Use upstream slack-go/slack again (#1018)

vendor/github.com/slack-go/slack/websocket.go

@@ -0,0 +1,103 @@
+package slack
+
+import (
+	"net/url"
+	"sync"
+	"time"
+
+	"github.com/gorilla/websocket"
+)
+
+const (
+	// MaxMessageTextLength is the current maximum message length in number of characters as defined here
+	// https://api.slack.com/rtm#limits
+	MaxMessageTextLength = 4000
+)
+
+// RTM represents a managed websocket connection. It also supports
+// all the methods of the `Client` type.
+//
+// Create this element with Client's NewRTM() or NewRTMWithOptions(*RTMOptions)
+type RTM struct {
+	// Client is the main API, embedded
+	Client
+
+	idGen        IDGenerator
+	pingInterval time.Duration
+	pingDeadman  *time.Timer
+
+	// Connection life-cycle
+	conn             *websocket.Conn
+	IncomingEvents   chan RTMEvent
+	outgoingMessages chan OutgoingMessage
+	killChannel      chan bool
+	disconnected     chan struct{}
+	disconnectedm    *sync.Once
+	forcePing        chan bool
+
+	// UserDetails upon connection
+	info *Info
+
+	// useRTMStart should be set to true if you want to use
+	// rtm.start to connect to Slack, otherwise it will use
+	// rtm.connect
+	useRTMStart bool
+
+	// dialer is a gorilla/websocket Dialer. If nil, use the default
+	// Dialer.
+	dialer *websocket.Dialer
+
+	// mu is mutex used to prevent RTM connection race conditions
+	mu *sync.Mutex
+
+	// connParams is a map of flags for connection parameters.
+	connParams url.Values
+}
+
+// signal that we are disconnected by closing the channel.
+// protect it with a mutex to ensure it only happens once.
+func (rtm *RTM) disconnect() {
+	rtm.disconnectedm.Do(func() {
+		close(rtm.disconnected)
+	})
+}
+
+// Disconnect and wait, blocking until a successful disconnection.
+func (rtm *RTM) Disconnect() error {
+	// always push into the kill channel when invoked,
+	// this lets the ManagedConnection() function properly clean up.
+	// if the buffer is full then just continue on.
+	select {
+	case rtm.killChannel <- true:
+		return nil
+	case <-rtm.disconnected:
+		return ErrAlreadyDisconnected
+	}
+}
+
+// GetInfo returns the info structure received when calling
+// "startrtm", holding metadata needed to implement a full
+// chat client. It will be non-nil after a call to StartRTM().
+func (rtm *RTM) GetInfo() *Info {
+	return rtm.info
+}
+
+// SendMessage submits a simple message through the websocket.  For
+// more complicated messages, use `rtm.PostMessage` with a complete
+// struct describing your attachments and all.
+func (rtm *RTM) SendMessage(msg *OutgoingMessage) {
+	if msg == nil {
+		rtm.Debugln("Error: Attempted to SendMessage(nil)")
+		return
+	}
+
+	rtm.outgoingMessages <- *msg
+}
+
+func (rtm *RTM) resetDeadman() {
+	rtm.pingDeadman.Reset(deadmanDuration(rtm.pingInterval))
+}
+
+func deadmanDuration(d time.Duration) time.Duration {
+	return d * 4
+}