Allow app to control reconnection behavior

R/shiny.R

@@ -241,6 +241,15 @@ workerId <- local({
 #'   This is the request that was used to initiate the websocket connection
 #'   (as opposed to the request that downloaded the web page for the app).
 #' }
+#' \item{allowReconnect(value)}{
+#'   If \code{value} is \code{TRUE}, this tells the browser that, if the
+#'   session ends due to the network connection closing, attempt to reconnect
+#'   to the server. If a reconnection is successful, the browser will send all
+#'   the current input values to the new session on the server, and the server
+#'   will recalculate any outputs and send them back to the client. If
+#'   \code{value} is \code{FALSE}, reconnections will be disabled (this is the
+#'   default state).
+#' }
 #' \item{sendCustomMessage(type, message)}{
 #'   Sends a custom message to the web page. \code{type} must be a
 #'   single-element character vector giving the type of message, while
@@ -530,6 +539,14 @@ ShinySession <- R6Class(
     setShowcase = function(value) {
       private$showcase <- !is.null(value) && as.logical(value)
     },
+
+    allowReconnect = function(value) {
+      if (!(identical(value, TRUE) || identical(value, FALSE))) {
+        stop("value must be TRUE or FALSE")
+      }
+      private$write(toJSON(list(allowReconnect = value)))
+    },
+
     defineOutput = function(name, func, label) {
       "Binds an output generating function to this name. The function can either
       take no parameters, or have named parameters for \\code{name} and

man/session.Rd

@@ -85,6 +85,15 @@
   This is the request that was used to initiate the websocket connection
   (as opposed to the request that downloaded the web page for the app).
 }
+\item{allowReconnect(value)}{
+  If \code{value} is \code{TRUE}, this tells the browser that, if the
+  session ends due to the network connection closing, attempt to reconnect
+  to the server. If a reconnection is successful, the browser will send all
+  the current input values to the new session on the server, and the server
+  will recalculate any outputs and send them back to the client. If
+  \code{value} is \code{FALSE}, reconnections will be disabled (this is the
+  default state).
+}
 \item{sendCustomMessage(type, message)}{
   Sends a custom message to the web page. \code{type} must be a
   single-element character vector giving the type of message, while

srcjs/shinyapp.js

@@ -17,6 +17,8 @@ var ShinyApp = function() {
   this.$pendingMessages = [];
   this.$activeRequests = {};
   this.$nextRequestId = 0;
+
+  this.$allowReconnect = false;
 };
 
 (function() {
@@ -74,6 +76,13 @@ var ShinyApp = function() {
 
       var ws = new WebSocket(protocol + '//' + window.location.host + defaultPath);
       ws.binaryType = 'arraybuffer';
+
+      // This flag indicates that reconnections are permitted by the server.
+      // When Shiny is running with Shiny Server, this flag will be present
+      // only on versions of SS that support reconnects. When running Shiny
+      // locally, this is set to true, because the "server" always permits
+      // reconnection.
+      ws.allowReconnect = true;
       return ws;
     };
 
@@ -118,7 +127,12 @@ var ShinyApp = function() {
       }
 
       self.$removeSocket();
-      self.$scheduleReconnect();
+
+      // To try a reconnect, both the app (self.$allowReconnect) and the
+      // server (socket.allowReconnect) must allow reconnections.
+      if (self.$allowReconnect === true && socket.allowReconnect === true) {
+        self.$scheduleReconnect();
+      }
     };
     return socket;
   };
@@ -563,6 +577,13 @@ var ShinyApp = function() {
     }
   });
 
+  addMessageHandler('allowReconnect', function(message) {
+    if (!(message === true || message === false)) {
+      throw "Invalid value for allowReconnect: " + message;
+    }
+    this.$allowReconnect = message;
+  });
+
   addMessageHandler('custom', function(message) {
     // For old-style custom messages - should deprecate and migrate to new
     // method