jkutner / libcnb.bash

A library for common buildpack functions

libcnb.bash

This is a Bash binding of the Cloud Native Buildpacks API. It is a non-opinionated implementation adding language constructs and convenience methods for working with the API.

Usage

Set the following vars in your bin/build (eventually these will because a part of the CNB spec and you won't need these lines):

CNB_BP_LAYERS_DIR="$1"
CNB_PLATFORM_DIR="$2"

Then source the libcnb.bash script directly from Github Releases:

source /dev/stdin <<< "$(curl -sL --retry 3 https://github.com/jkutner/libcnb.bash/releases/download/0.0.4/libcnb.bash)"

Or vendor the libcnb.bash script into your buildpack, and source it:

source $CNB_BUILDPACK_DIR/lib/libcnb.bash

Finally, in your buildpack's bin/build you can run functions like:

• cnb_load_env - loads all the environment variables passed into the buildpack (which are stored in the platform dir)
• cnb_create_layer <layer> - creates a new layer directory
• cnb_reset_layer <layer> - destroys and creates a layer directory (useful when caching)
• cnb_set_layer_env <layer> <var> <value> - sets an env var for the layer
• cnb_load_layer <layer> - loads all env vars and sets PATH as if this layer were used by a subsequent buildpack
• cnb_set_layer_metadata <layer> <metadata> - writes metadata to the layer TOML file
• cnb_create_process <type> <command> - adds a process type to the launch.toml

Example

#!/usr/bin/env bash

set -euo pipefail

CNB_BP_LAYERS_DIR="$1"
CNB_PLATFORM_DIR="$2"

source $CNB_BUILDPACK_DIR/lib/libcnb.bash

cnb_load_env

sample_layer="$(cnb_create_layer sample)"

version="$(cat version.txt)"

if [ -f ${sample_layer}.toml ] && [ "$(cat "${sample_layer}.toml" | yj -t | jq .metadata.version -r)" == "${version}" ]; then
  echo "Using cached version: ${version}"
else
  cnb_reset_layer sample
  echo "I'm a sample layer" > ${sample_layer}/sample.txt
  cnb_set_layer_metadata python """
version = \"$version\"
"""
fi

Testing

The test.bats script requires the bats framework. Once it's installed, you can run:

$ make test

License

MIT