New BSIP: Implement Buy Limit Order

BSIP:
Title: Implement Buy Limit Order
Authors: Abit More
Status: Draft
Type: Protocol
Created: 2017-11-02
Discussion: https://github.com/bitshares/bitshares-core/issues/342
Replaces: (optional)
Superseded-By: (optional)
Worker: (optional)

# Abstract

By now, in BitShares, since all markets are flip-able, all limit orders are implemented as *sell limit order*s. When a user placing a buy order via GUI, actually it's placed as a sell order in the flipped market. Although usually a flipped sell order is very close to a buy order, their behaviors are a bit different, as a result, this has led to some confusion. This BSIP proposes a protocol change to address this issue.

# Motivation

Make the exchange more user-friendly.

# Rational

A typical exchange should have both buy limit order and sell limit order with different behavior.

# Specifications

[WIP]

A limit sell order means a user set a minimum price and an exact amount of one asset (which she owns) to sell, expecting all of them to be bought, and expecting to get at least `amount*price` of the other asset (which she doesn't have). It's expected and acceptable that she will get more than she wanted when there are better offers in the market.

A limit buy order means a user set a maximum price and an exact amount of one asset (which she doesn't have) to buy, and willing to pay at most `amount*price` of the other asset (which she owns). It's NOT acceptable if she finally got more than she wanted, instead, it's expected and acceptable that she will pay less when there are better offers in the market. When the order is partially filled, if the remaining fund is not enough to pay for the rest desired amount on next match, the order should be cancelled.

All above are talking about taker orders, when placing the order, there may be better offers on the order book already. For maker orders, usually the owner won't get a better offer, unless caused by rounding.

# Discussion

# Summary for Shareholders

# Copyright

This document is placed in the public domain.

# See Also

* https://github.com/bitshares/bitshares-core/issues/342

Start by reading the BSIP draft and the linked discussion at bitshares/bitshares-core#342. The specifications are marked WIP, and the issue does not identify implementation files, tests, or a complete acceptance condition; the work is not ready to start until the protocol design and completion criteria are settled.

Written by the indexing model from the issue text.