I am new to SignalR and there is a small detail I can't get my head around.
My SignalR hub include many channels and the clients can join one or many of these channels via a server method:
joinChannel(string channelName)
What I don't understand is what this method should return.
If it were a normal "RPC" method I would return a status (200 - Ok, 404 - Not found, 403 - Forbidden etc) via IHttpActionResult.
How do I indicate success/failure in SignalR?
What determines if the reply gets to .done or .fail in the client?
Update
Currently my method returns a non-zero value in case of error.
int joinChannel(string channelName) {
...
return errorCode;
}
This works but it create unnecessarily complicated code in the client
hubProxy.server.joinChannel('channel1')
.done(function (result) {
if (result != 0) {
// error handling
}
})
.fail(function (error) {
// error handling
});
To confirm that your action was successfully performed, you can have a client method call. So, basically it would look like this:
public void ServerMethod(argumentList)
{
if (/* server code executed successfully */)
Clients.Caller.onSuccess(arguments);
else Clients.Caller.onFailure(arguments);
}
What this piece of code does is to notify the caller of the server method of a success/failure by calling a client method - method defined in JavaScript. You can also have a method executed on All clients, or only on specific users.
Since it is not an RPC mechanism, I think this is the closest thing you can do to simulate a return type in SignalR.
Hope this helps!
Best of luck!
What about
HubException in
Microsoft.AspNetCore.SignalR.
This is available in ASP.NET Core.
This exception is thrown on the server and sent to client. You can also derive from that class to put your own information in it.
Related
I am using web reactive in spring web flux. I have implemented a Handler function for POST request. I want the server to return immediately. So, I have implemeted the handler as below -:
public class Sample implements HandlerFunction<ServerResponse>{
public Mono<ServerResponse> handle(ServerRequest request) {
Mono bodyMono = request.bodyToMono(String.class);
bodyMono.map(str -> {
System.out.println("body got is " + str);
return str;
}).subscribe();
return ServerResponse.status(HttpStatus.CREATED).build();
}
}
But the print statement inside the map function is not getting called. It means the body is not getting extracted.
If I do not return the response immediately and use
return bodyMono.then(ServerResponse.status(HttpStatus.CREATED).build())
then the map function is getting called.
So, how can I do processing on my request body in the background?
Please help.
EDIT
I tried using flux.share() like below -:
Flux<String> bodyFlux = request.bodyToMono(String.class).flux().share();
Flux<String> processFlux = bodyFlux.map(str -> {
System.out.println("body got is");
try{
Thread.sleep(1000);
}catch (Exception ex){
}
return str;
});
processFlux.subscribeOn(Schedulers.elastic()).subscribe();
return bodyFlux.then(ServerResponse.status(HttpStatus.CREATED).build());
In the above code, sometimes the map function is getting called and sometimes not.
As you've found, you can't just arbitrarily subscribe() to the Mono returned by bodyToMono(), since in that case the body simply doesn't get passed into the Mono for processing. (You can verify this by putting a single() call in that Mono, it'll throw an exception since no element will be emitted.)
So, how can I do processing on my request body in the background?
If you really still want to just use reactor to do a long task in the background while returning immediately, you can do something like:
return request.bodyToMono(String.class).doOnNext(str -> {
Mono.just(str).publishOn(Schedulers.elastic()).subscribe(s -> {
System.out.println("proc start!");
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("proc end!");
});
}).then(ServerResponse.status(HttpStatus.CREATED).build());
This approach immediately publishes the emitted element to a new Mono, set to publish on an elastic scheduler, that is then subscribed in the background. However, it's kind of ugly, and it's not really what reactor is designed to do. You may be misunderstanding the idea behind reactor / reactive programming here:
It's not written with the idea of "returning a quick result and then doing stuff in the background" - that's generally the purpose of a work queue, often implemented with something like RabbitMQ or Kafka. It's "raison d'être" is instead to be non-blocking, so a single thread is never idly blocked, waiting for something else to complete.
The map() method isn't designed for side effects, it's designed to transform each object into another. For side effects, you want doOnNext() instead;
Reactor uses a single thread by default, so your "additional processing" in your map() method would still block that thread.
If your application is for anything more than quick demo purposes, and/or you need to make heavy use of this pattern, then I'd seriously consider setting up a proper work queue instead.
This is not possible.
Web servers (including Reactor Netty, Tomcat, etc) clean up and recycle resources when request processing is done. This means that when your controller handler is done, the HTTP resources, the request itself, reusable buffers, etc are recycled or closed. At that point, you cannot read from the request body anymore.
In your case, you need to read and buffer the whole request body first, then return a response and kick off a task for processing that request in a separate execution.
I have the following middleware code:
public class UoWMiddleware : OwinMiddleware
{
readonly IUoW uow;
public UoWMiddleware(OwinMiddleware next, IUoW uow) : base(next)
{
this.uow = uow;
}
public override async Task Invoke(IOwinContext context)
{
try
{
await Next.Invoke(context);
}
catch
{
uow.RollBack();
throw;
}
finally
{
if (uow.Status == Base.SharedDomain.UoWStatus.Running)
{
var response = context.Response;
if (response.StatusCode < 400)
{
Thread.Sleep(1000);
uow.Commit();
}
else
uow.RollBack();
}
}
}
}
Occasionally we observe that the response returns to client before calling uow.Commit() via fiddler. For example we put a break point to uow.Commit and we see the response is returned to client despite that we are on the breakpoint waiting. This is somewhat unexpected. I would think the response will strictly return after the Invoke method ends. Am I missing something?
In Owin/Katana the response body (and, of course, the headers) are sent to the client at the precise moment when a middleware calls Write on the Response object of the IOwinContext.
This means that if your next middleware is writing the response body your client will receive it before your server-side code returns from the call to await Next.Invoke().
That's how Owin is designed, and depends on the fact that the Response stream may be written just once in a single Request/Response life-cycle.
Looking at your code, I can't see any major problem in such behavior, because you are simply reading the response headers after the response is written to the stream, and thus not altering it.
If, instead, you require to alter the response written by your next middleware, or you strictly need to write the response after you execute further logic server-side, then your only option is to buffer the response body into a memory stream, and than copy it into the real response stream (as per this answer) when you are ready.
I have successfully tested this approach in a different use case (but sharing the same concept) that you may find looking at this answer: https://stackoverflow.com/a/36755639/3670737
Reference:
Changing the response object from OWIN Middleware
I've recently started using the Play! framework (v2.0.4) for writing a Java web application. In the majority of my controllers I'm following the paradigm of suspending the HTTP request until the promise of a web service response has been fulfilled. Once the promise has been fulfilled, I return an AsyncResult. This is what most of my actions look like (with a bunch of code omitted):
public static Result myActionMethod() {
Promise<MyWSResponse> wsResponse;
// Perform a web service call that will return the promise of a MyWSResponse...
return async(wsResponse.map(new Function<MyWSResponse, Result>() {
#Override
public Result apply(MyWSResponse response) {
// Validate response...
return ok(myScalaViewTemplate.render(response.data()));
}
}));
}
I'm now trying to internationalise my app, but hit the following error when I try to render a template from an async method:
[error] play - Waiting for a promise, but got an error: There is no HTTP Context available from here.
java.lang.RuntimeException: There is no HTTP Context available from here.
at play.mvc.Http$Context.current(Http.java:27) ~[play_2.9.1.jar:2.0.4]
at play.mvc.Http$Context$Implicit.lang(Http.java:124) ~[play_2.9.1.jar:2.0.4]
at play.i18n.Messages.get(Messages.java:38) ~[play_2.9.1.jar:2.0.4]
at views.html.myScalaViewTemplate$.apply(myScalaViewTemplate.template.scala:40) ~[classes/:na]
at views.html.myScalaViewTemplate$.render(myScalaViewTemplate.template.scala:87) ~[classes/:na]
at views.html.myScalaViewTemplate.render(myScalaViewTemplate.template.scala) ~[classes/:na]
In short, where I've got a message bundle lookup in my view template, some Play! code is attempting to access the original HTTP request and retrieve the accept-languages header, in order to know which message bundle to use. But it seems that the HTTP request is inaccessible from the async method.
I can see a couple of (unsatisfactory) ways to work around this:
Go back to the 'one thread per request' paradigm and have threads block waiting for responses.
Figure out which language to use at Controller level, and feed that choice into my template.
I also suspect this might not be an issue on trunk. I know that there is a similar issue in 2.0.4 with regards to not being able to access or modify the Session object which has recently been fixed. However I'm stuck on 2.0.4 for the time being, so is there a better way that I can resolve this problem?
Gonna answer my own question here. A colleague of mine found what was ultimately a simple solution:
public static Result myActionMethod() {
final Context ctx = ctx(); // (1)
Promise<MyWSResponse> wsResponse;
// Perform a web service call that will return the promise of a MyWSResponse...
return async(wsResponse.map(new Function<MyWSResponse, Result>() {
#Override
public Result apply(MyWSResponse response) {
Context.current.set(ctx); // (2)
// Validate response...
return ok(myScalaViewTemplate.render(response.data()));
}
}));
}
Obtain a reference to the HTTP context at the beginning of the action
Restore it in the ThreadLocal once you're in the async block
Ajax and Reflection
I am developing an ajax-based application and wondering, what role reflection plays or might play here?
Probably most importantly I am asking myself, if it would be a good approach to
handle all ajax responses through a single handler,
reflect or interpret the data or error
delegate further processing (e.g. where to inject the html) based upon the analysis.
Is this a budding procedure? What pros and cons come to mind?
Additional clearification
My current implementation, which I am not happy with, looks like this.
Register eventhandlers for user action, which lead to ajax requests.
For each request:
Determine which container is the target for the new content
Validate the ajax response
Pass the result to the appropiate rendering function if everything is as expected
Here is an example
function setGamedayScoringChangeHandlers() {
$("#community").delegate("div.community div.nav", "click", function() {
var orderId = $(this).html();
var communityId = $(this).closest('.communityView ').dashId();
requestGamedayScoringByOrderId(communityId, orderId);
});
}
function requestGamedayScoringByOrderId(communityId, orderId) {
var $targetContainer = $('#community-' + communityId + '-gameday');
$.ajax({
url: '?api=league&func=getGamedayScoringByCommunityIdAndOrderId',
data: {
communityId : communityId,
orderId : orderId
},
success: function(result) {
// custom indicator, that sth. didn't work as supposed
if (result.success === false) {
// a php error couldn't be handled as expected
if (result.error === 'phpRuntimeError') {
// ..
}
// ..
}
else {
renderGamedayScoring(result, $targetContainer);
}
}
});
}
Question
How can this and especially the redundant error checking be simplified? Could Reflection, in a sense of: "Is the response valid? And what does the error message say or data look like?" be a reasonable structure do deal with this? Additionally: Is the "coupling" of the actual ajax request and determing the $targetContainer a "normal" procedure?
Many thanks,
Robson
Yes I think register ajax handler trought one pipe is a good way, because it is more easy to control, you will have less redundant code and less boarding effects. If I look at your code comments it seems the response is not as you expect. I use to do like this for controling a group of ajax request talking with server script. I build one request object like :
// myscript.js
var rqPHP = {
url:'php/dispatcher.php', type:'POST', dataType:'json',
success:function(json, status, jXHR){
//console.log('rqPHP.succes : ', json);
if(!json) return console.warn('[rqPHP.success] json is null');
if(!json.cmd) return console.warn('[rqPHP.success] json.cmd is null');
if(!json.res) return console.warn('[rqPHP.success] json.res is null');
if(json.err && json.err.length){ console.warn('[rqPHP.success errors cmd:'+json.cmd+'] '+json.err);}
// so if no errors, dispatch actions based on original command asked
switch(json.cmd){
case 'loadfile' :
// do whatever with response
break;
case 'savefile' :
// do whatever with response
break;
}
},
error:function(jXHR, status, err){
console.warn('[rqPHP.error] ', status,',',err,',',jXHR.responseText);
}
};
then when use this object trought all my group of different actions and I precise wich action and arguments I pass. I use to ask for a json data so I am able to receive an easy parsing response, so I am able to return the original command asked, and some details on errors that may occured for example, and when I need to fire the request :
// myscript.js
rqPHP.data = {'cmd':'loadfile', 'filename':'file.dat', 'arg2':'other argument'};
$.ajax(rqPHP);
Then an example of one server script that will respond :
// dispatcher.php
$pv = $_POST;
$res = '';
$err = array();
// you check the command asked for :
switch(strtolower($pv['cmd'])){
case 'savefile' :
// do whatever
break;
case 'loadfile' :
// do whatever
if(any error){
$err[] = $loadError;// push error with whatever details you'll retrieve in javascript
}else{
$res = ',"res":"'.$dataLoaded.'"';// format json response so you'll check the var exist
}
break;
}
$jsonRes = '{"cmd":"'.$pv['cmd'].'"'.$res.',"err":"'.implode('|', $err).'"}';// json result
print $jsonRes;
They may be some errors, it is just for the principe, I hope that will help, just some last advices :
you should better use the requestObject.data to pass any arguments instead of setting the url like you did, this is much more easy because jQuery does the properly encoding work
you may use POST so the url stay clean, post vars are 'hidden'
in your case, because you may want to centralize server actions with ONE server script, you should use 'json' as dataType because it is much easier to retrieve details from the response, such errors. You have to distinct the ajax error that is trigger when the url doesn't exist, or access denied, well when the server replies it just can't respond to this request, and distinct the properly response of your server script, I mean the script responds well but it may occur an command error, for example for a 'loadfile' command, the argument fileUrl may be wrong or unreadable, so the action is done but the response will be not valid for you...
If you plan to fire many loads for differents parts (I mean you may don't wait response for an ajax before loading a new one), it should be better to set main success and errors functions for keeping centralization and then build one new request object each time you make a load
function rqSuccess(json, status, jXHR){
// put same checking code as before, then you can also retrieve some particular variables
// here, 'this' should correspond to the request object used for the $.ajax so :
console.log('myTarget is : ', this.myTarget, ' , myVariable is : ', this.myVariable);
}
function rqError(jXHR, status, err){
// put same checking code
}
// then each time you want make one or many independant calls, build a new request object
var myRq = {url:'dispatcher.php',type:'POST',dataType:'json',
success:rqSuccess,
error:rqError,
myTarget:$('#myblock'),// any variable you want to retrieve in response functions
myVariable:'Hello !',// after all it is an object, you can store anything you may need, just be carefull of reserved variables of the ajax object (see jQuery $.ajax doc)
// the data object is sanitized and sended to your server script, so put only variables it will need
data : {'cmd':'loadfile',...}
}
$.ajax(myRq);
// you may load an other independant one without waiting for the response of the first
var myRq2 = {...myTarget:$('#anotherblock'), data:{'cmd':'anotheraction'}...}
$.ajax(myRq2);
As a first step, you should change the error handling on the serverside to produce a non-OK/200 response for error cases, e.g. throw a 500. Then have that handled as an actual error on the clientside, along with other errors, instead of putting it through the success-callback.
That way you can use jQuery's abstractions for global error handling: http://api.jquery.com/ajaxError
I have a simple ExtJs (3.4) Grid with a Writer. When the user makes some changes the store is saved to the server as follows:
store.on('save', afterSave(resp));
All is fine. However, I want to get a response as to wheather the record has been saved successfully, failed or an update conflict happed. How to best do this?
Are you using Ext.data.proxy.Ajax to load your stores? If so, you can use the reader property to evaluate and handle the server responses.
Another option would be to make AJAX called directly and handle the responses from there as well
I used exception listener to parse the data as suggested here. But, is this the right way to do this.
Ext.data.DataProxy.addListener('exception', function(proxy, type, action,
options, res) {
if (type == 'response') {
var success = Ext.util.JSON.decode(res.responseText).success;
if (success) {
console.log('UPDATE OK');
} else {
console.log('UPDATE FAILED');
}
}
});