Network module SPI

[mscheibler]

I like to enable the Paho Java Client to be extended by custom NetworkModules without introducing dependencies into the Paho Java client project.
So it will be possible to create my custom NetworkModule and still be able to use the Java Client from the Paho Project without the need to maintain a separate fork.

During the review i would really like to add some more documentation to the org.eclipse.paho.client.mqttv3.internal.NetworkModule interface. Especially about when / how often are the methods called. What are the consequences of the exceptions? How is the NetworkModule expected to behave on Exceptions, e.g. like who is triggering a reconnect?

Please make sure that the following boxes are checked before submitting your Pull Request, thank you!

• You have signed the Eclipse ECA
• All of your commits have been signed-off with the correct email address (The same one that you used to sign the CLA)
• If This PR fixes an issue, that you reference the issue below. OR if this is a new issue that you are fixing straight away that you add some Description about the bug and how this will fix it.
• If this is new functionality, You have added the appropriate Unit tests.

[mscheibler]

I spent some time to understand the way the Paho client uses its NetworkModules and wrote an APIdoc based on my findings. If i misunderstood something or missed an important part, please let me know.

[jpwsutton]

Hi @mscheibler, Thank you for this contribution. It's definitely a nice way to refactor the older Network Module architecture and helpfully would resolve Enhancement #26 I think. The documentation and tests are a very welcome addition (We don't usually get those from contributors!). I'm going to pull your changes locally just to make sure that I fully understand how the SPI process works and once I'm happy I'll merge them in.

[mscheibler]

Hi @jpwsutton
Thanks for the review. I've come to an issue yesterday evening with the Android packaging. The files under META-INF/services are currently not packed into the Android library and so the services are not known. This is not a direct problem of the Paho Java client, but must be considered when using in Android.
Because i want to use the library in Android i will definitely look into this issue, but this may take a day or two. I would suggest not to merge before this is solved. I keep you updated.

[mscheibler]

Hi @jpwsutton
I did a small change for Android, so the ServiceLoader is able to find the declared Services under Android. The deployment problem did not really exist, i made a mistake in my own Android project. (transient dependencies are not included in the APK)
I was able to test my refactoring with the org.eclipse.paho.android.sample app. Unfortunately the unit-tests are currently stuck in the reconnect test, but this appears not to be related to my changes. I think the pull request can be merged if you see fit.
Best regards Maik

[mscheibler]

Hello @jpwsutton
Did you have a chance to review the pull request? We are already using a patched version without any problems.
Best regards Maik

[mscheibler]

Hello @jpwsutton
Is there anything i can do to help the pull request to get merged? I updated it again to resolve the conflicts.

[jpwsutton]

Hi @mscheibler, Sorry for the delay in getting this merged, I've finally had some time to sit down and go through it again, and am very glad to have merged it today. Thanks for all of your hard work!