From 73e0216f78f109b784aaea137e0fd0a840befe37 Mon Sep 17 00:00:00 2001
From: Kegan Dougal <kegan@matrix.org>
Date: Fri, 4 Dec 2015 17:27:16 +0000
Subject: [PATCH] Scrollback improvements

Add a 3s delay between scrollback requests if the previous scrollback request
failed.

Return the same promise if scrollback() is called multiple times whilst a
scrollback request is ongoing.
---
 lib/client.js        | 33 ++++++++++++++++++++++++++++++++-
 spec/mock-request.js |  7 +++++++
 2 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/lib/client.js b/lib/client.js
index cfdeb4b2a..264b14cce 100644
--- a/lib/client.js
+++ b/lib/client.js
@@ -19,6 +19,7 @@ var webRtcCall = require("./webrtc/call");
 var utils = require("./utils");
 var contentRepo = require("./content-repo");
 
+var SCROLLBACK_DELAY_MS = 3000;
 var CRYPTO_ENABLED = false;
 
 try {
@@ -155,6 +156,7 @@ function MatrixClient(opts) {
     this._syncingRetry = null;
     this._guestRooms = null;
     this._isGuest = false;
+    this._ongoingScrollbacks = {};
 }
 utils.inherits(MatrixClient, EventEmitter);
 
@@ -1767,6 +1769,12 @@ MatrixClient.prototype.roomState = function(roomId, callback) {
 
 /**
  * Retrieve older messages from the given room and put them in the timeline.
+ *
+ * If this is called multiple times whilst a request is ongoing, the <i>same</i>
+ * Promise will be returned. If there was a problem requesting scrollback, there
+ * will be a small delay before another request can be made (to prevent tight-looping
+ * when there is no connection).
+ *
  * @param {Room} room The room to get older messages in.
  * @param {Integer} limit Optional. The maximum number of previous events to
  * pull in. Default: 30.
@@ -1779,6 +1787,16 @@ MatrixClient.prototype.roomState = function(roomId, callback) {
 MatrixClient.prototype.scrollback = function(room, limit, callback) {
     if (utils.isFunction(limit)) { callback = limit; limit = undefined; }
     limit = limit || 30;
+    var timeToWaitMs = 0;
+
+    var info = this._ongoingScrollbacks[room.roomId] || {};
+    if (info.promise) {
+        return info.promise;
+    }
+    else if (info.errorTs) {
+        var timeWaitedMs = Date.now() - info.errorTs;
+        timeToWaitMs = Math.max(SCROLLBACK_DELAY_MS - timeWaitedMs, 0);
+    }
 
     if (room.oldState.paginationToken === null) {
         return q(room); // already at the start.
@@ -1801,8 +1819,16 @@ MatrixClient.prototype.scrollback = function(room, limit, callback) {
         dir: 'b'
     };
     var defer = q.defer();
+    info = {
+        promise: defer.promise,
+        errorTs: null
+    };
     var self = this;
-    this._http.authedRequest(callback, "GET", path, params).done(function(res) {
+    // wait for a time before doing this request
+    // (which may be 0 in order not to special case the code paths)
+    q.delay(timeToWaitMs).then(function() {
+        return self._http.authedRequest(callback, "GET", path, params);
+    }).done(function(res) {
         var matrixEvents = utils.map(res.chunk, _PojoToMatrixEventMapper(self));
         room.addEventsToTimeline(matrixEvents, true);
         room.oldState.paginationToken = res.end;
@@ -1810,10 +1836,15 @@ MatrixClient.prototype.scrollback = function(room, limit, callback) {
             room.oldState.paginationToken = null;
         }
         self.store.storeEvents(room, matrixEvents, res.end, true);
+        self._ongoingScrollbacks[room.roomId] = null;
         _resolve(callback, defer, room);
     }, function(err) {
+        self._ongoingScrollbacks[room.roomId] = {
+            errorTs: Date.now()
+        };
         _reject(callback, defer, err);
     });
+    this._ongoingScrollbacks[room.roomId] = info;
     return defer.promise;
 };
 
diff --git a/spec/mock-request.js b/spec/mock-request.js
index 9a541b757..867e4eb1c 100644
--- a/spec/mock-request.js
+++ b/spec/mock-request.js
@@ -28,6 +28,7 @@ HttpBackend.prototype = {
         var defer = q.defer();
         var self = this;
         var flushed = 0;
+        var triedWaiting = false;
         console.log(
             "HTTP backend flushing... (path=%s  numToFlush=%s)", path, numToFlush
         );
@@ -49,6 +50,12 @@ HttpBackend.prototype = {
                     setTimeout(tryFlush, 0);
                 }
             }
+            else if (flushed === 0 && !triedWaiting) {
+                // we may not have made the request yet, wait a generous amount of
+                // time before giving up.
+                setTimeout(tryFlush, 5);
+                triedWaiting = true;
+            }
             else {
                 console.log("  no more flushes. [%s]", path);
                 defer.resolve();