4 files changed, 221 insertions, 0 deletions
diff --git a/pkg/tcpip/link/muxed/BUILD b/pkg/tcpip/link/muxed/BUILD
new file mode 100644
index 000000000..92d2e3290
--- /dev/null
+++ b/pkg/tcpip/link/muxed/BUILD
@@ -0,0 +1,31 @@
+load("//tools/go_stateify:defs.bzl", "go_library", "go_test")
+
+package(licenses = ["notice"])  # Apache 2.0
+
+go_library(
+    name = "injectable",
+    srcs = ["injectable.go"],
+    importpath = "gvisor.googlesource.com/gvisor/pkg/tcpip/link/injectable",
+    visibility = [
+        "//visibility:public",
+    ],
+    deps = [
+        "//pkg/tcpip",
+        "//pkg/tcpip/buffer",
+        "//pkg/tcpip/stack",
+    ],
+)
+
+go_test(
+    name = "injectable_test",
+    size = "small",
+    srcs = ["injectable_test.go"],
+    embed = [":injectable"],
+    deps = [
+        "//pkg/tcpip",
+        "//pkg/tcpip/buffer",
+        "//pkg/tcpip/link/fdbased",
+        "//pkg/tcpip/network/ipv4",
+        "//pkg/tcpip/stack",
+    ],
+)
diff --git a/pkg/tcpip/link/muxed/injectable.go b/pkg/tcpip/link/muxed/injectable.go
new file mode 100644
index 000000000..1215ba1e7
--- /dev/null
+++ b/pkg/tcpip/link/muxed/injectable.go
@@ -0,0 +1,103 @@
+// Copyright 2019 Google LLC
+//
+// 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 injectable provides a muxed injectable endpoint.
+package injectable
+
+import (
+	"gvisor.googlesource.com/gvisor/pkg/tcpip"
+	"gvisor.googlesource.com/gvisor/pkg/tcpip/buffer"
+	"gvisor.googlesource.com/gvisor/pkg/tcpip/stack"
+)
+
+// MuxedInjectableEndpoint is an injectable multi endpoint. The endpoint has
+// trivial routing rules that determine which InjectableEndpoint a given packet
+// will be written to. Note that HandleLocal works differently for this
+// endpoint (see WritePacket).
+type MuxedInjectableEndpoint struct {
+	routes     map[tcpip.Address]stack.InjectableLinkEndpoint
+	dispatcher stack.NetworkDispatcher
+}
+
+// MTU implements stack.LinkEndpoint.
+func (m *MuxedInjectableEndpoint) MTU() uint32 {
+	minMTU := ^uint32(0)
+	for _, endpoint := range m.routes {
+		if endpointMTU := endpoint.MTU(); endpointMTU < minMTU {
+			minMTU = endpointMTU
+		}
+	}
+	return minMTU
+}
+
+// Capabilities implements stack.LinkEndpoint.
+func (m *MuxedInjectableEndpoint) Capabilities() stack.LinkEndpointCapabilities {
+	minCapabilities := stack.LinkEndpointCapabilities(^uint(0))
+	for _, endpoint := range m.routes {
+		minCapabilities &= endpoint.Capabilities()
+	}
+	return minCapabilities
+}
+
+// MaxHeaderLength implements stack.LinkEndpoint.
+func (m *MuxedInjectableEndpoint) MaxHeaderLength() uint16 {
+	minHeaderLen := ^uint16(0)
+	for _, endpoint := range m.routes {
+		if headerLen := endpoint.MaxHeaderLength(); headerLen < minHeaderLen {
+			minHeaderLen = headerLen
+		}
+	}
+	return minHeaderLen
+}
+
+// LinkAddress implements stack.LinkEndpoint.
+func (m *MuxedInjectableEndpoint) LinkAddress() tcpip.LinkAddress {
+	return ""
+}
+
+// Attach implements stack.LinkEndpoint.
+func (m *MuxedInjectableEndpoint) Attach(dispatcher stack.NetworkDispatcher) {
+	for _, endpoint := range m.routes {
+		endpoint.Attach(dispatcher)
+	}
+	m.dispatcher = dispatcher
+}
+
+// IsAttached implements stack.LinkEndpoint.
+func (m *MuxedInjectableEndpoint) IsAttached() bool {
+	return m.dispatcher != nil
+}
+
+// Inject implements stack.InjectableLinkEndpoint.
+func (m *MuxedInjectableEndpoint) Inject(protocol tcpip.NetworkProtocolNumber, vv buffer.VectorisedView) {
+	m.dispatcher.DeliverNetworkPacket(m, "" /* remote */, "" /* local */, protocol, vv)
+}
+
+// WritePacket writes outbound packets to the appropriate LinkInjectableEndpoint
+// based on the RemoteAddress. HandleLocal only works if r.RemoteAddress has a
+// route registered in this endpoint.
+func (m *MuxedInjectableEndpoint) WritePacket(r *stack.Route, hdr buffer.Prependable, payload buffer.VectorisedView, protocol tcpip.NetworkProtocolNumber) *tcpip.Error {
+	if endpoint, ok := m.routes[r.RemoteAddress]; ok {
+		return endpoint.WritePacket(r, hdr, payload, protocol)
+	}
+	return tcpip.ErrNoRoute
+}
+
+// NewMuxedInjectableEndpoint creates a new multi-fd-based injectable endpoint.
+func NewMuxedInjectableEndpoint(routes map[tcpip.Address]stack.InjectableLinkEndpoint, mtu uint32) (tcpip.LinkEndpointID, *MuxedInjectableEndpoint) {
+	e := &MuxedInjectableEndpoint{
+		routes: routes,
+	}
+	return stack.RegisterLinkEndpoint(e), e
+}
diff --git a/pkg/tcpip/link/muxed/injectable_test.go b/pkg/tcpip/link/muxed/injectable_test.go
new file mode 100644
index 000000000..8a1a863ff
--- /dev/null
+++ b/pkg/tcpip/link/muxed/injectable_test.go
@@ -0,0 +1,78 @@
+// Copyright 2019 Google LLC
+//
+// 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 injectable
+
+import (
+	"bytes"
+	"net"
+	"os"
+	"syscall"
+	"testing"
+
+	"gvisor.googlesource.com/gvisor/pkg/tcpip"
+	"gvisor.googlesource.com/gvisor/pkg/tcpip/buffer"
+	"gvisor.googlesource.com/gvisor/pkg/tcpip/link/fdbased"
+	"gvisor.googlesource.com/gvisor/pkg/tcpip/network/ipv4"
+	"gvisor.googlesource.com/gvisor/pkg/tcpip/stack"
+)
+
+func TestMuxedEndpointDispatch(t *testing.T) {
+	endpoint, sock, dstIP := makeMuxedTestEndpoint(t)
+	hdr := buffer.NewPrependable(1)
+	hdr.Prepend(1)[0] = 0xFA
+	packetRoute := stack.Route{RemoteAddress: dstIP}
+
+	endpoint.WritePacket(&packetRoute, hdr,
+		buffer.NewViewFromBytes([]byte{0xFB}).ToVectorisedView(), ipv4.ProtocolNumber)
+
+	buf := make([]byte, 6500)
+	bytesRead, err := sock.Read(buf)
+	if err != nil {
+		t.Fatalf("Unable to read from socketpair: %v", err)
+	}
+	if got, want := buf[:bytesRead], []byte{0xFA, 0xFB}; !bytes.Equal(got, want) {
+		t.Fatalf("Read %v from the socketpair, wanted %v", got, want)
+	}
+}
+
+func TestMuxedEndpointDispatchHdrOnly(t *testing.T) {
+	endpoint, sock, dstIP := makeMuxedTestEndpoint(t)
+	hdr := buffer.NewPrependable(1)
+	hdr.Prepend(1)[0] = 0xFA
+	packetRoute := stack.Route{RemoteAddress: dstIP}
+	endpoint.WritePacket(&packetRoute, hdr,
+		buffer.NewView(0).ToVectorisedView(), ipv4.ProtocolNumber)
+	buf := make([]byte, 6500)
+	bytesRead, err := sock.Read(buf)
+	if err != nil {
+		t.Fatalf("Unable to read from socketpair: %v", err)
+	}
+	if got, want := buf[:bytesRead], []byte{0xFA}; !bytes.Equal(got, want) {
+		t.Fatalf("Read %v from the socketpair, wanted %v", got, want)
+	}
+}
+
+func makeMuxedTestEndpoint(t *testing.T) (*MuxedInjectableEndpoint, *os.File, tcpip.Address) {
+	dstIP := tcpip.Address(net.ParseIP("1.2.3.4").To4())
+	pair, err := syscall.Socketpair(syscall.AF_UNIX,
+		syscall.SOCK_SEQPACKET|syscall.SOCK_CLOEXEC|syscall.SOCK_NONBLOCK, 0)
+	if err != nil {
+		t.Fatal("Failed to create socket pair:", err)
+	}
+	_, underlyingEndpoint := fdbased.NewInjectable(pair[1], 6500)
+	routes := map[tcpip.Address]stack.InjectableLinkEndpoint{dstIP: underlyingEndpoint}
+	_, endpoint := NewMuxedInjectableEndpoint(routes, 6500)
+	return endpoint, os.NewFile(uintptr(pair[0]), "test route end"), dstIP
+}
diff --git a/pkg/tcpip/stack/registration.go b/pkg/tcpip/stack/registration.go
index 6becd9426..010d51886 100644
--- a/pkg/tcpip/stack/registration.go
+++ b/pkg/tcpip/stack/registration.go
@@ -253,6 +253,15 @@ type LinkEndpoint interface {
 	IsAttached() bool
 }
 
+// InjectableLinkEndpoint is a LinkEndpoint where inbound packets are
+// delivered via the Inject method.
+type InjectableLinkEndpoint interface {
+	LinkEndpoint
+
+	// Inject injects an inbound packet.
+	Inject(protocol tcpip.NetworkProtocolNumber, vv buffer.VectorisedView)
+}
+
 // A LinkAddressResolver is an extension to a NetworkProtocol that
 // can resolve link addresses.
 type LinkAddressResolver interface {