From 7c551f17ecd256b98cce577ddcf935dd3f385583 Mon Sep 17 00:00:00 2001 From: Oliver Gugger Date: Mon, 5 Aug 2024 14:48:54 +0200 Subject: [PATCH] README+docs: create document explaining decimal display and RFQ --- README.md | 6 + docs/rfq-and-price-oracle.md | 244 +++++++++++++++++++++++++++++++++++ 2 files changed, 250 insertions(+) create mode 100644 docs/rfq-and-price-oracle.md diff --git a/README.md b/README.md index 2ec1a67cc..8e5da1c82 100644 --- a/README.md +++ b/README.md @@ -139,6 +139,12 @@ updates the daemon's funds-custody material. Merely having the `lnd` seed phrase is **NOT** enough to restore assets minted or received. **WITHOUT BACKUP BEFORE DELETION, FUNDS ARE DESTROYED**. +## RFQ, asset display unit and price oracle + +[Everything related to the RFQ (Request For Quote) system, the asset's currency +precision (decimal display) and the RFQ price oracle can be found in this +document](./docs/rfq-and-price-oracle.md). + ## Submit feature requests The [GitHub issue tracker](https://github.com/lightninglabs/taproot-assets/issues) can be used to request specific improvements or report bugs. diff --git a/docs/rfq-and-price-oracle.md b/docs/rfq-and-price-oracle.md new file mode 100644 index 000000000..fa717b3a7 --- /dev/null +++ b/docs/rfq-and-price-oracle.md @@ -0,0 +1,244 @@ +# Asset Decimal Display + +Within the Taproot Assets Protocol, an asset's unit is an integer (`uint64`). +That means, the protocol cannot represent fractions of an asset. +Therefore, any asset that represents a fiat currency would need to issue assets +equivalent to at least the smallest unit in use. +For example, an asset that represents the US-Dollar would need to be minted in a +way that one asset unit would represent one USD **cent**. +Or in other words, 100 units of such an asset would represent 1 US-Dollar. + +Because wallet software user interfaces aren't expected to know what +"resolution" or precision any asset in the wild represents, a new field called +`decimal_display` was added to the JSON metadata of new assets minted with +`tapd v0.4.0-alpha` and later (this field is encoded in the metadata field as a +JSON field, therefore it is only compatible with assets that have a JSON +metadata field). + +An issuer can specify `tapcli assets mint --decimal_display X` to specify the +number of decimal places the comma should be shifted to the left when displaying +a sum of asset units. + +For the example above, a USD asset would choose `--decimal_display 2` to +indicate that 100 units ($10^2$) should be displayed as `$1.00` in the wallet +UI. Or another example: 1234 USD cent asset units would be displayed as `$12.34` +in the UI. + +## Precision requirement for assets in the Lightning Network + +Due to the non-divisible (integer) nature of Taproot Asset units, the smallest +asset amount that can be transferred with a Lightning Network HTLC is one asset +unit. + +If one such asset unit represents significantly more than one satoshi, then in +some cases, due to integer division and rounding up, the user might end up +spending more assets than necessary when paying an invoice. + +**Example 1: Paying a 1 satoshi invoice**: + +While writing this article, one USD cent is roughly equivalent to 19 satoshi. + +So if a user with USD cent assets in their wallet attempted to pay an invoice +denominated over 1 satoshi, they would need to send a full USD cent to satisfy +the invoice (again, only full asset units can be transported over an HTLC). + +Even if one cent isn't much, the overpayment would still be roughly `19x`. + +**Example 2: Paying an invoice with MPP**: + +Multi-Part Payments (MPP) allow a single payment to be split up into multiple +parts/paths, resulting in multiple HTLCs per payment. + +If a user wants to pay an invoice over `1,000,000` satoshi, that would be +equivalent to `52,631.5789` USD cents. +If the user were to pay this amount in a single HTLC, they would send `52,632` +USD cents (need to round up to satisfy integer asset amount and invoice minimum +amount requirements), overpaying by `0.4211` cents. + +If the user's wallet decided to split up the payment into 16 parts for example, +then each part would correspond to `3289.4737` cents. To satisfy the integer +asset amount and invoice minimum amount requirement, each of the 16 HTLCs would +send out `3290` cents. That's a full `8.4211` cents of overpayment. + +## What precision should I choose when minting an asset for the Lightning Network? + +To address the issue of rounding up when splitting payments or representing +small satoshi amounts as asset units, an issuer of assets should use a high +enough value for `decimal_display` when minting. + +**But what is a good value for `decimal_display`?** + +The rule of thumb is: The closer to representing 1 satoshi with one asset unit, +the better (the smaller the potential overpayment due to integer division). + +Let's look at a few examples below. For the examples we assume that the normal +maximum number of parts for an MPP is 16 (can be higher in rare cases but 16 is +the default), and the maximum theoretical overpayment is up to 16 asset units. + +**Example 1: US-Dollar, decimal display of 2**: + +```text +Satoshi per USD = 1972 (1 BTC = 50,702 USD) +Decimal Display = 2 +Satoshi per Asset Unit = 19.72 (19720 milli-satoshi per Asset Unit) +Maximum overpayment = 16 units (= 0.16 USD) +``` + +**Example 2: US-Dollar, decimal display of 4**: + +```text +Satoshi per USD = 1972 (1 BTC = 50,702 USD) +Decimal Display = 4 +Satoshi per Asset Unit = 0.1972 (197 milli-satoshi per Asset Unit) +Maximum overpayment = 16 units (= 0.0016 USD) +``` + +**Example 3: Japanese Yen, decimal display of 1**: + +```text +Satoshi per JPY = 13.62 (1 BTC = 7,341,847 JPY) +Decimal Display = 1 +Satoshi per Asset Unit = 1.362 (1362 milli-satoshi per Asset Unit) +Maximum overpayment = 16 units (= 0.16 JPY) +``` + + +# RFQ + +The RFQ system is responsible for acquiring real-time price quotes for +converting between asset units and satoshi (both directions) or between +different asset types. + +There are two main user stories (as seen from the point of view of the wallet +end user): + +1. Sending out assets: The user wants to pay a Lightning Network invoice that + is denominated in satoshi. The user only has assets in their wallet, they + (or their wallet software) want to find out how many asset units they need to + send in order to satisfy the invoice amount in satoshi. +2. Receiving assets: The user wants to get paid in a specific asset. The user + only knows about the asset, so they (or their wallet software) want to find + out what the asset amount corresponds to in satoshi. + +## Sell order + +The sell order covers the first user story: The user wants to pay a +satoshi-denominated invoice with assets. The end result is that the user sells +some of their assets in their channel to the RFQ peer (edge node), requesting +them to forward satoshi to the network. + +Formal definition (TODO: refine): +- Use case: sending assets as a payment, selling `buxx` for `msat` +- User query: `Q = how many out_asset units for in_asset amount?` (how many + `buxx` do I need to seel to pay this payment denominated in `msat`?) +- `out_asset`: `buxx` (user sells `buxx` asset to RFQ peer) +- `in_asset`: `msat` (user "receives" `msat` from RFQ peer, which are then + routed to the network) +- `max_amount`: `in_asset` (what is the maximum amount of `msat` the RFQ peer + has to forward to the network? Equal to invoice amount plus user-defined max + routing fee limit) +- `price_rate`: `in_asset/out_asset` (`msat / buxx`) + +## Buy order + +The buy order covers the second user story: The user wants to get paid, they +create a satoshi-denominated invoice from their chosen asset amount they want to +receive. The end result is that the user buys assets into their asset channel +from their RFQ peer (edge node) and the RFQ peer is paid in satoshi by the +network. + +Formal definition (TODO: refine): +- Use case: receiving assets through an invoice, selling `msat` for `buxx` +- User query: `Q = how many out_asset units for in_asset amount?` (how many + `msat` should I denominate my invoice with to receive a given amount of + `buxx`?) +- `out_asset`: `msat` (user sells sats to RFQ peer, which are routed to them by + the network) +- `in_asset`: `buxx` (user buys `buxx` from RFQ peer) +- `max_amount`: `in_asset` (what is the maximum number of `buxx` the RFQ peer + has to sell? Equal to the amount in the user query) +- `price_rate`: `out_asset/in_asset` (`msat / buxx`) + +## Examples + +**Case 1**: Buying/selling USD against BTC. + +```text +In Asset: USD with decimal display = 4 (10_000 asset units = 1 USD) +Out Asset: satoshi / milli-satoshi + +Example 1: +---------- + +What is price rate when 1 BTC = 20,000.00 USD? + +Satoshi per USD: 5,000 +Satoshi per Asset Unit: 0.5 +Price rate: 500 (msat / asset unit) +Asset Units per Satoshi: 2 + + +Example 2: +---------- + +What is price rate when 1 BTC = 1,000,000.00 USD? + +Satoshi per USD: 100 +Satoshi per Asset Unit: 0.01 +Price rate: 10 (msat / asset unit) +Asset Units per Satoshi: 100 + + +Example 3: +---------- + +What is price rate when 1 BTC = 10,000,000.00 USD? + +Satoshi per USD: 10 +Satoshi per Asset Unit: 0.001 +Price rate: 1 (msat / asset unit) +Asset Units per Satoshi: 1000 +``` + +**Case 2**: Buying/selling USD against JPY. + +```text +In Asset: USD with decimal display = 4 (10_000 asset units = 1 USD) +Out Asset: JPY with decimal display = 1 (10 asset units = 1 JPY) + +Assumption: 1 USD = 142 JPY + +Example 1: +---------- + +What is price rate when 1 BTC = 20,000.00 USD (1 BTC = 2,840,000 JPY)? + +Satoshi per USD: 5,000 +Satoshi per In Asset Unit: 0.5 +Milli-satoshi per In Asset Unit: 500 + +Satoshi per JPY: 35.211 +Satoshi per Out Asset Unit: 3.521 +Milli-Satoshi per Out Asset Unit: 3521 + +Price rate (Sell Order): 500/3521 = 0.142 ~= 0 +Price rate (Buy Order): 3521/500 = 7.042 ~= 7 + + +Example 2: +---------- + +What is price rate when 1 BTC = 1,000,000.00 USD (1 BTC = 142,000,000 JPY)? + +Satoshi per USD: 100 +Satoshi per In Asset Unit: 0.01 +Milli-satoshi per In Asset Unit: 10 + +Satoshi per JPY: 0.704 +Satoshi per Out Asset Unit: 0.0704 +Milli-Satoshi per Out Asset Unit: 70 + +Price rate (Sell Order): 10/70 = 0.142 ~= 0 +Price rate (Buy Order): 70/10 = 7 +``` +