I know this question has been asked before..a lot in fact. But I can't seem to get the wheels turning on this thing. To be honest I'm a bit lost on mating client side and server scripting and the examples I've seen are either far to simplistic or way above my head.
Goal:
My goal is to take a long running process I've writtin in VB.NET on the server, which happens to be loop based, and calculate a percentage complete (I know the range of the index values) and relay that back to the user by some means.
Idea:
As the loop iterates I want to pass back up to the client an integer of percent complete or poll it from the client.
What I've done:
Is very limited, I have little to no experience here, I've been doing a lot of googling and I've played with the UpdatePanel and UpdateProgress controls from AJAX a bit, but this method so far seems to lean towards an idicator, like GIF.
As always any help is appreciated, and if I can answer any questions I will.
Have you considered using an inline frame (iFrame) to host your long running process and report back status to the client via the Response object of the long running .aspx page?
If so, then I suggest you read Easy incremental status updates for long requests.
The example uses a button as the display for the progress after the user clicks it, but you could direct output to another DOM element if you wish.
Related
First - I am having a hard time formulating this question, so please bear with me, and ask for clarification and I'll try to provide as much as I can. I am just starting to learn meteor, so be patient please.
I have several inputs that save immediately as people type on them. (with a slight 300 ms delay to not overload database).
Basically, on "keyup" it goes and saves. All that works fine. However, I'd like to add a visual indicator (say a green checkmark, or a tiny "saved") when the database actually stores what they typed.
Graphically:
[___________________]
[Typed something_____] (saved)
[___________________]
I am not sure how to go about this, but it's something common, that plenty of you have already done. If I didn't care about the database feedback, I'd just use JQuery, target a class beside the input and make the checkmark or word visible after a keyup, or add it to the DOM. Fairly straight forward.The only when I am sure it has been stored in Mongodb part confuses me.
Any help would be gladly appreciated.
Thank you
Addendum with code:
Template.dibs.events({
'keyup input.name': _.throttle(function(event) {
Dibs.update(this._id, {$set: {name: event.target.value}});
$(':focus + .glyphicon-ok').css('opacity',1);
}, 300),
Can you explain where/how you would add the code? (For spinner, or the words).
Coming from JQuery I did something that I know is not the right way. This is in the client portion (I know just demo code, and it's not secure) but I wanted to know the best way leveraging meteor to do it. I already have checkmarks stating it was saved in the page, but they are all hidden, this code just makes them visible on keyup for the field.
I read through the article, and didn't quite see how I'd go about doing the intermediate step (spinner or the like) then the finalized checkmark after code is saved. I've also being going through the new 1.0 tutorial (which is great) but I'm still missing the visual indicators. It's great that meteor updates the UI if it fails in the server to reflect that it didn't save, since I am assuming success, I don't think that tapping into the Meteor.Error makes sense. Should there not be a Meteor.Success or equivalent?
Again, I apologize for the long message, I'm trying to wrap my head around this, because the technology looks very promising
Welcome to Meteor! Meteor was in fact designed (among other things) to handle just this type of situation, via a mechanism called Latency Compensation. You can read more about it at Meteor.methods.
Calling a method on the server requires a round-trip over the network. It would be really frustrating if users had to wait a whole second to see their comment show up due to this delay. That's why Meteor has a feature called method stubs. If you define a method on the client with the same name as a server method, Meteor will run it to attempt to predict the outcome of the server method. When the code on the server actually finishes, the prediction generated on the client will be replaced with the actual outcome of the server method.
You can use Latency Compensation by defining a Meteor method to save the input text to the database, with a client stub that displays a spinner instead of "saved", and "saved" when its callback is called successfully.
Alternatively, you can call the update method on the collection directly, and add a callback on the client, which will be called with (error, numberOfDocsUpdated) after the server method returns.
Read more on when to use Meteor methods and when to use client-side operations.
As Dan has said, the Latency Comp takes care of needing to do this. Another way of doing this is in a template event. You can set a session variable on keyup with the contents of the text field and in the helper, set a flag that will render the checkmark when the session variable and current user input matches.
Is there a way to determine if the request coming to a handler (lets assume the handler responds to get and post) is being performed by a real browser versus a programmatic client?
I already know that it is easy to spoof things like the User Agent and the Referrer, but are there other headers that are more difficult to spoof? Maybe headers that are not commonly available in classes like .net's HttpWebRequest?
The other path that I looked at is maybe using the Encrypted View State to send a value to the browser that gets validated on the server side, though couldn't that value simply be scraped from the previous response and added as a post parameter to the next request?
Any help would be much appreciated,
Cheers,
There is no easy way to differentiate because in the end, a post programitically looks the same to the server as a post by a user from the browser.
As mentioned, captcha's can be used to control posting but are not perfect (as it is very hard but not impossible for a computer to solve them). They also can annoy users.
Another route is only allowing authenticated users to post, but this can also still be done programatically.
If you want to get a good feel for how people are going to try to abuse your site, then you may want to look at http://seleniumhq.org/
This is very similar to the famous Halting Problem in computer science. See some more on the proof, and Alan Turing here: http://webcache.googleusercontent.com/search?q=cache:HZ7CMq6XAGwJ:www-inst.eecs.berkeley.edu/~cs70/fa06/lectures/computability/lec30.ps+alan+turing+infinite+loop+compiler&cd=1&hl=en&ct=clnk&gl=us
The most common way is using captcha's. Of course captcha's have their own issues (users don't really care for them) but they do make it much more difficult to programatically post data. Doesn't really help with GETs though you can force them to solve a captcha before delivering content.
Many ways to do this, like dynamically generated XHR requests that can only be made with human tasks.
Here's a great article on NP-Hard problems. I can see a huge possibility here:
http://www.i-programmer.info/news/112-theory/3896-classic-nintendo-games-are-np-hard.html
One way: You could use some tricky JS to handle tokens on click. So your server issues token-id's to elements on the page during the backend render phase. Log these in a database or data file. Then, when users click around and submit, you can compare the id's sent via the onclick() function. There's plenty of ways around this, but you could apply some heuristics to determine if posts are too fast to be a human or not, that is, even if they scripted the hijacking of the token-ids and auto submitted, you could check that the time between click events appears automated. Signed up for a twitter account lately? They use passive human detection that while not 100% foolproof, it is slower and more difficult to break. Many if not all of the spam accounts there had to be human opened.
Another Way: http://areyouahuman.com/
As long as you are using encrypted methods verifying humanity without crappy CAPTCHA is possible.I mean, don't ignore your headers either. These are complimentary ways.
The key is to have enough complexity to make for an NP-Complete problem in terms of number of ways to solve the total number of problems is extraordinary. http://en.wikipedia.org/wiki/NP-complete
When the day comes when AI can solve multiple complex Human problems on their own, we will have other things to worry about than request tampering.
http://louisville.academia.edu/RomanYampolskiy/Papers/1467394/AI-Complete_AI-Hard_or_AI-Easy_Classification_of_Problems_in_Artificial
Another company doing interesting research is http://www.vouchsafe.com/play-games they actually use games designed to trick the RTT into training the RTT how to be more solvable by only humans!
The Problem
In the stack that we re-use between projects, we are putting a little bit too much data in the session for passing data between pages. This was good in theory because it prevents tampering, replay attacks, and so on, but it creates as many problems as it solves.
Session loss itself is an issue, although it's mostly handled by implementing Session State Server (or by using SQL Server). More importantly, it's tricky to make the back button work correctly, and it's also extra work to create a situation where a user can, say, open the same screen in three tabs to work on different records.
And that's just the tip of the iceberg.
There are workarounds for most of these issues, but as I grind away, all this friction gives me the feeling that passing data between pages using session is the wrong direction.
What I really want to do here is come up with a best practice that my shop can use all the time for passing data between pages, and then, for new apps, replace key parts of our stack that currently rely on Session.
It would also be nice if the final solution did not result in mountains of boilerplate plumbing code.
Proposed Solutions
Session
As mentioned above, leaning heavily on Session seems like a good idea, but it breaks the back button and causes some other problems.
There may be ways to get around all the problems, but it seems like a lot of extra work.
One thing that's very nice about using session is the fact that tampering is just not an issue. Compared to passing everything via the unencrypted QueryString, you end up writing much less guard code.
Cross-Page Posting
In truth I've barely considered this option. I have a problem with how tightly coupled it makes the pages -- if I start doing PreviousPage.FindControl("SomeTextBox"), that seems like a maintenance problem if I ever want to get to this page from another page that maybe does not have a control called SomeTextBox.
It seems limited in other ways as well. Maybe I want to get to the page via a link, for instance.
QueryString
I'm currently leaning towards this strategy, like in the olden days. But I probably want my QueryString to be encrypted to make it harder to tamper with, and I would like to handle the problem of replay attacks as well.
On 4 guys from Rolla, there's an article about this.
However, it should be possible to create an HttpModule that takes care of all this and removes all the encryption sausage-making from the page. Sure enough, Mads Kristensen has an article where he released one. However, the comments make it sound like it has problems with extremely common scenarios.
Other Options
Of course this is not an exaustive look at the options, but rather the main options I'm considering. This link contains a more complete list. The ones I didn't mention such as Cookies and the Cache not appropriate for the purpose of passing data between pages.
In Closing...
So, how are you handling the problem of passing data between pages? What hidden gotchas did you have to work around, and are there any pre-existing tools around this that solve them all flawlessly? Do you feel like you've got a solution that you're completely happy with?
Thanks in advance!
Update: Just in case I'm not being clear enough, by 'passing data between pages' I'm talking about, for instance, passing a CustomerID key from a CustomerSearch.aspx page to Customers.aspx, where the Customer will be opened and editing can occur.
First, the problems with which you are dealing relate to handling state in a state-less environment. The struggles you are having are not new and it is probably one of the things that makes web development harder than windows development or the development of an executable.
With respect to web development, you have five choices, as far as I'm aware, for handling user-specific state which can all be used in combination with each other. You will find that no one solution works for everything. Instead, you need to determine when to use each solution:
Query string - Query strings are good for passing pointers to data (e.g. primary key values) or state values. Query strings by themselves should not be assumed to be secure even if encrypted because of replay. In addition, some browsers have a limit on the length of the url. However, query strings have some advantages such as that they can be bookmarked and emailed to people and are inherently stateless if not used with anything else.
Cookies - Cookies are good for storing very tiny amounts of information for a particular user. The problem is that cookies also have a size limitation after which it will simply truncate the data so you have to be careful with putting custom data in a cookie. In addition, users can kill cookies or stop their use (although that would prevent use of standard Session as well). Similar to query strings, cookies are better, IMO, for pointers to data than for the data itself unless the data is tiny.
Form data - Form data can take quite a bit of information however at the cost of post times and in some cases reload times. ASP.NET's ViewState uses hidden form variables to maintain information. Passing data between pages using something like ViewState has the advantage of working nicer with the back button but can easily create ginormous pages which slow down the experience for the user. In general, ASP.NET model does not work on cross page posting (although it is possible) but instead works on posts back to the same page and from there navigating to the next page.
Session - Session is good for information that relates to a process with which the user is progressing or for general settings. You can store quite a bit of information into session at the cost of server memory or load times from the databases. Conceptually, Session works by loading the entire wad of data for the user all at once either from memory or from a state server. That means that if you have a very large set of data you probably do not want to put it into session. Session can create some back button problems which must be weighed against what the user is actually trying to accomplish. In general you will find that the back button can be the bane of the web developer.
Database - The last solution (which again can be used in combination with others) is that you store the information in the database in its appropriate schema with a column that indicates the state of the item. For example, if you were handling the creation of an order, you could store the order in the Order table with a "state" column that determines whether it was a real order or not. You would store the order identifier in the query string or session. The web site would continue to write data into the table to update the various parts and child items until eventually the user is able to declare that they are done and the order's state is marked as being a real order. This can complicate reports and queries in that they all need to differentiate "real" items from ones that are in process.
One of the items mentioned in your later link was Application Cache. I wouldn't consider this to be user-specific since it is application wide. (It can obviously be shoe-horned into being user-specific but I wouldn't recommend that either). I've never played with storing data in the HttpContext outside of passing it to a handler or module but I'd be skeptical that it was any different than the above mentioned solutions.
In general, there is no one solution to rule them all. The best approach is to assume on each page that the user could have navigated to that page from anywhere (as opposed to assuming they got there by using a link on another page). If you do that, back button issues become easier to handle (although still a pain). In my development, I use the first four extensively and on occasion resort to the last solution when the need calls for it.
Alright, so I want to preface my answer with this; Thomas clearly has the most accurate and comprehensive answer so far for people starting fresh. This answer isn't in the same vein at all. My answer is coming from a "business developer's" standpoint. As we all know too well; sometimes it's just not feasible to spend money re-writing something that already exists and "works"... at least not all in one shot. Sometimes it's best to implement a solution which will let you migrate to a better alternative over time.
The only thing I'd say Thomas is missing is; client-side javascript state. Where I work we've found customers are coming to expect "Web 2.0"-type applications more and more. We've also found these sorts of applications typically result in much higher user satisfaction. With a little practice, and the help of some really great javascript libraries like jQuery (we've even started using GWT and found it to be AWESOME) communicating with JSON-based REST services implemented in WCF can be trivial. This approach also provides a very nice way to start moving towards a SOA-based architecture, and clean separation of UI and business logic.
But I digress.
It sounds to me as though you already have an application, and you've already stretched the limits of ASP.NET's built-in session state management. So... here's my suggestion (assuming you've already tried ASP.NET's out-of-process session management, which scales signifigantly better than the in-process/on-box session management, and it sounds like you have because you mentioned it); NCache.
NCache provides you with a "drop-in" replacement for ASP.NET's session management options. It's super easy to implement, and could "band-aid" your application more than well enough to get you through - without any significant investment in refactoring your existing codebase immediately.
You can use the extra time and money to start reducing your technical debt by focusing new development on things with immediate business-value - using a new approach (such as any of the alternatives offered in the other answers, or mine).
Just my thoughts.
Several months later, I thought I would update this question with the technique I ended up going with, since it has worked out so well.
After playing with more involved session state handling (which resulted in a lot of broken back buttons and so on) I ended up rolling my own code to handle encrypted QueryStrings. It's been a huge win -- all of my problem scenarios (back button, multiple tabs open at the same time, lost session state, etc) are solved and the complexity is minimal since the usage is very familiar.
This is still not a magic bullet for everything but I think it's good for about 90% of the scenarios you run into.
Details
I built a class called CorePage that inherits from Page. It has methods called SecureRequest and SecureRedirect.
So you might call:
SecureRedirect(String.Format("Orders.aspx?ClientID={0}&OrderID={1}, ClientID, OrderID)
CorePage parses out the QueryString and encrypts it into a QueryString variable called CoreSecure. So the actual request looks like this:
Orders.aspx?CoreSecure=1IHXaPzUCYrdmWPkkkuThEes%2fIs4l6grKaznFGAeDDI%3d
If available, the currently logged in UserID is added to the encryption key, so replay attacks are not as much of a problem.
From there, you can call:
X = SecureRequest("ClientID")
Conclusion
Everything works seamlessly, using familiar syntax.
Over the last several months I've also adapted this code to work with edge cases, such as hyperlinks that trigger a download - sometimes you need to generate a hyperlink on the client that has a secure QueryString. That works really well.
Let me know if you would like to see this code and I will put it up somewhere.
One last thought: it's weird to accept my own answer over some of the very thoughtful posts other people put on here, but this really does seem to be the ultimate answer to my problem. Thanks to everyone who helped get me there.
After going through all the above scenarios and answers and this link Data pasing methods My final advice would be :
COOKIES for:
ENCRYPT[userId's]
ENCRYPT[productId]
ENCRYPT[xyzIds..]
ENCRYPT[etc..]
DATABASE for:
datasets BY COOKIE ID
datatables BY COOKIE ID
all other large chunks BY COOKIE ID
My advise also depends on the below statistics and this link details Data pasing methods :
I would never do this. I have never had any issues storing all session data in the database, loading it based on the users cookie. It's a session as far as anything is concerned, but I maintain control over it. Don't give up control of your session data to your web server...
With a little work, you can support sub sessions, and allow multi-tasking in different tabs/windows.
As a starting point, I find using the critical data elements, such as a Customer ID, best put into the query string for processing. You can easily track/filter bad data coming off of these elements, and it also allows for some integration with e-mail or other related sites/applications.
In a previous application, the only way to view an employee or a request record involving them was to log into the application, do a search for the employee or do a search for recent records to find the record in question. This became problematic and a big time sink when somebody from a related department needed to do a simple view on records for auditing purposes.
In the rewrite, I made both the employee Id, and request Ids available through a basic URL of "ViewEmployee.aspx?Id=XXX" and "ViewRequest.aspx?Id=XXX". The application was setup to A) filter out bad Ids and B) authenticate and authorize the user before allowing them to these pages. What this allowed the primarily application users to do was to send simple e-mails to the auditors with a URL in the e-mail. When they were in a big hurry, they were in their bulk processing time, they were able to simply click down a list of URLs and do the appropriate processing.
Other session related data, such as modification dates and maintaining the "state" of the user's interaction with the application gets a little more complex, but hopefully this provides a starting poing for you.
I've asked this before but I was hoping for another answer and perhaps some code samples because I've been having a difficult time with this. I have an asp.net page. The user hits the "Run" button and I have code IN AN ASSEMBLY, not in the APP_CODE folder that is called and runs a long process that moves product info from a file into the database. While the user waits, I would like them to see status updates like what product the import process in on and status info. I'm assuming I'd break off into another thread and use Ajax but I have no idea how to do this. Some code samples would be very helpful, thanks.
A simpler way to do this without needing to go into multi threading (which can cause all sorts of nasty, hard to track down bugs) is to use AsyncResults in .NET and AJAX which allow you to query a process.
A good example to start you off can be found here.
found it by using HttpResponse.Flush
I'm building a Web Page that allows the user to pick a color and size. Once they have these selected I need to perform a lookup to see if inventory exists or not and update some UI elements based on this.
I was thinking that putting all the single product data into multidimensional JavaScript array (there is only 10-50 records for any page instance) and writing some client side routines around that, would be the way to go for two reasons. One because it keeps the UI fast and two it minimizes callbacks to the server. What i'm worried about with this solution is code smell.
As an alternative i'm thinking about using a more AJAX purist approach of using HTTP handlers and JSON, or perhaps a hybrid with a bit of both. My question is what are your thoughts as to the best solution to this problem using the ASP.Net 2.0 stack?
[Edit]
I also should mention that this page will be running in a SharePoint environment.
Assuming the data is static, I would vote option #1. Storing and retrieving data elements in a JavaScript array is relatively foolproof and entirely within your control. Calling back to the server introduces a lot of possible failure points. Besides, I think keeping the data in-memory within the page will require less code overall and be more readable to anyone with a more than rudimentary understanding of JavaScript.
i'm against Ajax for such tasks, and vote (and implemented) the first option.
As far as I understand, you won't create Code smells if the JS part is being written by your server-side.
From a user point-of-view, Ajax is an experience-killer for wireless browsing, since any little glitch or mis-service will fail or simply lengthen the interaction by factors of 20(!).
I've implemented even more records than yours in my site, and the users love it. Since some of my users use internet-caffee, or dubious hotel wifi, it wouldn't work otherwise.
Besides, Ajax makes your server-vs-client interaction code much more complex, IMO, which is the trickiest part in web programming.
I would go with your second option by far. As long as the AJAX call isn't performing a long running process for this case, it should be pretty fast.
The application I work on does lots with AJAX and HttpHandler, and our calls execute fast. Just ensure you are minimizing the size of your JSON returned in the response.
Go with your second option. If there are that few items involved, the AJAX call should perform fairly well. You'll keep your code off the client side, hopefully prevent any browser based issues that the client side scripting might have caused, and have a cleaner application.
EDIT
Also consider that client side script can be modified by the user. If there's no other validation occuring to the user's selection, this could allow them to configure a product that is out of stock.