I also have a same problem as mentioned here. But, I went ahead with the approach of randomizing my resource so as to maintain the session in multiple tabs/windows. Also, I get carbon message (LINK) in all tabs/windows.
My only concern is, I'm saving chat history using (store.js) in my browser. And if 5 tabs are opened, then message gets saved 5 times. Which is a repeat.
How can I determine to how many tabs/windows the message was sent?
Based on the count I want to apply my logic to save the message only once.
You can count the number of tabs from Javascript because, you are sandbox to your own tab for security reason.
However, what you can do is ensure your client have unique id on the message tag and you can check on write if your message has already been written in your store or not.
Related
In our design we have something of a paradox. We have a database of projects. Each project has a status. We have a REST api to change a project from “Ready” status to “Cleanup” status. Two things must happen.
update the status in the database
send out an email to the approvers
Currently RESTful api does 1, and if that is successful, do 2.
But sometimes the email fails to send. But since (1) is already committed, it is not possible to rollback.
I don't want to send the email prior to commit, because I want to make sure the commit is successful before sending the email.
I thought about undoing step 1, but that is very hard. The status change involves adding new records to the history table, so I need to delete them. And if another person make other changes concurrently, the undo might get messed up.
So what can I do? If (2) fails, should I return “200 OK” to the client?
Seems like the best option is to return “500 Server Error” with error message that says “The project status was changed. However, sending the email to the approvers failed. Please take appropriate action.”
Perhaps I should not try to do 1 + 2 in a single operation? But that just puts the burden on the client, which is worse!
Just some random thoughts:
You can have a notification sent status flag along with a datetime of submission. When an email is successful then it flips, if not then it stays. When changes are submitted then your code iterates through ALL unsent notifications and tries to send. No idea what backend db you are suing but I believe many have the functionality to send emails as well. You could have a scheduled Job (SQL Server Agent for MSSQL) that runs hourly and tries to send if the datetime of the submission is lapsed a certain amount or starts setting off alarms if it fails as well.
If ti is that insanely important then maybe you could integrate a third party service such as sendgrid to run as a backup sending mech. That of course would be more $$ though...
Traditionally I've always separated functions like this into a backend worker process that handles this kind of administrative tasking stuff across many different applications. Some notifications get sent out every morning. Some get sent out every 15 minutes. Some are weekly summaries. If I run into a crash and burn then I light up the event log and we are (lucky/unlucky) enough to have server monitoring tools that alert us on specified application events.
I'm trying to implement chat for my webapp with following features:
When user logs in he should see a number of unread messages (which is both offline messages and "unseen", I will explain "unseen" in next step).
When user is anywhere in the app but on chat window he should be notified that he has a new message. Message should be marked "unseen" and must be added to the count of unread messages.
The first point is quite easily achieved using XEP-0013: Flexible Offline Message Retrieval. So I can retrieve offline messages and when I'm sure user has seen them - I remove them from unread list. But the problem is: how do I achieve same thing for "unseen" messages?
In short what I need is: any message should be marked as offline, unless user sees it and it's removed from the list by explicit request.
Can I achieve that with XMPP and how do I do that?
Thanks in advance.
What you are trying to do is to basically store a counter of unseen stuff in your account. I think you do not need flexible offline retrieval as when you connect the messages would simply become unseen. You thus only have to deal with one case: Unseen.
I will reply from the perspective of ejabberd, that I know better as one of the developer: I would use private storage to store your current state of unseen count and conversation.
I am developing a chat robot that works with private messages on facebook. The person sends a private message to a page that I own, and then I will send an answer for each message.
Everything is working, but I need to be sure facebook won't complain about the amount of messages I will send. This application will receive a lot of interactions at the same time, but in some early tests one of my messages were received like that:
http://cl.ly/image/1C1n0Z2L0R05
I am now using Batch Requests to send all messages, on an interval of 15s.
Do someone know some way to test it with multiple users and multiple messages at the same time? How the process of identification of spam messages work on facebook? How many messages can I send at the same time and in what time range to prevent that kind of behaviour?
Thanks.
There is no set limit or guideline on volume.
But really volume should not be the issue. There's a huge number of factors that is taken into account to determine if a message is spam... too many to discuss here. But you can assume basics: the content of the messages, the volume per user in a given time period, the content variation per user, has this app been flagged as spammy before, by how many users, etc. I would say its reasonable to assume your test user is probably going to be triggered as spammy because you're likely using it far far more than the average user would.
So, in short: it depends entirely on what exactly you're doing every 15 seconds.
Tip (although I cannot verify it): if you are trying to batch send a message to a number of users at once, without them very recently contacting you, you're probably gonna be flagged as spammy.
I'm working on an email client for iOS. Currently I'm using MailCore for IMAP/SMTP interactions. I'm currently working on getting message previews for the inbox view. The only way I can think to do this would be to actually fetch the whole message body (only body for speed) from the server, and then display only a portion of the message. But then I would have to download the whole message again (this time all headers, etc) when the user opens the message. This seems a bit inefficient to me, but I can't figure out another way to approach this. I've considered just downloading the entirety of each message to begin with, but that seems like an abuse of user's mobile data, and it would be slower to populate the inbox with previews. Any thoughts on how to approach message previews?
Also, for the purposes of this question, assume that the message sender name, date, subject and flags are already loaded on the device.
there exists a raw fetch command but am not sure if there exists any wrapper api on top it.
FETCH 2 (BODY[]<0.size>)
for example if you want to fetch first 100 bytes of mail then you can fire a command as
FETCH 2 (BODY[]<0.100>)
I am building an GWT application with lot's of forms. I am using gwt-platform with its dispatch module.
The next step in my mind is to prevent double-submits ON SERVER SIDE. The problem is that I don't know how to do it exactly...
I thought of something like this:
When application loads the server gives some generated token to the client
The server stores the token inside HTTPSession
When the client submits a form it will send the token from (1.) along with the form
The server checks if the sent token == token inside HTTPSession
In the answer to the client it will send a new token
Is it safe to store the token inside HTTPSession? Or should I simply create a HashMap on the server that maps from SESSION_ID to generated token?
Or maybe there is already an implementation of that in GWT or gwt-platform or somewhere else?
Thanks
The question you'll have to ask yourself first is: What is the kind of problem scenario you want to avoid?
The user accidentally (or out of frustration, ...) clicking a button twice.
A resource that is available only once (like a reservation for a certain seat in an airplane) being consumed twice.
Don't just say "I want to avoid both". Even if you do, you'll have to deal with the two problems separately.
Problem 1
This is better solved on the client side (e.g. by disabling the button once it is clicked).
It can also be solved on the server side (by checking sequence numbers or tokens or maybe the hash code of the contents, ...), but I don't really see the point. If the user really wants to submit twice (e.g. by manipulating the JavaScript such that the button doesn't get disabled), then just let them: Problem 1 is not about security.
Problem 2
This must (except in very specific situations) be solved on the server side. It's chiefly about security. But when you think about it, this problem can't be solved by double-submit prevention! Why not?
Let's look at our example: A seat in an airplane must be reserved only once. This can be violated in multiple ways:
By double-submit.
By the same user submitting at the same time e.g. from different browser windows.
By mutliple users trying to reserve at the same time.
The clean way to solve the problem is to check for availability of the seat atomically with reserving the seat. It doesn't really matter, if a violation was caused by double-submit (accidental double-submits are covered by problem 1).
... and Problem 3
If you have implemented some auto-resubmit mechanism, then you might also encounter a third kind of problem:
Let's say the user wants to add an item to his shopping cart. The client submits, and doesn't receive a response from the server before time-out. So it sends again automatically. The server however receives both messages, and tries to process them both - so it adds the item twice to the shopping cart.
The best solution to avoid this in my opinion is generally not to use actions like "add one item to the cart", but "set the target count of items to 1". Again, you could also work with sequence numbers etc.