Timer on server side in Rails - ruby-on-rails

What am trying to achieve is:
1. User pressess button and starts time-limited form.
2. Timer starts.
3. After X time when timer reaches 0 and user did not finish the form, rails create a record in database and do some session cleaning actions (Model.create and session.delete).
This timer will work like safety measure if user starts the form and then becomes unavailable (closes web brower or shuts PC).
Could you point to me to right direction? Where I should start? What language/framework should I use to do that?

You can use timestamps to record when something happened. Rails already has a great example of this in the updated_at and created_at fields.
You can re-use this concept to store when the user first started filling out the form, perhaps on the resource's new route, which usually coincides with the opening of the form.
As for performing the cleanup, you have two options that would could even both work together, depending on the situation:
If the cleanup isn't security-sensitive, you could have a timer kick off on the front-end and then send an AJAX request to the back-end when it expires.
If the cleanup isn't time-sensitive, you could run a task every few minutes or so, which performs the cleanup on any forms that haven't been cleaned up yet. It would look at the timestamps to determine this.
Aside from those suggestions, we'd have to know more about your use cases to answer more questions.
Is the cleanup time-sensitive?
Is the cleanup security-sensitive?
There are more options - you could run the task more granularly or more securely.
Tight timing
One option if your timing is very tight (down to seconds) is to implement both options above, and in addition the following functionality:
Use ActionCable to keep a web socket open with the user. Periodically have them ping the server to check their status.
In a before_filter, probably in ApplicationController, check first if they have permission to continue the action, i.e. the timestamp hasn't expired yet. If the timestamp has expired, and the cleanup hasn't been performed yet, then perform it now.
Limitations of this approach:
If the user closes the website entirely, the cleanup is not going to happen until the next cleanup task happens.
There are vulnerabilities on the front-end. The user can disable the front-end checks, and then avoid submitting the form, which will delay the cleanup in the same way as #1.

Related

How to handle skipWaiting and lazyloaded resources

So this is something I've been racking my brain about a bit, consider the following scenario:
I'm working on my project, I build it, and in my bundle is a lazyloaded module: module-a-[oldhash].js, that will get lazyloaded at some point in time.
Everything is fine and dandy.
I do some more work on my project, create a new bundle, deploy, and now my content hash has changed: module-a-[newhash].js. I deploy, go to my page, my service worker calls skipWaiting, but my page still tries to request module-a-[oldhash].js, which now no longer exists.
How do I go about this? The only way that I can think of handling this, is show an 'update available' message that posts a skipWaiting message to the service worker, and reloads the page on controllerchange event. But I'm curious if theres no way to achieve to same thing without having to include such a notification/toast pattern and a reload.
Additionally, its my understanding that this would only pose a problem with lazyloaded resources
Is my understanding of these problems correct? What are some common patterns for dealing with this?
Pretty much everything you describe there is correct. I'll just point out that this is a problem that extends beyond the use of a service worker. It can easily happen with long-lived single page apps that attempt to lazy-load a URL that has been replaced server-side with a new deployment.
There's some general information about the problem and potential solutions collected on at this Paying Attention while Loading Lazily site and associated video.
In general, the best practice is to:
Always assume that lazy-loading might fail (for whatever reason) and handle those failures gracefully. One approach might be to ask a user to reload the page upon encountering a failure.
Using a cache-first service worker can help protect against lazy-loading failures, at the expense of delaying updates until the newly installed service worker moves from waiting to active. As you mentioned, the best practice tends to be to show something in your UI letting a user know that updates are available, and once they opt-in to accepting those updates, postMessage() to the service worker telling it to call skipWaiting(). And finally, listening for the controllerchange event and calling window.location.reload() when that's fired.

How to dispaly a holding screen whilst ActiveJob retrieves lots of data from an external API

I have an application that makes API requests to salesforce using restforce.
Specifically the application finds a contact object, returns IDs for all related objects and then pulls the full record for every related object based on their ID.
This takes a long time for two reasons:
There are a lot of request to an external API, usually takes a few fractions of a second for each to reply and for some there can be +500 individual requests.
There is often a large amount of data being pulled back via each request.
All requests currently fall within the salesforce rest API limits but I'm getting timeout errors from my development server as it can take 5+ minutes for some of these requests to process.
Rails 4.2 - How best to handle this?
My question is how do I best get rails to handle this?
I can fire the API requests either from the controller (which definitely violates the skinny controllers) or from the view (via helper methods, which seems like a dodgy hack).
Ideally I'd like to get it running in a background job, but i'm unsure if I can just include all the authentication and other methods in a job in the same way I can include helper methods?
Even if I could get it to work in a background job, I'm unsure what best practice might be for the user experience. Ideally I'd like to route them to a page telling them to "hang tight, go get a coffee" with a progress bar, and then auto route them to the final page once the request is complete...
But I'm unsure how to generate a temporary display until a job has been completed?
Could anyone recommend any gems or strategies that might help me digest this problem?
You should definitely use a background job for this.
Give a database object to the job, which it will update to signal that is has finished, and maybe from time to time to indicate progress.
On the user side, simply tell them that the background job is working, with eventually a progress indicator, and display the result once the database object giving to the job tells you it's ready.

Background processing in Rails

A certain function in my controller takes a lot of time to process (heavy db work) . So when my user clicks on "submit" on the form he has to wait for the process to complete which is quite long. Is there any way that on "submitting", the user is redirected to the next view without any delay while the processing continues in the back-end without making the user wait ?
Thanks & Cheers !
When the user's request is made, queue up the job and then redirect the request where you want it.
There are two popular Ruby Gems for job processing:
Delayed Job
Resque
Delayed job is probably the easier to setup since it does not require Redis.
For things like this, I usually dump things into a database queue, and then use a cronjob to actually run it.
For instance, say I had to send out an email to all the clients using the software. I'd put the message into a database table, along with some information about who should get it, and then a cron job would actually do the sending.
It sounds to me that you need to fork the process that takes so long.
For example:
fork { "this code is being ran in background" }
The problem is that this code won't work nice with sql since the connection is not persistent. To handle this problem I've been using the spawn plugin for a while with excelent results.

Showing status of current request by AJAX

I'm trying to develop an application which modifies a couple of tasks of the famous Online-TODO List RememberTheMilk (rememberthemilk.com) using the REST API.
Unfortunately the modifying takes a lot of time, so I want to give a feedback to the users.
My idea was just to display a couple of text lines (e.g. modifying task 1 of n...).
Therefore I used the periodically_call_remote on my page and called a which reads a Singleton.
In the request I store the text that should be displayed in the same singleton. But I found out, that once I set up a request, the periodically_call_remote does not update the specified div.
My question to this:
1. is this a good way to implement this behaviour?
2. if it is, how do get the periodically_call_remote to work during a submit?
Using a Singleton is most definitely a bad idea. In an advanced production setup it isn't guaranteed that subsequent requests will go to the same process or to the same machine (and subsequently will have a different Singleton). Plus, if you have many users, I don't even want to think about what'll happen to those poor Singletons.
Does any of this stuff actually need to go through your Rails app? It seems like you can call the RTM API via Javascript from the page the user is on and then update the page when the XHR request is complete.

How to go about sending email x hours after a user signs up in Ruby on Rails?

How would I go about sending an email to a user, say, 48 hours after they sign up, in Ruby on Rails? Thanks!
As Joseph Daigle mentioned, you need to obviously record the exact date and time the user registered. After that, you need a cron running every certain number of minutes (every hour, for example) checking to see if there's any new users whose registration time is greater than 48 hours, send a mail to said user and mark that user as already emailed, so you don't email them again.
As per the actual mail sending, check out the following documentation page:
http://wiki.rubyonrails.org/rails/pages/HowToSendEmailsWithActionMailer
It has all you need to know to send mails with RoR.
I recommend that you use the latest version of BackgrounDRb to handle this. You can read about BackgrounDRb here: http://backgroundrb.rubyforge.org/
In order to queue a message for later delivery, the BackgrounDRb client code (in your application model's after_create callback, maybe) could look something like this:
MiddleMan(:email_worker).enq_send_email_task(:message => #message,
:job_key => "notify1",
:scheduled_at => Time.now + 48.hours)
You'd have to build a BackgrounDRb worker to handle sending the email:
# RAILS_ROOT/lib/workers/email_worker.rb
class EmailWorker < BackgrounDRb::MetaWorker
set_worker_name :email_worker
def send_email_task(message)
# ... Code to send the email message
end
end
Note that in order to use BackgrounDRb in this way, you have to use persistent job queues, so make sure you run the migration included with BackgrounDRb to set up the persistence table in your application.
BackgrounDRb is started separately from Rails (mongrel, apache, etc) using 'script/backgroundrb start', so make sure that you add the daemon to whatever process monitoring you're using (god, monit, etc) or that you create an /etc/init.d script for it.
First you're going to need a running daemon or background service which can poll your queue (probably from in a database) every few minutes.
The algorithm is pretty simple. Record the time of the user event in the queue. When the daemon checks that item in the queue, and the time difference is greater than 48 hours, prepare the e-mail to send.
You can queue jobs with a delay using async observer. Ideally, anything you have that isn't known to be instant (or very close to it) all the time should pass through something like that.
I wrote a plugin called acts_as_scheduled that may help you out.
acts_as_scheduled allows you to manage
scheduled events for your models.
A good example of this is scheduling
the update of RSS Feeds in a
background process using Cron or
BackgroundRB.
With acts_as_scheduled your schedule
manager can simply call
"Model.find_next_scheduled()" to grab
the next item from the database.
How I would approach this is by creating a scheduling controller, that will query the database for the next_scheduled and then use a mailer to send the message. The you set up a Cron Job to call the controller periodically using WGET or CURL. The advantage of the Cron/Controller approach is that no further infrastructure or configuration is required on the server and you avoid complicated threading code.
I think I'd be inclined to store the need for the email and the earliest time after which it should be sent, somewhere separate, then have my things-to-do task look at that. That way I only have to process as many records as there are emails to be sent, rather than examine every user every time, which would either get tedious or require an otherwise probably unnecessary index. As a bonus, if I had other tasks to be performed on some sort of a diarised basis, the same construct would be useful with little modification.

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