCSuite) TestGRPCWithRetry(c *check.C) {
+	lis, err := net.Listen("tcp", ":0")
+	_, port, err := net.SplitHostPort(lis.Addr().String())
+	c.Assert(err, check.IsNil)
+
+	go func() {
+		err := startGRPCServer(lis, &myserver{})
+		c.Log(err)
+		c.Assert(err, check.IsNil)
+	}()
+
+	file := s.adaptFile(c, "fixtures/grpc/config_retry.toml", struct {
+		CertContent    string
+		KeyContent     string
+		GRPCServerPort string
+	}{
+		CertContent:    string(LocalhostCert),
+		KeyContent:     string(LocalhostKey),
+		GRPCServerPort: port,
+	})
+
+	defer os.Remove(file)
+	cmd, display := s.traefikCmd(withConfigFile(file))
+	defer display(c)
+
+	err = cmd.Start()
+	c.Assert(err, check.IsNil)
+	defer cmd.Process.Kill()
+
+	// wait for Traefik
+	err = try.GetRequest("http://127.0.0.1:8080/api/providers/file/routers", 1*time.Second, try.BodyContains("Host(`127.0.0.1`)"))
+	c.Assert(err, check.IsNil)
+
+	var response string
+	err = try.Do(1*time.Second, func() error {
+		response, err = callHelloClientGRPC("World", true)
+		return err
+	})
+	c.Assert(err, check.IsNil)
+	c.Assert(response, check.Equals, "Hello World")
+}