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147 lines
7.9 KiB
Markdown
147 lines
7.9 KiB
Markdown
# XMR to BTC Atomic Swap - Automated Swap Backend (ASB)
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## Quick Start ASB
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1. Download [latest release](https://github.com/comit-network/xmr-btc-swap/releases/latest) of the `asb` binary
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2. Ensure that you have the Monero Wallet RPC running with `--wallet-dir` and `--disable-rpc-login`:
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1. `monero-wallet-rpc --stagenet --daemon-host STAGENET-NODE-URL --rpc-bind-port STAGENET-NODE-PORT --disable-rpc-login --wallet-dir PATH/TO/WALLET/DIR`
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3. Run the ASB in terminal: `./asb start`
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4. Follow the setup wizard in the terminal
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Public Monero stagenet nodes for running the Monero Wallet RPC:
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- `monero-stagenet.exan.tech:38081`
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- `stagenet.community.xmr.to:38081`
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Run `./asb --help` for more information.
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## ASB Details
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The ASB is a long running daemon that acts as the trading partner to the swap CLI.
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The CLI user is buying XMR (i.e. receives XMR, sends BTC), the ASB service provider is selling XMR (i.e. sends XMR, receives BTC).
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The ASB can handle multiple swaps with different peers concurrently.
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The ASB communicates with the CLI on various [libp2p](https://libp2p.io/)-based network protocols.
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Both the ASB and the CLI can be run by anybody.
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The CLI is designed to run one specific swap against an ASB.
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The ASB is designed to run 24/7 as a daemon that responds to CLIs connecting.
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Since the ASB is a long running task we specify the person running an ASB as service provider.
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### ASB discovery
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Currently, there is no automated discovery for service providers running an ASB.
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A service provider has to manually provide the connection details to users that will run the CLI.
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[Libp2p addressing](https://docs.libp2p.io/concepts/addressing/) is used to identify a service provider by multi-address and peer-id.
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The Peer-ID is printed upon startup of the ASB.
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The multi-address typically consists of IP-address or URL (if DNS entry configured) of the service provider.
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When configuring a domain name for the ASB through a DNS entry, a service provider can configure it by using the [`dnsaddr` format](https://github.com/multiformats/multiaddr/blob/master/protocols/DNSADDR.md) for the TXT entry.
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This will simplify the connection detail `--seller-addr` for CLI users connecting to the ASB and provides more flexibility with e.g. ports (i.e. `/dnsaddr/your.domain.tld` instead of `/dns4/your.domain.tld/tcp/port`).
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Each service provider running an ASB can decide how/where to share these connection details.
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Eventually, more elaborate discovery mechanisms can be added.
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The **CLI** user can specify a service providers's multiaddress and peer-id with `--seller-addr` and `--seller-peer-id`, see `./swap --help` for details.
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### Setup Details
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In order to understand the different components of the ASB and CLI better here is a component diagram showcasing the ASB and CLI setup using public Bitcoin and Monero infrastructure:
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Contrary, here is a diagram that showcases a service provider running it's own blockchain infrastructure for the ASB:
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The diagram shows that the `asb` group (representing the `asb` binary) consists of three components:
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1. Monero Wallet
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2. Bitcoin Wallet
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3. ASB
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The `ASB` depicted in the diagram actually consists of multiple components (protocol impl, network communication, ...) that sums up the functionality to execute concurrent swaps in the role of Alice.
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#### Monero Wallet Setup
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The ASB uses the running Monero wallet RPC to create / open Monero wallets.
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Currently you cannot connect to an existing Monero wallet, but the ASB will create the wallet `asb-wallet` upon intial startup.
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In order to accept trades with a CLI you will have to send XMR to that wallet.
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The wallet's address is printed upon startup of the ASB.
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Currently the `asb-wallet` does not have a password.
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Upon startup of the ASB the `asb-wallet` is opened in the wallet RPC.
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You can then interact with the wallet RPC for basic wallet management as well.
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#### Bitcoin Wallet Setup
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The ASB has an internally managed Bitcoin wallet.
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The Bitcoin wallet is created upon initial startup and stored in the data folder of the ASB (configured through initial startup wizard).
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#### Market Making
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In order to be able to trade, the ASB must define a price to be able to agree on the amounts to be swapped with a CLI.
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Currently we use a spot-price mode, i.e. the ASB dictates the price to the CLI.
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A CLI can connect to the ASB at any time and request a quote for buying XMR.
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The ASB then returns the current price and the maximum amount tradeable.
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The maximum amount tradeable can be configured with the `--max-buy-btc` parameter.
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The `XMR<>BTC` price is currently determined by the price from the central exchange Kraken.
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Upon startup the ASB connects to the Kraken price websocket and listens on the stream for price updates.
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Currently the spot price is equal to the market price on Kraken.
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#### Swap Execution
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Swap execution within the ASB is automated.
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Incoming swaps request will be automatically processed and the swap will execute automatically.
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Swaps where Bob does not act, so Alice cannot redeem, will be automatically refunded or punished.
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When the ASB is restarted unfinished swaps will be resumed automatically.
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The refund scenario is a scenario where the CLI refunds the Bitcoin.
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The ASB can then refund the Monero which will be automatically transferred to the `asb-wallet`.
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The punish scenario is a scenario where the CLI does not refund and hence the ASB cannot refund the Monero.
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After a second timelock expires the ASB will automatically punish the CLI user by taking the Bitcoin.
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More information about the protocol in this [presentation](https://youtu.be/Jj8rd4WOEy0) and this [blog post](https://comit.network/blog/2020/10/06/monero-bitcoin).
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All claimed Bitcoin ends up in the internal Bitcoin wallet of the ASB.
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The ASB offers a commands to withdraw Bitcoin and check the balance, run `./asb --help` for details.
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If the ASB has insufficient Monero funds to accept a swap the swap setup is rejected.
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Note that currently there is no specific error sent back to the CLI for such kind of cases, so a user might not know why the swap execution was rejected.
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Note that there is currently no notification service implemented for low funds.
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The ASB provider has to monitor Monero funds to make sure the ASB still has liquidity.
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#### Tor and hidden services
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The ASB supports Tor and will automatically create a Tor hidden service if the Tor control port can be found.
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By default, the ASB will look for the control port under `localhost:9051`.
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To allow the ASB to create a hidden service, enable the control port and authentication in your torrc file:
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```
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ControlPort 9051
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CookieAuthentication 1
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CookieAuthFileGroupReadable 1
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```
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It is important that the user running the ASB has the correct user rights, i.e. is in the same group as the user running Tor.
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E.g. if running on debian and having Tor install via apt, add your user to the following group:
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`sudo adduser $(whoami) debian-tor`.
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When configured correctly, your ASB will print the created onion addresses upon startup:
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```bash
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./bin/asb start
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May 01 01:31:27.602 INFO Initialized tracing with level: debug
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...
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May 01 01:32:05.018 INFO Tor found. Setting up hidden service.
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May 01 01:32:07.475 INFO /onion3/z4findrdwtfbpoq64ayjtmxvr52vvxnsynerlenlfkmm52dqxsl4deyd:9939
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May 01 01:32:07.476 INFO /onion3/z4findrdwtfbpoq64ayjtmxvr52vvxnsynerlenlfkmm52dqxsl4deyd:9940
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```
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