WIP: Cancel message

[LipuFei]

Use cancel message to replace undo message.
All undo message code remain the same.

[LipuFei]

@whirm I'll remove the pep8 commit for now, otherwise the PR is too difficult to review.

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[whirm]

@LipuFei yes, those should always go alone

[NielsZeilemaker]

@LipuFei why are you adding the cancel to the permission triplet? That shouldn't be neccesary. You authorise someone to send a dispersy_cancel message etc.

[LipuFei]

@NielsZeilemaker I made this PR to make it easy for us to review. Thanks! I'll check everything again.

[LipuFei]

@NielsZeilemaker What does the permission_triplets mean?

[NielsZeilemaker]

Basically, you can authorize/revoke or grant someone the permission to create a message of a certain type. I wouldn't start messing with this as its never tested/understood by me.
Moreover, are you sure you want to introduce a cancel callback? Maybe calling the undo callback would suffice. Chaning it slightly to allow you to pass a cancelled/undone/done variable instead of the undone/done currently used.

[NielsZeilemaker]

Btw, the documentation regarding the permissions should still be correct. You can have a look there.

[LipuFei]

@NielsZeilemaker I had thought about it and I decided to duplicate the undo stuff instead of messing them up. Later, when we want to remove the undo, we can simply remove every undo-related thing without worry about causing damage to the cancel message. I will read the permission docs. Thanks!

[NielsZeilemaker]

I would remove the cancel here, but leave it in timeline.py. E.g. add it when the "undo" thingy is there.

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[LipuFei]

@whirm I guess this is more or less it. I will check the unit tests one more time after my presentation rehearsal. Also, before we merge, we should change the AllChannel community to use this cancel message and test on jenkins.

[whirm]

Ok, let's review it later

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[LipuFei]

@NielsZeilemaker One of the cancel message tests didn't pass. The test does the following:

Three nodes: SELF, NODE, OTHER
What they do:
1. SELF gives NODE the permission to cancel.
2. OTHER created message M1.
3. NODE cancels M1 with cancel message C1.
4. M1 should be found as cancelled by NODE (This one passed).
5. SELF revokes NODE's cancel permission.
6. M1 should still be marked as cancelled by NODE (This one failed).

This test was passing before. Am I doing it correctly? If a user's cancel permission has been revoked, should his old cancel messages be regarded as invalid as well?

[NielsZeilemaker]

@LipuFei maybe create a wiki page describing the cancel message, and what it should do. Then afterwards, I can have a look and maybe we can modify the behaviour of your implementation accordingly.
Also describe situations such as the one above. A gets the permission to cancel other, A's permission gets revoke -> what should be do with the messages cancelled by A.

[LipuFei]

@NielsZeilemaker I've made a wiki page: https://github.com/Tribler/dispersy/wiki/Cancel-Message. Hope it explains.

[NielsZeilemaker]

@LipuFei I made some changes to the document. I guess cancel messages should also not cancel an authorize message right? Or are we adding that? Additionally, we should think about being able to drop cancelled messages from the database in order to save space.

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[LipuFei]

Hi @NielsZeilemaker, could you review this PR again? Thanks!