2333f024d3
pay sometimes ignores exclusions. WONTFIX.
```
with pytest.raises(RpcError, match=r'is not reachable directly and all routehints were unusable.'):
> l1.rpc.pay(inv, exclude=[scid12])
tests/test_pay.py:5279:
...
elif "error" in resp:
> raise RpcError(method, payload, resp['error'])
E pyln.client.lightning.RpcError: RPC call failed: method: pay, payload: {'bolt11': 'lnbcrt1230n1p54mma3sp5x7uerjgyg7ws6fnzdwxc7pgpj6j25uhpqp5uvx3fk8dkcqm37m2spp5k02racjc9knux958u5rgtva24jfvxtr5w3t53pfeavn3thmyny0qdq8v3jhxccxqyjw5qcqp9rzjqgkjyd3q5dv6gllh77kygly9c3kfy0d9xwyjyxsq2nq3c83u5vw4jqqqvuqqqqgqqqqqqqqpqqqqqzsqqc9qxpqysgqcmv875mmzcjl8mwxxndy9an6p870ffpdxdtypmgf5gzsydnt2d68n4kjph0rcprye6tfz0ex0c5clgj3zwm8jgd5vs0fdv7hf7dqr8cqdrg3gf', 'exclude': ['103x2x0/1']}, error: {'code': 210, 'message': 'Ran out of routes to try after 6 attempts: see `paystatus`', 'attempts': [{'status': 'failed', 'failreason': 'No path found', 'partid': 0, 'amount_msat': 123000}, {'status': 'pending', 'failreason': 'No path found', 'partid': 1, 'amount_msat': 123000, 'parent_partid': 0}, {'status': 'failed', 'failreason': 'No path found', 'partid': 2, 'amount_msat': 57006, 'parent_partid': 1}, {'status': 'failed', 'failreason': 'No path found', 'partid': 4, 'amount_msat': 57006, 'parent_partid': 2}, {'status': 'failed', 'failreason': 'No path found', 'partid': 3, 'amount_msat': 65994, 'parent_partid': 1}, {'status': 'failed', 'failreason': 'No path found', 'partid': 5, 'amount_msat': 65994, 'parent_partid': 3}]}
```
The logs show that it doesn't exclude the routehint early: in successful runs we get "After filtering routehints we're left with 0 usable hints". Perhaps this is something to do with the timing of our own notifications?
```
2026-01-07T05:51:10.7902502Z lightningd-1 2026-01-07T05:31:29.706Z DEBUG plugin-pay: cmd -c:pay#64/cln:pay#121 partid 0: Received getchaininfo blockcount=108, headercount=108
2026-01-07T05:51:10.7903334Z lightningd-1 2026-01-07T05:31:29.715Z DEBUG plugin-pay: cmd -c:pay#64/cln:pay#121 partid 0: waitblockheight reports syncheight=108
2026-01-07T05:51:10.7904256Z lightningd-1 2026-01-07T05:31:29.734Z DEBUG plugin-pay: cmd -c:pay#64/cln:pay#121 partid 0: Updated a channel hint for 103x2x0/1: enabled true, estimated capacity 978718000msat
2026-01-07T05:51:10.7905355Z lightningd-1 2026-01-07T05:31:29.734Z DEBUG plugin-pay: cmd -c:pay#64/cln:pay#121 partid 0: Updated a channel hint for 7269357x11669990x33910/1: enabled false, estimated capacity UNKNOWN
2026-01-07T05:51:10.7906580Z lightningd-1 2026-01-07T05:31:29.735Z DEBUG plugin-pay: cmd -c:pay#64/cln:pay#121 partid 0: Updated a channel hint for 103x2x0/1: enabled false, estimated capacity UNKNOWN
2026-01-07T05:51:10.7907665Z lightningd-1 2026-01-07T05:31:29.735Z INFO plugin-pay: cmd -c:pay#64/cln:pay#121 partid 0: Payment fee constraint 615msat is below exemption threshold, allowing a maximum fee of 5000msat
2026-01-07T05:51:10.7908845Z lightningd-1 2026-01-07T05:31:29.752Z DEBUG plugin-pay: Received a channel_hint {.scid = 103x2x0/1, .enabled = 1, .estimate = 978718000msat, .capacity = 1000000000msat }
2026-01-07T05:51:10.7909710Z lightningd-1 2026-01-07T05:31:29.754Z INFO plugin-pay: cmd -c:pay#64/cln:pay#121 partid 0: Filtering out 1 routehints
2026-01-07T05:51:10.7910544Z lightningd-1 2026-01-07T05:31:29.779Z DEBUG plugin-pay: cmd -c:pay#64/cln:pay#121 partid 0: Checking hint {.scid=103x2x0/1, .enabled=1, .estimate=978718000msat}
2026-01-07T05:51:10.7911470Z lightningd-1 2026-01-07T05:31:29.780Z DEBUG plugin-pay: cmd -c:pay#64/cln:pay#121 partid 0: After filtering routehints we're left with 1 usable hints
2026-01-07T05:51:10.7912385Z lightningd-1 2026-01-07T05:31:29.780Z DEBUG plugin-pay: cmd -c:pay#64/cln:pay#121 partid 0: Checking hint {.scid=103x2x0/1, .enabled=1, .estimate=978718000msat}
2026-01-07T05:51:10.7913471Z lightningd-1 2026-01-07T05:31:29.780Z DEBUG plugin-pay: cmd -c:pay#64/cln:pay#121 partid 0: Using routehint 022d223620a359a47ff7f7ac447c85c46c923da53389221a0054c11c1e3ca31d59 (103x1x0) cltv_delta=6
```
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Core Lightning (CLN): A specification compliant Lightning Network implementation in C
Core Lightning (previously c-lightning) is a lightweight, highly customizable and standard compliant implementation of the Lightning Network protocol.
Project Status
This implementation has been in production use on the Bitcoin mainnet since early 2018, with the launch of the Blockstream Store.
We recommend getting started by experimenting on testnet (testnet4 or regtest), but the implementation is considered stable and can be safely used on mainnet.
Reach Out to Us
Any help testing the implementation, reporting bugs, or helping with outstanding issues is very welcome. Don't hesitate to reach out to us on the implementation-specific mailing list, or on CLN Discord, or on CLN Telegram, or on IRC at dev/gen channel.
Getting Started
Core Lightning only works on Linux and macOS, and requires a locally (or remotely) running bitcoind (version 25.0 or above) that is fully caught up with the network you're running on, and relays transactions (ie with blocksonly=0).
Pruning (prune=n option in bitcoin.conf) is partially supported, see here for more details.
Installation
There are 3 supported installation options:
- Installation of a pre-compiled binary from the release page on GitHub.
- Using one of the provided docker images on the Docker Hub.
- Compiling the source code yourself as described in the installation documentation.
Starting lightningd
Regtest (local, fast-start) Option
If you want to experiment with lightningd, there's a script to set
up a bitcoind regtest test network of two local lightning nodes,
which provides a convenient start_ln helper. See the notes at the top
of the startup_regtest.sh file for details on how to use it.
. contrib/startup_regtest.sh
Mainnet Option
To test with real bitcoin, you will need to have a local bitcoind node running:
bitcoind -daemon
Wait until bitcoind has synchronized with the network.
Make sure that you do not have walletbroadcast=0 in your ~/.bitcoin/bitcoin.conf, or you may run into trouble.
Notice that running lightningd against a pruned node may cause some issues if not managed carefully, see below for more information.
You can start lightningd with the following command:
lightningd --network=bitcoin --log-level=debug
This creates a .lightning/ subdirectory in your home directory: see man -l doc/lightningd.8 (or https://docs.corelightning.org/docs) for more runtime options.
Using The JSON-RPC Interface
Core Lightning exposes a JSON-RPC 2.0 interface over a Unix Domain socket; the lightning-cli tool can be used to access it, or there is a python client library.
You can use lightning-cli help to print a table of RPC methods; lightning-cli help <command>
will offer specific information on that command.
Useful commands:
- newaddr: get a bitcoin address to deposit funds into your lightning node.
- listfunds: see where your funds are.
- connect: connect to another lightning node.
- fundchannel: create a channel to another connected node.
- invoice: create an invoice to get paid by another node.
- pay: pay someone else's invoice.
- plugin: commands to control extensions.
Care And Feeding Of Your New Lightning Node
Once you've started for the first time, there's a script called
contrib/bootstrap-node.sh which will connect you to other nodes on
the lightning network.
There are also numerous plugins available for Core Lightning which add capabilities: in particular there's a collection at: https://github.com/lightningd/plugins
For a less reckless experience, you can encrypt the HD wallet seed: see HD wallet encryption.
You can also chat to other users at Discord core-lightning; we are always happy to help you get started!
Opening A Channel
First you need to transfer some funds to lightningd so that it can
open a channel:
# Returns an address <address>
lightning-cli newaddr
lightningd will register the funds once the transaction is confirmed.
Alternatively you can generate a taproot address should your source of funds support it:
# Return a taproot address
lightning-cli newaddr p2tr
Confirm lightningd got funds by:
# Returns an array of on-chain funds.
lightning-cli listfunds
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>:
lightning-cli connect <node_id> <ip> [<port>]
lightning-cli fundchannel <node_id> <amount_in_satoshis>
This opens a connection and, on top of that connection, then opens a channel.
The funding transaction needs 3 confirmation in order for the channel to be usable, and 6 to be announced for others to use.
You can check the status of the channel using lightning-cli listpeers, which after 3 confirmations (1 on testnet) should say that state is CHANNELD_NORMAL; after 6 confirmations you can use lightning-cli listchannels to verify that the public field is now true.
Sending and Receiving Payments
Payments in Lightning are invoice based.
The recipient creates an invoice with the expected <amount> in
millisatoshi (or "any" for a donation), a unique <label> and a
<description> the payer will see:
lightning-cli invoice <amount> <label> <description>
This returns some internal details, and a standard invoice string called bolt11 (named after the BOLT #11 lightning spec).
The sender can feed this bolt11 string to the decodepay command to see what it is, and pay it simply using the pay command:
lightning-cli pay <bolt11>
Note that there are lower-level interfaces (and more options to these interfaces) for more sophisticated use.
Configuration File
lightningd can be configured either by passing options via the command line, or via a configuration file.
Command line options will always override the values in the configuration file.
To use a configuration file, create a file named config within your top-level lightning directory or network subdirectory
(eg. ~/.lightning/config or ~/.lightning/bitcoin/config). See man -l doc/lightningd-config.5.
A sample configuration file is available at contrib/config-example.
Further information
Pruning
Core Lightning requires JSON-RPC access to a fully synchronized bitcoind in order to synchronize with the Bitcoin network.
Access to ZeroMQ is not required and bitcoind does not need to be run with txindex like other implementations.
The lightning daemon will poll bitcoind for new blocks that it hasn't processed yet, thus synchronizing itself with bitcoind.
If bitcoind prunes a block that Core Lightning has not processed yet, e.g., Core Lightning was not running for a prolonged period, then bitcoind will not be able to serve the missing blocks, hence Core Lightning will not be able to synchronize anymore and will be stuck.
In order to avoid this situation you should be monitoring the gap between Core Lightning's blockheight using lightning-cli getinfo and bitcoind's blockheight using bitcoin-cli getblockchaininfo.
If the two blockheights drift apart it might be necessary to intervene.
HD wallet encryption
You can encrypt the hsm_secret content (which is used to derive the HD wallet's master key) by passing the --encrypted-hsm startup argument, or by using the lightning-hsmtool (which you can find in the tool/ directory at the root of this repo) with the encrypt method. You can unencrypt an encrypted hsm_secret using the lightning-hsmtool with the decrypt method.
If you encrypt your hsm_secret, you will have to pass the --encrypted-hsm startup option to lightningd. Once your hsm_secret is encrypted, you will not be able to access your funds without your password, so please beware with your password management. Also, beware of not feeling too safe with an encrypted hsm_secret: unlike for bitcoind where the wallet encryption can restrict the usage of some RPC command, lightningd always needs to access keys from the wallet which is thus not locked (yet), even with an encrypted BIP32 master seed.
Developers
Developers wishing to contribute should start with the developer guide here.