add cancel command for conflict attribute

[superboyiii]

Related to: neo-project/neo#2818

1. Add cancel command.
2. Check if aimed tx is in mempool, if it is, choose the max networkfee between the current and the aimed. If it isn't, wait for inputting networkfee manually.
3. Add a NOP to tx.script to ensure not rejected by consensus.
4. Return error when aimed tx is already confirmed.

[vncoelho]

What is the reason behind this PR?
There is a logic that needs to work if the TX is send.

[superboyiii]

What is the reason behind this PR? There is a logic that needs to work if the TX is send.

Do you mean check if tx is already confirmed? It's just to avoid meaningless operation. No one wants to pay fee to cancel an already existed transaction. And if it's existed, no need to execute the rest code.

[vncoelho]

I mean the cancel command

[vncoelho]

Can the node current cancel a normal tx with command?
That is why I'm asking about the conflict. Why this "feature" is really needed? In particular, manually.

[superboyiii]

Can the node current cancel a normal tx with command? That is why I'm asking about the conflict. Why this "feature" is really needed? In particular, manually.

Cancel tx when it's not on-chain yet.(In mempool)

[shargon]

I mean the cancel command

It's for use Conflicts attribute.

[vncoelho]

Cancel tx when it's not on-chain yet.(In mempool)

Why do not add this feature to any tx in this case as well? Why just the ability to cancel conflict (if not on-chain)?

[superboyiii]

Cancel tx when it's not on-chain yet.(In mempool)

Why do not add this feature to any tx in this case as well? Why just the ability to cancel conflict (if not on-chain)?

It's any tx, just in a new transaction attribute called Conflicts

[vncoelho]

Thanks, @superboyiii ,I will check code and test here as well.

[Jim8y]

@superboyiii format update please

[superboyiii]

@superboyiii format update please

Done