terraform/rpc/mux_broker.go

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2014-09-28 19:49:27 +02:00
package rpc
import (
"encoding/binary"
"fmt"
"math/rand"
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"net"
"sync"
"time"
"github.com/hashicorp/yamux"
)
// muxBroker is responsible for brokering multiplexed connections by unique ID.
//
// This allows a plugin to request a channel with a specific ID to connect to
// or accept a connection from, and the broker handles the details of
// holding these channels open while they're being negotiated.
type muxBroker struct {
session *yamux.Session
streams map[uint32]*muxBrokerPending
sync.Mutex
}
type muxBrokerPending struct {
ch chan net.Conn
doneCh chan struct{}
}
func newMuxBroker(s *yamux.Session) *muxBroker {
return &muxBroker{
session: s,
streams: make(map[uint32]*muxBrokerPending),
}
}
// Accept accepts a connection by ID.
//
// This should not be called multiple times with the same ID at one time.
func (m *muxBroker) Accept(id uint32) (net.Conn, error) {
var c net.Conn
p := m.getStream(id)
select {
case c = <-p.ch:
close(p.doneCh)
case <-time.After(5 * time.Second):
m.Lock()
defer m.Unlock()
delete(m.streams, id)
return nil, fmt.Errorf("timeout waiting for accept")
}
// Ack our connection
if err := binary.Write(c, binary.LittleEndian, id); err != nil {
c.Close()
return nil, err
}
return c, nil
}
// Close closes the connection and all sub-connections.
func (m *muxBroker) Close() error {
return m.session.Close()
}
// Dial opens a connection by ID.
func (m *muxBroker) Dial(id uint32) (net.Conn, error) {
// Open the stream
stream, err := m.session.OpenStream()
if err != nil {
return nil, err
}
// Write the stream ID onto the wire.
if err := binary.Write(stream, binary.LittleEndian, id); err != nil {
stream.Close()
return nil, err
}
// Read the ack that we connected. Then we're off!
var ack uint32
if err := binary.Read(stream, binary.LittleEndian, &ack); err != nil {
stream.Close()
return nil, err
}
if ack != id {
stream.Close()
return nil, fmt.Errorf("bad ack: %d (expected %d)", ack, id)
}
return stream, nil
}
// NextId returns a unique ID to use next. There is no need for seeding the
// rand package as the returned ID's aren't stored or used anywhere outside
// the current runtime. So it's perfectly fine to get the same pseudo-random
// numbers each time terraform is running.
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func (m *muxBroker) NextId() uint32 {
return rand.Uint32()
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}
// Run starts the brokering and should be executed in a goroutine, since it
// blocks forever, or until the session closes.
func (m *muxBroker) Run() {
for {
stream, err := m.session.AcceptStream()
if err != nil {
// Once we receive an error, just exit
break
}
// Read the stream ID from the stream
var id uint32
if err := binary.Read(stream, binary.LittleEndian, &id); err != nil {
stream.Close()
continue
}
// Initialize the waiter
p := m.getStream(id)
select {
case p.ch <- stream:
default:
}
// Wait for a timeout
go m.timeoutWait(id, p)
}
}
func (m *muxBroker) getStream(id uint32) *muxBrokerPending {
m.Lock()
defer m.Unlock()
p, ok := m.streams[id]
if ok {
return p
}
m.streams[id] = &muxBrokerPending{
ch: make(chan net.Conn, 1),
doneCh: make(chan struct{}),
}
return m.streams[id]
}
func (m *muxBroker) timeoutWait(id uint32, p *muxBrokerPending) {
// Wait for the stream to either be picked up and connected, or
// for a timeout.
timeout := false
select {
case <-p.doneCh:
case <-time.After(5 * time.Second):
timeout = true
}
m.Lock()
defer m.Unlock()
// Delete the stream so no one else can grab it
delete(m.streams, id)
// If we timed out, then check if we have a channel in the buffer,
// and if so, close it.
if timeout {
select {
case s := <-p.ch:
s.Close()
}
}
}