nextflow-io / nf-hello

Nextflow plugin implementation skeleton

nf-hello plugin

This project contains a simple Nextflow plugin called nf-hello which provides examples of different plugin extensions:

• A custom trace observer that prints a message when the workflow starts and when the workflow completes
• A custom channel factory called reverse
• A custom operator called goodbye
• A custom function called randomString

NOTE: If you want to use this project as a starting point for a custom plugin, you must rename the plugins/nf-hello folder and update settings.gradle with your plugin name.

See the Nextflow documentation for more information about developing plugins.

Plugin structure

• settings.gradle

  Gradle project settings.

• plugins/nf-hello

  The plugin implementation base directory.

• plugins/nf-hello/build.gradle

  Plugin Gradle build file. Project dependencies should be added here.

• plugins/nf-hello/src/resources/META-INF/MANIFEST.MF

  Manifest file defining the plugin attributes e.g. name, version, etc. The attribute Plugin-Class declares the plugin main class. This class should extend the base class nextflow.plugin.BasePlugin e.g. nextflow.hello.HelloPlugin.

• plugins/nf-hello/src/resources/META-INF/extensions.idx

  This file declares one or more extension classes provided by the plugin. Each line should contain the fully qualified name of a Java class that implements the org.pf4j.ExtensionPoint interface (or a sub-interface).

• plugins/nf-hello/src/main

  The plugin implementation sources.

• plugins/nf-hello/src/test

  The plugin unit tests.

Plugin classes

• HelloConfig: shows how to handle options from the Nextflow configuration

• HelloExtension: shows how to create custom channel factories, operators, and fuctions that can be included into pipeline scripts

• HelloFactory and HelloObserver: shows how to react to workflow events with custom behavior

• HelloPlugin: the plugin entry point

Unit testing

To run your unit tests, run the following command in the project root directory (ie. where the file settings.gradle is located):

./gradlew check

Testing and debugging

To build and test the plugin during development, configure a local Nextflow build with the following steps:

1. Clone the Nextflow repository in your computer into a sibling directory:

   git clone --depth 1 https://github.com/nextflow-io/nextflow ../nextflow

2. Configure the plugin build to use the local Nextflow code:

   echo "includeBuild('../nextflow')" >> settings.gradle

   (Make sure to not add it more than once!)

3. Compile the plugin alongside the Nextflow code:

   make assemble

4. Run Nextflow with the plugin, using ./launch.sh as a drop-in replacement for the nextflow command, and adding the option -plugins nf-hello to load the plugin:

   ./launch.sh run nextflow-io/hello -plugins nf-hello

Testing without Nextflow build

The plugin can be tested without using a local Nextflow build using the following steps:

1. Build the plugin: make buildPlugins
2. Copy build/plugins/<your-plugin> to $HOME/.nextflow/plugins
3. Create a pipeline that uses your plugin and run it: nextflow run ./my-pipeline-script.nf

Package, upload, and publish

The project should be hosted in a GitHub repository whose name matches the name of the plugin, that is the name of the directory in the plugins folder (e.g. nf-hello).

Follow these steps to package, upload and publish the plugin:

1. Create a file named gradle.properties in the project root containing the following attributes (this file should not be committed to Git):

   • github_organization: the GitHub organisation where the plugin repository is hosted.
   • github_username: The GitHub username granting access to the plugin repository.
   • github_access_token: The GitHub access token required to upload and commit changes to the plugin repository.
   • github_commit_email: The email address associated with your GitHub account.

2. Use the following command to package and create a release for your plugin on GitHub:

   ./gradlew :plugins:nf-hello:upload

3. Create a pull request against nextflow-io/plugins to make the plugin accessible to Nextflow.