/
star.go
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/
star.go
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// Copyright 2018 The Mangos Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use 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 star implements a new, experimental protocol called "STAR".
// This is like the BUS protocol, except that each member of the network
// automatically forwards any message it receives to any other peers.
// In a star network, this means that all members should receive all messages,
// assuming that there is a central server. Its important to ensure that
// the topology is free from cycles, as there is no protection against
// that, and cycles can lead to infinite message storms. (TODO: Add a TTL,
// and basic message ID / anti-replay protection.)
package star
import (
"sync"
"time"
"nanomsg.org/go-mangos"
)
type starEp struct {
ep mangos.Endpoint
q chan *mangos.Message
x *star
}
type star struct {
sock mangos.ProtocolSocket
eps map[uint32]*starEp
raw bool
w mangos.Waiter
ttl int
sync.Mutex
}
func (x *star) Init(sock mangos.ProtocolSocket) {
x.sock = sock
x.eps = make(map[uint32]*starEp)
x.ttl = 8
x.w.Init()
x.w.Add()
go x.sender()
}
func (x *star) Shutdown(expire time.Time) {
x.w.WaitAbsTimeout(expire)
x.Lock()
peers := x.eps
x.eps = make(map[uint32]*starEp)
x.Unlock()
for id, peer := range peers {
delete(peers, id)
mangos.DrainChannel(peer.q, expire)
close(peer.q)
}
}
// Bottom sender.
func (pe *starEp) sender() {
for {
m := <-pe.q
if m == nil {
break
}
if pe.ep.SendMsg(m) != nil {
m.Free()
break
}
}
}
func (x *star) broadcast(m *mangos.Message, sender *starEp) {
x.Lock()
if sender == nil || !x.raw {
for _, pe := range x.eps {
if sender == pe {
continue
}
m = m.Dup()
select {
case pe.q <- m:
default:
// No room on outbound queue, drop it.
if m != nil {
m.Free()
}
}
}
}
x.Unlock()
// Grab a local copy and send it up if we aren't originator
if sender != nil {
select {
case x.sock.RecvChannel() <- m:
case <-x.sock.CloseChannel():
m.Free()
return
default:
// No room, so we just drop it.
m.Free()
}
} else {
// Not sending it up, so we need to release it.
m.Free()
}
}
func (x *star) sender() {
defer x.w.Done()
cq := x.sock.CloseChannel()
sq := x.sock.SendChannel()
for {
select {
case <-cq:
return
case m := <-sq:
if m == nil {
sq = x.sock.SendChannel()
continue
}
x.broadcast(m, nil)
}
}
}
func (pe *starEp) receiver() {
for {
m := pe.ep.RecvMsg()
if m == nil {
return
}
if len(m.Body) < 4 {
m.Free()
continue
}
if m.Body[0] != 0 || m.Body[1] != 0 || m.Body[2] != 0 {
// non-zero reserved fields are illegal
m.Free()
continue
}
if int(m.Body[3]) >= pe.x.ttl { // TTL expired?
// XXX: bump a stat
m.Free()
continue
}
m.Header = append(m.Header, 0, 0, 0, m.Body[3]+1)
m.Body = m.Body[4:]
// if we're in raw mode, this does only a sendup, otherwise
// it does both a retransmit + sendup
pe.x.broadcast(m, pe)
}
}
func (x *star) AddEndpoint(ep mangos.Endpoint) {
depth := 16
if i, err := x.sock.GetOption(mangos.OptionWriteQLen); err == nil {
depth = i.(int)
}
pe := &starEp{ep: ep, x: x, q: make(chan *mangos.Message, depth)}
x.Lock()
x.eps[ep.GetID()] = pe
x.Unlock()
go pe.sender()
go pe.receiver()
}
func (x *star) RemoveEndpoint(ep mangos.Endpoint) {
x.Lock()
if peer := x.eps[ep.GetID()]; peer != nil {
delete(x.eps, ep.GetID())
close(peer.q)
}
x.Unlock()
}
func (*star) Number() uint16 {
return mangos.ProtoStar
}
func (*star) PeerNumber() uint16 {
return mangos.ProtoStar
}
func (*star) Name() string {
return "star"
}
func (*star) PeerName() string {
return "star"
}
func (x *star) SetOption(name string, v interface{}) error {
var ok bool
switch name {
case mangos.OptionRaw:
if x.raw, ok = v.(bool); !ok {
return mangos.ErrBadValue
}
return nil
case mangos.OptionTTL:
if ttl, ok := v.(int); !ok {
return mangos.ErrBadValue
} else if ttl < 1 || ttl > 255 {
return mangos.ErrBadValue
} else {
x.ttl = ttl
}
return nil
default:
return mangos.ErrBadOption
}
}
func (x *star) GetOption(name string) (interface{}, error) {
switch name {
case mangos.OptionRaw:
return x.raw, nil
case mangos.OptionTTL:
return x.ttl, nil
default:
return nil, mangos.ErrBadOption
}
}
func (x *star) SendHook(m *mangos.Message) bool {
if x.raw {
// TTL header must be present.
return true
}
// new message has a zero hop count
m.Header = append(m.Header, 0, 0, 0, 0)
return true
}
// NewSocket allocates a new Socket using the STAR protocol.
func NewSocket() (mangos.Socket, error) {
return mangos.MakeSocket(&star{}), nil
}