Develop Reference

How to force MQTT broker to NOT clean session from Android Paho client?

I'm trying to use MQTT (Paho library on Android, mosquitto message broker on a linux server) to pass moves in a turn-based game, replacing a custom server I wrote years ago. Its simplicity and pub-sub design seem perfect: each device subscribes to a unique id as "topic" and communicates that as its "address." Then other devices can reach it by publishing to that address.
It works perfectly in my test Linux client (connecting using the mosquitto-dev library on Ubuntu). And it works perfectly on Android WHEN THE ANDROID APP IS RUNNING. In the Linux client case, if a message is sent while the app isn't running or connected the app receives the message as soon as it does connect and subscribe. On Android, however, this doesn't happen. Only messages sent (or resent) by another client while the android client is subscribed are ever delivered.
I'm new to MQTT, but it seems pretty clear that the "cleanSession" connection parameter is what controls this: unless you "clean" a session, you get everything that was published to your topic while you were not subscribed. On the Linux client side, passing "true" to mosquitto_new(..., clean_session, ...) does indeed prevent my Linux client from getting pre-connection messages. But on the Android side, calling .setCleanSession(boolean) has no effect when the MqttConnectOptions instance is passed to .connect().
I'm using 1.1.+ of paho. Per the tags in the repo at https://github.com/eclipse/paho.mqtt.android.git, v1.1.1 is the latest.
implementation "org.eclipse.paho:org.eclipse.paho.client.mqttv3:1.1.+"
implementation "org.eclipse.paho:org.eclipse.paho.android.service:1.1.+"
I suspect that this is simply a bug in the Android Paho library (which doesn't seem to have been worked on in four years.) But I hope I'm wrong! Is there a way to accomplish what I want?
Alternatively, is there a better library? The googling I've done suggests that in spite of its age Paho is still what most Android devs are using to speak MQTT.
Thanks!

About the cleanSession flag.
The Client and Server can store Session state to enable reliable messaging to continue across a sequence of Network Connections. This bit is used to control the lifetime of the Session state.
If CleanSession is set to 0, the Server MUST resume communications with the Client based on state from the current Session (as identified by the Client identifier). If there is no Session associated with the Client identifier the Server MUST create a new Session. The Client and Server MUST store the Session after the Client and Server are disconnected. After the disconnection of a Session that had CleanSession set to 0, the Server MUST store further QoS 1 and QoS 2 messages that match any subscriptions that the client had at the time of disconnection as part of the Session state. It MAY also store QoS 0 messages that meet the same criteria.
More about cleanSession on : https://docs.oasis-open.org/mqtt/mqtt/v3.1.1/csprd02/mqtt-v3.1.1-csprd02.html
If I understand correctly your requirement, then indeed you need to use clenSession=true. You can also try publishing and subscribing with QoS=0. Some brokers do not store QoS=0 messages, mosquitto as well. (as per https://mosquitto.org/man/mqtt-7.html)

I've found a workaround, and in the process confirmed my suspicion that the MqttAndroidClient class is broken in not honoring that setting. Instead of using MqttConnectOptions I tried using MqttAsyncClient. The code changes are trivial, though underneath there's considerable change as the Android client knows about and uses background Services. With the simple change of using this different class, I'm able to connect & subscribe and immediately receive all messages that were published while I was not connected.

Phoenix channels with Android client

I'm trying to create a websocket connection to my Phoenix app from an Android client. I'm trying to use this library but I'm running into this issue and I'm unable to successfully join a channel.
Upon reviewing the source code of the above java phoenix client library, it looks like the initial request from the client to connect to the socket is made with http schema and not ws (the source code explicitly changes the provided url to make sure it always uses http). It's not clear to me how this would work without additional configuration in my Phoenix app: if a socket connect request is made to http://localhost:4000/socket, the request will fail because there is no route for /socket when the schema is http.
There's nothing in the library docs that says any additional config is required in my Phoenix app to make this work, but I don't see how it could work for the reason stated above.
Does a Phoenix app have built in handling for the connection upgrade, etc, required on handshake as specified here?
As a note, I have no issues making websocket connections from my javascript web client to my Phoenix backend.
Any suggestions are appreciated!

Have you tried using the default path for a channel http://localhost:4000/socket/websocket ?

SignalR Android and Headers

I used to use HTTP Headers to pass some authentication data from my SignalR Client (Android) to our SignalR.
After updating my project to use the lastest source from GitHub, this technique has stopped working.
After some research, I noted that this happens because the new default transport used is websocket, and websocket don´t allow us to use Http Headers.
So,
Is there any way to use HTTP Headers with SignalR and WebSockets transport?
If no, how could I pass some parameters to my server? Is there any other option available than using QueryStrings?
Thanks!

In general you should be able to set headers in the client and it should send them to the server when the websocket is being opened (the connect request). Not sure what client you use but this this is possible when for sure with C# client. However, as opposed to other transports, sending or receiving messages when using websockets does not require creating new HTTP requests and therefore if you set headers after the websocket is opened they won't be sent to the server until the next time the client has to send an HTTP request which is either when the client needs to reconnect or when the connection is stopped.
Another option (if your client does not support headers for websockets) is to send parameters using query string. On the server side you can get the request using the HubCallerContext.Request property which allows you accessing the query string like this (you can also read cookies the same way):
Context.Request.QueryString
Again, query string will only be sent to the server if the client is making an HTTP request, which in case of websockets after the connection is established happens when the connection is reconnecting or is being stopped.
Finally, you already have a connection to the server so maybe you can just send your parameters using this connection which should work regardless of the transport you are using.

Can't connect to GCM using node-xmpp client

I am attempting to run gcm server using node-xmpp, but xmpp client does not seem to open at all and closes after timeout.
var xmpp = require('node-xmpp-client');
var options = {
type: 'client',
jid: 'fake-project-123#gcm.googleapis.com',
password: 'ApiKeyHere',
port: 5235,
host: 'gcm.googleapis.com',
legacySSL: true,
preferredSaslMechanism : 'PLAIN'
};
console.log("Creating XMPP Application");
var cl = new xmpp.Client(options);
cl.on('online', function()
{
console.log("XMPP Online");
});
Rest of the code was omitted. In the console, I never get to see "XMPP Online".
How do I check if xmpp is even connecting, and where it fails to open?

I got the same problem and found out that the Connection.startStream() was never called, although the socket was opened successfully.
Here's my pull request:
https://github.com/node-xmpp/node-xmpp-client/pull/61
Until it gets merged, you can use my fork, which should work for GCM:
https://github.com/Riplexus/node-xmpp-client

I followed this from gcm google groups and it worked for me.
And for timeouts you can try
xmppClient.connection.socket.setTimeout(0)
xmppClient.connection.socket.setKeepAlive(true, 10000)
Don't forget to whitelist your server ip in google console.

I have given up the hope of using node-xmpp and game smack client a try. Sadly it did not work, but I did get an error saying my project is not whitelisted. When project is whitelisted, it can receive messages from android devices, which is exactly what I need and is the sole reason why I went straight to CCS (XMPP). Without the whitelist, it is not possible to use CCS (XMPP) for sending the messages to android devices. In order to use HTTP method, the project does not need to be whitelisted, but has a limitation to being able to send messages only. I have signed up upstream GCM but have yet to receive response.
https://services.google.com/fb/forms/gcm/

Check HTTP request against reliable server

In my android app i keep getting timeouts in the messages between the app and my server.
In an attempt to see if the problem is in the app or my server,
i want to try and Send an HTTP request from my app to
some other server i am sure is up and reliable and then see if i get timeouts.
Is there any server address i can check against?
Thanks in advance!
BTW : i am using a glass Fish servlet for my server

We've successfully sent a simple HTTP GET to google.com -- with a couple of fall-backs (I've also seen internic.org used) in the past, in similar cases.