MXCrypto: Use the last olm session that got a message

With the add MXOlmSession.lastReceivedMessageTs

element-hq/element-ios#2128

Author: manuroe

CHANGES.rst

@@ -1,13 +1,14 @@
 Changes in Matrix iOS SDK in 0.12.1 (2012-12-xx)
 ===============================================
 
+Improvements:
+* MXCrypto: Use the last olm session that got a message (vector-im/riot-ios/issues/2128).
+* MXScanManager: Support the encrypted body (the request body is now encrypted by default using the server public key).
+* MXMediaManager: Support the encrypted body.
+
 Bug Fix:
  * MXCryptoStore: Stop duplicating devices in the store (vector-im/riot-ios/issues/2132).
 
-Improvements:
- * MXScanManager: Support the encrypted body (the request body is now encrypted by default using the server public key).
- * MXMediaManager: Support the encrypted body.
-
 Changes in Matrix iOS SDK in 0.12.0 (2018-12-06)
 ===============================================
 

MatrixSDK/Crypto/Data/MXOlmSession.h

@@ -37,6 +37,18 @@ NS_ASSUME_NONNULL_BEGIN
  */
 @property (nonatomic, readonly) OLMSession *session;
 
+/**
+ Timestamp at which the session last received a message.
+ */
+@property (nonatomic) NSTimeInterval lastReceivedMessageTs;
+
+
+/**
+ Notify this model that a message has been received on this olm session
+ so that it updates `lastReceivedMessageTs`
+ */
+- (void)didReceiveMessage;
+
 @end
 
 NS_ASSUME_NONNULL_END

MatrixSDK/Crypto/Data/MXOlmSession.m

@@ -24,8 +24,14 @@ - (instancetype)initWithOlmSession:(OLMSession *)session
     if (self)
     {
         _session = session;
+        _lastReceivedMessageTs = 0;
     }
     return self;
 }
 
+- (void)didReceiveMessage
+{
+    _lastReceivedMessageTs = [[NSDate date] timeIntervalSince1970];
+}
+
 @end

MatrixSDK/Crypto/Data/Store/MXCryptoStore.h

@@ -202,7 +202,7 @@
 
 /**
  Retrieve all end-to-end sessions between the logged-in user and another
- device.
+ device sorted by `lastReceivedMessageTs`, the most recent(higest value) first.
 
  @param deviceKey the public key of the other device.
  @return a array of end-to-end sessions.

MatrixSDK/Crypto/Data/Store/MXRealmCryptoStore/MXRealmCryptoStore.m

@@ -23,7 +23,7 @@
 #import "MXSession.h"
 #import "MXTools.h"
 
-NSUInteger const kMXRealmCryptoStoreVersion = 8;
+NSUInteger const kMXRealmCryptoStoreVersion = 9;
 
 static NSString *const kMXRealmCryptoStoreFolder = @"MXRealmCryptoStore";
 
@@ -84,6 +84,7 @@ + (NSString *)primaryKey
 @interface MXRealmOlmSession : RLMObject
 @property NSString *sessionId;
 @property NSString *deviceKey;
+@property NSTimeInterval lastReceivedMessageTs;
 @property NSData *olmSessionData;
 @end
 
@@ -621,6 +622,8 @@ - (void)storeSession:(MXOlmSession*)session forDevice:(NSString*)deviceKey
                                                                          @"deviceKey": deviceKey,
                                                                          @"olmSessionData": [NSKeyedArchiver archivedDataWithRootObject:session.session]
                                                                          }];
+            realmOlmSession.lastReceivedMessageTs = session.lastReceivedMessageTs;
+
             [realm addObject:realmOlmSession];
         }
     }];
@@ -634,7 +637,9 @@ - (MXOlmSession*)sessionWithDevice:(NSString*)deviceKey andSessionId:(NSString*)
                                                                       where:@"sessionId = %@ AND deviceKey = %@", sessionId, deviceKey].firstObject;
 
     OLMSession *olmSession = [NSKeyedUnarchiver unarchiveObjectWithData:realmOlmSession.olmSessionData];
+
     MXOlmSession *mxOlmSession = [[MXOlmSession alloc] initWithOlmSession:olmSession];
+    mxOlmSession.lastReceivedMessageTs = realmOlmSession.lastReceivedMessageTs;
 
     return mxOlmSession;
 }
@@ -643,7 +648,9 @@ - (MXOlmSession*)sessionWithDevice:(NSString*)deviceKey andSessionId:(NSString*)
 {
     NSMutableArray<MXOlmSession*> *sessionsWithDevice;
 
-    RLMResults<MXRealmOlmSession *> *realmOlmSessions = [MXRealmOlmSession objectsInRealm:self.realm where:@"deviceKey = %@", deviceKey];
+    RLMResults<MXRealmOlmSession *> *realmOlmSessions = [[MXRealmOlmSession objectsInRealm:self.realm
+                                                                                     where:@"deviceKey = %@", deviceKey]
+                                                         sortedResultsUsingKeyPath:@"lastReceivedMessageTs" ascending:NO];
     for (MXRealmOlmSession *realmOlmSession in realmOlmSessions)
     {
         if (!sessionsWithDevice)
@@ -652,7 +659,9 @@ - (MXOlmSession*)sessionWithDevice:(NSString*)deviceKey andSessionId:(NSString*)
         }
 
         OLMSession *olmSession = [NSKeyedUnarchiver unarchiveObjectWithData:realmOlmSession.olmSessionData];
+
         MXOlmSession *mxOlmSession = [[MXOlmSession alloc] initWithOlmSession:olmSession];
+        mxOlmSession.lastReceivedMessageTs = realmOlmSession.lastReceivedMessageTs;
 
         [sessionsWithDevice addObject:mxOlmSession];
     }
@@ -1203,6 +1212,23 @@ + (RLMRealm*)realmForUser:(NSString*)userId
                     // make queries. So, the cleaning will be done afterwards.
                     cleanDuplicatedDevices = YES;
                 }
+
+                case 8:
+                {
+                    // MXRealmOlmSession.lastReceivedMessageTs has been added to implement:
+                    // Use the last olm session that got a message
+                    // https://github.com/vector-im/riot-ios/issues/2128
+
+                    NSLog(@"[MXRealmCryptoStore] Migration from schema #8 -> #9");
+
+                    NSLog(@"    Add lastReceivedMessageTs = 0 to all MXRealmOlmSession objects");
+                    [migration enumerateObjects:MXRealmOlmSession.className block:^(RLMObject *oldObject, RLMObject *newObject) {
+
+                        newObject[@"lastReceivedMessageTs"] = 0;
+                    }];
+
+                    NSLog(@"[MXRealmCryptoStore] Migration from schema #6 -> #7 completed");
+                }
             }
         }
     };

MatrixSDK/Crypto/MXOlmDevice.m

@@ -149,6 +149,12 @@ - (NSString *)createOutboundSession:(NSString *)theirIdentityKey theirOneTimeKey
     if (olmSession)
     {
         MXOlmSession *mxOlmSession = [[MXOlmSession alloc] initWithOlmSession:olmSession];
+
+        // Pretend we've received a message at this point, otherwise
+        // if we try to send a message to the device, it won't use
+        // this session
+        [mxOlmSession didReceiveMessage];
+
         [store storeSession:mxOlmSession forDevice:theirIdentityKey];
         return olmSession.sessionIdentifier;
     }
@@ -186,6 +192,11 @@ - (NSString*)createInboundSession:(NSString*)theirDeviceIdentityKey messageType:
         }
 
         MXOlmSession *mxOlmSession = [[MXOlmSession alloc] initWithOlmSession:olmSession];
+
+        // This counts as a received message: set last received message time
+        // to now
+        [mxOlmSession didReceiveMessage];
+
         [store storeSession:mxOlmSession forDevice:theirDeviceIdentityKey];
 
         return olmSession.sessionIdentifier;
@@ -213,17 +224,9 @@ - (NSString*)createInboundSession:(NSString*)theirDeviceIdentityKey messageType:
 
 - (NSString *)sessionIdForDevice:(NSString *)theirDeviceIdentityKey
 {
-    NSString *sessionId;
-
-    NSArray<NSString *> *sessionIds = [self sessionIdsForDevice:theirDeviceIdentityKey];
-    if (sessionIds.count)
-    {
-        // Use the session with the lowest ID.
-        NSArray *sortedSessionIds = [sessionIds sortedArrayUsingSelector:@selector(compare:)];
-        sessionId = sortedSessionIds[0];
-    }
-
-    return sessionId;
+    // Use the session that has most recently received a message
+    // This is the first item in the sorted array returned by the store
+    return [store sessionsWithDevice:theirDeviceIdentityKey].firstObject.session.sessionIdentifier;
 }
 
 - (NSDictionary *)encryptMessage:(NSString *)theirDeviceIdentityKey sessionId:(NSString *)sessionId payloadString:(NSString *)payloadString
@@ -272,6 +275,7 @@ - (NSString*)decryptMessage:(NSString*)ciphertext withType:(NSUInteger)messageTy
             NSLog(@"[MXOlmDevice] decryptMessage failed: %@", error);
         }
 
+        [mxOlmSession didReceiveMessage];
         [store storeSession:mxOlmSession forDevice:theirDeviceIdentityKey];
     }