Add OnSendToSubscriber Event Hooks

[leijux]

See #377

[werbenhu]

@leijux Would merging the onAclCheck and OnSendToSubscriber into one make it cleaner and tidier? Just need to modify the parameters of onAclCheck.
Change

func (h *HookBase) OnACLCheck(cl *Client, topic string, write bool) bool

to

func (h *HookBase) OnACLCheck(cl *Client, pk packets.Packet, write bool) bool

[werbenhu]

If we directly modify the parameters of OnACLCheck, won't it affect compatibility with older versions? @mochi-co @thedevop , what are your thoughts on this?

[thedevop]

If we directly modify the parameters of OnACLCheck, won't it affect compatibility with older versions? @mochi-co @thedevop , what are your thoughts on this?

I do like merging this into OnACLCheck, in addition to the benefits you outlined, it is also a bit more performant, as hooks are not "free".

Note, this capability is only usable for embedded use case as current auth hook doesn't provide mechanism to examine packet.

[mochi-co]

@werbenhu @thedevop @leijux I'm also in favour of changing the signature of OnACLCheck, as we will otherwise be creating significant duplicated functionality. However, it will be a breaking change to OnACLCheck (and server references and tests), so I recommend opening a new PR which specifically targets this method.

[coveralls]

Pull Request Test Coverage Report for Build 8585944022

Details

• 11 of 14 (78.57%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.05%) to 98.756%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
server.go	1	4	25.0%

Totals
Change from base Build 8510971796:	-0.05%
Covered Lines:	6115
Relevant Lines:	6192

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💛 - Coveralls

[leijux]

@mochi-co @werbenhu @thedevop Thank you everyone for your opinions. I agree very much with merging into OnACLCheck. I will close this PR and try to merge into OnACLCheck and submit a new PR.