According to the HTTP 1.1 spec, browsers should retry a request if they pass a certain time limit or if an error response is received. POST requests are no exception.
Occasionally, slow connections combined with a processor heavy request can cause an ajax POST request to time out, and the browser will fire a second POST request with the same data. This leads to unexpected and erroneous behaviors. Is there any way to prevent that browser timeout from triggering and firing a second POST request?
Based on my understanding you can't restrict the client to stop automatic retries.
The best option is to handle the identical requests in the server side by using unique GUID's.
https://blogs.oracle.com/ravello/beware-http-requests-automatic-retries/comment-submitted?cid=b956dee8-7352-4d88-ad40-71ff9fd1eb53
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When doing CORS requests that require preflight, they fail to work on our network. Instead of Chrome making two requests, the OPTIONS and PUT, it fires two OPTIONS requests that are exactly the same, this ends up in the following error:
XMLHttpRequest cannot load http://server/api/foo. Response for preflight is invalid (redirect)
Digging into the problem, there are two things that stand out.
If I turn on Throttling in the Network section of the Chrome developer tools, things work and the OPTIONS request is followed by a PUT.
Under the timing tab, it almost looks like as if it tries to fire both (First request,
Second request) requests simultaneously. Despite the fact that a request is queued at a later time, the Started At time shows it at the same request as the initial OPTIONS request.
The throttled working, and non-working requests look fairly similar for comparison.
I am facing issue where i am sending one GET request using Jmeter. Response headers shows every time it miss Varnish cache on Server and response is returned from Application Sever. Please find below header
X-Cache: MISS
X-Cache-Hits: 0
If i send exact same request using Postman, first time it miss Varnish cache but if i send same request again, it hits Varnish cache and cache hits counts increased.
X-Cache → HIT
X-Cache-Hits → 1
I have tried Jmeter versions 2.6,2.9,2.11 and 2.13, but observed same behavior. Even when request is sent from Fiddler, i can see from header response is returned from Varnish Cache itself.
It just simple get request. I have compared JMeter and Postman request, both requests are exact same. Please let me know how i can resolve this issue.
Based on when you wrote above, I can guess that:
All 1st requests are processed in the same way, doesn't matter how they were send.
As a part of response to your first request, server returns you a command to set up new header, in the same way as it process cookies (SET-COOKIE logic). So, server expects that your next request will contain this required X-Cache header.
But Jmeter is not a browser and doesn't correlate next request with previously received data (by default at least). So, all is OK if you replay this scenario with browser (and its extensions). And your Jmeter sends the same request every time.
If you compare 1st and 2nd request sent by your browser, you'll find that your 2nd request contains required hearer.
So, if I'm right, to resolve the issue:
Identify the way how your server tells the client to add new header to next request (Javascript?)
Implement this logic in your Jmeter scenario.
Or just add X-Cache header to your request.
My expectation is that Postman (whatever it is) respects ETag header while JMeter doesn't.
I believe adding HTTP Cache Manager should resolve your issue.
I have added unique key in header every time request goes top server and it started returning response from Varnish cache. Unique is random number.
i also checked Postman also send one unique parameter in each and every request. Though I am still not sure why unique is making difference here.
In, for example, JavaScript AJAX libraries it is possible to abort an AJAX request. Is there any server side advantage to this or is it just for client-side cleanliness? Is it part of TCP?
If, for example, I am requesting via AJAX a Python based server service – which is resource intensive – from my JavaScript Web App and abort this AJAX request, is it possible that aborting will ease the load on the server, or will the my ajax library just ignore the response from the server?
It does not affect the server-side if you use your frameworks abort feature. The server will still process the request regardless.
Once you made an HTTP request to a resource URL on your server (be it Asynch or not, aka ajax or "regular"), you can't abort it from your client / with another http request (unless your service has some weird listener that awaits for potential consequent http requests and stops itself up receiving one). My proposition, if you have one resource and time consuming operation, either split it into simpler operations, parallelize it or at east make some periodic responses to at least inform the user that it's still working and hasn't died
Cross domain AJAX requests are reported as "aborted" in firebug. I know this is supposed to be security feature but where exactly these requests get rejected ? At the browser end or at the server end ?
Browser - they don't get sent at all. If you check your HTTP traffic (e.g. using Fiddler), you'll see that there is no corresponding HTTP request initiated for those aborted AJAX requests.
(That is also the only place where such blocking makes sense, as the server doesn't have a reliable way to distinguish between AJAX requests and normal requests; only the browser has enough context to make such decision.)
I have writen searching in my site and now I am trying to make it search every time I start printing. So now I am sending many requests which contains different text to search for using AJAX one by one and every next reqest has to wait, before previous one is finished. Apperently I dont need old requests to be answered, but I need the only one response for the last request.
How can I kill the queue of not actual requests in Django?
Does anybody know the answer?
On the server side, it's probably too late to cancel requests, but you can ignore the responses on the client side. I would suggest aborting a pending AJAX request before sending a new one.
Here is how:
Abort Ajax requests using jQuery
An easier way to do this could be by waiting a bit before sending your request to the server. After each input, set up a timer that stops the previous (setTimout) and only send the request if the timeout is met.
If a request was already performed and has not returned you can still kill it as suggested in another answer.
I'm not aware of how to stop other requests using django -- hope that it's not even possible, it would be a security thread if requests could be killed by others.