TipsAndTricks/NPM

Background

JavaScript is becoming a leading programming language for IoT due to the popularity of Node.js [1] [2] [3]. However Node.js application packages (or modules as they are typically known) tend to have many dependencies and often are not very descriptive of what versions of these dependencies they require. Node.js modules are managed by a tool called Node Package Manager (NPM) which accesses a module registry to install dependencies. In previous versions of Yocto Node.js module recipes created the package by running npm in the do_compile task that would look something like this

SRC_URI = "https://github.com/gruntjs/grunt-cli.git"

do_compile() {
    # changing the home directory to the working directory, the .npmrc will be created in this directory
    export HOME=${WORKDIR}

    # configure cache to be in working directory
    npm set cache ${WORKDIR}/npm_cache

    # clear local cache prior to each compile
    npm cache clear

    # compile and install node modules in source directory
    npm --arch=${TARGET_ARCH} --verbose install
}

The problem with this approach is that the npm install command triggers download of dependent modules. You have to manually track down the licences of all these component and add them to the recipe. Also due the loose specification of dependent package versioning, building with the same recipe at a later date may result in different package contents. Furthermore, as web operations are not expected in the do_compile task, proxy variables are not propagated so recipes must be extended to add configuration for handling corporate firewalls. In summary although this approach is functional, it's far from ideal.

NPM fetcher and recipetool support was added in Yocto 2.1 and improved in 2.2. This simplifies the locking down the packaging of Node.js modules as well as helping you check your licensing requirements.

Aspects of these features are not yet documented in the bitbake manual [4], so this article will help you get the best out of it.

Creating NPM Packages

Documented on the Yocto Project manual

NPM Projects in Development

Although it is useful to package modules already in the registry, adding node.js projects in development is a more common developer use case. The is very similar to the "registry" approach, but instead we give devtool a URL to the source code. To create the cute-files example above from source code we would have done as follows:

devtool add https://github.com/martinaglv/cute-files.git

If you look at the generated recipe, it will be very similar, but the SRC_URI will look like this:

SRC_URI = "git://github.com/martinaglv/cute-files.git;protocol=https \
          npm://registry.npmjs.org;name=commander;version=2.9.0;subdir=node_modules/commander \
          npm://registry.npmjs.org;name=express;version=4.14.0;subdir=node_modules/express \
          npm://registry.npmjs.org;name=content-disposition;version=0.3.0;subdir=node_modules/content-disposition \
          "

You can see that the main module is taken from git repo and dependents obtained from registry. Other than that, recipe is fairly similar and can be built and deployed as above.

Yocto 3.1 (dunfell) update

The npm fetch system has been refactored for the dunfell release.

Importing a recipe that uses npm from zeus to dunfell it is not an straightforward process. Syntax and fetch has changed, so you might encounter errors like the following:

ERROR: cute-files-1.0.2-r0 do_fetch: URL: 'npm://registry.npmjs.org/;name=cute-files;version=1.0.2' is missing the required parameter 'Parameter 'package' required'

In this case the error is related to the registry syntax. When using the registry url (from devtool or in your recipe) from dunfell release, the package name is specified by the "package" parameter instead of "name". Other errors might occur, so importing npm recipes to dunfell release might require a migration process.

Migrating NPM recipes

1. Regenerate the shrinkwrap file

As described above, the devtool add offers the possibility to create recipes and shrinkwrap files for npm applications (either from registry, git, local sources...).

You can create an updated shrinkwrap for your application with:

devtool add <app>

where <app> refers to the npm registry, git repository or local sources to your application.

Once the command has been successfully executed you can overwrite your previous shrinkwrap with the content of build/workspace/recipes/<app>/<app>/npm-shrinkwrap.json.

2. Clean workspace

In order to avoid duplicated recipes you should remove the newly generated one:

rm -rf build/workspace/recipes/<app> build/workspace/appends/<app> build/workspace/sources/<app>

3. Adapt old recipe

• Update SRC_URI variable: A common use case for npm developers is to integrate a non-registered application that has dependencies to fetch from the registry. As described on the documentation, until zeus release, this recipe would describe the sources to fetch with the following syntax:

 SRC_URI = "git://github.com/martinaglv/cute-files.git;protocol=https \
               npm://registry.npmjs.org;name=commander;version=2.9.0;subdir=node_modules/commander \
               npm://registry.npmjs.org;name=express;version=4.14.0;subdir=node_modules/express \
               npm://registry.npmjs.org;name=content-disposition;version=0.3.0;subdir=node_modules/content-disposition \
               "

where the first line represents the repository for the main package and the other three the registry dependencies.

However, with the refactoring made on the dunfell release, the fetcher is capable of getting all the dependencies from a single shrinkwrap file (which is very convenient for large applications). So the SRC_URI of your recipe can be left as:

SRC_URI = " \
    git://github.com/tutorialzine/cute-files.git;protocol=https \
    npmsw://${THISDIR}/${BPN}/npm-shrinkwrap.json \
    " 

Note that the syntax uses npmsw:// instead of npm://.

• Remove obsolete variables: Another change that might be necessary is to remove the obsolete variables NPM_SHRINKWRAP and NPM_LOCKDOWN from your recipe.

NPM_SHRINKWRAP := "${THISDIR}/${PN}/npm-shrinkwrap.json"
NPM_LOCKDOWN := "${THISDIR}/${PN}/package-lock.json"

• Remove package-lock.json: The file package-lock.json can also be removed from your recipe folder.