Python CNAB Library
Work-in-progress library for working with CNAB in Python.
There are probably three main areas of interest for a CNAB client:
- Handling the
bundle.jsonformat (101) - Building invocation images (102)
- Running actions against a CNAB (103)
Claims and Signing are optional but will be worked on once the above are stable.
Installation
The module is published on PyPi and can be installed from there.
pip install cnabParsing bundle.json
Nothing too fancy here, the Bundle class has a from_dict static method which
builds a full Bundle object.
import json
from cnab import Bundle
with open("bundle.json") as f:
data = json.load(f)
bundle = Bundle.from_dict(data)This could for example be used for validation purposes, or for building user interfaces for bundle.json files.
Describing bundle.json in Python
You can also describe the bundle.json file in Python. This will correctly validate the
structure based on the current specification and would allow for building a custom DSL or other
user interface for generating bundle.json files.
from cnab import Bundle, InvocationImage
bundle = Bundle(
name="hello",
version="0.1.0",
invocation_images=[
InvocationImage(
image_type="docker",
image="technosophos/helloworld:0.1.0",
digest="sha256:aaaaaaa...",
)
],
)
print(bundle.to_json())Running CNABs
The module supports running actions on a CNAB, using the docker driver.
from cnab import CNAB
# The first argument can be a path to a bundle.json file, a dictionary
# or a full `Bundle` object
app = CNAB("fixtures/helloworld/bundle.json")
# list available actions
print(app.actions)
# list available parameters
print(app.parameter)
# run the install action
print(app.run("install"))
# run the install action specifying a parameters
print(app.run("install", parameters={"port": 9090}))
# Many applications will require credentials
app = CNAB("fixtures/hellohelm/bundle.json")
# list required credentials
print(app.credentials)
# Here we pass the value for the required credential
# in this case by reading the existing configuration from disk
with open("/home/garethr/.kube/config") as f:
print(app.run("status", credentials={"kubeconfig": f.read()}))Note that error handling for this is very work-in-progress.
Working with invocation images
pycnab also has a class for working with invocation images.
from cnab import CNABDirectory
directory = CNABDirectory("fixtures/invocationimage")
# Check whether the directory is valid
# Raises `InvalidCNABDirectory` exception if invalid
directory.valid()
# Returns the text of the associated README file if present
directory.readme()
# Returns the text of the associated LICENSE file if present
directory.license()Thanks
Thanks to QuickType for bootstrapping the creation of the Python code for manipulating bundle.json based on the current JSON Schema.