c-lightning: A specification compliant Lightning Network implementation in C

c-lightning is a standard compliant implementation of the Lightning Network protocol. The Lightning Network is a scalability solution for Bitcoin, enabling secure and instant transfer of funds between any two party for any amount.

For more information about the Lightning Network please refer to http://lightning.network.

Project Status

This implementation is still very much work in progress, and, although it can be used for testing, it should not be used for real funds. We do our best to identify and fix problems, and implement missing feature.

Any help testing the implementation, reporting bugs, or helping with outstanding issues is very welcome. Don't hesitate to reach out to us on IRC at #lightning-dev @ freenode.net, #c-lightning @ freenode.net, or on the mailing list lightning-dev@lists.linuxfoundation.org.

Getting Started

c-lightning currently only works on Linux (and possibly Mac OS with some tweaking), and requires a locally running bitcoind (version 0.15 or above) that is fully caught up with the network you're testing on.

Installation

Please refer to the installation documentation for detailed instructions. For the impatient here's the gist of it for Ubuntu and Debian:

sudo apt-get install -y autoconf build-essential git libtool libgmp-dev libsqlite3-dev python3 net-tools
git clone https://github.com/ElementsProject/lightning.git
cd lightning
make

Or if you like to throw docker into the mix:

sudo docker run \
	-v $HOME/.lightning:/root/.lightning \
	-v $HOME/.bitcoin:/root/.bitcoin \
	-p 9735:9735 \
	cdecker/lightningd:latest

Starting lightningd

In order to start lightningd you will need to have a local bitcoind node running in either testnet or regtest mode:

bitcoind -daemon -testnet

Wait until bitcoind has synchronized with the testnet network. In case you use regtest, make sure you generate at least 432 blocks to activate SegWit.

Make sure that you do not have walletbroadcast=0 in your ~/.bitcoin/bitcoin.conf, or you may run into trouble.

You can start lightningd with the following command:

lightningd/lightningd --network=testnet --log-level=debug

Opening a channel on the Bitcoin testnet

First you need to transfer some funds to lightningd so that it can open a channel:

# Returns an address <address>
cli/lightning-cli newaddr

# Returns a transaction id <txid>
bitcoin-cli -testnet sendtoaddress <address> <amount>

# Retrieves the raw transaction <rawtx>
bitcoin-cli -testnet getrawtransaction <txid>

# Notifies `lightningd` that there are now funds available:
cli/lightning-cli addfunds <rawtx>

Eventually lightningd will include its own wallet making this transfer easier, but for now this is how it gets its funds. If you don't have any testcoins you can get a few from a faucet such as TPs' testnet faucet or Kiwi's testnet faucet.

Once lightningd has funds, we can connect to a node and open a channel. Let's assume the remote node is accepting connections at <ip> (and optional <port>, if not 9735) and has the node ID <node_id>:

cli/lightning-cli connect <node_id> <ip> [<port>]
cli/lightning-cli fundchannel <node_id> <amount>

This opens a connection and, on top of that connection, then opens a channel. The funding transaction needs 6 confirmations in order for the channel to be usable. You can check the status of the channel using cli/lightning-cli getpeers, which after 1 confirmation should say that the status is in Normal operation. After 6 confirmations you can use cli/lightning-cli getchannels to verify that the channel shows up in the list of open channels.

Receiving and receiving payments

Payments in Lightning are invoice based. The recipient creates an invoice with the expected <amount> in millisatoshi, a <label> and a <description>:

cli/lightning-cli invoice <amount> <label> <description>

This returns a random value called rhash that is part of the invoice. The recipient needs to communicate its ID <recipient_id>, <rhash> and the desired <amount> to the sender.

The sender needs to compute a route to the recipient, and use that route to actually send the payment. The route contains the path that the payment will take through the Lightning Network and the respective funds that each node will forward.

route=$(cli/lightning-cli getroute <recipient_id> <amount> 1 | jq --raw-output .route -)
cli/lightning-cli sendpay "$route" <rhash>

Notice that in the first step we stored the route in a variable and reused it in the second step. lightning-cli should return a preimage that serves as a receipt, confirming that the payment was successful.

This low-level interface is still experimental and will eventually be complemented with a higher level interface that is easier to use.

Further information

JSON-RPC interface is documented in the following manual pages:

• invoice
• listinvoice
• waitinvoice
• waitanyinvoice
• delinvoice
• getroute
• sendpay

For simple access to the JSON-RPC interface you can use the cli/lightning-cli tool, or the python API client.