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# Lightning Loop
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Lightning Loop is a non-custodial service offered by
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[Lightning Labs](https://lightning.engineering/) to bridge on-chain and
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off-chain Bitcoin using submarine swaps. This repository is home to the Loop
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client and depends on the Lightning Network daemon
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[lnd](https://github.com/lightningnetwork/lnd). All of lnd’s supported chain
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backends are fully supported when using the Loop client: Neutrino, Bitcoin
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Core, and btcd.
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In the current iteration of the Loop software, only off-chain to on-chain
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exchanges are supported, where the Loop client sends funds off-chain in
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exchange for the funds back on-chain.
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The service can be used in various situations:
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- Acquiring inbound channel liquidity from arbitrary nodes on the Lightning
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network
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- Depositing funds to a Bitcoin on-chain address without closing active
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channels
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- Paying to on-chain fallback addresses in the case of insufficient route
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liquidity
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Future iterations of the Loop software will also allow on-chain to off-chain
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swaps. These swaps can be useful for additional use-cases:
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- Refilling depleted channels with funds from cold-wallets or exchange
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withdrawals
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- Servicing off-chain Lightning withdrawals using on-chain payments, with no
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funds in channels required
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- As a failsafe payment method that can be used when channel liquidity along a
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route is insufficient
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## Development and Support
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The Loop client is current in an early beta state, and offers a simple command
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line application. Future APIs will be added to support implementation or use of
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the Loop service.
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The [GitHub issue tracker](https://github.com/lightninglabs/loop/issues) can be
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used to request specific improvements or register and get help with any
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problems. Community support is also available in the
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[LND Slack](https://join.slack.com/t/lightningcommunity/shared_invite/enQtMzQ0OTQyNjE5NjU1LWRiMGNmOTZiNzU0MTVmYzc1ZGFkZTUyNzUwOGJjMjYwNWRkNWQzZWE3MTkwZjdjZGE5ZGNiNGVkMzI2MDU4ZTE)
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.
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## Setup and Install
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LND and the loop client are using Go modules. Make sure that the `GO111MODULE`
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env variable is set to `on`.
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In order to execute a swap, LND will need to be rebuilt with sub servers
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enabled.
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### LND
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* Checkout branch `master`
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- `make install tags="signrpc walletrpc chainrpc"` to build and install lnd
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with required sub-servers enabled.
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- Make sure there are no macaroons in the lnd dir
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`~/.lnd/data/chain/bitcoin/mainnet`. If there are, lnd has been started
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before and in that case, it could be that `admin.macaroon` doesn't contain
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signer permission. Stop lnd, delete `*.macaroon` files, restart lnd to
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regenerate them with the signer permission.
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DO NOT DELETE `wallet.db` !
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- Start lnd
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### Loopd
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- `git clone https://github.com/lightninglabs/loop.git`
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- `cd loop/cmd`
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- `go install ./...`
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## Execute a swap
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* Swaps are executed by a client daemon process. Run:
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`loopd`
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By default `loopd` attempts to connect to an lnd instance running on
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`localhost:10009` and reads the macaroon and tls certificate from `~/.lnd`.
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This can be altered using command line flags. See `loopd --help`.
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`loopd` only listens on localhost and uses an unencrypted and unauthenticated
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connection.
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* To initiate a swap, run:
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`loop out <amt_sat>`
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When the swap is initiated successfully, `loopd` will see the process through.
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* To query and track the swap status, run `loop` without arguments.
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## Resume
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When `loopd` is terminated (or killed) for whatever reason, it will pickup
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pending swaps after a restart.
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Information about pending swaps is stored persistently in the swap database.
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Its location is `~/.loopd/<network>/loop.db`.
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## Multiple simultaneous swaps
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It is possible to execute multiple swaps simultaneously.
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