Improve end session event

Amplitude/AMPDatabaseHelper.m

@@ -386,16 +386,9 @@ - (NSMutableArray*)getEventsFromTable:(NSString*) table upToId:(long long) upToI
                 continue;
             }
             NSString *eventString = [NSString stringWithUTF8String:rawEventString];
-            if ([AMPUtils isEmptyString:eventString]) {
-                AMPLITUDE_LOG(@"Ignoring empty event string for event id %lld from table %@", eventId, table);
-                continue;
-            }
-
-            NSData *eventData = [eventString dataUsingEncoding:NSUTF8StringEncoding];
-            NSError *error = nil;
-            id eventImmutable = [NSJSONSerialization JSONObjectWithData:eventData options:0 error:&error];
-            if (error != nil) {
-                AMPLITUDE_LOG(@"Error JSON deserialization of event id %lld from table %@: %@", eventId, table, error);
+            NSDictionary *eventImmutable = [AMPUtils deserializeEventString:eventString];
+            if (eventImmutable == nil) {
+                AMPLITUDE_LOG(@"Failed to deserialize event from table %@", table);
                 continue;
             }
 

Amplitude/AMPUtils.h

@@ -12,5 +12,6 @@
 + (id) makeJSONSerializable:(id) obj;
 + (BOOL) isEmptyString:(NSString*) str;
 + (NSDictionary*) validateGroups:(NSDictionary*) obj;
++ (NSDictionary*) deserializeEventString:(NSString*) eventString;
 
 @end

Amplitude/AMPUtils.m

@@ -141,4 +141,20 @@ + (NSDictionary *) validateGroups:(NSDictionary *) obj
     return [NSDictionary dictionaryWithDictionary:dict];
 }
 
++ (NSDictionary *) deserializeEventString:(NSString *)eventString
+{
+    if ([self isEmptyString:eventString]) {
+        return nil;
+    }
+
+    NSData *eventData = [eventString dataUsingEncoding:NSUTF8StringEncoding];
+    NSError *error = nil;
+    id event = [NSJSONSerialization JSONObjectWithData:eventData options:0 error:&error];
+    if (error != nil) {
+        AMPLITUDE_LOG(@"Error JSON deserialization of event: %@", error);
+        return nil;
+    }
+    return event;
+}
+
 @end

Amplitude/Amplitude.m

@@ -628,6 +628,8 @@ - (void)logEvent:(NSString*) eventType withEventProperties:(NSDictionary*) event
         }
         if ([eventType isEqualToString:IDENTIFY_EVENT]) {
             (void) [self.dbHelper addIdentify:jsonString];
+        } else if ([eventType isEqualToString:kAMPSessionEndEvent]) {
+            (void) [self.dbHelper insertOrReplaceKeyValue:kAMPSessionEndEvent value:jsonString];
         } else {
             (void) [self.dbHelper addEvent:jsonString];
         }
@@ -1102,6 +1104,7 @@ - (void)enterBackground
     [self runOnBackgroundQueue:^{
         _inForeground = NO;
         [self refreshSessionTime:now];
+        [self sendSessionEvent:kAMPSessionEndEvent timestamp:now];
         [self uploadEventsWithLimit:0];
     }];
 }
@@ -1151,29 +1154,45 @@ - (BOOL)startOrContinueSession:(NSNumber*) timestamp
 - (void)startNewSession:(NSNumber*) timestamp
 {
     if (_trackingSessionEvents) {
-        [self sendSessionEvent:kAMPSessionEndEvent];
+
+        // try to load saved end session event from key value table, else fall back to re-logging
+        NSNumber *lastEventTime = [self lastEventTime];
+        NSString *endSessionEventString = [self.dbHelper getValue:kAMPSessionEndEvent];
+        if ([AMPUtils isEmptyString:endSessionEventString]) {
+            [self sendSessionEvent:kAMPSessionEndEvent timestamp:lastEventTime];
+        } else {
+            // sanity check the event
+            NSNumber *endSessionTimestamp = nil;
+            NSDictionary *endSessionEvent = [AMPUtils deserializeEventString:endSessionEventString];
+            if (endSessionEvent != nil) {
+                endSessionTimestamp = [endSessionEvent objectForKey:@"timestamp"];
+            }
+            if (endSessionEvent == nil || endSessionTimestamp == nil || [endSessionTimestamp longLongValue] != [lastEventTime longLongValue]) {
+                [self sendSessionEvent:kAMPSessionEndEvent timestamp:lastEventTime];
+            }
+        }
+
+        // transfer end session event from key value table into the event queue
+        endSessionEventString = [self.dbHelper getValue:kAMPSessionEndEvent];
+        if (![AMPUtils isEmptyString:endSessionEventString]) {
+            [self.dbHelper addEvent:endSessionEventString];
+            [self.dbHelper insertOrReplaceKeyValue:kAMPSessionEndEvent value:nil];
+        }
     }
     [self setSessionId:[timestamp longLongValue]];
     [self refreshSessionTime:timestamp];
     if (_trackingSessionEvents) {
-        [self sendSessionEvent:kAMPSessionStartEvent];
+        [self sendSessionEvent:kAMPSessionStartEvent timestamp:timestamp];
     }
 }
 
-- (void)sendSessionEvent:(NSString*) sessionEvent
+- (void)sendSessionEvent:(NSString*) sessionEvent timestamp:(NSNumber *) timestamp
 {
-    if (_apiKey == nil) {
-        AMPLITUDE_ERROR(@"ERROR: apiKey cannot be nil or empty, set apiKey with initializeApiKey: before sending session event");
-        return;
-    }
-
-    if (![self inSession]) {
+    if (_apiKey == nil || ![self inSession]) {
         return;
     }
 
-    NSMutableDictionary *apiProperties = [NSMutableDictionary dictionary];
-    [apiProperties setValue:sessionEvent forKey:@"special"];
-    NSNumber* timestamp = [self lastEventTime];
+    NSDictionary *apiProperties = [NSDictionary dictionaryWithObject:sessionEvent forKey:@"special"];
     [self logEvent:sessionEvent withEventProperties:nil withApiProperties:apiProperties withUserProperties:nil withGroups:nil withTimestamp:timestamp outOfSession:NO];
 }
 

AmplitudeTests/SessionTests.m

@@ -17,6 +17,7 @@
 #import "Amplitude.h"
 #import "Amplitude+Test.h"
 #import "BaseTestCase.h"
+#import "AMPUtils.h"
 
 @interface SessionTests : BaseTestCase
 
@@ -150,6 +151,8 @@ - (void)testEnterBackgroundDoesNotTrackEvent {
 }
 
 - (void)testTrackSessionEvents {
+    AMPDatabaseHelper *dbHelper = [AMPDatabaseHelper getDatabaseHelper];
+
     id mockAmplitude = [OCMockObject partialMockForObject:self.amplitude];
     NSDate *date = [NSDate dateWithTimeIntervalSince1970:1000];
     [[[mockAmplitude expect] andReturnValue:OCMOCK_VALUE(date)] currentTime];
@@ -201,6 +204,83 @@ - (void)testTrackSessionEvents {
     [mockAmplitude identify:identify outOfSession:YES];
     [mockAmplitude flushQueue];
     XCTAssertEqual([mockAmplitude queuedEventCount], 5); // does not trigger session events
+
+    // test new end session logic -> go to background
+    NSDate *date5 = [NSDate dateWithTimeIntervalSince1970:1000 + 4 * self.amplitude.minTimeBetweenSessionsMillis];
+    [[[mockAmplitude expect] andReturnValue:OCMOCK_VALUE(date5)] currentTime];
+    [mockAmplitude enterBackground]; // simulate app entering background
+    [mockAmplitude flushQueue];
+    XCTAssertEqual([mockAmplitude queuedEventCount], 5); // no actual events logged
+
+    // verify end session event is added to key value table
+    NSString *endSessionEventString = [dbHelper getValue:kAMPSessionEndEvent];
+    XCTAssertFalse([AMPUtils isEmptyString:endSessionEventString]);
+    NSDictionary *endSessionEvent = [AMPUtils deserializeEventString:endSessionEventString];
+    XCTAssertNotNil(endSessionEvent);
+    NSNumber *endSessionTimestamp = [endSessionEvent objectForKey:@"timestamp"];
+    NSNumber *expectedTimestamp = [NSNumber numberWithLongLong:[date5 timeIntervalSince1970] * 1000];
+    XCTAssertEqualObjects(expectedTimestamp, endSessionTimestamp);
+
+    // verify that the end session event sent is loaded from key value table
+    // we can modify the value in the database and verify the modified event is the one that is sent
+    // adding a value for version_name
+    endSessionEventString = @"{\"uuid\":\"CC83932C-7520-4AAD-BC95-8E59D30057D6\",\"device_manufacturer\":\"Apple\",\"library\":{\"name\":\"amplitude-ios\",\"version\":\"3.11.1\"},\"event_type\":\"session_end\",\"os_name\":\"ios\",\"sequence_number\":10,\"timestamp\":1201000000,\"event_properties\":{},\"api_properties\":{\"special\":\"session_end\",\"ios_idfv\":\"AFD750D7-1A23-44AB-A091-673A6229647A\"},\"groups\":{},\"user_properties\":{},\"platform\":\"iOS\",\"language\":\"English\",\"device_id\":\"AFD750D7-1A23-44AB-A091-673A6229647A\",\"os_version\":\"10.1\",\"session_id\":601000000,\"device_model\":\"Simulator\",\"country\":\"United States\",\"version_name\":\"test_version\"}";
+    [dbHelper insertOrReplaceKeyValue:kAMPSessionEndEvent value:endSessionEventString];
+
+    // force app to foreground and verify new session logic
+    NSDate *date6 = [NSDate dateWithTimeIntervalSince1970:1000 + 5 * self.amplitude.minTimeBetweenSessionsMillis];
+    [[[mockAmplitude expect] andReturnValue:OCMOCK_VALUE(date6)] currentTime];
+    [mockAmplitude enterForeground];
+    [mockAmplitude flushQueue];
+    XCTAssertEqual([mockAmplitude queuedEventCount], 7); // end and start session events logged
+
+    NSArray *events = [dbHelper getEvents:-1 limit:-1];
+    XCTAssertEqual([events count], 7);
+    endSessionEvent = [events objectAtIndex:5];
+    XCTAssertEqualObjects([endSessionEvent objectForKey:@"event_type"], kAMPSessionEndEvent);
+    XCTAssertEqualObjects([endSessionEvent objectForKey:@"timestamp"], expectedTimestamp);
+    XCTAssertEqualObjects([endSessionEvent objectForKey:@"version_name"], @"test_version");
+    XCTAssertNil([dbHelper getValue:kAMPSessionEndEvent]);
+
+    // the start session event should be missing the version_name
+    expectedTimestamp = [NSNumber numberWithLongLong:[date6 timeIntervalSince1970] * 1000];
+    NSDictionary *startSessionEvent = [events objectAtIndex:6];
+    XCTAssertEqualObjects([startSessionEvent objectForKey:@"event_type"], kAMPSessionStartEvent);
+    XCTAssertEqualObjects([startSessionEvent objectForKey:@"timestamp"], expectedTimestamp);
+    XCTAssertNil([startSessionEvent objectForKey:@"version_name"]);
+
+    // test new session logic -> verify saved end session event is discarded if the timestamp does not match
+    // the start session event logged at date6 should have updated the lastEventTime
+    [[[mockAmplitude expect] andReturnValue:OCMOCK_VALUE(date6)] currentTime];
+    [mockAmplitude enterBackground]; // simulate app entering background
+    [mockAmplitude flushQueue];
+    XCTAssertEqual([mockAmplitude queuedEventCount], 7); // no actual events logged
+
+    // if we try to re-send our modified endSessionEventString with date5, it should discard it and log a new one
+    endSessionEventString = @"{\"uuid\":\"CC83932C-7520-4AAD-BC95-8E59D30057D6\",\"device_manufacturer\":\"Apple\",\"library\":{\"name\":\"amplitude-ios\",\"version\":\"3.11.1\"},\"event_type\":\"session_end\",\"os_name\":\"ios\",\"sequence_number\":10,\"timestamp\":1201000000,\"event_properties\":{},\"api_properties\":{\"special\":\"session_end\",\"ios_idfv\":\"AFD750D7-1A23-44AB-A091-673A6229647A\"},\"groups\":{},\"user_properties\":{},\"platform\":\"iOS\",\"language\":\"English\",\"device_id\":\"AFD750D7-1A23-44AB-A091-673A6229647A\",\"os_version\":\"10.1\",\"session_id\":601000000,\"device_model\":\"Simulator\",\"country\":\"United States\",\"version_name\":\"test_version\"}";
+    [dbHelper insertOrReplaceKeyValue:kAMPSessionEndEvent value:endSessionEventString];
+
+    // force app to foreground and verify new session logic
+    NSDate *date7 = [NSDate dateWithTimeIntervalSince1970:1000 + 6 * self.amplitude.minTimeBetweenSessionsMillis];
+    [[[mockAmplitude expect] andReturnValue:OCMOCK_VALUE(date7)] currentTime];
+    [mockAmplitude enterForeground];
+    [mockAmplitude flushQueue];
+    XCTAssertEqual([mockAmplitude queuedEventCount], 9); // end and start session events logged
+
+    events = [dbHelper getEvents:-1 limit:-1];
+    XCTAssertEqual([events count], 9);
+    endSessionEvent = [events objectAtIndex:7];
+    XCTAssertEqualObjects([endSessionEvent objectForKey:@"event_type"], kAMPSessionEndEvent);
+    XCTAssertEqualObjects([endSessionEvent objectForKey:@"timestamp"], expectedTimestamp);
+    XCTAssertNil([endSessionEvent objectForKey:@"version_name"]);  // should be missing the version_name since a brand new end session event is logged
+    XCTAssertNil([dbHelper getValue:kAMPSessionEndEvent]);
+
+    // the start session event should be missing the version_name
+    startSessionEvent = [events objectAtIndex:8];
+    XCTAssertEqualObjects([startSessionEvent objectForKey:@"event_type"], kAMPSessionStartEvent);
+    XCTAssertEqualObjects([startSessionEvent objectForKey:@"timestamp"], [NSNumber numberWithLongLong:[date7 timeIntervalSince1970] * 1000]);
+    XCTAssertNil([startSessionEvent objectForKey:@"version_name"]);
+
 }
 
 - (void)testSessionEventsOn32BitDevices {