I have a webpage that uses ajax polling to get stock market updates from the server. I'd like to use SignalR instead, but I'm having trouble understanding how/if it would work.
ok, it's not really stock market updates, but the analogy works.
The SignalR examples I've seen send messages to either the current connection, all connections, or groups. In my example the stock updates happen outside of the current connection, so there's no such thing as the 'current connection'. And a user's account is associated with a few stocks, so sending a stock notification to all connections or to groups doesn't work either. I need to be able to find a connection associated with a certain userId.
Here's a fake code example:
foreach(var stock in StockService.GetStocksWithBigNews())
{
var userIds = UserService.GetUserIdsThatCareAboutStock(stock);
var connections = /* find connections associated with user ids */;
foreach(var connection in connections)
{
connection.Send(...);
}
}
In this question on filtering connections, they mention that I could keep current connections in memory but (1) it's bad for scaling and (2) it's bad for multi node websites. Both of these points are critically important to our current application. That makes me think I'd have to send a message out to all nodes to find users connected to each node >> my brain explodes in confusion.
THE QUESTION
How do I find a connection for a specific user that is scalable? Am I thinking about this the wrong way?
I created a little project last night to learn this also. I used 1.0 alpha and it was Straight forward. I created a Hub and from there on it just worked :)
I my project i have N Compute Units(some servers processing work), when they start up they invoke the ComputeUnitRegister.
await HubProxy.Invoke("ComputeUnitReqisted", _ComputeGuid);
and every time they do something they call
HubProxy.Invoke("Running", _ComputeGuid);
where HubProxy is :
HubConnection Hub = new HubConnection(RoleEnvironment.IsAvailable ?
RoleEnvironment.GetConfigurationSettingValue("SignalREndPoint"):
"http://taskqueue.cloudapp.net/");
IHubProxy HubProxy = Hub.CreateHubProxy("ComputeUnits");
I used RoleEnviroment.IsAvailable because i can now run this as a Azure Role , a Console App or what ever in .NET 4.5. The Hub is placed in a MVC4 Website project and is started like this:
GlobalHost.Configuration.ConnectionTimeout = TimeSpan.FromSeconds(50);
RouteTable.Routes.MapHubs();
public class ComputeUnits : Hub
{
public Task Running(Guid MyGuid)
{
return Clients.Group(MyGuid.ToString()).ComputeUnitHeartBeat(MyGuid,
DateTime.UtcNow.ToEpochMilliseconds());
}
public Task ComputeUnitReqister(Guid MyGuid)
{
Groups.Add(Context.ConnectionId, "ComputeUnits").Wait();
return Clients.Others.ComputeUnitCameOnline(new { Guid = MyGuid,
HeartBeat = DateTime.UtcNow.ToEpochMilliseconds() });
}
public void SubscribeToHeartBeats(Guid MyGuid)
{
Groups.Add(Context.ConnectionId, MyGuid.ToString());
}
}
My clients are Javascript clients, that have methods for(let me know if you need to see the code for this also). But basicly they listhen for the ComputeUnitCameOnline and when its run they call on the server SubscribeToHeartBeats. This means that whenever the server compute unit is doing some work it will call Running, which will trigger a ComputeUnitHeartBeat on javascript clients.
I hope you can use this to see how Groups and Connections can be used. And last, its also scaled out over multiply azure roles by adding a few lines of code:
GlobalHost.HubPipeline.EnableAutoRejoiningGroups();
GlobalHost.DependencyResolver.UseServiceBus(
serviceBusConnectionString,
2,
3,
GetRoleInstanceNumber(),
topicPathPrefix /* the prefix applied to the name of each topic used */
);
You can get the connection string on the servicebus on azure, remember the Provider=SharedSecret. But when adding the nuget packaged the connectionstring syntax is also pasted into your web.config.
2 is how many topics to split it about. Topics can contain 1Gb of data, so depending on performance you can increase it.
3 is the number of nodes to split it out on. I used 3 because i have 2 Azure Instances, and my localhost. You can get the RoleNumber like this (note that i hard coded my localhost to 2).
private static int GetRoleInstanceNumber()
{
if (!RoleEnvironment.IsAvailable)
return 2;
var roleInstanceId = RoleEnvironment.CurrentRoleInstance.Id;
var li1 = roleInstanceId.LastIndexOf(".");
var li2 = roleInstanceId.LastIndexOf("_");
var roleInstanceNo = roleInstanceId.Substring(Math.Max(li1, li2) + 1);
return Int32.Parse(roleInstanceNo);
}
You can see it all live at : http://taskqueue.cloudapp.net/#/compute-units
When using SignalR, after a client has connected to the server they are served up a Connection ID (this is essential to providing real time communication). Yes this is stored in memory but SignalR also can be used in multi-node environments. You can use the Redis or even Sql Server backplane (more to come) for example. So long story short, we take care of your scale-out scenarios for you via backplanes/service bus' without you having to worry about it.
Related
I'm new to Realm Sync (and Realm). I'm trying to convert a REST / SQL Server system to Realm Sync (to avoid having to write my own local-device caching code).
I got a simple configuration working, with a single API-key user and the null partition, read and write permissions just set to true.
But for my more complex application, I want smaller sub-partitions to reduce the amount of data that needs to be cached on local devices, and I want the sub-partitions to be able to be created dynamically by the client. Ideally, I would like to allow an API-key user to connect to any partition whose name starts with their user id (or some other known string, e.g. the profile name). But I can't find a way to get a "starts with" condition into the permissions.
My best attempt was to try setting Read and Write sync permissions to:
{
"%%partition": {
"$regex": "^%%user.id"
}
}
but my client just fails to connect, saying Permission denied (BIND, REFRESH). (Yes, I tried using "$regex": /^%%user.id/ but the Realm UI rejected that syntax.) The Realm Sync log says "user does not have permission to sync on partition (ProtocolErrorCode=206)".
As you can see in the log image, the partition name was equal to the user id for this test.
Is what I'm trying to do possible? If so, how do I set up the Sync Permissions to make it work?
This can be done using a function. If, like me, you're new to Realm Sync and not fluent in Javascript, don't worry - it turns out to be not too hard to do, after all. (Thanks Jay for encouraging me to try it!)
I followed the instructions on the Define a Function page to create my userCanAccessPartition function like this:
exports = function(partition){
return partition.startsWith(context.user.id);
};
Then I set my sync permissions to:
{
"%%true": {
"%function": {
"name": "userCanAccessPartition",
"arguments": ["%%partition"]
}
}
}
I'm working on a fairly complex Xamarin.Forms application. We make a lot of REST requests. It's been reported that our application isn't respecting DNS failover for load balancing in a timely manner, so I started investigating. I'm running dnsmasq so I can look at when the app makes DNS requests. The code is currently using HttpWebRequest, and I noticed it's making DNS queries at least 10 minutes apart.
I understand part of this is because most .NET networking bits use a keepalive connection. I certainly see a higher rate of DNS queries if I force the headers to not use keepalive, but that adds network overhead so it's not a desirable solution. But I didn't initially see a clear way to control how HttpWebRequest makes DNS queries.
It looked promising that I could get its ServicePoint property and set the ConnectionLeaseTimeout on that. Unfortunately, that throws NotImplementedException in Xamarin so it's not going to be part of any solution.
I thought that perhaps HttpClient would be more configurable. I see a lot of discussion about how to use it properly, and that if you do it that way you need to set ServicePointManager.DnsRefreshTimeout to a smaller value for use cases where you want to expect DNS to update frequently. But this is usually done in conjunction with getting the ServicePoint for the deisred endpoint and also modifying ConnectionLeaseTimeout, which isn't possible.
I've been testing with a very simple app that reuses an HttpClient and makes the same request any time I push a button. Slap this ViewModel behind some Xaml with a button:
using System;
using Xamarin.Forms;
using System.Net.Http;
using System.Net;
namespace TestDns {
public class MainPageViewModel {
private const string _URL = "http://www.example.com";
private HttpClient _httpClient;
private ServicePoint _sp;
public MainPageViewModel() {
var sp = ServicePointManager.FindServicePoint(new Uri(_URL));
_sp = sp;
//_sp.ConnectionLeaseTimeout = 100; // throws NIE
_httpClient = new HttpClient();
ServicePointManager.DnsRefreshTimeout = 100;
}
public Command WhenButtonIsClicked {
get {
return new Command(() => SendRequest());
}
}
private async void SendRequest() {
Console.WriteLine($"{_sp.CurrentConnections}");
var url = "http://www.example.com";
var response = await _httpClient.GetAsync(url);
Console.WriteLine($"{response.Content}");
}
}
}
I didn't expect ConnectionLeaseTimeout to throw. I expected this code to only cache DNS requests for 100ms, I was going to choose a more reasonable timeframe like 2-3 minutes in more production-oriented tests. But since I can't get this simple example to function like I want, it seems moot to increase the delays.
Surely someone else has had this problem in a Xamarin app? Is my only solution going to be to look deeper and try to use native networking constructs?
If you're doing this on Android, DNS is cached for 10 minutes, and I don't believe you have any access to the expiration/refresh time from inside of your app. There are a number of ways to force a refresh but they all involve user actions like going into Network Connections and flipping from Static to DHCP and back, etc.
The only way I can think of to be sure of getting a fresh DNS lookup from inside your app is to have 10+ minutes worth of DNS entries that all alias to your server, and cycle your app through them, so every time you ask for a DNS lookup, it's a new name and not in the cache.
For example, look for 1.server.example.com 2.server.example.com, etc. Each new name will force a new lookup and won't be pulled from the cache because it's not there.
It seems that Java has decided the solution to "some people implement DNS improperly and ignore TTL" is to make the problem worse by ensuring devices that use Java implement DNS improperly. There is a single TTL used for all DNS entries in the cache. There's some philosophical debate and what led me to the answer in this question which I adapted for the answer.
In terms of Xamarin projects, add this somewhere (I chose early in MainActivity):
Java.Security.Security.SetProperty("networkaddress.cache.ttl", "<integer seconds>");
Replace "<integer seconds>" with your desired TTL for all DNS entries. Be aware lower values might mean you make more DNS queries than you used to, if you're seriously trying to save networking bytes this could be an issue.
I'm leaving Terry Carmen's answer selected as "the answer".
I'm building a fairly simple single page app. It's basically a list of items, where each item has some details, an activity log, and a current status along with some buttons to trigger actions on the server to advance the status along a workflow.
It was originally written using MVC and REST/Web API but I got stuck on the problem of keeping concurrent users up to date. For example, if User A adds an item, we want the list on User B's screen to now update to include it.
To solve this I looked into SignalR which works great. But I had a problem.
When adding an item (using POST) the callback adds the item on the requesting client. This is fine.
I then triggered a SignalR broadcast on the server to tell all clients about the new item. This worked fine except the local client, who now has 2 items.
I was looking into filtering the duplicate id client-side, or sending the connection id with the POST, then broadcast to all clients except the requester but it seems a bit needlessly complicated.
Instead I'm just doing this.
public class UpdateHub : Hub
{
public void AddNewItem(NewItem item)
{
// and some server-side stuff, persist in the data store, etc
item.trackingID = new Guid();
item.addLogEntry("new item");
// ...
dataStore.addItem(item);
// send message type and data payload
Clients.All.broadcastMessage("add", item);
}
}
It seems a lot simpler to just get rid of all the REST stuff altogether, so am I missing anything important?
It'll run on an intranet for a handful of users using IE11+ and I guess we do lose some commonly-understood semantics around HTTP response codes for error handling, but I don't think that's a huge deal in this situation.
In order to solve duplicate you can try to use Clients.Others inside Hub class, or AllExcept(id) if you not in the Hub class.
Clients.Others.broadcastMessage("add", item);
In your case using SignalR shouldn`t have any downsides.
I want to pull documents with username attribute
as user1 for user1 like that for each user only attribute with their name.
This is my replication code.
private void setupreplication(){
Console.WriteLine ("Setting up replication");
Uri Server = new Uri("http://192.168.1.213:4984/aussie-coins-syncgw/");
var pull = _db.CreatePullReplication (Server);
var push = _db.CreatePushReplication (Server);
pull.Filter = "byUser";
pull.FilterParams = new Dictionary<string, object> { {"type", "user1"} };
pull.Continuous = true;
push.Continuous = true;
pull.Start();
push.Start();
}
This is my set filter code
_couchBaseLiteLocal.SetFilter("byUser", (revision, filterParams) =>
{
var typeParam = filterParams["type"].ToString();
return (typeParam != null) && typeParam.Equals("user1");
});
With the above code generic pull itself not working.
I just tried to do as given in the documentation.
I do not understand how the setfilter function works to filter data from server. It would be great if someone help in understanding how setfilter works and to make the above code working
Thanks in advance.
The filter function in pull replications can indeed return the specific documents you are interested in. But it's not very efficient, the filter function will run on all the documents on the remote database to determine which ones to pull, every time a pull replication is started.
Instead Sync Gateway introduces the concept of a sync function that incrementally routes and computes access control rules on documents. That way, when starting the pull replication, it's fast and straightforward for Sync Gateway to return the specific documents the user has access to.
You can specify individual channels in a pull replication from Sync Gateway if needed. But the thing to remember is that filtered pull replication between Sync Gateway and Couchbase Lite is not based on filter functions. It's based on the sync function and channel based filtering if needed.
In a P2P scenario (replications between two Couchbase Lite instances), the filter function model is used.
I'm working on an automation service for lync that will automatically add people to an IM conversation based on their availability/lync "presence". It essentially goes down a list, checks who is online, and adds the first person to a call.
The problem I'm getting is that sometimes (usually when lync had to be restarted), it does not always fetch the contact's presence.
First I just had it grab the presence. Then I added code to check for the ContactInformationChanged event firing, but that does not seem to happen unless I go into the app and manually type the alias I'm looking for.
Is there a Refresh() method I'm missing somewhere? Or is there any way to force it to find this? Here's my search methods:
public Contact GetContact(string emailAddress)
{
Contact user;
lock (ContactLookupCache)
{
while (!ContactLookupCache.TryGetValue(emailAddress.ToLower(), out user))
{
lock (Client)
{
Client.ContactManager.BeginSearch(emailAddress, this.HandleContactLookup, null);
}
Monitor.Wait(ContactLookupCache);
}
}
return user;
}
public string GetContactPresenceState(Contact contact)
{
string presenceStatus = contact.GetContactInformation(ContactInformationType.Activity).ToString();
// see if the status is either "Presence unknown" or "Updating..."
if (IsUnknownPresenceState(presenceStatus))
{
lock (contact)
{
//bug?? This event seems to only fire sometimes when you search on the app for contact details
contact.ContactInformationChanged += (object sender, ContactInformationChangedEventArgs e) =>
{
if (e.ChangedContactInformation.Contains(ContactInformationType.Activity))
{
lock (contact)
{
presenceStatus = contact.GetContactInformation(ContactInformationType.Activity).ToString();
if(!IsUnknownPresenceState(presenceStatus))
Monitor.PulseAll(contact);
}
}
};
Monitor.Wait(contact);
}
}
return presenceStatus;
}
Also, sorry for the crappy code... I was just trying to get it to work and kept throwing more junk code in hoping something would help.
Could you verify that the code works fine for all the contacts in your contact list and it's just the ones that aren't listed where presence change events aren't raised correctly?
This makes sense to me given you are using the client SDK which will only tell you about events the client is interested in. For example it would be pretty traffic intensive if all 85,000 clients received the presence changes for the other 85,000 clients in a company.
I think you are in the realms of either polling the presence at regular intervals or adding the contacts to the client (perhaps under a relevant group just to keep things tidy).
Failing that you may want to looking into the UCMA SDK which is better suited to centralised services than the client SDK.