h-assets

Pyramid views for serving compiled static assets


License
OSET-PL-2.1
Install
pip install h-assets==1.0.4

Documentation

h-assets

This package provides Pyramid views for serving collections of compiled static assets (eg. bundles of JavaScript and CSS).

Compared to Pyramid's builtin static asset functionality , this provides a convenient way to serve assets based on certain assumptions about how assets are generated and opinions about how they should be served:

  • The assets are assumed to be compiled artefacts in an output directory populated by frontend build tooling, rather than source files inside the Python package. Typically Hypothesis applications use a build directory in the root of the repository.
  • Cache busting is always enabled and is done via query strings. These query strings are checked, if present, when serving a request to avoid responses being stored under the wrong keys in downstream caches.
  • It is assumed that compressing bytes (eg. with gzip or Brotli) will be handled by a service like Cloudflare, not the Python application.

Additionally h-assets provides a way to define collections (bundles) of assets and methods to generate cache-busted URLs for all assets in the bundle. This is useful for example to render all the <script> or <style> tags that are needed by a certain part of a site.

Usage

Using h-assets in a Pyramid project involves three steps:

  1. Prepare the compiled assets for use with h-assets
  2. During Pyramid application configuration, create an asset Environment to handle asset URL generation and register a view to serve assets from that environment
  3. Expose the URL-generation methods from the asset Environment to your templating system so that templates can generate asset URLs

Preparing assets for use with h-assets

  1. Set up a process to compile or copy assets from source files into an output directory. Conventionally Hypothesis projects use a folder called build in the repository root.

  2. In the output directory generate a JSON manifest file (eg. manifest.json) that maps asset paths to URLs with cache-busting query strings. Example content:

    {
      "scripts/app.bundle.js": "scripts/app.bundle.js?abcdef",
      "scripts/vendor.bundle.js": "scripts/vendor.bundle.js?xyz123"
    }

    Any format is allowed for the cache-buster. Hypothesis projects typically use the first few characters of a hash (eg. SHA-1) of the file's contents.

  3. Create an INI file (eg. assets.ini) that defines collections ("bundles") of assets that are used together. Example content:

    [bundles]
    
    frontend_apps_js =
      scripts/browser_check.bundle.js
      scripts/frontend_apps.bundle.js
    
    frontend_apps_css =
      styles/frontend_apps.css

Registering a Pyramid view to serve assets

To serve assets using h-assets, a Pyramid view needs to be created using the assets_view function.

In the Pyramid app configuration, define a route where the URL is a base URL followed by a *subpath:

def includeme(config):
    config.add_route("assets", "/assets/*subpath")

To register the view associated with this route, first create an Environment to handle generation of asset URLs. Then use assets_view to create the view callable for use with config.add_view:

import os.path

from h_assets import Environment, assets_view


def includeme(config):
    # This assumes the following repository structure:
    #   build/ - Compiled frontend assets
    #     manifest.json
    #   projectname/
    #     assets.py - This module
    #     routes.py - Route definitions
    #     assets.ini
    root_dir = os.path.dirname(__file__)

    assets_env = Environment(
        assets_base_url="/assets",
        bundle_config_path="{root_dir}/assets.ini",
        manifest_path=f"{root_dir}/../build/manifest.json",
    )

    # Store asset environment in registry for use in registering `asset_urls`
    # Jinja2 helper in `app.py`.
    config.registry["assets_env"] = assets_env

    config.add_view(route_name="assets", view=assets_view(assets_env))

Referencing assets in templates

To get a list of asset URLs for assets in a bundle, use the urls method of the asset Environment. A common pattern is to expose these methods as global helpers in the templating environment being used to generate HTML responses. For example, in a project using pyramid_jinja2:

jinja2_env = config.get_jinja2_environment()
jinja2_env.globals["asset_url"] = config.registry["assets_env"].url
jinja2_env.globals["asset_urls"] = config.registry["assets_env"].urls

Then a template can generate URLs using:

{% for url in asset_urls("frontend_apps_js") %}
  <script async defer src="{{ url }}"></script>
{% endfor %}

Hacking

Installing h-assets in a development environment

You will need

  • Git

  • pyenv Follow the instructions in the pyenv README to install it. The Homebrew method works best on macOS. On Ubuntu follow the Basic GitHub Checkout method.

Clone the git repo

git clone https://github.com/hypothesis/h-assets.git

This will download the code into a h-assets directory in your current working directory. You need to be in the h-assets directory for the rest of the installation process:

cd h-assets

Run the tests

make test

That's it! You’ve finished setting up your h-assets development environment. Run make help to see all the commands that're available for linting, code formatting, packaging, etc.

Updating the Cookiecutter scaffolding

This project was created from the https://github.com/hypothesis/h-cookiecutter-pypackage/ template. If h-cookiecutter-pypackage itself has changed since this project was created, and you want to update this project with the latest changes, you can "replay" the cookiecutter over this project. Run:

make template

This will change the files in your working tree, applying the latest updates from the h-cookiecutter-pypackage template. Inspect and test the changes, do any fixups that are needed, and then commit them to git and send a pull request.

If you want make template to skip certain files, never changing them, add these files to "options.disable_replay" in .cookiecutter.json and commit that to git.

If you want make template to update a file that's listed in disable_replay simply delete that file and then run make template, it'll recreate the file for you.