I'm trying to understand how to use the IOwinRequest.CallCancelled CancellationToken IOwinRequest. I assumed that the token would get flagged any time the request became invalid (for the following cases):
Disposing the object returned by WebApp.Start.
The HttpClient.GetAsync Task is cancelled or disposed.
In all these cases, it seems that the CallCancelled request is never flagged. Why?
EDIT: I found an error in my code and my first point "Disposing the object returned by WebApp.Start" works now. Disposed/Cancelled client requests still don't trigger the server request token to flag though.
For some background, I am trying to implement long-polling, where the server suspended the request thread until some data arrived to return to the client, or if the request is cancelled. To implement this, my suspending loop will fall out if the cancellation token is flagged. If it's not flagged, the request thread will NEVER end unless there is something to return. Since the token is never flagged, my server could end up with an infinite number of requests that never end.
Related
I need to verify a text/event-stream response for its content up to a certain point in time after the request was sent. The response stream is kept alive indefinitely for new events.
The following code does not work:
given()
.contentType(JSON)
.when()
.get("/mypath/") // This method blocks indefinitely, never reaching the "then" block
.then()
.response()
.extract()
.asString()
How can we close the response stream at a certain point to access what it has so far? Or perhaps intercept the underlying InputStream of the response asynchronously somehow?
I'm using Postman to debug my WebAPI.
There are 2 cases where Postman does not get any answer from my API:
1. When I set a breakpoint for incoming requests
2. When my API is not running
In 1st case, Postman waits (for inifinity theoretically), but in the other it returns me an information that something is wrong after a few seconds.
So my question is: How does that work? In the 1st case, request gets to my server, but it doesn't send any response until I stop debugging, which can take minutes possibly. In the 2nd case, Postman also does not egt any repsonse, but somehow it knows after a few seconds that it will never get it.
In first request the connect to server is successful and it waits for a reply until postman timeout defined.
Second request it connect to server and get reply immediately with an error.
You can increase or decrease max time postman wait for response by using XHR Timeout
Set how long the app should wait for a response before saying that the server isn't responding.
As stated in the title, i would like to know what happens when an AJAX request is sent to a controller action and, during this time, a network timeout happens for a few ms before the request is completed.
Reply from <Server IP>: bytes=32 time=31ms TTL=122
Request timed out
Reply from <Server IP>: bytes=32 time=28ms TTL=122
Considering the timeout happens only for a couple of ms, what effects would this have on my AJAX request?
This is in continuation to a problem we are facing in our application as explained in this SO question and i would like to know if they are somehow related.
I have googled for similar issues but couldn't find anything useful.
Edit: Apart from the impact on AJAX, would it affect the action method's behavior (server)?
Regardless of whether the timeout happens only for a couple of ms or more, the request will fail. The success callback function of your AJAX request will not be executed and the request will end with the execution of complete callback function. By default, all AJAX requests will have a timeout of 0ms (unlimited), but it will hit the default timeout of the browser.
When an AJAX request times out, the error callback function will be invoked. The second argument of this function is a string describing the type of error and in this case, it will have the value timeout. You can handle request timeouts by handling this callback function and by optionally specifying a timeout value (if not specified, works on the default value) in the AJAX request body:
$.ajax({
...
timeout: 5000, //specify the timeout value in milliseconds
error: function(jqXHR, textStatus, errorThrown) {
if(textStatus==="timeout") {
//code to execute when timeout occurs
}
}
});
Additionally, you can also check if the request has timed out in the complete callback function (in a similar way as shown above) by checking the second argument which is a string and it will have the value timeout if the request was timed out.
Also, note this:
The timeout period starts at the point the $.ajax call is made; if several other requests are in progress and the browser has no connections available, it is possible for a request to time out before it can be sent.
Request timeouts are usually either left at their default or set as a global default using $.ajaxSetup() rather than being overridden for specific requests with the timeout option.
I would suggest you to use an alternative HTTP/s traffic monitoring tool like fiddler to find the mystery behind the second request.
More info: jQuery ajax documentation
The request will "fail", meaning it will enter the onError state of your AJAX request. The status code will then be 0, since there is no response from the server to determine the real status code (eg. 200 OK or 500 Internal Server Error).
In case of time-out your success callback wont execute so you have to write an error callback at the client side to handle such issues.
You have to raise an exception from server side in case of time-out so that it will get back to the client as an error that is the one way you can handle the time-out.
I realize this might sound like an odd question, but I'm seeing some odd results in my network calls so I'm trying to figure out if perhaps I'm misunderstanding something.
I see situations where in isolated incidents, when I'm uploading data, even though the response is 200, the data doesn't appear on the server. My guess is that the 200 response arrives during the initial HTTP handshake and then something goes wrong after the fact. Is that a correct interpretation of the order of events? Or is the 200 delivered once the server has collected whatever data the sending Header tells it is in the request? (cause if so then I'm back to the drawing board as to how I'm seeing what I'm seeing).
It means it has been successfully finished. From the HTTP /1.1 Spec
10.2.1 200 OK
The request has succeeded. The information returned with the response is dependent on the method used in the request, for example:
GET an entity corresponding to the requested resource is sent in the response;
HEAD the entity-header fields corresponding to the requested resource are sent in the response without any message-body;
POST an entity describing or containing the result of the action;
TRACE an entity containing the request message as received by the end server.
Finished. It doesn't make sense otherwise. Something might go wrong and the code could throw an error. How could the server send that error code when it already sent 200 OK.
What you experience might be lag, caching, detached thread running after the server sent the 200 etc.
A success reply, like 200, is not sent until after server has received and processed the full request. Error replies, on the other hand, may be sent before the request is fully received. If that happens, stop sending your request.
I've poked around a bit, but I don't see an HTTP status code for when a request's succeeds, but there is an error after the "point of no return".
e.g., Say you process a request, its committed to the database, but while returning the result you run of memory, or encounter a NPE, or what have you. It would have been a 200 response, but now, internally, you aren't able to return the proper, well-formed response.
202 Accepted doesn't seem to fit since we've already processed the request.
What status code means "Success, but errors"? Does one even exist?
HTTP doesn't have such a status code, but there is a best practice that allows you to handle such situations - redirect the user after a POST operation.
Here is a break down -
A POST request tries to modify data on the server
If the server fails, it sends a 500 error to indicate failure
If the server succeeds, it sends a 302 redirect response
The browser then sends a fresh GET request to the server
If this fails, you get a 500 error, otherwise you get a 200
So, your use case of 'Saved data but can't retrieve it immediately' translates to a 302 redirect for the initial POST, followed by a 500 for the subsequent GET.
This approach has other advantages - you get rid of the annoying 'Are you sure you want to resubmit the data?' message. Also keeps your back/forward/refresh buttons usable.
If the server is aware that it has encountered a problem, it should normally return a 5xx error. The most generic one is the 500 Server Error, which the RFC 2616 defines as follows:
500 Internal Server Error
The server encountered an unexpected condition which prevented it
from fulfilling the request.
Then it's the client's responsibility to reattempt the request. If the previous request was partially committed, it's the server's (or the database's) responsibility to roll that back, or to handle the duplicate transaction appropriately.
I agree with #Daniel that the proper response is an HTTP 500 (server error). The web application has to be written to roll back the transaction when there is an error, not leave things half-finished.
One thing you can leverage in your web application is "idempotency". This is the property of a function (or operation) that you can repeat it as many times as you like with the same result. For instance if a read fails, the client can simply retry it until it succeeds. If a deletion appears to fail, the client can again retry and the server will treat the request as valid whether or not the resource being deleted is already gone. And if an update appears to fail, the client can retry that until it gets a successful return from the server. The REST approach to architecting web services makes heavy use of idempotency to make operations robust in the face of error.