Contributor Workflow

Learn the practical process and guidelines for contributing.

Build and Development

Install the following dependencies for best results:

sudo apt update
sudo apt install jq valgrind cppcheck shellcheck libsecp256k1-dev libpq-dev

Re-run configure and build using make:

make -j$(nproc)


There are various development options enabled by running with --developer. You can log console messages with log_info() in lightningd and status_debug() in other subdaemons.

You can debug crashing subdaemons with the argument --dev-debugger=channeld, where channeld is the subdaemon name. It will run gnome-terminal by default with a gdb attached to the subdaemon when it starts. You can change the terminal used by setting the DEBUG_TERM environment variable, such as DEBUG_TERM="xterm -e" or DEBUG_TERM="konsole -e".

It will also print out (to stderr) the gdb command for manual connection. The subdaemon will be stopped (it sends itself a SIGSTOP); you'll need to continue in gdb.

make -j$(nproc)

Making BOLT Modifications

All of code for marshalling/unmarshalling BOLT protocol messages is generated directly from the spec. These are pegged to the BOLTVERSION, as specified in Makefile.

Source code analysis

An updated version of the NCC source code analysis tool is available at

It can be used to analyze the lightningd source code by running make clean && make ncc. The output (which is built in parallel with the binaries) is stored in .nccout files. You can browse it, for instance, with a command like nccnav lightningd/lightningd.nccout.

Code Coverage

Code coverage can be measured using Clang's source-based instrumentation.

First, build with the instrumentation enabled:

make clean
./configure --enable-coverage CC=clang
make -j$(nproc)

Then run the test for which you want to measure coverage. By default, the raw coverage profile will be written to ./default.profraw. You can change the output file by setting LLVM_PROFILE_FILE:

LLVM_PROFILE_FILE="full_channel.profraw" ./channeld/test/run-full_channel

Finally, generate an HTML report from the profile. We have a script to make this easier:

./contrib/ channeld/test/run-full_channel \
    full_channel.profraw full_channel.html
firefox full_channel.html

For more advanced report generation options, see the Clang coverage documentation.


There are a few subtleties you should be aware of as you modify deeper parts of the code:

  • ccan/structeq's STRUCTEQ_DEF will define safe comparison function foo_eq() for struct foo, failing the build if the structure has implied padding.
  • command_success, command_fail, and command_fail_detailed will free the cmd you pass in.
    This also means that if you tal-allocated anything from the cmd, they will also get freed at those points and will no longer be accessible afterwards.
  • When making a structure part of a list, you will instance a struct list_node. This has to be the first field of the structure, or else dev-memleak command will think your structure has leaked.

Protocol Modifications

The source tree contains CSV files extracted from the v1.0 BOLT specifications (wire/extracted_peer_wire_csv and wire/extracted_onion_wire_csv). You can regenerate these by first deleting the local copy(if any) at directory .tmp.bolts, setting BOLTDIR and BOLTVERSION appropriately, and finally running make extract-bolt-csv. By default the bolts will be retrieved from the directory ../bolts and a recent git version.

e.g., make extract-bolt-csv BOLTDIR=../bolts BOLTVERSION=ee76043271f79f45b3392e629fd35e47f1268dc8

Pushing Up Changes to PR Branches

If you want to pull down and run changes to a PR branch, you can use the convenient
pr/<pr#> branch tags to do this. First you'll need to make sure you have the following
in your .github/config.

[remote "origin"]
fetch = +refs/pull/*/head:refs/remotes/origin/pr/*

Once that's added, run git fetch and then you should be able to check out PRs by their number.

git checkout pr/<pr#>

If you make changes, here's how to push them back to the original PR originator's
branch. NOTE: This assumes they have turned on "allow maintainers to push changes".

First you'll want to make sure that their remote is added to your local git. You
can do this with remote -v which lists all current remotes.

git remote -v

If it's not there, you can add it with

git remote add <name> <repo_url>

For example, here's how you'd add niftynei's git lightning clone.

git remote add niftynei [email protected]:niftynei/lightning.git

To push changes to the remote, from a pr/<pr#> branch, you'll need to
know the name of the branch on their repo that made the PR originally. You
can find this on the PR on github.

You'll also need to make sure you've got a ref to that branch from their repo;
you can do this by fetching the latest branches for them with the following command.

git fetch niftynei

You may need to fetch their latest set of commits before pushing yours, you can do
this with

git pull -r niftynei <pr-branch/name>

Finally, you're good to go in terms of pushing up the latest commits that you've made
(or changed) on their branch.

git push <name> HEAD:<pr-branch/name>

For example, here's how you'd push changes to a branch named "nifty/add-remote-to-readme".

git push niftynei HEAD:nifty/add-remote-to-readme

If that fails, go check with the PR submitter that they have the ability to push changes
to their PR turned on. Also make sure you're on the right branch before you push!