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// 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 (
"context"
"errors"
"sync"
)
var (
// ErrNotificationsUnsupported is returned when the connection doesn't support notifications
ErrNotificationsUnsupported = errors.New("notifications not supported")
// ErrNotificationNotFound is returned when the notification for the given id is not found
ErrSubscriptionNotFound = errors.New("subscription not found")
)
// ID defines a pseudo random number that is used to identify RPC subscriptions.
type ID string
// a Subscription is created by a notifier and tight to that notifier. The client can use
// this subscription to wait for an unsubscribe request for the client, see Err().
type Subscription struct {
ID ID
namespace string
err chan error // closed on unsubscribe
}
// Err returns a channel that is closed when the client send an unsubscribe request.
func (s *Subscription) Err() <-chan error {
return s.err
}
// notifierKey is used to store a notifier within the connection context.
type notifierKey struct{}
// Notifier is tight to a RPC connection that supports subscriptions.
// Server callbacks use the notifier to send notifications.
type Notifier struct {
codec ServerCodec
subMu sync.RWMutex // guards active and inactive maps
stopped bool
active map[ID]*Subscription
inactive map[ID]*Subscription
}
// newNotifier creates a new notifier that can be used to send subscription
// notifications to the client.
func newNotifier(codec ServerCodec) *Notifier {
return &Notifier{
codec: codec,
active: make(map[ID]*Subscription),
inactive: make(map[ID]*Subscription),
}
}
// 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
}
// CreateSubscription returns a new subscription that is coupled to the
// RPC connection. By default subscriptions are inactive and notifications
// are dropped until the subscription is marked as active. This is done
// by the RPC server after the subscription ID is send to the client.
func (n *Notifier) CreateSubscription() *Subscription {
s := &Subscription{ID: NewID(), err: make(chan error)}
n.subMu.Lock()
n.inactive[s.ID] = s
n.subMu.Unlock()
return s
}
// Notify sends a notification to the client with the given data as payload.
// If an error occurs the RPC connection is closed and the error is returned.
func (n *Notifier) Notify(id ID, data interface{}) error {
n.subMu.RLock()
defer n.subMu.RUnlock()
sub, active := n.active[id]
if active {
notification := n.codec.CreateNotification(string(id), sub.namespace, data)
if err := n.codec.Write(notification); err != nil {
n.codec.Close()
return err
}
}
return nil
}
// Closed returns a channel that is closed when the RPC connection is closed.
func (n *Notifier) Closed() <-chan interface{} {
return n.codec.Closed()
}
// unsubscribe a subscription.
// If the subscription could not be found ErrSubscriptionNotFound is returned.
func (n *Notifier) unsubscribe(id ID) error {
n.subMu.Lock()
defer n.subMu.Unlock()
if s, found := n.active[id]; found {
close(s.err)
delete(n.active, id)
return nil
}
return ErrSubscriptionNotFound
}
// activate enables a subscription. Until a subscription is enabled all
// notifications are dropped. This method is called by the RPC server after
// the subscription ID was sent to client. This prevents notifications being
// send to the client before the subscription ID is send to the client.
func (n *Notifier) activate(id ID, namespace string) {
n.subMu.Lock()
defer n.subMu.Unlock()
if sub, found := n.inactive[id]; found {
sub.namespace = namespace
n.active[id] = sub
delete(n.inactive, id)
}
}
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