In WCF, I'm able to use this call to get the service contract and then in that service contract I can invoke a method which calls back the client. Ok fine.
OperationContext.Current.GetCallbackChannel<IMyServiceContract>
But, ultimately, this is just a bare bones service contract. The method named "GetCallbackChannel" indicates to me that a Channel object should be returned here. You know, a channel object that has a state property such as Closed, Open, etc, as well as events for state change.
WCF sure makes it difficult to grab the async channel that it is keeping open for the Async call. How else can I grab this channel?
Ok, I found an answer. I had tried something similar, but providing the CommunicationObject type in the GetCallbackChannel didn't work. Casting it to ICommuicationObject after getting the channel does work.
var c = OperationContext.Current.GetCallbackChannel<IMyServiceContract>();
ICommunicationObject chan = (ICommunicationObject)c;
Related
I'm wondering if I'm doing something wrong, I expected MassTransit would automatically register ReceiveEndpoints in the EndpointConvention.
Sample code:
services.AddMassTransit(x =>
{
x.AddServiceBusMessageScheduler();
x.AddConsumersFromNamespaceContaining<MyNamespace.MyRequestConsumer>();
x.UsingAzureServiceBus((context, cfg) =>
{
// Load the connection string from the configuration.
cfg.Host(context.GetRequiredService<IConfiguration>().GetValue<string>("ServiceBus:ConnectionString"));
cfg.UseServiceBusMessageScheduler();
// Without this line I'm getting an error complaining about no endpoint convention for x could be found.
EndpointConvention.Map<MyRequest>(new Uri("queue:queue-name"));
cfg.ReceiveEndpoint("queue-name", e =>
{
e.MaxConcurrentCalls = 1;
e.ConfigureConsumer<MyRequestConsumer>(context);
});
cfg.ConfigureEndpoints(context);
});
});
I thought this line EndpointConvention.Map<MyRequest>(new Uri("queue:queue-name")); wouldn't be necessary to allow sending to the bus without specifing the queue name, or am I missing something?
await bus.Send<MyRequest>(new { ...});
The EndpointConvention is a convenience method that allows the use of Send without specifying the endpoint address. There is nothing in MassTransit that will automatically configured this because, frankly, I don't use it. And I don't think anyone else should either. That stated, people do use it for whatever reason.
First, think about the ramifications - if every message type was registered as an endpoint convention, what about messages that are published and consumed on multiple endpoints? That wouldn't work.
So, if you want to route messages by message type, MassTransit has a feature for that. It's called Publish and it works great.
But wait, it's a command, and commands should be Sent.
That is true, however, if you are in control of the application and you know that there is only one consumer in your code base that consumes the KickTheTiresAndLightTheFires message contract, publish is as good as send and you don't need to know the address!
No, seriously dude, I want to use Send!
Okay, fine, here are the details. When using ConfigureEndpoints(), MassTransit uses the IEndpointNameFormatter to generate the receive endpoint queue names based upon the types registered via AddConsumer, AddSagaStateMachine, etc. and that same interface can be used to register your own endpoint conventions if you want to use Send without specifying a destination address.
You are, of course, coupling the knowledge of your consumer and message types, but that's your call. You're already dealing with magic (by using Send without an explicit destination) so why not right?
string queueName = formatter.Consumer<T>()
Use that string for the message types in that consumer as a $"queue:{queueName}" address and register it on the EndpointConvention.
Or, you know, just use Publish.
I got a bot which may:
start talk when user say somethibng in DM with the bot.
start talk only when user mentioned the bot in some channel.
Question:
How can I know it's a DM channel or a normal channel?
I guess https://api.slack.com/methods/channels.info might help, but I'm not sure which property indicates it.
Your best approach is to use the conversations.info API method. It will tell you exactly what kind of channel it is. It actually replaces the older channels.info method (which only works for public channels anyways).
Among other you get:
"is_channel": true
"is_group": false
"is_im": false
Here is how those terms are used in the API and (mostly) in the documentation:
channel = public channel
group = private channel
im = direct message.
conversation = any kind of channel
Alternatively you can also guess the channel type based on the first letter of it's ID. That is not 100% though, because channels can be converted from one type to another while keeping their ID.
C: public channel
G: private chanel / MPIM
D: Direct Message / IM
TLDR: Can I register callback functions in golang to get notified if a struct member is changed?
I would like to create a simple two-way-binding between a go server and an angular client. The communication is done via websockets.
Example:
Go:
type SharedType struct {
A int
B string
}
sharedType := &SharedType{}
...
sharedType.A = 52
JavaScript:
var sharedType = {A: 0, B: ""};
...
sharedType.A = 52;
Idea:
In both cases, after modifying the values, I want to trigger a custom callback function, send a message via the websocket, and update the value on the client/server side accordingly.
The sent message should only state which value changed (the key / index) and what the new value is. It should also support nested types (structs, that contain other structs) without the need of transmitting everything.
On the client side (angular), I can detect changes of JavaScript objects by registering a callback function.
On the server side (golang), I could create my own map[] and slice[] implementations to trigger callbacks everytime a member is modified (see the Cabinet class in this example: https://appliedgo.net/generics/).
Within these callback-functions, I could then send the modified data to the other side, so two-way binding would be possible for maps and slices.
My Question:
I would like to avoid things like
sharedType.A = 52
sharedType.MemberChanged("A")
// or:
sharedType.Set("A", 52) //.. which is equivalent to map[], just with a predifined set of allowed keys
Is there any way in golang to get informed if a struct member is modified? Or is there any other, generic way for easy two-way binding without huge amounts of boiler-plate code?
No, it's not possible.
But the real question is: how do you suppose to wield all such magic in your Go program?
Consider what you'd like to have would be indeed possible.
Now an innocent assignment
v.A = 42
would—among other things—trigger sending stuff
over a websocket connection to the client.
Now what happens if the connection is closed (client disconnected),
and the sending fails?
What happens if sending fails to complete before a deadline is reached?
OK, suppose you get it at least partially right and actual modification of the local field happens only if sending succeeds.
Still, how should sending errors be handled?
Say, what should happen if the third assignment in
v.A = 42
v.B = "foo"
v.C = 1e10-23
fails?
you could try using server sent events (SSE) to send realtime data to the frontend, while sending a single post request with ur changes. That way you can monitor in the back and send data every second.
I'm having some trouble with a Qt application; specifically with the QNetworkAccessManager class. I'm attempting to perform a simple HTTP upload of a binary file using the post() method of the QNetworkAccessManager. The documentation states that I can give a pointer to a QIODevice to post(), and that the class will transmit the data found in the QIODevice. This suggests to me that I ought to be able to give post() a pointer to a QFile. For example:
QFile compressedFile("temp");
compressedFile.open(QIODevice::ReadOnly);
netManager.post(QNetworkRequest(QUrl("http://mywebsite.com/upload") ), &compressedFile);
What seems to happen on the Windows system where I'm developing this is that my Qt application pushes the data from the QFile, but then doesn't complete the request; it seems to be sitting there waiting for more data to show up from the file. The post request isn't "closed" until I manually kill the application, at which point the whole file shows up at my server end.
From some debugging and research, I think this is happening because the read() operation of QFile doesn't return -1 when you reach the end of the file. I think that QNetworkAccessManager is trying to read from the QIODevice until it gets a -1 from read(), at which point it assumes there is no more data and closes the request. If it keeps getting a return code of zero from read(), QNetworkAccessManager assumes that there might be more data coming, and so it keeps waiting for that hypothetical data.
I've confirmed with some test code that the read() operation of QFile just returns zero after you've read to the end of the file. This seems to be incompatible with the way that the post() method of QNetworkAccessManager expects a QIODevice to behave. My questions are:
Is this some sort of limitation with the way that QFile works under Windows?
Is there some other way I should be using either QFile or QNetworkAccessManager to push a file via post()?
Is this not going to work at all, and will I have to find some other way to upload my file?
Any suggestions or hints would be appreciated.
Update: It turns out that I had two different problems: one on the client side and one on the server side. On the client side, I had to ensure that my QFile object stayed around for the duration of the network transaction. The post() method of QNetworkAccessManager returns immediately but isn't actually finished immediately. You need to attach a slot to the finished() signal of QNetworkAccessManager to determine when the POST is actually finished. In my case it was easy enough to keep the QFile around more or less permanently, but I also attached a slot to the finished() signal in order to check for error responses from the server.
I attached the signal to the slot like this:
connect(&netManager, SIGNAL(finished(QNetworkReply*) ), this, SLOT(postFinished(QNetworkReply*) ) );
When it was time to send my file, I wrote the post code like this (note that compressedFile is a member of my class and so does not go out of scope after this code):
compressedFile.open(QIODevice::ReadOnly);
netManager.post(QNetworkRequest(QUrl(httpDestination.getCString() ) ), &compressedFile);
The finished(QNetworkReply*) signal from QNetworkAccessManager triggers my postFinished(QNetworkReply*) method. When this happens, it's safe for me to close compressedFile and to delete the data file represented by compressedFile. For debugging purposes I also added a few printf() statements to confirm that the transaction is complete:
void CL_QtLogCompressor::postFinished(QNetworkReply* reply)
{
QByteArray response = reply->readAll();
printf("response: %s\n", response.data() );
printf("reply error %d\n", reply->error() );
reply->deleteLater();
compressedFile.close();
compressedFile.remove();
}
Since compressedFile isn't closed immediately and doesn't go out of scope, the QNetworkAccessManager is able to take as much time as it likes to transmit my file. Eventually the transaction is complete and my postFinished() method gets called.
My other problem (which also contributed to the behavior I was seeing where the transaction never completed) was that the Python code for my web server wasn't fielding the POST correctly, but that's outside the scope of my original Qt question.
You're creating compressedFile on the stack, and passing a pointer to it to your QNetworkRequest (and ultimately your QNetworkAccessManager). As soon as you leave the method you're in, compressedFile is going out of scope. I'm surprised it's not crashing on you, though the behavior is undefined.
You need to create the QFile on the heap:
QFile *compressedFile = new QFile("temp");
You will of course need to keep track of it and then delete it once the post has completed, or set it as the child of the QNetworkReply so that it it gets destroyed when the reply gets destroyed later:
QFile *compressedFile = new QFile("temp");
compressedFile->open(QIODevice::ReadOnly);
QNetworkReply *reply = netManager.post(QNetworkRequest(QUrl("http://mywebsite.com/upload") ), compressedFile);
compressedFile->setParent(reply);
You can also schedule automatic deletion of a heap-allocated file using signals/slots
QFile* compressedFile = new QFile(...);
QNetworkReply* reply = Manager.post(...);
// This is where the tricks is
connect(reply, SIGNAL(finished()), reply, SLOT(deleteLater());
connect(reply, SIGNAL(destroyed()), compressedFile, SLOT(deleteLater());
IMHO, it is much more localized and encapsulated than having to keep around your file in the outer class.
Note that you must remove the first connect() if you have your postFinished(QNetworkReply*) slot, in which you must then not forget to call reply->deleteLater() inside it for the above to work.
I'm new to XMPP and the xmpp4r library, so please forgive my noob question if this is obviously documented somewhere.
What's the most straightforward way, in a synchronous manner, to find out if a given JID is online? (so that I can call something like is_online?(jid) in an if statement)
My details:
I'm writing a Sinatra app that will attempt to send a message to a user when a particular url gets requested on the web server, but it should only try to send the message to the user if that user is currently online. Figuring out if a given JID is online is my problem.
Now, I know that if I connect and wait a few seconds for all the initial presence probe responses to come back to the Roster helper, then I can inspect any of those presences from my Roster and call #online? on them to get the correct value. But, I don't know when all of the presence updates have been sent, so there's a race condition there and sometimes calling #online? on a presence from my roster will return false if I just haven't received that presence probe response yet.
So, my current thinking is that the most straightforward way to find out if someone is online is to construct a new Presence message of type :probe and send that out to the JID that I'm interested in. Here's how I'm doing it right now:
#jabber is the result of Client::new
#email is the jid I'm interested in polling
def is_online?(jabber, email)
online = false
p = Presence.new
p.set_to(email)
p.set_from(jabber.jid)
p.set_type(:probe)
pres = jabber.send(p) do |returned_presence|
online = returned_presence.nil?
end
return online
end
Now, this works in cases where the user is actually online, but when the user is offline, it looks like the presence probe message that comes back is being caught by some other presence_callback handler that doesn't know what to do with it, and my is_online? function never finishes returning a value.
Can anyone help me by providing a simple example is_online? function that I can call, or point me in the right direction for how I can detect when the roster is done getting all the initial presence updates before I try checking a presence for #online?
As it turns out, there's not a synchronous way to ask for a JID presence. You've just got to ask for what you want, then wait for your response handler to fire when the response arrives.