New guarantee mechanism

[mmyyrroonn]

Fix #95
Guarantor increasing his votes won't bring side-effect.

• Questions
  • What will happen when several guarantors guarantee concurrently.
  • Guarantor can attack the blockchain by calling guarantee millions of times. Each time he just increases his vote with a minimal staking.

Fix #118

[badkk]

Fix #95

Guarantor increasing his votes won't bring side-effect.

• Questions

  • What will happen when several guarantors guarantee concurrently.

  • Guarantor can attack the blockchain by calling guarantee millions of times. Each time he just increases his vote with a minimal staking.

• The first question is about tx pool in substrate, I cannot give a certain answer but we can obey substrate's runtime module function rules, AFAIK, this is an atomic operation.
• The second question is all about ddos. They can hardly do this cause they need to pay tx fee. So the 2nd question is not our problem.

[badkk]

Currently, we combine {add new guarantee, delete old guarantee} into A single guarantee action, however, once we wanna resolve #95 , this became confusing of code logic, maybe we can split into totally 2 functions to simplify the logic @myronfanqiu

[badkk]

Fix #95
Guarantor increasing his votes won't bring side-effect.

• Questions

  • What will happen when several guarantors guarantee concurrently.
  • Guarantor can attack the blockchain by calling guarantee millions of times. Each time he just increases his vote with a minimal staking.

Added to the 1st question, it includes 2 scenarios:

1. Concurrency happens in the same node: it will be sorted by tx pool, and if v's stake limit reached, later priority guarantee tx will be rejected;
2. Concurrency happens in the different nodes: if the tx sync is not on time(for example, if G1->V1 comes later than G2->V1, but G2->V1 already be accepted in another node's block); this depends on tx sync speed. If this happens(low priority), 1 of these 2 txs will be illegal(the tx included into final main-chain will be valid, at most 12s? in our system).

[badkk]

Talked offline, basically, this PR will make guarantee function into 2 separated functions:

1. guarantee: guarantee new stake to validator;
2. cut_guarantee: cut stake to current guarantee;