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actioncable.go
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actioncable.go
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package actioncable
import (
"encoding/json"
"errors"
"fmt"
"log"
"net/http"
"sync"
"time"
"github.com/gorilla/websocket"
"github.com/jpillora/backoff"
)
// HeaderFunc is a function that returns HTTP headers or an error.
type HeaderFunc func() (*http.Header, error)
// Client is an ActionCable websocket client.
type Client struct {
u string
dialer *websocket.Dialer
inactivityTimeout time.Duration
inactivityTimeoutTimer *time.Timer
outboundc chan *Command
subc chan string
// TODO: what actually needs a mutex??
mu sync.Mutex
subscData map[string]json.RawMessage
connHdrFunc HeaderFunc
subscriptions map[string]chan *EventOrErr
closed bool
donec chan struct{}
waitc chan struct{}
ref int
}
// NewClient creates a new Client that connects to the provided url using the
// HTTP headers from connHdrFunc, which will be called once for each connection
// attempt. If connHdrFunc returns an error when called, that will cause the
// connection attempt to fail.
func NewClient(url string, connHdrFunc HeaderFunc) *Client {
c := &Client{
u: url,
dialer: &websocket.Dialer{
HandshakeTimeout: 10 * time.Second,
},
inactivityTimeout: 6 * time.Second, // 2 * the 3 sec ping interval
outboundc: make(chan *Command, 32),
subc: make(chan string, 32),
subscData: make(map[string]json.RawMessage),
connHdrFunc: connHdrFunc,
subscriptions: make(map[string]chan *EventOrErr),
donec: make(chan struct{}),
waitc: make(chan struct{}),
}
go c.connLoop()
return c
}
// Close closes any active connection on the Client and stops it from making
// additional connections.
func (c *Client) Close() {
c.mu.Lock()
defer c.mu.Unlock()
if c.donec != nil && !c.closed {
close(c.donec)
<-c.waitc
c.closed = true
}
}
// ErrAlreadySubscribed is returned when the client has already subscribed to
// a given channel.
var ErrAlreadySubscribed = errors.New("channel already subscribed")
// Subscribe establishes a subscription to a specific channel. If the channel
// is already subscribed, ErrAlreadySubscribed is returned. Otherwise an
// subscription channel will return. If the subscription is rejected at any
// point (including after a future reconnect), the channel will be closed. It
// will also be closed if Unsubscribe is called for that subscription.
//
// The channel will receive a confirm_subscription event anytime the
// subscription is confirmed (including every time the client reconnects) and
// will receive any events sent to that channel. Events may be missed during
// disconnects, so a confirm_subscription event might be a good time to
// resynchronize state that might be stale.
func (c *Client) Subscribe(channel string) (<-chan *EventOrErr, error) {
var err error
c.mu.Lock()
defer c.mu.Unlock()
if _, alreadySubscribed := c.subscriptions[channel]; alreadySubscribed {
return nil, ErrAlreadySubscribed
}
c.subscriptions[channel] = make(chan *EventOrErr, 32)
c.subscData[channel], err = json.Marshal(&innerIdentifier{Channel: channel})
if err != nil {
panic(err)
}
// Add subscription command to outbound queue.
go func() {
c.subc <- channel
}()
return c.subscriptions[channel], nil
}
var ErrNoChannelName = errors.New("Subscription data must contain a channel name")
// SubscribeWith subscribes to a channel giving parameters
// the params must contain a field "channel" containing the channe to subscribe to
func (c *Client) SubscribeWith(params json.RawMessage) (<-chan *EventOrErr, error) {
var id innerIdentifier
err := json.Unmarshal(params, &id)
if err != nil {
return nil, err
}
if id.Channel == "" {
return nil, ErrNoChannelName
}
channel := id.Channel
c.mu.Lock()
defer c.mu.Unlock()
if _, alreadySubscribed := c.subscriptions[channel]; alreadySubscribed {
return nil, ErrAlreadySubscribed
}
c.subscriptions[channel] = make(chan *EventOrErr, 32)
c.subscData[channel] = params
// Add subscription command to outbound queue.
go func() {
c.subc <- channel
}()
return c.subscriptions[channel], nil
}
// Unsubscribe stops subscribing to channel.
func (c *Client) Unsubscribe(channel string) {
c.mu.Lock()
defer c.mu.Unlock()
ch, ok := c.subscriptions[channel]
if !ok {
return
}
delete(c.subscriptions, channel)
delete(c.subscData, channel)
close(ch)
cmd := &Command{
Command: "unsubscribe",
Identifier: CommandIdentifier{
Channel: channel,
},
}
go func() {
c.outboundc <- cmd
}()
}
// Send an action on a channel. The "action" field of data will be overridden.
// The return channel will send an error if one is encountered, or will close
// if the send completes.
func (c *Client) Send(channel, action string, data map[string]interface{}) <-chan error {
if data == nil {
data = make(map[string]interface{})
}
data["action"] = action
errc := make(chan error, 1)
b, err := json.Marshal(data)
if err != nil {
errc <- err
return errc
}
doubleEncoded, err := json.Marshal(string(b))
if err != nil {
errc <- err
return errc
}
cmd := &Command{
Command: "message",
Identifier: CommandIdentifier{
Channel: channel,
},
Data: doubleEncoded,
errc: errc,
}
c.outboundc <- cmd
return errc
}
func (c *Client) connLoop() {
b := backoff.Backoff{
Min: 100 * time.Millisecond,
Max: 10 * time.Second,
Factor: 2,
Jitter: true,
}
for {
err := c.connOnce(c.u, b.Reset)
if err != nil {
log.Printf("conn error: %s", err)
}
log.Println("disconnected")
select {
case <-c.donec:
close(c.waitc)
return
// TODO: backoff
case <-time.After(b.Duration()):
log.Println("reconnecting")
}
}
}
func (c *Client) drainSubc() {
for {
select {
case <-c.subc:
// discard
default:
return
}
}
}
func (c *Client) connOnce(url string, f func()) error {
// per docs, this resp.Body doesn't need to be closed
connHdr, err := c.connHdrFunc()
if err != nil {
return err
}
conn, _, err := c.dialer.Dial(c.u, *connHdr)
if err != nil {
return err
}
defer conn.Close()
c.inactivityTimeoutTimer = time.NewTimer(c.inactivityTimeout)
defer c.inactivityTimeoutTimer.Stop()
recvc := make(chan EventOrErr, 1)
go c.receiveMsg(conn, recvc)
if err = checkWelcome(recvc); err != nil {
return err
}
fmt.Printf("connected to %s\n", conn.RemoteAddr())
if f != nil {
f()
}
// drain the old subscription requests and resubscribe
c.drainSubc()
c.resubscribe()
for {
go c.receiveMsg(conn, recvc)
select {
case <-c.donec:
return nil
case eventOrErr := <-recvc:
if eventOrErr.Err != nil {
return err
}
c.handleEvent(eventOrErr.Event)
case chanName := <-c.subc:
c.mu.Lock()
params := c.subscData[chanName]
c.mu.Unlock()
cmd := &Command{
Command: "subscribe",
Identifier: CommandIdentifier{
Channel: chanName,
RawData: params,
},
}
if err := conn.WriteJSON(cmd); err != nil {
return err
}
case cmd := <-c.outboundc:
if err := conn.WriteJSON(cmd); err != nil {
// TODO: save cmd to a var to be written after reconnect
if cmd.errc != nil {
cmd.errc <- err
}
return err
}
if cmd.errc != nil {
close(cmd.errc)
}
case <-c.inactivityTimeoutTimer.C:
return fmt.Errorf("timeout waiting for ping from server")
}
}
}
func checkWelcome(recvc <-chan EventOrErr) error {
eventOrErr := <-recvc
if eventOrErr.Err != nil {
return eventOrErr.Err
}
if eventOrErr.Event.Type != "welcome" {
return fmt.Errorf("received unexpected %q message after connect", eventOrErr.Event.Type)
}
return nil
}
func (c *Client) handleEvent(evt *Event) {
// If we've received any kind of event, the channel must be alive.
c.inactivityTimeoutTimer.Reset(c.inactivityTimeout)
switch evt.Type {
case "ping":
// do nothing
case "reject_subscription":
ch := c.getAndRemoveSub(evt.Identifier.Channel)
if ch == nil {
return
}
fmt.Printf("sub rejected: %#v %#v\n", evt, evt.Identifier)
ch <- &EventOrErr{Err: errors.New("subscription rejected")}
close(ch)
default:
ch := c.getSub(evt.Identifier.Channel)
if ch == nil {
log.Printf("received msg for unsubscribed channel: %s", evt.Identifier.Channel)
return
}
select {
case ch <- &EventOrErr{Event: evt}:
default:
log.Printf("no receiver ready, dropping message: %#v\n", evt)
}
}
}
func (c *Client) getAndRemoveSub(name string) chan *EventOrErr {
c.mu.Lock()
defer c.mu.Unlock()
ch, ok := c.subscriptions[name]
if !ok {
return nil
}
delete(c.subscriptions, name)
return ch
}
func (c *Client) getSub(name string) chan *EventOrErr {
c.mu.Lock()
defer c.mu.Unlock()
return c.subscriptions[name]
}
func (c *Client) receiveMsg(conn *websocket.Conn, recvc chan<- EventOrErr) {
event := &Event{}
if err := conn.ReadJSON(event); err != nil {
recvc <- EventOrErr{Err: err}
return
}
recvc <- EventOrErr{Event: event}
}
func (c *Client) resubscribe() {
c.mu.Lock()
defer c.mu.Unlock()
chans := make([]string, 0, len(c.subscriptions))
for name := range c.subscriptions {
chans = append(chans, name)
}
go func() {
for _, name := range chans {
c.subc <- name
}
}()
}
// EventOrErr is an Event or error returned on a subscription channel.
type EventOrErr struct {
Event *Event
Err error
}
// Command is a command issued on a channel.
type Command struct {
Command string `json:"command"`
Data json.RawMessage `json:"data,omitempty"`
Identifier CommandIdentifier `json:"identifier"`
errc chan error
}
// CommandIdentifier identifies which Channel a Command occurs on.
type CommandIdentifier struct {
// Channel is the name of the channel.
Channel string
RawData json.RawMessage
}
type innerIdentifier struct {
Channel string `json:"channel"`
}
// MarshalJSON encodes the CommandIdentifier to JSON.
func (c *CommandIdentifier) MarshalJSON() ([]byte, error) {
var err error
if c.RawData == nil {
c.RawData, err = json.Marshal(innerIdentifier{
Channel: c.Channel,
})
if err != nil {
return nil, err
}
}
return json.Marshal(string(c.RawData))
}
// UnmarshalJSON decodes the CommandIdentifier from JSON.
func (c *CommandIdentifier) UnmarshalJSON(data []byte) error {
str := ""
if err := json.Unmarshal(data, &str); err != nil {
return err
}
c.RawData = json.RawMessage(str)
inner := innerIdentifier{}
if err := json.Unmarshal(c.RawData, &inner); err != nil {
return err
}
c.Channel = inner.Channel
return nil
}
// Event is a subscription event received on a channel.
type Event struct {
Type string `json:"type"`
Message json.RawMessage `json:"message"`
Data json.RawMessage `json:"data"`
Identifier *CommandIdentifier `json:"identifier"`
}