From 2b623c935446972bbc6122e809640144e1f0d396 Mon Sep 17 00:00:00 2001
From: manuroe <manu@matrix.org>
Date: Thu, 1 Jun 2017 16:10:33 +0200
Subject: [PATCH] Crypto: Fix race in device list updates

Don't consider device lists up-to-date when we have another request for the
relevant user in the queue.

Port of https://github.com/matrix-org/matrix-js-sdk/pull/431
---
 MatrixSDK/Crypto/Data/MXDeviceList.m | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/MatrixSDK/Crypto/Data/MXDeviceList.m b/MatrixSDK/Crypto/Data/MXDeviceList.m
index 7dff6c2be2..6168502807 100644
--- a/MatrixSDK/Crypto/Data/MXDeviceList.m
+++ b/MatrixSDK/Crypto/Data/MXDeviceList.m
@@ -30,6 +30,10 @@ @interface MXDeviceList ()
     // userId -> MXDeviceTrackingStatus*
     NSMutableDictionary<NSString*, NSNumber*> *deviceTrackingStatus;
 
+    // The current request for each user.
+    // userId -> MXDeviceListOperation
+    NSMutableDictionary<NSString*, MXDeviceListOperation*> *keyDownloadsInProgressByUser;
+
     /**
      The pool which the http request is currenlty being processed.
      (nil if there is no current request).
@@ -61,6 +65,8 @@ - (id)initWithCrypto:(MXCrypto *)theCrypto
         // Retrieve tracking status from the store
         deviceTrackingStatus = [NSMutableDictionary dictionaryWithDictionary:[crypto.store deviceTrackingStatus]];
 
+        keyDownloadsInProgressByUser = [NSMutableDictionary dictionary];
+
         for (NSString *userId in deviceTrackingStatus.allKeys)
         {
             // if a download was in progress or failed when we got shut down, it isn't any more.
@@ -102,7 +108,7 @@ - (MXHTTPOperation*)downloadKeys:(NSArray<NSString*>*)userIds forceDownload:(BOO
         }
     }
 
-    MXDeviceListOperation *operation;
+    __block MXDeviceListOperation *operation;
 
     if (usersToDownload.count)
     {
@@ -122,6 +128,16 @@ - (MXHTTPOperation*)downloadKeys:(NSArray<NSString*>*)userIds forceDownload:(BOO
 
             for (NSString *userId in succeededUserIds)
             {
+                // we may have queued up another download request for this user
+                // since we started this request. If that happens, we should
+                // ignore the completion of the first one.
+                if (keyDownloadsInProgressByUser[userId] != operation)
+                {
+                    NSLog(@"[MXDeviceList] downloadKeys: Another update in the queue for %@ - not marking up-to-date", userId);
+                    continue;
+                }
+                [keyDownloadsInProgressByUser removeObjectForKey:userId];
+
                 MXDeviceTrackingStatus trackingStatus = MXDeviceTrackingStatusFromNSNumber(deviceTrackingStatus[userId]);
                 if (trackingStatus == MXDeviceTrackingStatusDownloadInProgress)
                 {
@@ -155,6 +171,11 @@ - (MXHTTPOperation*)downloadKeys:(NSArray<NSString*>*)userIds forceDownload:(BOO
 
         } failure:failure];
 
+        for (NSString *userId in usersToDownload)
+        {
+            keyDownloadsInProgressByUser[userId] = operation;
+        }
+
         if (doANewQuery)
         {
             NSLog(@"[MXDeviceList] downloadKeys: waiting for next key query");