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package plugin
import (
"encoding/binary"
"fmt"
"log"
"net"
"sync"
"sync/atomic"
"time"
"github.com/hashicorp/yamux"
)
// MuxBroker is responsible for brokering multiplexed connections by unique ID.
//
// It is used by plugins to multiplex multiple RPC connections and data
// streams on top of a single connection between the plugin process and the
// host process.
//
// 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.
//
// The Plugin interface has access to these for both Server and Client.
// The broker can be used by either (optionally) to reserve and connect to
// new multiplexed streams. This is useful for complex args and return values,
// or anything else you might need a data stream for.
type MuxBroker struct {
nextId uint32
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
}
// AcceptAndServe is used to accept a specific stream ID and immediately
// serve an RPC server on that stream ID. This is used to easily serve
// complex arguments.
//
// The served interface is always registered to the "Plugin" name.
func (m *MuxBroker) AcceptAndServe(id uint32, v interface{}) {
conn, err := m.Accept(id)
if err != nil {
log.Printf("[ERR] plugin: plugin acceptAndServe error: %s", err)
return
}
serve(conn, "Plugin", v)
}
// 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.
//
// It is possible for very long-running plugin hosts to wrap this value,
// though it would require a very large amount of RPC calls. In practice
// we've never seen it happen.
func (m *MuxBroker) NextId() uint32 {
return atomic.AddUint32(&m.nextId, 1)
}
// Run starts the brokering and should be executed in a goroutine, since it
// blocks forever, or until the session closes.
//
// Uses of MuxBroker never need to call this. It is called internally by
// the plugin host/client.
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()
}
}
}
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