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// Copyright 2018 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 loopback provides the implemention of loopback data-link layer
// endpoints. Such endpoints just turn outbound packets into inbound ones.
//
// Loopback endpoints can be used in the networking stack by calling New() to
// create a new endpoint, and then passing it as an argument to
// Stack.CreateNIC().
package loopback
import (
"gvisor.dev/gvisor/pkg/tcpip"
"gvisor.dev/gvisor/pkg/tcpip/buffer"
"gvisor.dev/gvisor/pkg/tcpip/header"
"gvisor.dev/gvisor/pkg/tcpip/stack"
)
type endpoint struct {
dispatcher stack.NetworkDispatcher
}
// New creates a new loopback endpoint. This link-layer endpoint just turns
// outbound packets into inbound packets.
func New() stack.LinkEndpoint {
return &endpoint{}
}
// Attach implements stack.LinkEndpoint.Attach. It just saves the stack network-
// layer dispatcher for later use when packets need to be dispatched.
func (e *endpoint) Attach(dispatcher stack.NetworkDispatcher) {
e.dispatcher = dispatcher
}
// IsAttached implements stack.LinkEndpoint.IsAttached.
func (e *endpoint) IsAttached() bool {
return e.dispatcher != nil
}
// MTU implements stack.LinkEndpoint.MTU. It returns a constant that matches the
// linux loopback interface.
func (*endpoint) MTU() uint32 {
return 65536
}
// Capabilities implements stack.LinkEndpoint.Capabilities. Loopback advertises
// itself as supporting checksum offload, but in reality it's just omitted.
func (*endpoint) Capabilities() stack.LinkEndpointCapabilities {
return stack.CapabilityRXChecksumOffload | stack.CapabilityTXChecksumOffload | stack.CapabilitySaveRestore | stack.CapabilityLoopback
}
// MaxHeaderLength implements stack.LinkEndpoint.MaxHeaderLength. Given that the
// loopback interface doesn't have a header, it just returns 0.
func (*endpoint) MaxHeaderLength() uint16 {
return 0
}
// LinkAddress returns the link address of this endpoint.
func (*endpoint) LinkAddress() tcpip.LinkAddress {
return ""
}
// Wait implements stack.LinkEndpoint.Wait.
func (*endpoint) Wait() {}
// WritePacket implements stack.LinkEndpoint.WritePacket. It delivers outbound
// packets to the network-layer dispatcher.
func (e *endpoint) WritePacket(_ *stack.Route, _ *stack.GSO, protocol tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer) *tcpip.Error {
views := make([]buffer.View, 1, 1+len(pkt.Data.Views()))
views[0] = pkt.Header.View()
views = append(views, pkt.Data.Views()...)
// Because we're immediately turning around and writing the packet back
// to the rx path, we intentionally don't preserve the remote and local
// link addresses from the stack.Route we're passed.
e.dispatcher.DeliverNetworkPacket("" /* remote */, "" /* local */, protocol, &stack.PacketBuffer{
Data: buffer.NewVectorisedView(len(views[0])+pkt.Data.Size(), views),
})
return nil
}
// WritePackets implements stack.LinkEndpoint.WritePackets.
func (e *endpoint) WritePackets(*stack.Route, *stack.GSO, stack.PacketBufferList, tcpip.NetworkProtocolNumber) (int, *tcpip.Error) {
panic("not implemented")
}
// WriteRawPacket implements stack.LinkEndpoint.WriteRawPacket.
func (e *endpoint) WriteRawPacket(vv buffer.VectorisedView) *tcpip.Error {
// There should be an ethernet header at the beginning of vv.
hdr, ok := vv.PullUp(header.EthernetMinimumSize)
if !ok {
// Reject the packet if it's shorter than an ethernet header.
return tcpip.ErrBadAddress
}
linkHeader := header.Ethernet(hdr)
vv.TrimFront(len(linkHeader))
e.dispatcher.DeliverNetworkPacket("" /* remote */, "" /* local */, linkHeader.Type(), &stack.PacketBuffer{
Data: vv,
LinkHeader: buffer.View(linkHeader),
})
return nil
}
// ARPHardwareType implements stack.LinkEndpoint.ARPHardwareType.
func (*endpoint) ARPHardwareType() header.ARPHardwareType {
return header.ARPHardwareLoopback
}
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