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node2nix

Deploy NPM Package Manager (NPM) packages with the Nix package manager!

Table of Contents

Table of Contents

Installation

There are two ways this package can installed.

To install this package through the Nix package manager, obtain a copy of Nixpkgs and run:

$ nix-env -f '<nixpkgs>' -iA nodePackages.node2nix

Alternatively, this package can also be installed through NPM by running:

$ npm install -g node2nix

Usage

node2nix can be used for a variety of use cases.

Deploying a Node.js development project

The primary use case of node2nix is to deploy a development project as a NPM package.

What Node.js developers typically do in a development setting is opening the source code folder and running:

$ npm install

The above command-line instruction deploys all dependencies declared in the package.json configuration file so that the application can be run.

With node2nix you can use the Nix package manager for exactly the same purpose. Running the following command generates a collection of Nix expressions from package.json:

$ node2nix

The above command generates three files node-packages.nix containing Nix expressions for the requested packge, node-env.nix contains the build logic and default.nix is a composition expression allowing users to deploy the package.

By running the following Nix command with these expressions, the project can be built:

$ nix-build -A package

The above instruction places a result symlink in the current working dir pointing to the build result. An executable part of the project can be run as follows:

$ ./result/bin/node2nix

Generating a tarball from a Node.js development project

The expressions that are generated by node2nix (shown earlier) can also be used to generate a tarball from the project:

$ nix-build -A tarball

The above command-line instruction produces a tarball that can is placed in the following location:

$ ls result/tarballs/node2nix-1.0.1.tgz

The above tarball can be distributed to others and installed with NPM by running:

$ npm install node2nix-1.0.1.tgz

Deploying a development environment of a Node.js development project

Besides deploying a development project, it may also be useful to only install the project's dependencies and spawning a shell session in which they can be found.

The following command-line instruction uses the earlier generated expressions to deploy all the dependencies and opens a development environment:

$ nix-shell -A shell

Within this shell session, files can be modified and run without any hassle. For example, the following command should work without any trouble:

$ node bin/node2nix.js --help

Deploying a collection of NPM packages from the NPM registry

The secondary use of node2nix is deploying existing NPM packages from the NPM registry.

Deployment of packages from the registry is driven by a JSON specification that looks as follows:

[
  "async",
  "underscore",
  "slasp",
  { "mocha" : "1.21.x" },
  { "mocha" : "1.20.x" },
  { "nijs": "0.0.18" },
  { "node2nix": "git://github.com/svanderburg/node2nix.git" }
]

The above specification is basically an array of objects. For each element that is a string, the latest version is obtained from the registry.

To obtain a specific version of a package, an object must defined in which the keys are the name of the packages and the values the versions that must be obtained.

Any version specification that NPM supports can be used, such as version numbers, version ranges, HTTP(S) URLs, Git URLs, and GitHub identifiers.

Nix expressions can be generated from this JSON specification as follows:

$ node2nix -i node-packages.json

And by using the generated Nix expressions, we can install async through Nix as follows:

$ nix-env -f default.nix -iA async

For every package for which the latest version has been requested, we can directly refer to the name of the package to deploy it.

For packages for which a specific version has been specified, we must refer to it using an attribute that name that is composed of its name and version specifier.

The following command can be used to deploy the first specific version of mocha declared in the JSON configuration:

$ nix-env -f default.nix -iA '"mocha-1.21.x"'

node2nix can be referenced as follows:

$ nix-env -f default.nix -iA '"node2nix-git://github.com/svanderburg/node2nix.git"'

Since every NPM package resolves to a package name and version number we can also deploy any package by using an attribute consisting of its name and resolved version number.

This command deploys NiJS version 0.0.18:

$ nix-env -f default.nix -iA '"nijs-0.0.18"'

Generating packages for Node.js 6.x

By default, node2nix generates Nix expressions that should be used in conjuction with Node.js 4.x, the current LTS release. Node.js 6.x contains the newer npm 3.x, that stores dependencies in a more flat structure.

The flat structure can be simulated by adding the --flatten parameter. Additionally, to enable all flags to make generation for Node.js 6.x work, add the -6 parameter. For example, running the following command generates expressions that can be used with Node.js 6.x:

$ node2nix -6 -i node-package.json

By running the following command, Nix deploys NiJS version 0.0.18 using Node.js 6.x and npm 3.x:

$ nix-env -f default.nix -iA '"nijs-0.0.18"'

Advanced options

node2nix also has a number of advanced options.

Development mode

By default, NPM packages are deployed in production mode, meaning that the development dependencies are not installed by default. By adding the --development command line option, you can also deploy the development dependencies:

$ node2nix --development

Specifying paths

If no options are specified, node2nix makes implicit assumptions on the filenames of the input JSON specification and the output Nix expressions. These filenames can be modified with command-line options:

$ node2nix --input package.json --output registry.nix --composition default.nix --node-env node-env.nix

Using alternative NPM registries

You can also use an alternative NPM registry (such as a private one), by adding the --registry option:

$ node2nix -i node-packages.json --registry http://private.registry.local

Adding unspecified dependencies

A few exotic NPM packages may have dependencies on native libraries that reside somewhere on the user's host system. Unfortunately, NPM's metadata does not specify them, and as a consequence, it may result in failing Nix builds due to missing dependencies.

As a solution, the generated expressions by node2nix are made overridable. The override mechanism can be used to manually inject additional unspecified dependencies.

The easiest way to do this is to create a wrapper Nix expression that imports the generated composition expression from node2nix and injects additional dependencies.

Consider the following package collection file (named: node-packages.json) that installs one NPM package named floomatic:

[
  "floomatic"
]

We can generate Nix expressions from the above specification, by running:

$ node2nix -i node-packages.json

One of floomatic's dependencies is an NPM package named native-diff-match-patch that requires the Qt 4.x library and pkgconfig, which are native dependencies not detected by the node2nix generator.

With the following wrapper expression (named: override.nix), we can inject these dependencies ourselves:

{pkgs ? import <nixpkgs> {
    inherit system;
}, system ? builtins.currentSystem}:

let
  nodePackages = import ./default.nix {
    inherit pkgs system;
  };
in
nodePackages // {
  floomatic = nodePackages.floomatic.override (oldAttrs: {
    buildInputs = oldAttrs.buildInputs ++ [ pkgs.pkgconfig pkgs.qt4 ];
  });
}

The expression does the following:

  • We import the composition expression (default.nix) generated by node2nix.
  • We take the old derivation that builds the floomatic package, and we add the missing native dependencies as build inputs by defining an override.

With the above wrapper expression, we can correctly deploy floomatic, by running:

$ nix-build override.nix -A floomatic

Adding additional/global NPM packages to a packaging process

Sometimes it may also be required to supplement a packaging process with additional NPM packages. For example, when building certain NPM projects, some dependencies have to be installed globally.

A prominent example of such a workflow is a Grunt project. The grunt CLI is typically installed globally, whereas its plugins are installed as development dependencies.

We can automate such a workflow as follows. Consider the following package.json example:

{
  "name": "grunt-test",
  "version": "0.0.1",
  "private": "true",
  "devDependencies": {
    "grunt": "*",
    "grunt-contrib-jshint": "*",
    "grunt-contrib-watch": "*"
  }
}

The above configuration declares grunt and two grunt plugins (jshint and watch) as development dependencies.

We can create a supplemental package specification that represents additional NPM packages that are supposed to be installed globally:

[
  "grunt-cli"
]

The above configuration (supplement.json) states that we need the grunt-cli as an additional package, installed globally.

Running the following command-line instruction generates the Nix expressions for the project:

$ node2nix -d -i package.json --supplement-input supplement.json

By overriding the generated expressions, we can instruct the builder to execute grunt after the dependencies have been deployed:

{ pkgs ? import <nixpkgs> {}
, system ? builtins.currentSystem
}:

let
  nodePackages = import ./default.nix {
    inherit pkgs system;
  };
in
nodePackages // {
  package = nodePackages.package.override {
    postInstall = "grunt";
  };
}

The above expression (override.nix) defines a postInstall hook that executes grunt after the NPM package has been deployed.

Running the following command executes the packaging process, including the grunt post-processing step:

$ nix-build override.nix -A package

Disabling running NPM install

node2nix tries to mimic npm's dependency resolver as closely as possible. However, it may happen that there is a small difference and the deployment fails a result.

A mismatch is typically caused by versions that can't be reliably resolved (e.g. due to wildcards) or errors in lifting bundled dependencies (with the --flatten option enabled). In many cases, the package should still work despite the error.

To prevent the deployment from failing, we can disable the npm install step, by overriding the package:

{pkgs ? import <nixpkgs> {
  inherit system;
}, system ? builtins.currentSystem}:

let
  nodePackages = import ./default.nix {
    inherit pkgs system;
  };
in
nodePackages // {
  express = nodePackages.express.override (oldAttrs: {
    dontNpmInstall = true;
  });
}

By overriding a package and setting the dontNpmInstall parameter to true, we skip the install step (which merely serves as a check). The generated expression is actually responsible for obtaining and extracting the dependencies.

API documentation

This package includes API documentation, which can be generated with JSDuck. The Makefile in this package contains a duck target to generate it and produces the HTML files in build/:

$ make duck

License

The contents of this package is available under the MIT license

Acknowledgements

This package is based on ideas and principles pioneered in npm2nix.