Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>I've been doing some work with MQTT on Android and I've experienced exactly the same issue.</p> <p>As Dale says, the old version of the MQTT client used to have an explicit ping() method, but unfortunately this is now hidden away.</p> <p>The simplest approach, and the one I use, is to explicitly publish a 1 byte message to a particular topic, to serve as the keepalive. I don't think this should add much to the overhead of your application and, while I'm not familiar with Mosquitto's ACL, I assume you could have every client use the same 'keepalive' topic and just provide write access to all. This shouldn't affect security as long as no-one can read from the topic.</p> <p>An alternative approach would be to have the server send the client(s) a 'keepalive' message at QoS 1 or 2 (pub/sub through a single topic to all for efficiency) as, due to the QoS flows, this will involve the client sending a message back to the server under the covers; which will serve as the keepalive. This has the advantage of keeping your clients as subscriber only; however it's incompatible with 'clean session = false' (as you would have large amounts of messages queued up for delivery to clients who are offline for a while - needlessly affecting performance on reconnect).</p> <p>Unfortunately these are the only two workarounds that I can currently think of.</p> <hr> <p>Also, as a brief aside, I've experienced a number of issues using the MqttDefaultFilePersistence on Android, so you might want to be aware of this. In particular to do with file locking and problems when re-instantiating the client. To get around this I've created an implementation of MqttClientPersistence built on top of an SQLite database and this is much more robust; you might want to do the same.</p>
    singulars
    1. This table or related slice is empty.
    1. POHow to send ping using Eclipse Paho MQTT client?
      singulars
      1. PTQuestion
    1. PTAnswer
    1. This table or related slice is empty.
    1. USstephendnicholas
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. POHow to send ping using Eclipse Paho MQTT client?
      singulars
      1. PTQuestion
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTAcceptedByOriginator
    1. COThank you! The reason of not allowing the clients to publish is I saw the [max length](https://answers.launchpad.net/mosquitto/+question/188424) of messages supported by MQTT/Mosquitto is too high, according to the link ~260MB. Do you think this puts a threat on the server? As the free brokers (Mosquitto/RSMB) doesn't support SSL, plain username/password based authentication didn't seem secure enough to me, so I wanted to forbid publish access to anybody but the server itself, where Man-in-the-middle attack is not possible. I'm not security expert, this is just assumption.
      singulars
      1. PO
      1. USMehdi
    2. COOne more thing on the side note: Eclipse Paho has an internal memory persistence class `org.eclipse.paho.client.mqttv3.internal.MemoryPersistence` , I'm using that to avoid the hassles you mentioned.
      singulars
      1. PO
      1. USMehdi
    3. COHmm, tough one. I guess it depends how robust the broker is and whether it can handle someone bombarding it with ~260MB messages in an attempt to swamp it; as this is the only attack I think this would leave you open to. As you say, plain username/password isn't going to provide any protection since it could just be sniffed on the wire.
      singulars
      1. PO
      1. USstephendnicholas
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload