| // Copyright 2018 Google Inc. |
| // |
| // 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 ( |
| "github.com/google/netstack/tcpip" |
| "github.com/google/netstack/tcpip/buffer" |
| "github.com/google/netstack/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() tcpip.LinkEndpointID { |
| return stack.RegisterLinkEndpoint(&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.CapabilityChecksumOffload | 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 "" |
| } |
| |
| // WritePacket implements stack.LinkEndpoint.WritePacket. It delivers outbound |
| // packets to the network-layer dispatcher. |
| func (e *endpoint) WritePacket(_ *stack.Route, hdr buffer.Prependable, payload buffer.VectorisedView, protocol tcpip.NetworkProtocolNumber) *tcpip.Error { |
| views := make([]buffer.View, 1, 1+len(payload.Views())) |
| views[0] = hdr.View() |
| views = append(views, payload.Views()...) |
| vv := buffer.NewVectorisedView(len(views[0])+payload.Size(), 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(e, "" /* remoteLinkAddr */, "" /* localLinkAddr */, protocol, vv) |
| |
| return nil |
| } |