Test TCP should piggyback ACK in ESTAB state

TCP, in ESTABLISHED state, SHOULD piggyback acknowledgement with a segment being
transmitted (whenever possible) without incurring undue delay

PiperOrigin-RevId: 306474550

test/packetimpact/tests/BUILD

@@ -52,6 +52,18 @@ packetimpact_go_test(
     ],
 )
 
+packetimpact_go_test(
+    name = "tcp_should_piggyback",
+    srcs = ["tcp_should_piggyback_test.go"],
+    # TODO(b/153680566): Fix netstack then remove the line below.
+    netstack = False,
+    deps = [
+        "//pkg/tcpip/header",
+        "//test/packetimpact/testbench",
+        "@org_golang_x_sys//unix:go_default_library",
+    ],
+)
+
 sh_binary(
     name = "test_runner",
     srcs = ["test_runner.sh"],

test/packetimpact/tests/tcp_should_piggyback_test.go

@@ -0,0 +1,53 @@
+// Copyright 2020 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package tcp_should_piggyback_test
+
+import (
+	"testing"
+	"time"
+
+	"golang.org/x/sys/unix"
+	"gvisor.dev/gvisor/pkg/tcpip/header"
+	tb "gvisor.dev/gvisor/test/packetimpact/testbench"
+)
+
+func TestPiggyback(t *testing.T) {
+	dut := tb.NewDUT(t)
+	defer dut.TearDown()
+	listenFd, remotePort := dut.CreateListener(unix.SOCK_STREAM, unix.IPPROTO_TCP, 1)
+	defer dut.Close(listenFd)
+	conn := tb.NewTCPIPv4(t, tb.TCP{DstPort: &remotePort, WindowSize: tb.Uint16(12)}, tb.TCP{SrcPort: &remotePort})
+	defer conn.Close()
+
+	conn.Handshake()
+	acceptFd, _ := dut.Accept(listenFd)
+	defer dut.Close(acceptFd)
+
+	dut.SetSockOptInt(acceptFd, unix.IPPROTO_TCP, unix.TCP_NODELAY, 1)
+
+	sampleData := []byte("Sample Data")
+
+	dut.Send(acceptFd, sampleData, 0)
+	conn.ExpectData(tb.TCP{Flags: tb.Uint8(header.TCPFlagAck | header.TCPFlagPsh)}, sampleData, time.Second)
+
+	// Cause DUT to send us more data as soon as we ACK their first data segment because we have
+	// a small window.
+	dut.Send(acceptFd, sampleData, 0)
+
+	// DUT should ACK our segment by piggybacking ACK to their outstanding data segment instead of
+	// sending a separate ACK packet.
+	conn.Send(tb.TCP{Flags: tb.Uint8(header.TCPFlagAck | header.TCPFlagPsh)}, &tb.Payload{Bytes: sampleData})
+	conn.ExpectData(tb.TCP{Flags: tb.Uint8(header.TCPFlagAck | header.TCPFlagPsh)}, sampleData, time.Second)
+}