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resolver.go
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resolver.go
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// Copyright 2019 ETH Zurich, Anapaya Systems
//
// 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 svc
import (
"bytes"
"context"
"time"
"github.com/opentracing/opentracing-go"
"github.com/scionproto/scion/go/lib/addr"
"github.com/scionproto/scion/go/lib/common"
"github.com/scionproto/scion/go/lib/l4"
"github.com/scionproto/scion/go/lib/overlay"
"github.com/scionproto/scion/go/lib/sciond"
"github.com/scionproto/scion/go/lib/snet"
"github.com/scionproto/scion/go/lib/spath"
"github.com/scionproto/scion/go/lib/svc/internal/ctxconn"
)
// Internal resolver errors. These are implementation details and can change,
// and calling code should not depend on them.
const (
errNilPacket common.ErrMsg = "packet is nil"
errNilOverlay common.ErrMsg = "overlay is nil"
errUnsupportedPld common.ErrMsg = "unsupported payload type"
errRegistration common.ErrMsg = "unable to open conn"
errWrite common.ErrMsg = "unable to write"
errRead common.ErrMsg = "unable to read"
errDecode common.ErrMsg = "decode failed"
errBadPath common.ErrMsg = "unable to parse return path"
)
// Resolver performs SVC address resolution.
type Resolver struct {
// LocalIA is the local AS.
LocalIA addr.IA
// ConnFactory is used to open ports for SVC resolution messages.
ConnFactory snet.PacketDispatcherService
// Machine is used to derive addressing information for local conns.
Machine snet.LocalMachine
// RoundTripper performs the request/reply exchange for SVC resolutions. If
// nil, the default round tripper is used.
RoundTripper RoundTripper
// Payload is used for the data part of SVC requests.
Payload []byte
}
// LookupSVC resolves the SVC address for the AS terminating the path.
func (r *Resolver) LookupSVC(ctx context.Context, p snet.Path, svc addr.HostSVC) (*Reply, error) {
var span opentracing.Span
span, ctx = opentracing.StartSpanFromContext(ctx, "svc.resolution")
defer span.Finish()
// FIXME(scrye): Assume registration is always instant for now. This,
// however, should respect ctx.
conn, port, err := r.ConnFactory.RegisterTimeout(r.LocalIA, r.Machine.AppAddress(),
nil, addr.SvcNone, 0)
if err != nil {
return nil, common.NewBasicError(errRegistration, err)
}
requestPacket := &snet.SCIONPacket{
SCIONPacketInfo: snet.SCIONPacketInfo{
Source: snet.SCIONAddress{
IA: r.LocalIA,
Host: r.Machine.AppAddress().L3,
},
Destination: snet.SCIONAddress{
IA: p.Destination(),
Host: svc,
},
Path: p.Path(),
L4Header: &l4.UDP{
SrcPort: port,
},
Payload: common.RawBytes(r.Payload),
},
}
return r.getRoundTripper().RoundTrip(ctx, conn, requestPacket, p.OverlayNextHop())
}
func (r *Resolver) getRoundTripper() RoundTripper {
if r.RoundTripper == nil {
return DefaultRoundTripper()
}
return r.RoundTripper
}
// RoundTripper does a single SVC resolution request/reply interaction over a
// connection, using the specified request packet and overlay address.
type RoundTripper interface {
// RoundTrip performs the round trip interaction.
RoundTrip(ctx context.Context, c snet.PacketConn, request *snet.SCIONPacket,
ov *overlay.OverlayAddr) (*Reply, error)
}
// DefaultRoundTripper returns a basic implementation of the RoundTripper
// interface.
func DefaultRoundTripper() RoundTripper {
return roundTripper{}
}
var _ RoundTripper = (*roundTripper)(nil)
type roundTripper struct{}
func (roundTripper) RoundTrip(ctx context.Context, c snet.PacketConn, pkt *snet.SCIONPacket,
ov *overlay.OverlayAddr) (*Reply, error) {
cancelF := ctxconn.CloseConnOnDone(ctx, c)
defer cancelF()
if pkt == nil {
return nil, common.NewBasicError(errNilPacket, nil)
}
if ov == nil {
return nil, common.NewBasicError(errNilOverlay, nil)
}
if err := c.WriteTo(pkt, ov); err != nil {
return nil, common.NewBasicError(errWrite, err)
}
var replyPacket snet.SCIONPacket
var replyOv overlay.OverlayAddr
if err := c.ReadFrom(&replyPacket, &replyOv); err != nil {
return nil, common.NewBasicError(errRead, err)
}
b, ok := replyPacket.Payload.(common.RawBytes)
if !ok {
return nil, common.NewBasicError(errUnsupportedPld, nil, "payload", replyPacket.Payload)
}
var reply Reply
if err := reply.DecodeFrom(bytes.NewBuffer([]byte(b))); err != nil {
return nil, common.NewBasicError(errDecode, err)
}
if replyPacket.Path != nil {
if err := replyPacket.Path.Reverse(); err != nil {
return nil, common.NewBasicError(errBadPath, err)
}
if err := replyPacket.Path.InitOffsets(); err != nil {
return nil, common.NewBasicError(errBadPath, err)
}
}
reply.ReturnPath = &path{
spath: replyPacket.Path,
overlay: &replyOv,
destination: replyPacket.Source.IA,
}
return &reply, nil
}
type path struct {
spath *spath.Path
overlay *overlay.OverlayAddr
destination addr.IA
}
func (p *path) Fingerprint() string {
return ""
}
func (p *path) OverlayNextHop() *overlay.OverlayAddr {
return p.overlay
}
func (p *path) Path() *spath.Path {
return p.spath
}
func (p *path) Interfaces() []sciond.PathInterface {
return nil
}
func (p *path) Destination() addr.IA {
return p.destination
}
func (p *path) MTU() uint16 {
return 0
}
func (p *path) Expiry() time.Time {
return time.Time{}
}
func (p *path) Copy() snet.Path {
return &path{
spath: p.spath.Copy(),
overlay: p.overlay.Copy(),
destination: p.destination,
}
}