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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 (
"context"
"net"
"github.com/opentracing/opentracing-go"
"github.com/opentracing/opentracing-go/ext"
"google.golang.org/protobuf/proto"
"github.com/scionproto/scion/go/lib/addr"
"github.com/scionproto/scion/go/lib/common"
"github.com/scionproto/scion/go/lib/serrors"
"github.com/scionproto/scion/go/lib/snet"
"github.com/scionproto/scion/go/lib/svc/internal/ctxconn"
cppb "github.com/scionproto/scion/go/pkg/proto/control_plane"
)
// 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"
errNilUnderlay common.ErrMsg = "underlay 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"
)
// For now, the request payload does not need to be dynamic. We initialize it
// once on application start.
var requestPayload []byte
func init() {
var err error
if requestPayload, err = proto.Marshal(&cppb.ServiceResolutionRequest{}); err != nil {
panic(err)
}
}
// 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
// LocalIP is the default L3 address for connections originating from this process.
LocalIP net.IP
// RoundTripper performs the request/reply exchange for SVC resolutions. If
// nil, the default round tripper is used.
RoundTripper RoundTripper
}
// 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")
span.SetTag("svc", svc.String())
span.SetTag("isd_as", p.Destination().String())
defer span.Finish()
u := &net.UDPAddr{
IP: r.LocalIP,
}
conn, port, err := r.ConnFactory.Register(ctx, r.LocalIA, u, addr.SvcNone)
if err != nil {
ext.Error.Set(span, true)
return nil, serrors.Wrap(errRegistration, err)
}
requestPacket := &snet.Packet{
PacketInfo: snet.PacketInfo{
Source: snet.SCIONAddress{
IA: r.LocalIA,
Host: addr.HostFromIP(r.LocalIP),
},
Destination: snet.SCIONAddress{
IA: p.Destination(),
Host: svc,
},
Path: p.Dataplane(),
Payload: snet.UDPPayload{
SrcPort: port,
Payload: requestPayload,
},
},
}
reply, err := r.getRoundTripper().RoundTrip(ctx, conn, requestPacket, p.UnderlayNextHop())
if err != nil {
ext.Error.Set(span, true)
return nil, err
}
return reply, nil
}
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 underlay address.
type RoundTripper interface {
// RoundTrip performs the round trip interaction.
RoundTrip(ctx context.Context, c snet.PacketConn, request *snet.Packet,
u *net.UDPAddr) (*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.Packet,
u *net.UDPAddr) (*Reply, error) {
cancelF := ctxconn.CloseConnOnDone(ctx, c)
defer cancelF()
if pkt == nil {
return nil, errNilPacket
}
if u == nil {
return nil, errNilUnderlay
}
if err := c.WriteTo(pkt, u); err != nil {
select {
case <-ctx.Done():
return nil, ctx.Err()
default:
}
return nil, serrors.Wrap(errWrite, err)
}
var replyPacket snet.Packet
var replyOv net.UDPAddr
if err := c.ReadFrom(&replyPacket, &replyOv); err != nil {
select {
case <-ctx.Done():
return nil, ctx.Err()
default:
}
return nil, serrors.Wrap(errRead, err)
}
udp, ok := replyPacket.Payload.(snet.UDPPayload)
if !ok {
return nil, serrors.WithCtx(errUnsupportedPld,
"type", common.TypeOf(replyPacket.Payload))
}
var reply Reply
if err := reply.Unmarshal(udp.Payload); err != nil {
return nil, serrors.Wrap(errDecode, err)
}
rpath, ok := replyPacket.Path.(snet.RawPath)
if !ok {
return nil, serrors.New("unexpected path", "type", common.TypeOf(replyPacket.Path))
}
replyPath, err := snet.DefaultReplyPather{}.ReplyPath(rpath)
if err != nil {
return nil, serrors.WrapStr("creating reply path", err)
}
reply.ReturnPath = &path{
dataplane: replyPath,
underlay: &replyOv,
source: replyPacket.Destination.IA,
destination: replyPacket.Source.IA,
}
return &reply, nil
}
type path struct {
dataplane snet.DataplanePath
underlay *net.UDPAddr
destination addr.IA
source addr.IA
}
func (p *path) UnderlayNextHop() *net.UDPAddr {
return p.underlay
}
func (p *path) Dataplane() snet.DataplanePath {
return p.dataplane
}
func (p *path) Interfaces() []snet.PathInterface {
return nil
}
func (p *path) Source() addr.IA {
return p.source
}
func (p *path) Destination() addr.IA {
return p.destination
}
func (p *path) Metadata() *snet.PathMetadata {
return nil
}
func (p *path) Copy() snet.Path {
if p == nil {
return nil
}
return &path{
dataplane: p.dataplane,
underlay: snet.CopyUDPAddr(p.underlay),
source: p.source,
destination: p.destination,
}
}