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respondent.go
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respondent.go
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// Copyright 2015 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 respondent implements the RESPONDENT protocol. This protocol
// receives SURVEYOR requests, and responds with an answer.
package respondent
import (
"encoding/binary"
"sync"
"time"
"github.com/gdamore/mangos"
)
type resp struct {
sock mangos.ProtocolSocket
peer *respPeer
raw bool
surveyID uint32
surveyOk bool
senders mangos.Waiter
sync.Mutex
}
type respPeer struct {
q chan *mangos.Message
ep mangos.Endpoint
x *resp
}
func (x *resp) Init(sock mangos.ProtocolSocket) {
x.sock = sock
x.senders.Init()
go x.sender()
}
// Shutdown just returns. There is no point in draining a survey --
// we're going to close before we can receive any responses anyway.
func (x *resp) Shutdown(linger time.Duration) {
x.senders.WaitRelTimeout(linger)
}
func (x *resp) sender() {
// This is pretty easy because we have only one peer at a time.
// If the peer goes away, we'll just drop the message on the floor.
sq := x.sock.SendChannel()
for {
m := <-sq
if m == nil {
// We want to send the nil down to the peer to alert it
// to drain.
x.Lock()
if peer := x.peer; peer != nil {
select {
case peer.q <- nil:
default:
}
}
x.Unlock()
break
}
x.Lock()
peer := x.peer
x.Unlock()
if peer == nil {
m.Free()
continue
}
// Put it on the outbound queue
select {
case peer.q <- m:
default:
// Backpressure, drop it.
m.Free()
}
}
}
// When sending, we should have the survey ID in the header.
func (peer *respPeer) sender() {
for {
m := <-peer.q
if m == nil {
break
}
if peer.ep.SendMsg(m) != nil {
m.Free()
break
}
}
peer.x.senders.Done()
}
func (peer *respPeer) receiver() {
rq := peer.x.sock.RecvChannel()
cq := peer.x.sock.CloseChannel()
for {
m := peer.ep.RecvMsg()
if m == nil {
return
}
if len(m.Body) < 4 {
m.Free()
continue
}
// Get survery ID -- this will be passed in the header up
// to the application. It should include that in the response.
m.Header = append(m.Header, m.Body[:4]...)
m.Body = m.Body[4:]
select {
case rq <- m:
case <-cq:
m.Free()
return
}
}
}
func (x *resp) RecvHook(m *mangos.Message) bool {
if x.raw {
// Raw mode receivers get the message unadulterated.
return true
}
x.Lock()
defer x.Unlock()
if len(m.Header) < 4 {
return false
}
x.surveyID = binary.BigEndian.Uint32(m.Header)
x.surveyOk = true
return true
}
func (x *resp) SendHook(m *mangos.Message) bool {
if x.raw {
// Raw mode senders expected to have prepared header already.
return true
}
x.Lock()
defer x.Unlock()
if !x.surveyOk {
return false
}
v := x.surveyID
m.Header = append(m.Header,
byte(v>>24), byte(v>>16), byte(v>>8), byte(v))
x.surveyOk = false
return true
}
func (x *resp) AddEndpoint(ep mangos.Endpoint) {
x.Lock()
if x.peer != nil {
x.Unlock()
ep.Close()
return
}
peer := &respPeer{ep: ep, x: x, q: make(chan *mangos.Message, 1)}
x.peer = peer
x.Unlock()
x.senders.Add()
go peer.receiver()
go peer.sender()
}
func (x *resp) RemoveEndpoint(ep mangos.Endpoint) {
x.Lock()
if x.peer.ep == ep {
x.peer = nil
}
x.Unlock()
}
func (*resp) Number() uint16 {
return mangos.ProtoRespondent
}
func (*resp) PeerNumber() uint16 {
return mangos.ProtoSurveyor
}
func (*resp) Name() string {
return "respondent"
}
func (*resp) PeerName() string {
return "surveyor"
}
func (x *resp) SetOption(name string, v interface{}) error {
switch name {
case mangos.OptionRaw:
x.raw = v.(bool)
return nil
default:
return mangos.ErrBadOption
}
}
func (x *resp) GetOption(name string) (interface{}, error) {
switch name {
case mangos.OptionRaw:
return x.raw, nil
default:
return nil, mangos.ErrBadOption
}
}
// NewProtocol returns a new RESPONDENT protocol object.
func NewProtocol() mangos.Protocol {
return &resp{}
}
// NewSocket allocates a new Socket using the RESPONDENT protocol.
func NewSocket() (mangos.Socket, error) {
return mangos.MakeSocket(&resp{}), nil
}