This might sound like a question that gets asked frequently but I am not looking for solutions to handle duplicate requests. I just want to know what could cause Apache to receive duplicate requests in the first place.
I have been running into a rather sporadic problem. I have a form that does a POST request on submit but the request can somehow get duplicated just a second later (according to access logs). This used to be a more frequent problem because we were not handling it as gracefully so I put in some client side code to disable the submit button during the form submit event. This prevents double submission (obviously as long as javascript is enabled), but the problem still persists in a very randomly manner. One thing I noticed from logs is clients that cause the issue are android phones running Chrome. Does mobile Chrome do funky things like retry POST requests on it's own? When testing it on my own, I could never get duplicate POST requests to occur, unless I remove the javascript code that disables the submit button.
Web server setup is super simple. No load balancing or anything, just a single server running Apache 2.2.15. We use PHP 5.6 but that probably has nothing to do with this.
I guess it is users doubleclicking rather than clicking, and the application they use transforms every click into a new POST request. Here I'd look into the application design.
Usually I use frameworks that totally cover this and thus can only guess. Clicking the button should not only trigger the POST request but also disable the button while the action is in progress. So JavaScript code could look like
disable button
post the data
enable button
If, due to the POST, the browser navigates to another page this would not be harmful at all.
EDIT: Seeing you did exactly what I suggested, maybe there is another cause.
Suppose users POST their data, and then the screen goes dark, or they switch applications. When they reactivate the browser, is it possible the browser reloads the page by repeating the last request?
I think frameworks cover such situations by responding with a redirect as response to POST, and the redirect would retrieve the data via GET. Since GET is idempotent, it can be run repeatedly without further damage.
Related
I have a question regarding executeJs function.
page.executeJs("$0.click();", downloadAnchor.getElement());
This line of code is not working in real iPhone Safari browser, though it works in mobile responsive mode from desktop safari. Appreciate your help on this
Browsers will be "suspicious" of anything starting a download that isn't a direct reaction to interaction by the user. This is done as a security precaution since starting to download files without the user's explicit consent can be dangerous in specific cases. Different browsers and configurations have different policies for exactly where to draw the line.
In your case, the download isn't started as a direct consequence of user interaction but instead as direct consequence of receiving a message from the server. This kind of pattern will simply not work reliably no matter what you do.
Instead, you need to design the interaction so that the download is directly triggered by the user. The easiest way of doing that is by having the user directly click on the actual download link. If you want to have some indirection, then you still need to make the action work directly in the browser without going through the server.
I want to create an app for faster payment of parking.
This question is more about logic of my app, and what tools I need to use about creating it.
At this point, I use a parking place every day and I pay for it through the web page.
I do it like this.
Login to page.
click on the menu and it redirects me to www.parkingexample.page/payments
there is a search menu and I enter my car plate number if my car is found it returns me how much I need to pay, and "Pay" Button appears.
I click "Pay" buttons and then it's all done.
So my goal is to create an app that when I start it will automatically connect to the page and will search for my plate and if found and payment is needed there would be just one button "Pay"
So I think I should do it like this, but as I haven't created any web app(I'm 100% back-end developer) I ask you is my thought process is correct.
And also I don't want to use WebView as I think it's not necessary for me.
When I start my app it sends "POST" request to page to login.
Then I send 'GET' request to www.parkingexample.page/payments with params = 'mycarspaltenumber'
Somehow I need to click on PAY button on page when it appears so I think it's probably again 'POST' request, but at this point, I'm not sure.
So a QUESTION is, is my logic valid? or it can be done in some other way?
UPDATE. ADDED SCREENSHOTS
First Screen shoot this is the menu after I logged in with the search bar where I need to enter my card plate.
Second screen is where I found my car(Entered plate number and clicked search)
and now the page is updated with sum I have to pay and there is a button "PAID" in the bottom right corner I need to click.
And that's all i need.
To validate whether your suggested sequence is correct I would start by capturing your typical browser session between yourself and your parking provider with something like Fiddler. Then I would use HTTP client library of choice (for C# it would be something like HttpClient) and emulate the same flow with correct headers, query parameters and such like.
Looknig at your screenshots it seems the application is ASP.NET Web Forms, which can get a bit painful to emulate due to way its state management works: you will likely need to decode View state object (to ensure you're passing it back correctly) and locate all dynamic field ids that it uses for postbacks. This however is very doable.
If you discover that the above is too hard to emulate (or there's javascript involved) it might be easier to explore Remote Selenium WebDriver coupled with a headless browser like PhantomJS. You'd then have your PhantomJS interact with the page on your server, and you'll drive it with your mobile app. Basically you'll reduce the complexity of your parking provider page to a well documented API.
Hopefully that gives you a starting point
In your application, all that you will need is services call and the security part of logging a new user everytime to check for payment.
So It will be a simple spring-boot application, where you can use the security part for logging, and you can exactly use the simple way , for example you don't need to have a database, just to redirect your page, and if you are not familiar to front-end framework, you can use a basic html-css pages for client side.
Another important point, you should start by designing your application, before coding, because it's very important to know all the ideas behind your application.
Enjoy your doing time!
I am stuck with one issue here. There are some adshowing malwares which are loading on top of my website at the client's system. These are ajax calls happening in between my requests.
I suspect these malwares are resulting in increased page load time for my site.
If it's a browser related one, best is to try use AdwCleaner.
When I had some "weird" issues with the browser this one solved the issue.
If you haven't already, give it a try!
I did comprehensive Google research but I cannot find any good solution, so any help (or just showing direction of next research) would by REALLY appreciated!
What I need is simple in idea, but looks like hard to implement:
I have data (say just picture) I want to show to all (even anonymous) users of website in the very same time. This data should change regularly (say once in 5 minutes), so the browsers of all users must refresh in given time.
The woflow is simple:
User will open page with countdown (which will show of course different time for each user depends of when the user has had connected).
At the end of countdown shall all browsers of connected users refresh to see new content.
The refresh should be ideally invoked by server to prevent prematured refresh when data doesn't changed yet.
I was thinking of "refresh" meta tag, but it is problematic for SEO and it rely on user computer's clock.
It can be done by javascript, but in that moment I rely on user computer's clock.
I have hearded it is possible "push" data from server to browser using e.g. Perl, it is correct (is there somewhere some example)?
And in which scripting language would you write script which would "tick". I cannot see way in PHP I am familiar with (use cron to execute counting script every minute looks really ugly)...
Thank you!
Michal
It's not possible to push data from a web server to a web brower, given the request-response architecture of HTTP. It is, however, possible to poll the webserver using JavaScript and window.setInterval(); combined with AJAX.
If not using local system time is an issue, why not respond to periodic AJAX requests with the number of microseconds until the next reload of data should commence? I would suggest you use AJAX for all of this instead of refreshing the browser with META REFRESH, or window.location.
The server-side code could be anything really, you simply need a page that will return the number of microseconds until the next schedule refresh (And perhaps an error if no refresh is scheduled yet, telling the client JavaScript to poll again in a few seconds).
As a newbie to Safari Extensions I have what I am sure is a terribly trivial question ...
Here goes: I'm building an extension to work with some search engines. To cut a long story short I have boiled my issue down to its simplest form. I have an injected script (an end script). This fires as planned on the Google homepage. But when I enter a query to Google the script does not fire when the subsequent results page loads.
For example, to keep things really basic for testing I created a simple script that just writes to the console; I've set the access level to All so that it fires for all pages. I can see the console message when I open the Google homepage but I dont see it when the subsequent results pages load.
For all intents and purposes it seems as if the transition from Google homepage to results page is not a normal one (that is, not a conventional page load) and does not cause injected scripts to fire. I've only seen this problem on Google so I assume it is something to do with their page loading mechanism. I've tried it with Google Instant on and off and both produce the same behaviour.
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It's one of those problems that seems so basic as to be stupefying! Please help.