Johan T. Halseth
Check returned error to make linter happy.
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Lightning Loop is a non-custodial service offered by Lightning Labs to bridge on-chain and off-chain Bitcoin using submarine swaps. This repository is home to the Loop client and depends on the Lightning Network daemon lnd. All of lnd’s supported chain backends are fully supported when using the Loop client: Neutrino, Bitcoin Core, and btcd.
In the current iteration of the Loop software, two swap types are supported:
We call off-chain to on-chain swaps, a Loop Out. The service can be used in various situations:
We call our on-chain to off-chain swaps, a Loop In. This allows you to use on-chain funds to increase the local balance of a channel, effectively "refilling" an existing channel.
Potential uses for Loop In:
The Loop client is currently in an early beta state, and offers a simple command line application. Future APIs will be added to support implementation or use of the Loop service.
LND and the loop client are using Go modules. Make sure that the
env variable is set to
In order to execute a swap, You need to run lnd 0.7.1+, or master built with sub-servers enabled.
If you are building from source, and not using a 0.7.1 or higher release of
lnd, make sure that you are using the
master branch of lnd. You can get this
by git cloning the repository
git clone https://github.com/lightningnetwork/lnd.git
Once the lnd repository is cloned, it will need to be built with special build tags that enable the swap. This enables the required lnd rpc services.
cd lnd make install tags="signrpc walletrpc chainrpc invoicesrpc routerrpc"
Check to see if you have already installed lnd. If you have, you will need to
.macaroon files from your lnd directory and restart lnd.
Do not delete any other files other than the
// Example on Linux to see macaroons in the default directory: ls ~/.lnd/data/chain/bitcoin/mainnet
This should show no
.macaroon files. If it does? Stop lnd, delete macaroons,
Now delete the .macaroon files and restart lnd. (don't delete any other files)
After lnd is installed, you will need to clone the Lightning Loop repo and install the command line interface and swap client service.
git clone https://github.com/lightninglabs/loop.git cd loop/cmd go install ./...
After you have lnd and the Loop client installed, you can execute a Loop swap.
The Loop client needs its own short-lived daemon which will deal with the swaps in progress.
Command to start
loopd // Or if you want to do everything in the same terminal and background loopd loopd & // For testnet mode, you'll need to specify the network as mainnet is the default: loopd --network=testnet
loopd attempts to connect to the lnd instance running on
localhost:10009 and reads the macaroon and tls certificate from
This can be altered using command line flags. See
loopd only listens on localhost and uses an unencrypted and unauthenticated
Now that loopd is running, you can initiate a simple Loop Out. This will pay out Lightning off-chain funds and you will receive Bitcoin on-chain funds in return. There will be some chain and routing fees associated with this swap.
NAME: loop out - perform an off-chain to on-chain swap (looping out) USAGE: loop out [command options] amt [addr] DESCRIPTION: Attempts loop out the target amount into either the backing lnd's wallet, or a targeted address. The amount is to be specified in satoshis. Optionally a BASE58/bech32 encoded bitcoin destination address may be specified. If not specified, a new wallet address will be generated. OPTIONS: --channel value the 8-byte compact channel ID of the channel to loop out (default: 0) --addr value the optional address that the looped out funds should be sent to, if left blank the funds will go to lnd's wallet --amt value the amount in satoshis to loop out (default: 0)
It's possible to receive more inbound capacity on a particular channel
--channel), and also have the
loop daemon send the coins to a target
addr). The latter option allows ones to effectively send on-chain
from their existing channels!
loop out <amt_in_satoshis>
This will take some time, as it requires an on-chain confirmation. When the
swap is initiated successfully,
loopd will see the process through.
To query in-flight swap statuses, run
Additionally, Loop In is now also supported for mainnet as well. A Loop In swap lets one refill their channel (ability to send more coins) by sending to a special script on-chain.
NAME: loop in - perform an on-chain to off-chain swap (loop in) USAGE: loop in [command options] amt DESCRIPTION: Send the amount in satoshis specified by the amt argument off-chain. OPTIONS: --amt value the amount in satoshis to loop in (default: 0) --external expect htlc to be published externally
--external argument allows the on-chain HTLC transacting to be published
externally. This allows for a number of use cases like using this address to
withdraw from an exchange into your Lightning channel!
A Loop In swap can be executed a follows:
loop in <amt_in_satoshis>
loopd is terminated (or killed) for whatever reason, it will pickup
pending swaps after a restart.
Information about pending swaps is stored persistently in the swap database.
Its location is
It is possible to execute multiple swaps simultaneously. Just keep loopd running.