Implementation of XEP-0191 "Blocking command"

[bartekgorny]

This PR implements XEP-0191. Mostly as a separate module, though there were some minor changes to mod_privacy (so that it doesn't handle what it should not) and to ejabberd_c2s (since part of privacy logic is there, and there were bits and pieces of blocking commands implementation already).

[Nyco]

In the doc/modules/mod_blocking.md:

• "This extension is allows": remove the "is"
• "with a single commands.": remove the s, "command"
• "The protocol is much simpler then in privacy lists.": "The protocol is much simpler than privacy lists."

Otherwise, thanks a lot!

[ludwikbukowski]

I would catch some Variable instead of wildcard and return it in {error, Other} tuple. I think bare e is too little meaningful

[michalwski]

This suite looks quite comprehensive. I don't see it run though.

1. It's not present here: http://mongooseim-ct-results.s3-website-eu-west-1.amazonaws.com/branch/master/1619/1/big/index.html
2. The coverage for mod_blocking is very low: https://coveralls.io/builds/6502277/source?filename=apps%2Fejabberd%2Fsrc%2Fmod_blocking.erl
3. It's not present in default.spec

How can we be sure the implementation works as expected? Do we need this suite at all?

[michalwski]

Also I'd rather make most of the tests parallel, if this is possible.

[bartekgorny]

Grrr, I forgot to add it to default.spec...

[ludwikbukowski]

since the blocking_commands module uses privacy lists API functions there shouldn't be any inconsistency on the backend side. Due to XEP-0191:Blocking Commands/Relationship to Privacy Lists seems that protocol also allows such a situation but:

Because of the potential for confusion between block lists and privacy lists, it is NOT RECOMMENDED for a client to request both the block list and privacy lists in the same session.

In my opinion, If we'd like to allow users to use both modules maybe we should intruduce some tests with scenarios where client uses both privacy and blocking commands

[michalwski]

I think we shouldn't allow users to use both modules in the same session. And since blocking commands are simpler than privacy lists and do most of the job user wants, I think we should have only mod_blocking enabled by default. If someone needs more advanced features provided by mod_privacy, the module can be enabled.

[bartekgorny]

Needs some testing, but can be done, no problem

[bartekgorny]

edit: nope, it is a problem, blocking commands don't work because privacy backend is not loaded. Can probably be worked around somehow, but is it worth it? Client has been warned...

[michalwski]

Right, I've forgotten about this. Let's leave it as is.