Buyback accounts

[theoreticalbts]

Buyback -- as returns to holders of an asset (see #452 and #524) -- will be implemented by creating a standard account with an extension and null authority.

The account will then act autonomously by reserving all of the asset it receives, and using all other assets to place a market order each maintenance interval to attempt to clear out the market. It will then cancel its order.

There are several desirable features to using an account in this role, as opposed to a new object:

• Leverages already-existing maker-taker logic for walking the book.
• Leverages already-existing account history UI to allow people to monitor the buyback program's actions.
• Gives a meaningful account_id for market orders.
• Bounded resources: The only network resources needed are the equivalent of one market order per asset per maintenance interval. An ordinary asset creation fee should be sufficient to cover this cost. Fee circumvention is not much of an issue as the other side of each trade will still pay fees.
• Buyback objects cannot interact, so even if assets A and B both have buyback, only one buyback order will be active at a time, so the orders can't match against each other.

[xeroc]

Am I assuming right that

• everyone will be able to create such an account
• everyone will be able to use such an account
• the account has a set of predefined markets to sell its assets on?

[theoreticalbts]

You're right, it will need to have a set of predefined markets of bounded size -- maybe 4? We just need to make it a parameter.

[abitmore]

Why not the FBA:BTS market only? You got all fees in BTS. The FBA owners own only FBA. What are other markets?

[theoreticalbts]

@abitmore : I designed this to be a general primitive which may be used for more than just FBA.

[theoreticalbts]

Force-pushed new version based #566 which also doesn't suffer from #575

[theoreticalbts]

Implemented, merged.