Disconnect client only if Slack disconnect is intentional

If the disconnection from Slack is intentiona, just keep closing the IRC
client connection as previously. However, if the disconnection is not
intentional, it's not necessary to disconnect the IRC client, as the
Slack reconnection will be handled by Slack's RTM.ManageConnection.
This should reduce the amount of disconnect/reconnect on the IRC client
side.

Signed-off-by: Andrea Barberio <insomniac@slackware.it>

Author: insomniacslk

event_handler.go

@@ -319,9 +319,19 @@ func eventHandler(ctx *IrcContext, rtm *slack.RTM) {
 			log.Info("Connected to Slack")
 			ctx.SlackConnected = true
 		case *slack.DisconnectedEvent:
-			log.Warningf("Disconnected from Slack (intentional: %v)", msg.Data.(*slack.DisconnectedEvent).Intentional)
+			de := msg.Data.(*slack.DisconnectedEvent)
+			log.Warningf("Disconnected from Slack (intentional: %v, cause: %s)", de.Intentional, de.Cause)
 			ctx.SlackConnected = false
-			ctx.Conn.Close()
+			// only close the IRC client connection if the disconnection from
+			// Slack was intentional. Otherwise RTM.ManageConnection will retry
+			// automatically to connect. If reconnection fails, it will surface
+			// in a subsequent event, so it's safe here not to wait for a
+			// reconnection.
+			if de.Intentional {
+				if err := ctx.Conn.Close(); err != nil {
+					log.Warningf("Failed to close connection to IRC client: %v", err)
+				}
+			}
 			return
 		case *slack.MemberJoinedChannelEvent, *slack.MemberLeftChannelEvent:
 			// refresh the users list