Move reusable IPv4 test code into a testutil module and refactor it

The refactor aims to simplify the package, by replacing the Go channel with a
PacketBuffer slice.

This code will be reused by tests for IPv6 fragmentation.

PiperOrigin-RevId: 331860411

2 files changed, 109 insertions, 0 deletions

diff --git a/pkg/tcpip/network/testutil/BUILD b/pkg/tcpip/network/testutil/BUILD
new file mode 100644
index 000000000..e218563d0
--- /dev/null
+++ b/pkg/tcpip/network/testutil/BUILD
@@ -0,0 +1,17 @@
+load("//tools:defs.bzl", "go_library")
+
+package(licenses = ["notice"])
+
+go_library(
+    name = "testutil",
+    srcs = [
+        "testutil.go",
+    ],
+    visibility = ["//pkg/tcpip/network/ipv4:__pkg__"],
+    deps = [
+        "//pkg/tcpip",
+        "//pkg/tcpip/buffer",
+        "//pkg/tcpip/link/channel",
+        "//pkg/tcpip/stack",
+    ],
+)
diff --git a/pkg/tcpip/network/testutil/testutil.go b/pkg/tcpip/network/testutil/testutil.go
new file mode 100644
index 000000000..bf5ce74be
--- /dev/null
+++ b/pkg/tcpip/network/testutil/testutil.go
@@ -0,0 +1,92 @@
+// 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 testutil defines types and functions used to test Network Layer
+// functionality such as IP fragmentation.
+package testutil
+
+import (
+	"fmt"
+	"math/rand"
+
+	"gvisor.dev/gvisor/pkg/tcpip"
+	"gvisor.dev/gvisor/pkg/tcpip/buffer"
+	"gvisor.dev/gvisor/pkg/tcpip/link/channel"
+	"gvisor.dev/gvisor/pkg/tcpip/stack"
+)
+
+// TestEndpoint is an endpoint used for testing, it stores packets written to it
+// and can mock errors.
+type TestEndpoint struct {
+	*channel.Endpoint
+
+	// WrittenPackets is where we store packets written via WritePacket().
+	WrittenPackets []*stack.PacketBuffer
+
+	packetCollectorErrors []*tcpip.Error
+}
+
+// NewTestEndpoint creates a new TestEndpoint endpoint.
+//
+// packetCollectorErrors can be used to set error values and each call to
+// WritePacket will remove the first one from the slice and return it until
+// the slice is empty - at that point it will return nil every time.
+func NewTestEndpoint(ep *channel.Endpoint, packetCollectorErrors []*tcpip.Error) *TestEndpoint {
+	return &TestEndpoint{
+		Endpoint:              ep,
+		WrittenPackets:        make([]*stack.PacketBuffer, 0),
+		packetCollectorErrors: packetCollectorErrors,
+	}
+}
+
+// WritePacket stores outbound packets and may return an error if one was
+// injected.
+func (e *TestEndpoint) WritePacket(_ *stack.Route, _ *stack.GSO, _ tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer) *tcpip.Error {
+	e.WrittenPackets = append(e.WrittenPackets, pkt)
+
+	if len(e.packetCollectorErrors) > 0 {
+		nextError := e.packetCollectorErrors[0]
+		e.packetCollectorErrors = e.packetCollectorErrors[1:]
+		return nextError
+	}
+
+	return nil
+}
+
+// MakeRandPkt generates a randomized packet. transportHeaderLength indicates
+// how many random bytes will be copied in the Transport Header.
+// extraHeaderReserveLength indicates how much extra space will be reserved for
+// the other headers. The payload is made from Views of the sizes listed in
+// viewSizes.
+func MakeRandPkt(transportHeaderLength int, extraHeaderReserveLength int, viewSizes []int, proto tcpip.NetworkProtocolNumber) *stack.PacketBuffer {
+	var views buffer.VectorisedView
+
+	for _, s := range viewSizes {
+		newView := buffer.NewView(s)
+		if _, err := rand.Read(newView); err != nil {
+			panic(fmt.Sprintf("rand.Read: %s", err))
+		}
+		views.AppendView(newView)
+	}
+
+	pkt := stack.NewPacketBuffer(stack.PacketBufferOptions{
+		ReserveHeaderBytes: transportHeaderLength + extraHeaderReserveLength,
+		Data:               views,
+	})
+	pkt.NetworkProtocolNumber = proto
+	if _, err := rand.Read(pkt.TransportHeader().Push(transportHeaderLength)); err != nil {
+		panic(fmt.Sprintf("rand.Read: %s", err))
+	}
+	return pkt
+}