Yet another PrivateSend refactoring/optimization - core part

[UdjinM6]

That's the core part of #1120. Progress of fixing/refactoring/cleanup can be checked there (see checkboxes and/or merged references). The rest of changes is pretty much about changing the way mixing states are handled i.e. core feature so I think it makes sense to push them all at once. I squashed the history into one commit to exclude previous fixes and all "fix", "another fix", "cleanup" changes :) I also tried to break changes in kind of sub-categories below, hope it helps a bit.

Refactoring:

• IsDenomCompatibleWithSession, split in 3 - CreateNewSession, AddUserToExistingSession and IsAcceptableDenomAndCollateral
• CheckTimeout:
  • should not rely on CDarkSendEntry nTimeAdded to clear entries, instead should rely on time of the last successful step i.e. nLastTimeChanged
  • nLastTimeChanged should only be set when mixing moved forward in some way

State related:

• local pool should be in POOL_STATE_IDLE initially
• local pool should switch to POOL_STATE_QUEUE when connected to mn
• local pool should set session id only when in POOL_STATE_QUEUE
• SetState should set state local only, no relaying
• mixing wallets should rely on local logic and expected set of state switches rather then updates from masternodes
• deprecate STATUS_SET_STATE, POOL_STATE_UNKNOWN, POOL_STATE_TRANSMISSION, POOL_STATE_FINALIZE_TRANSACTION

Session related:

• deprecate fSessionFoundMasternode, use nSessionID instead
• deprecate nSessionUsers, use vecSessionCollaterals.size() instead

Other:

• deprecate IsNull()
• move few things to private
• remove deprecated
• bump min ps peer proto

[UdjinM6]

rebased

[UdjinM6]

So, just a quick high-level overview of how states/messages should work now:

• client side: state POOL_STATE_IDLE ---(send DSACCEPT)---> state POOL_STATE_QUEUE ---(DSQUEUE with fReady == true received)---> send inputs (DSVIN), state POOL_STATE_ACCEPTING_ENTRIES ---(DSFINALTX recieved)---> sign your inputs in final tx and send it back (DSSIGNFINALTX), state POOL_STATE_SIGNING ---(DSCOMPLETE received)---> state POOL_STATE_IDLE
• mn side: state POOL_STATE_IDLE ---(DSACCEPT received)---> state POOL_STATE_QUEUE, relay DSQUEUE ---(enough DSACCEPT received)---> state POOL_STATE_ACCEPTING_ENTRIES, create and relay new DSQUEUE with fReady == true ---(enough DSVIN received)---> state POOL_STATE_SIGNING, relay tx to sign ---(enough DSSIGNFINALTX received)---> relay DSTX and DSCOMPLETE, state POOL_STATE_IDLE

Reviewers wanted :)

@crowning- ? ;)

[crowning-]

That's quite some work, so it would be nice if someone else would review it as well.

Since I can't do a complete review I'll update whenever I find some time.

[crowning-]

Is nLastTimeChanged reinitialized (aka is CreateNewSession called) when the client tries again?
If not he would immediately run into a timeout when he tries again, so a nLastTimeChanged = GetTimeMillis(); would be needed here.

[UdjinM6]

nLastTimeChanged is changed at every successful step, not only as a part of CreateNewSession() - in both SetNull() and DoAuto() if we talk about (re)starting a session. Also it times out only when nState != POOL_STATE_IDLE. Technically, time is set first DoAuto() before switching from idle to queue, but it's two lines next to each other in the same function and I doubt it can cause issues. I think it won't hurt changing the order of instructions though for better readability/logic of handling them. Also nLastTimeChanged name itself doesn't say what it really does now, I'll fix that too.

[UdjinM6]

2 more fixes:

• rename UpdatePoolStateOnClient to CheckPoolStateUpdate
• reset pSubmittedToMasternode in SetNull()

[UdjinM6]

Ok, no more comments for the last week so I guess it's ok to merge :)
Note: this will break mixing on testnet until proto bump, that's expected, not an issue