Can Firebase get accurate time for offline records which have been stored in device when the device's clock has been changed? The device's clock might be changed when the user rebooted the device or when the user adjusts the date time manually.
My case is quite similar to Get actual DateTime of a device in Offline Mode which I can quote here 1) The application can work in online as well as offline. The app has a feature to create and save the NOTES inside the application. Also, When the app gets internet connection, I need to send the NOTES to backend server. I have a field called 'DATECREATED' in each NOTE (the datetime where the actual NOTE was created) ISSUE: If the User has set the DateTime wrongly in the device, My application sends the incorrect DATETIME to server.
I am going to handle the offline issue on Android and IOS platform, so I came out with another possible solution such as get the GPS time, using some sort of background counter, etc. Based on my experiment, the solution are not reliable enough and some might difficult to do. That's why I decided to get the accurate timestamp using Firebase.
I read a reference https://firebase.google.com/docs/database/flutter/offline-capabilities#clock_skew, but I am not quite sure whether it can help me to get accurate time for offline records.
There is no way you can get a server timestamp while offline. Why? Simply because the timestamp is totally generated on the server. And since you're offline and cannot communicate with the server, you cannot get an estimation. So there is no other system that can generate a timestamp other than the Firebase server.
Besides that, a date that can be generated on the client can be manipulated, so you cannot rely on that.
The option that you have in my opinion would be to have two fields. One is for the real timestamp, which you'll be received when you're back online and the other one is what the client provides. In that way, you make a comparison, if this is what you want.
Edit:
Firestore, is a Cloud hosted NoSQL database. So there is no way you can generate an accurate time while the user is offline. What you can certainly do is calculate the period of time while the user is offline. This means that you have to calculate the number of minutes the user has lost connectivity. Let's say a user losses connectivity for 10 minutes, when it regains connectivity, you receive the Firestore timestamp. Now, all you have to do is to subtract those 10 minutes from the received timestamp in order to have the accurate time that you're looking for.
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I have a multi-user single-page mobile app developed with Ionic 1, PouchDB and CouchDB. User's management is achieved with SuperLogin.
I would like to add a feature computing a score (something similar to the score in the Waze app) for each user based on his current data, and keeping a track of the former values of that score every past day.
I am wondering about the best way to implement this.
About my app:
it should be able to work offline, and then sync with the server when online (this is why I am using PouchDB and CouchDB, working great so far). So on the server, I have one CouchDB database per user, storing his own data
on the server. The PouchDB database in the app is syncing with the one of the user on the server.
I am considering various options for the score, but none of them really satisfy me, so your advice would be welcome (possibly for yet another option)
Option 1: The score is computed in the app by the Ionic code. The result is stored as a local database object, with a date and a score value. This happens whenever the user changes its data. As the DB is synced with the server, these scores are updated in the server too. However, if some days the user does not use the application, the score won't be computed for these days. More over, if the user runs the app on 2 different devices, and update some data on one of them, this will make the score recomputed locally, then propagated on the server. When the changed data propagate to the server and to the other device, this will trigger a new score computation on this other device, and might lead to conflicts on the score object in the server. Finally, if at some point in time, I want to change the way of computing the score, the value given to each user will depend on whether he has upgraded to the latest app version.
Option 2: have a server-side process that triggers every day, and compute each user's score by connecting to each user's DB on the server, reading its data, computing the corresponding score, and storing it (date+value) back in the server DB. This option looks cleaner to me, but it would require further developments, and an additional process to maintain and keep alive on the server. And if the user inputs data to the application while not connected to the internet, the score will not be updated in the app until he gets connected again (which would cause the server process to recompute the score, and propagate it back to the app through CouchDB sync)
Option 3: have some kind of "stored procedure" in the CouchDB server, triggering every time related data change, in charge of computing the score of each user. But I don't think this is doable with CouchDB.
So how would you do this score computation please??
Many thanks!
I have a lobby in which I want the users to be in sync. So when a user turns off his internet while the app is running, he should be removed. I know Firebase does not support server side coding, so the coding needs to be client side. The answers from How to delete firebase data after "n" days and Delete firebase data older than 2 hours do not answer this question since they expect that the user is online and they have an internet connection. So my question is if is possible to delete users when they got no internet? I thought maybe it is an idea to let the users update a value every 5 seconds, and when that update is not done, the other users in that lobby remove the player. This way is not good, since every player needs to retrieve and upload alot of data every 5 seconds. What is the best way to solve this?
Edit: to make it short, lets say each user has an image. The image should be green when the user is connected, and grey when disconnected.
Edit 2: after thinking it over, it is really hard to accurate present the connected users on a client-side server. That is why, if nobody has a different solution, I should add another server which can execute server-side codes. Because of the larges amount of servers, I would like to know which server I should use. The server should run a simple function which only checks if the users are connected or disconnected and can communicate with Firebase. If I am correct it should look like this:
But the server also needs to communicate with the users directly. I have absoluty no idea where to start.
If I'm not completely wrong, you should be able to use onDisconnect.
From the Firebase, documentation:
How onDisconnect:Works:
When an onDisconnect() operation is established, it lives on the Firebase Realtime Database server. The server checks security to make sure the user can perform the write event requested, and informs the client if it is invalid. The server then monitors the connection. If at any point it times out, or is actively closed by the client, the server checks security a second time (to make sure the operation is still valid) and then invokes the event.
In app in production I'm using onDisconnectRemoveValue, and when I close the app, the user removes himself from the lobby. Not sure how it works when you turn the device in airplane mode, but from the documentation it seems there should be no problem.
One thing: when you test it better do it on real device, the simulator have issues with turning it off and on, at least the on I have installed.
Edit: So i checked the onDisconnect when you put the device on airplane mode and it works! The question is, that it removes the user in about a 1:30 min, approximately, so if you read the documentation or ask the support, you may be (and only may be) able to find a way to set the time you want.
I am developing an application that must work online and also offline. This application should sync informations with our server. For this, we need that the device utilize the server clock.
I found a lot of information, and I get the following idea:
When the user logins online I will force him to get the server clock time. In this moment he obrigatory must have internet connection, so it is ok.
When I get the clock server time, I get the systemUptime information that says the interval that the device is turned on, and I store it. I can get systemUptime like this:
[NSProcessInfo processInfo].systemUptime
When the user to create a new local file, I will know the current interval based on systemUptime function, so I know the current time, and I don't depend the iOS system clock.
The problem is: Everytime that device is rebooted, or turned off, the systemUptime is reseted. Until here OK, I can solve it forcing the user to login again, and getting the server clock time again. My problem is to know when the device was rebooted. Can you help me? Thank you guys!
My advice would be to not refer to the device time at all. Get the the files from the server and have the server also answer the server time that the files are retrieved. You can store this in the file, in the file name, or separately on the device.
At some point in the future ask the server if there's a file newer than the server time you recorded earlier.
In this sense, the time isn't really a time at all, it's a version number, and you could make that explicit with the server too, using just an integer from the server that indicates progressing sequence of versions.
If it's important that your app be strong in this way, your only choice is to remain independent of device time. Otherwise, there are too many ways it can break (including small time errors due to latency on the time check, or device factory resets or malicious actions by a user). It's better to remain independent of device time if you can.
When you get the systemUptime the first time, subtract it from the current (iOS) date and time. That's the time the system was last brought up.
Then recalculate this value whenever necessary. If the "time the system was last brought up" has changed, then you know it's time to log in again.
However, as suggested by another commenter, I suspect there's a better way to tackle this from scratch.
I am still learning xcode and objective-c. I use to build app for iphone environment only.
However I am in need of realizing an application with an existing prefilled sql database.
For prefilling the database I wouldn't like to use code in the ditributed app, but I would rather prefer to have a separate app for doing that.
The reason is that, the app could only download the updated database, rather than a whole code update .
So, questions are:
is this a possible scenario
if yes, what kind of application
should I build in xcode for
prefilling database ?
thanks
There's no reason that you can't have one app that both uses the database and downloads updates. Keeping the database updated without downloading the whole thing is pretty simple.
If you record the creation and modification timestamps of rows in the database on the server and keep track of those same modification timestamps on the device, updating the database works like this:
The device determines latest modification timestamp it has for a given table. We'll call it latestTimestamp. It sends the latestTimestamp to the server.
The server compares the latestTimestamp to the creation and modification timestamps in the database. The server sends back data based on the comparison result:
If the modification timestamp is earlier than latestTimestamp it doesn't need to send the record, the device already has it;
If the modification timestamp is later than latestTimestamp and the creation timestamp is earlier than latestTimestamp, it sends the record back noting that it is to be updated in the device database;
If the modification timestamp is later than latestTimestamp and the creation timestamp is later than latestTimestamp, it sends the record back noting that it is to be added in the device database.
Lastly, the server database needs to keep track of deleted records and a deletion timestamp for every record recorded. If latestTimestamp is later than the deletion timestamp, it sends back that the record needs to be deleted.
Obviously it gets a bit more complicated when you have a variety of connected tables, but as long as things are sent back in the correct order, it works great.
Use asynchronous data requests (the ASIHTTPRequest library makes it a breeze) and update the data in the background while the user uses the app. If it's essential that the data be updated prior to any interaction with it you can display an activity indicator and have the user wait.
No need at all for a separate app.
I would discourage you from doing that. No matter it is a pre-filled-database-purpose app, or a normal-purpose app, Apple Review Team would treat them with the same procedure, leaving the developer waiting for weeks before that app is finally available on App Store.
Besides, as far as I know, communication between apps is still strictly limited. If the data you would like to transfer between your main app and your db app is larger than a few lines of, let's say, NSString, it might be technically un-plausible.
hi i am making an app in which user sends xml to server and get response....
now i have to save the date and time of sending and response of that request....for this should i use iphone's date or check it online?
because my thinking is that the iphone's date and time may not be correct.....always...so it is better to check the time online ....
i know the local part but need help regarding online check....please help
Just use the local time. It will save you a lot of trouble and work. Or is your app so absolutely dependent on the correct time, like to display the current position of the sun or something ? If not, the local time is likely "good enough".
If you need the same time as the server, then it would seem that you need to establish the offset between server time and local time, and then you can adjust your local timestamp.
Is there a way to get the (current) time from the server?
Assuming the timestamp you're saving is for the request sent from the iphone and the response received by the iphone, then it would actually seem logical to use local (iphone) time.
You could always use NTP (http://en.wikipedia.org/wiki/Network_Time_Protocol) to get the current time, but that doesn't guarantee the time is thesame as the server.
You usually don't need absolute time of some sort, just the same time source as your server and your server's database.
So compare your local time with whatever the server thinks the time is and adjust accordingly.