eclair

A scala implementation of the Lightning Network.

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Quick Overview

Eclair is an implementation of the Lightning Network protocol, designed to work with Bitcoin. It's a Scala-based project that aims to provide a robust, scalable, and user-friendly Lightning Network node and wallet solution. Eclair supports both on-chain and off-chain Bitcoin transactions, making it a versatile tool for developers and users alike.

Pros

Written in Scala, offering strong type safety and functional programming features
Supports both mainnet and testnet Bitcoin networks
Provides a comprehensive API for developers to integrate Lightning Network functionality
Actively maintained with regular updates and improvements

Cons

Requires some technical knowledge to set up and operate
Documentation could be more extensive for newcomers
Limited GUI options compared to some other Lightning implementations
Scala may have a steeper learning curve for developers not familiar with the language

Code Examples

Creating a new Lightning Network channel:

val channelParams = ChannelParams(
  localParams = LocalParams(...),
  channelFeatures = ChannelFeatures(...)
)
val channel = Channel.create(channelParams, ...)

Sending a payment through the Lightning Network:

val paymentRequest = PaymentRequest.read("lnbc...")
val payment = SendPayment(
  amount = MilliSatoshi(10000),
  paymentHash = paymentRequest.paymentHash,
  nodeId = paymentRequest.nodeId,
  routeParams = RouteParams.default
)
nodeParams.db.payments.addOutgoingPayment(payment)
sender ! payment

Handling incoming Lightning Network payments:

def receive: Receive = {
  case BITCOIN_FUNDING_DEPTHOK =>
    // Channel is ready to use
    context.become(ready)
  case p: IncomingPayment =>
    // Process incoming payment
    handleIncomingPayment(p)
}

Getting Started

To get started with Eclair, follow these steps:

Clone the repository:

git clone https://github.com/ACINQ/eclair.git

Build the project:
```
cd eclair
mvn package
```

Run Eclair:

./eclair-node/target/eclair-node-<version>-<commit_short_id>-bin/bin/eclair-node.sh

Make sure you have Java 11+ and Maven installed on your system before building and running Eclair.

Competitor Comparisons

lnd

7,670

Lightning Network Daemon ⚡️

Pros of lnd

Larger community and more extensive documentation
Better support for multiple cryptocurrencies beyond Bitcoin
More robust and feature-rich API

Cons of lnd

Higher resource requirements for running a node
Steeper learning curve for new developers
Less focus on privacy features compared to Eclair

Code Comparison

lnd

type LightningNode struct {
    Identity   *btcec.PublicKey
    Addresses  []net.Addr
    Features   *lnwire.FeatureVector
    AuthSig    *lnwire.Sig
    LastUpdate time.Time
}

Eclair

case class NodeAnnouncement(
  signature: ByteVector64,
  features: Features,
  timestamp: Long,
  nodeId: PublicKey,
  rgbColor: Color,
  alias: String,
  addresses: List[NodeAddress],
  unknownFields: ByteVector = ByteVector.empty
)

Both implementations define structures for representing Lightning Network nodes, but lnd uses Go while Eclair uses Scala. lnd's approach is more compact, while Eclair's case class provides more detailed information about the node, including color and alias.

lightning

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Core Lightning — Lightning Network implementation focusing on spec compliance and performance

Pros of lightning

More extensive documentation and user guides
Larger community and contributor base
Supports multiple backend databases (SQLite, PostgreSQL)

Cons of lightning

Steeper learning curve for beginners
Requires more system resources
Less focus on mobile and lightweight implementations

Code comparison

lightning

static struct command_result *json_fundchannel(struct command *cmd,
                                               const char *buffer,
                                               const jsmntok_t *obj UNNEEDED,
                                               const jsmntok_t *params)
{
    u8 *msg;
    struct amount_sat amount;
    struct node_id *destination;

eclair

override def receive: Receive = {
  case init: Init =>
    log.info(s"initializing actor $self")
    context become main(init)
}

def main(init: Init): Receive = {
  case cmd: Command => handleCommand(cmd, init)

The lightning implementation is written in C, focusing on low-level performance, while eclair uses Scala, offering a more functional and concise approach. Lightning's code structure suggests a more complex system with detailed parameter handling, whereas eclair's actor-based model provides a higher level of abstraction for handling commands and initialization.

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README

Eclair (French for Lightning) is a Scala implementation of the Lightning Network.

This software follows the Lightning Network Specifications (BOLTs). Other implementations include core lightning, lnd, electrum, and ldk.

Lightning Network Specification Compliance
JSON API
Documentation
Installation
- Prerequisite: Bitcoin Core
- Installing Eclair
Configuration
Docker
Plugins
Testnet usage
Tools
Resources

Lightning Network Specification Compliance

Please see the latest release note for detailed information on BOLT compliance.

JSON API

Eclair offers a feature-rich HTTP API that enables application developers to easily integrate.

For more information please visit the API documentation website.

:rotating_light: Eclair's JSON API should NOT be accessible from the outside world (similarly to Bitcoin Core API)

Documentation

Please visit our docs folder to find detailed instructions on how to configure your node, connect to other nodes, open channels, send and receive payments, and help with more advanced scenarios.

You will also find detailed guides and frequently asked questions there.

Installation

Prerequisite: Bitcoin Core

Eclair relies on Bitcoin Core to interface with and monitor the blockchain and to manage on-chain funds: Eclair does not include an on-chain wallet, channel opening transactions are funded by your Bitcoin Core node, and channel closing transactions return funds to your Bitcoin Core node.

This means that instead of re-implementing them, Eclair benefits from the verifications and optimisations (including fee management with RBF/CPFP, ...) that are implemented by Bitcoin Core. Eclair uses our own bitcoin library to verify data provided by Bitcoin Core.

:warning: This also means that Eclair has strong requirements on how your Bitcoin Core node is configured (see below), and that you must back up your Bitcoin Core wallet as well as your Eclair node (see here):

Eclair needs a synchronized, segwit-ready, zeromq-enabled, wallet-enabled, non-pruning, tx-indexing Bitcoin Core node.
You must configure your Bitcoin node to use bech32 or bech32m (segwit) addresses. If your wallet has "non-segwit UTXOs" (outputs that are neither p2sh-segwit, bech32 or bech32m), you must send them to a bech32 or bech32m address before running Eclair.
Eclair requires Bitcoin Core 27.1 or higher. If you are upgrading an existing wallet, you may need to create a new address and send all your funds to that address.

Run bitcoind with the following minimal bitcoin.conf:

server=1
rpcuser=foo
rpcpassword=bar
txindex=1
addresstype=bech32
changetype=bech32
zmqpubhashblock=tcp://127.0.0.1:29000
zmqpubrawtx=tcp://127.0.0.1:29000

Depending on the actual hardware configuration, it may be useful to provide increased dbcache parameter value for faster verification and rpcworkqueue parameter value for better handling of API requests on bitcoind side.

# UTXO database cache size, in MiB
dbcache=2048
# Number of allowed pending RPC requests (default is 16)
rpcworkqueue=128

# How many seconds bitcoin will wait for a complete RPC HTTP request.
# after the HTTP connection is established.
rpcclienttimeout=30

Installing Eclair

Eclair is developed in Scala, a powerful functional language that runs on the JVM, and is packaged as a ZIP archive.

To run Eclair, you first need to install Java, we recommend that you use OpenJDK 11. Other runtimes also work, but we don't recommend using them.

Then download our latest release, unzip the archive and run the following command:

eclair-node-<version>-<commit_id>/bin/eclair-node.sh

You can then control your node via eclair-cli or the API.

:warning: Be careful when following tutorials/guides that may be outdated or incomplete. You must thoroughly read the official eclair documentation before running your own node.

Configuration

Configuration file

Eclair reads its configuration file, and write its logs, to ~/.eclair by default.

To change your node's configuration, create a file named eclair.conf in ~/.eclair. Here's an example configuration file:

eclair.node-alias=eclair
eclair.node-color=49daaa

Here are some of the most common options:

name	description	default value
eclair.chain	Which blockchain to use: regtest, testnet, signet or mainnet	mainnet
eclair.server.port	Lightning TCP port	9735
eclair.api.enabled	Enable/disable the API	false. By default the API is disabled. If you want to enable it, you must set a password.
eclair.api.port	API HTTP port	8080
eclair.api.password	API password (BASIC)	"" (must be set if the API is enabled)
eclair.bitcoind.rpcuser	Bitcoin Core RPC user	foo
eclair.bitcoind.rpcpassword	Bitcoin Core RPC password	bar
eclair.bitcoind.zmqblock	Bitcoin Core ZMQ block address	"tcp://127.0.0.1:29000"
eclair.bitcoind.zmqtx	Bitcoin Core ZMQ tx address	"tcp://127.0.0.1:29000"
eclair.bitcoind.wallet	Bitcoin Core wallet name	""

Quotes are not required unless the value contains special characters. Full syntax guide here.

→ see here for more configuration options.

Configure Bitcoin Core wallet

Eclair will use the default loaded Bitcoin Core wallet to fund any channels you choose to open. If you want to use a different wallet from the default one, you must set eclair.bitcoind.wallet accordingly in your eclair.conf.

:warning: Once a wallet is configured, you must be very careful if you want to change it: changing the wallet when you have channels open may result in a loss of funds (or a complex recovery procedure).

Eclair will return BTC from closed channels to the wallet configured. Any BTC found in the wallet can be used to fund the channels you choose to open.

We also recommend tweaking the following parameters in bitcoin.conf:

# This parameter ensures that your wallet will not create chains of unconfirmed
# transactions that would be rejected by other nodes.
walletrejectlongchains=1
# The following parameters set the maximum length of chains of unconfirmed
# transactions to 20 instead of the default value of 25.
limitancestorcount=20
limitdescendantcount=20

Setting these parameters lets you unblock long chains of unconfirmed channel funding transactions by using child-pays-for-parent (CPFP) to make them confirm.

With the default bitcoind parameters, if your node created a chain of 25 unconfirmed funding transactions with a low-feerate, you wouldn't be able to use CPFP to raise their fees because your CPFP transaction would likely be rejected by the rest of the network.

You can also configure Eclair to manage Bitcoin Core's private keys, see our guides for more details.

Java Environment Variables

Some advanced parameters can be changed with java environment variables. Most users won't need this and can skip this section.

However, if you're seeing Java heap size errors, you can try increasing the maximum memory allocated to the JVM with the -Xmx parameter.

You can for example set it to use up to 512 MB (or any value that fits the amount of RAM on your machine) with:

export JAVA_OPTS=-Xmx512m

:warning: Using separate datadir is mandatory if you want to run several instances of eclair on the same machine. You will also have to change ports in eclair.conf (see above).

name	description	default value
eclair.datadir	Path to the data directory	~/.eclair
eclair.printToConsole	Log to stdout (in addition to eclair.log)

For example, to specify a different data directory you would run the following command:

eclair-node-<version>-<commit_id>/bin/eclair-node.sh -Declair.datadir=/tmp/node1

Logging

Eclair uses logback for logging. To use a different configuration, and override the internal logback.xml, run:

eclair-node-<version>-<commit_id>/bin/eclair-node.sh -Dlogback.configurationFile=/path/to/logback-custom.xml

Backup

You need to backup:

your Bitcoin Core wallet
your Eclair channels

For Bitcoin Core, you need to backup the wallet file for the wallet that Eclair is using. You only need to do this once, when the wallet is created. See Managing Wallets in the Bitcoin Core documentation for more information.

For Eclair, the files that you need to backup are located in your data directory. You must backup:

your seeds (node_seed.dat and channel_seed.dat)
your channel database (eclair.sqlite.bak under directory mainnet, testnet, signet or regtest depending on which chain you're running on)

Your seeds never change once they have been created, but your channels will change whenever you receive or send payments. Eclair will create and maintain a snapshot of its database, named eclair.sqlite.bak, in your data directory, and update it when needed. This file is always consistent and safe to use even when Eclair is running, and this is what you should back up regularly.

For example, you could configure a cron task for your backup job. Or you could configure an optional notification script to be called by eclair once a new database snapshot has been created, using the following option:

eclair.file-backup.notify-script = "/absolute/path/to/script.sh"

Make sure your script is executable and uses an absolute path name for eclair.sqlite.bak.

Note that depending on your filesystem, in your backup process we recommend first moving eclair.sqlite.bak to some temporary file before copying that file to your final backup location.

Docker

A Dockerfile x86_64 image is built on each commit on docker hub for running a dockerized eclair-node. For arm64 platforms you can use an arm64 Dockerfile to build your own arm64 container.

You can use the JAVA_OPTS environment variable to set arguments to eclair-node.

docker run -ti --rm -e "JAVA_OPTS=-Xmx512m -Declair.api.binding-ip=0.0.0.0 -Declair.node-alias=node-pm -Declair.printToConsole" acinq/eclair

If you want to persist the data directory, you can make the volume to your host with the -v argument, as the following example:

docker run -ti --rm -v "/path_on_host:/data" -e "JAVA_OPTS=-Declair.printToConsole" acinq/eclair

If you enabled the API you can check the status of Eclair using the command line tool:

docker exec <container_name> eclair-cli -p foobar getinfo

Plugins

For advanced usage, Eclair supports plugins written in Scala, Java, or any JVM-compatible language.

A valid plugin is a jar that contains an implementation of the Plugin interface, and a manifest entry for Main-Class with the FQDN of the implementation.

Here is how to run Eclair with plugins:

eclair-node-<version>/bin/eclair-node.sh <plugin1.jar> <plugin2.jar> <...>

You can find more details about plugins in the eclair-plugins repository.

Testnet usage

Eclair is configured to run on mainnet by default, but you can still run it on testnet (or regtest/signet): start your Bitcoin node in testnet mode (add testnet=1 in bitcoin.conf or start with -testnet), and change Eclair's chain parameter and Bitcoin RPC port:

eclair.chain=testnet
eclair.bitcoind.rpcport=18332

For regtest, add regtest=1 in bitcoin.conf or start with -regtest, and modify eclair.conf:

eclair.chain = "regtest"
eclair.bitcoind.rpcport=18443

For signet, add signet=1 in bitcoin.conf or start with -signet, and modify eclair.conf:

eclair.chain = "signet"
eclair.bitcoind.rpcport=38332

You may also want to take advantage of the new configuration sections in bitcoin.conf to manage parameters that are network specific, so you can easily run your Bitcoin node on both mainnet and testnet. For example you could use:

server=1
txindex=1

addresstype=bech32
changetype=bech32

walletrejectlongchains=1
limitancestorcount=20
limitdescendantcount=20

[main]
rpcuser=<your-mainnet-rpc-user-here>
rpcpassword=<your-mainnet-rpc-password-here>
zmqpubhashblock=tcp://127.0.0.1:29000
zmqpubrawtx=tcp://127.0.0.1:29000

[test]
rpcuser=<your-testnet-rpc-user-here>
rpcpassword=<your-testnet-rpc-password-here>
zmqpubhashblock=tcp://127.0.0.1:29001
zmqpubrawtx=tcp://127.0.0.1:29001

Tools

Demo Shop - an example testnet Lightning web shop.
Network Explorer - a Lightning network visualization tool.

Resources

[1] The Bitcoin Lightning Network: Scalable Off-Chain Instant Payments by Joseph Poon and Thaddeus Dryja
[2] Reaching The Ground With Lightning by Rusty Russell
[3] Lightning Network Explorer - Explore testnet LN nodes you can connect to

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