// Copyright 2016 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
package rpc
import (
"errors"
"sync"
"time"
"github.com/ethereum/go-ethereum/logger"
"github.com/ethereum/go-ethereum/logger/glog"
"golang.org/x/net/context"
)
var (
// ErrNotificationsUnsupported is returned when the connection doesn't support notifications
ErrNotificationsUnsupported = errors.New("subscription notifications not supported by the current transport")
// ErrNotificationNotFound is returned when the notification for the given id is not found
ErrNotificationNotFound = errors.New("notification not found")
// errNotifierStopped is returned when the notifier is stopped (e.g. codec is closed)
errNotifierStopped = errors.New("unable to send notification")
// errNotificationQueueFull is returns when there are too many notifications in the queue
errNotificationQueueFull = errors.New("too many pending notifications")
)
// unsubSignal is a signal that the subscription is unsubscribed. It is used to flush buffered
// notifications that might be pending in the internal queue.
var unsubSignal = new(struct{})
// UnsubscribeCallback defines a callback that is called when a subcription ends.
// It receives the subscription id as argument.
type UnsubscribeCallback func(id string)
// notification is a helper object that holds event data for a subscription
type notification struct {
sub *bufferedSubscription // subscription id
data interface{} // event data
}
// A Notifier type describes the interface for objects that can send create subscriptions
type Notifier interface {
// Create a new subscription. The given callback is called when this subscription
// is cancelled (e.g. client send an unsubscribe, connection closed).
NewSubscription(UnsubscribeCallback) (Subscription, error)
// Cancel subscription
Unsubscribe(id string) error
}
type notifierKey struct{}
// NotifierFromContext returns the Notifier value stored in ctx, if any.
func NotifierFromContext(ctx context.Context) (Notifier, bool) {
n, ok := ctx.Value(notifierKey{}).(Notifier)
return n, ok
}
// Subscription defines the interface for objects that can notify subscribers
type Subscription interface {
// Inform client of an event
Notify(data interface{}) error
// Unique identifier
ID() string
// Cancel subscription
Cancel() error
}
// bufferedSubscription is a subscription that uses a bufferedNotifier to send
// notifications to subscribers.
type bufferedSubscription struct {
id string
unsubOnce sync.Once // call unsub method once
unsub UnsubscribeCallback // called on Unsubscribed
notifier *bufferedNotifier // forward notifications to
pending chan interface{} // closed when active
flushed chan interface{} // closed when all buffered notifications are send
lastNotification time.Time // last time a notification was send
}
// ID returns the subscription identifier that the client uses to refer to this instance.
func (s *bufferedSubscription) ID() string {
return s.id
}
// Cancel informs the notifier that this subscription is cancelled by the API
func (s *bufferedSubscription) Cancel() error {
return s.notifier.Unsubscribe(s.id)
}
// Notify the subscriber of a particular event.
func (s *bufferedSubscription) Notify(data interface{}) error {
return s.notifier.send(s.id, data)
}
// bufferedNotifier is a notifier that queues notifications in an internal queue and
// send them as fast as possible to the client from this queue. It will stop if the
// queue grows past a given size.
type bufferedNotifier struct {
codec ServerCodec // underlying connection
mu sync.Mutex // guard internal state
subscriptions map[string]*bufferedSubscription // keep track of subscriptions associated with codec
queueSize int // max number of items in queue
queue chan *notification // notification queue
stopped bool // indication if this notifier is ordered to stop
}
// newBufferedNotifier returns a notifier that queues notifications in an internal queue
// from which notifications are send as fast as possible to the client. If the queue size
// limit is reached (client is unable to keep up) it will stop and closes the codec.
func newBufferedNotifier(codec ServerCodec, size int) *bufferedNotifier {
notifier := &bufferedNotifier{
codec: codec,
subscriptions: make(map[string]*bufferedSubscription),
queue: make(chan *notification, size),
queueSize: size,
}
go notifier.run()
return notifier
}
// NewSubscription creates a new subscription that forwards events to this instance internal
// queue. The given callback is called when the subscription is unsubscribed/cancelled.
func (n *bufferedNotifier) NewSubscription(callback UnsubscribeCallback) (Subscription, error) {
id, err := newSubscriptionID()
if err != nil {
return nil, err
}
n.mu.Lock()
defer n.mu.Unlock()
if n.stopped {
return nil, errNotifierStopped
}
sub := &bufferedSubscription{
id: id,
unsub: callback,
notifier: n,
pending: make(chan interface{}),
flushed: make(chan interface{}),
lastNotification: time.Now(),
}
n.subscriptions[id] = sub
return sub, nil
}
// Remove the given subscription. If subscription is not found notificationNotFoundErr is returned.
func (n *bufferedNotifier) Unsubscribe(subid string) error {
n.mu.Lock()
sub, found := n.subscriptions[subid]
n.mu.Unlock()
if found {
// send the unsubscribe signal, this will cause the notifier not to accept new events
// for this subscription and will close the flushed channel after the last (buffered)
// notification was send to the client.
if err := n.send(subid, unsubSignal); err != nil {
return err
}
// wait for confirmation that all (buffered) events are send for this subscription.
// this ensures that the unsubscribe method response is not send before all buffered
// events for this subscription are send.
<-sub.flushed
return nil
}
return ErrNotificationNotFound
}
// Send enques the given data for the subscription with public ID on the internal queue. t returns
// an error when the notifier is stopped or the queue is full. If data is the unsubscribe signal it
// will remove the subscription with the given id from the subscription collection.
func (n *bufferedNotifier) send(id string, data interface{}) error {
n.mu.Lock()
defer n.mu.Unlock()
if n.stopped {
return errNotifierStopped
}
var (
subscription *bufferedSubscription
found bool
)
// check if subscription is associated with this connection, it might be cancelled
// (subscribe/connection closed)
if subscription, found = n.subscriptions[id]; !found {
glog.V(logger.Error).Infof("received notification for unknown subscription %s\n", id)
return ErrNotificationNotFound
}
// received the unsubscribe signal. Add it to the queue to make sure any pending notifications
// for this subscription are send. When the run loop receives this singal it will signal that
// all pending subscriptions are flushed and that the confirmation of the unsubscribe can be
// send to the user. Remove the subscriptions to make sure new notifications are not accepted.
if data == unsubSignal {
delete(n.subscriptions, id)
if subscription.unsub != nil {
subscription.unsubOnce.Do(func() { subscription.unsub(id) })
}
}
subscription.lastNotification = time.Now()
if len(n.queue) >= n.queueSize {
glog.V(logger.Warn).Infoln("too many buffered notifications -> close connection")
n.codec.Close()
return errNotificationQueueFull
}
n.queue <- ¬ification{subscription, data}
return nil
}
// run reads notifications from the internal queue and sends them to the client. In case of an
// error, or when the codec is closed it will cancel all active subscriptions and returns.
func (n *bufferedNotifier) run() {
defer func() {
n.mu.Lock()
defer n.mu.Unlock()
n.stopped = true
close(n.queue)
// on exit call unsubscribe callback
for id, sub := range n.subscriptions {
if sub.unsub != nil {
sub.unsubOnce.Do(func() { sub.unsub(id) })
}
close(sub.flushed)
delete(n.subscriptions, id)
}
}()
for {
select {
case notification := <-n.queue:
// It can happen that an event is raised before the RPC server was able to send the sub
// id to the client. Therefore subscriptions are marked as pending until the sub id was
// send. The RPC server will activate the subscription by closing the pending chan.
<-notification.sub.pending
if notification.data == unsubSignal {
// unsubSignal is the last accepted message for this subscription. Raise the signal
// that all buffered notifications are sent by closing the flushed channel. This
// indicates that the response for the unsubscribe can be send to the client.
close(notification.sub.flushed)
} else {
msg := n.codec.CreateNotification(notification.sub.id, notification.data)
if err := n.codec.Write(msg); err != nil {
n.codec.Close()
// unable to send notification to client, unsubscribe all subscriptions
glog.V(logger.Warn).Infof("unable to send notification - %v\n", err)
return
}
}
case <-n.codec.Closed(): // connection was closed
glog.V(logger.Debug).Infoln("codec closed, stop subscriptions")
return
}
}
}
// Marks the subscription as active. This will causes the notifications for this subscription to be
// forwarded to the client.
func (n *bufferedNotifier) activate(subid string) {
n.mu.Lock()
defer n.mu.Unlock()
if sub, found := n.subscriptions[subid]; found {
close(sub.pending)
}
}
