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

Using node2nix instead of the "vanilla" NPM is useful for a variety of reasons:

• To deploy NPM packages on NixOS and to manage complex software installations (that include non-NPM managed dependencies) by using a universal deployment solution (Nix).
• To integrate with other tools in the Nix-ecosystem: NixOS to manage an entire system from a single declarative specification, NixOps to deploy networks of machines (bare metal and in the cloud), and Disnix to manage service-oriented systems.

Table of Contents

• node2nix
• Table of Contents
• Installation
• Building a development version
• Usage
  • Deploying a Node.js development project
  • Generating a tarball from a Node.js development project
  • Deploying a development environment of a Node.js development project
  • Using the Node.js environment in other Nix derivations
  • Deploying a collection of NPM packages from the NPM registry
  • Using NPM lock files
  • Generating packages for specific Node.js versions
• Advanced options
  • Development mode
  • Specifying paths
  • Using alternative NPM registries
  • Adding unspecified dependencies
  • Wrapping or patching the code or any of its dependencies
  • Adding additional/global NPM packages to a packaging process
  • Using private Git repositories
  • Disable cache bypassing
• Troubleshooting
  • Deploying peer dependencies
  • Stripping optional dependencies
  • Updating the package lock file
  • Creating a symlink to the node_modules folder in a shell session
  • Disabling running NPM install
• API documentation
• License
• Acknowledgements

To be able to convert Git dependencies, the presence of the nix-hash command-line utility (that is included with the Nix package manager) is required.

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

A development version can be deployed by checking out the Git repository and running:

$ nix-env -f release.nix -iA package.x86_64-linux

The above command installs the development node2nix executable into the Nix profile of the user.

Alternatively, you can the use NPM to install the project dependencies:

$ npm install

The project only uses JavaScript dependencies and, as such, will also work on NixOS.

node2nix can be used for a variety of use cases.

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 capturing the packages that can be deployed including all its required dependencies, 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 (that is part of the project) can be started as follows:

$ ./result/bin/node2nix

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 is placed in the following location:

$ ls result/tarballs/node2nix-1.0.1.tgz

The above tarball can be distributed to any user that has the NPM package manager installed, and installed by running:

$ npm install node2nix-1.0.1.tgz

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:

$ node bin/node2nix.js --help

The node_modules environment generated by node2nix can also be used in downstream Nix expressions. This can be useful when you want to build a project that requires running a build system such as Webpack in your Node.js environment.

This environment can be found on the nodeDependencies attribute of the generated output. It contains two important paths: lib/node_modules and bin. The former should be copied or symlinked into your build directory, and the latter should be added to the PATH. (You can also use the NODE_PATH environment variable, but see the warnings about that below.)

Here's an example derivation showing this technique:

let
  nodeDependencies = (pkgs.callPackage ./default.nix {}).nodeDependencies;
in

stdenv.mkDerivation {
  name = "my-webpack-app";
  src = ./my-app;
  buildInputs = [nodejs];
  buildPhase = ''
    ln -s ${nodeDependencies}/lib/node_modules ./node_modules
    export PATH="${nodeDependencies}/bin:$PATH"

    # Build the distribution bundle in "dist"
    webpack
    cp -r dist $out/
  '';
}

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 with 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"'

(As a sidenote: because the attribute name contains dots: ., that also serve as an attribute selector in the Nix expression language, we have to quote the attribute name)

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"'

Node.js 8.x and higher (that includes npm 5.x or higher) can also work with so-called lock files that pinpoint the exact versions used of all dependencies and transitive dependencies, and provides a content addressable cache to speed up deployments.

Some Node.js development projects may include a package-lock.json file pinpointing the exact versions of the dependencies and transitive dependencies. node2nix can use this file to generate a Nix expression from it so that Nix uses the exact same packages:

$ node2nix -l package-lock.json

By default, node2nix generates Nix expressions that should be used in conjuction with Node.js 12.x, which is currently the oldest supported LTS release.

When it is desired, it is also possible to generate expressions for other Node.js versions. For example, Node.js 4.x does not use a flattening/deduplication algorithm, and 6.x that does not support lock files or caching.

The old non-flattening structure can be simulated by adding the --no-flatten parameter.

Additionally, to enable all flags to make generation for a certain Node.js work, node2nix provides convenience parameters. For example, by using the -4 parameter, we can generate expressions that can be used with Node.js 4.x:

$ node2nix -4 -i node-package.json

By running the following command, Nix deploys NiJS version 0.0.18 using Node.js 4.x and npm 2.x:

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

node2nix also has a number of advanced options.

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

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

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

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

$ node2nix \
  --registry "https://registry.npmjs.org" \
  --registry "https://npm.pkg.github.com/" \
  --registry-auth-token "XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX" \
  --registry-scope "@myorg"

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 {
    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

Some packages or any of its dependencies may also require some ad-hoc fixes to make them work. In such cases, we can implement a preRebuild hook with shell instructions that will be executed before the builder will run npm rebuild and npm install.

For example, consider the dnschain package:

[
  "dnschain"
]

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

$ node2nix -i node-packages.json

dnschain has a practical problem -- it requires OpenSSL to be in the PATH of the user. We can create an override.nix expression implementing a preRebuild hook that wraps the executable in a script that adds openssl to the PATH:

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

let
  nodePackages = import ./default.nix {
    inherit pkgs system;
  };
in
nodePackages // {
  dnschain = nodePackages.dnschain.override {
    preRebuild = ''
      wrapProgram $out/bin/dnschain --suffix PATH : ${pkgs.openssl.bin}/bin
    '';
  };
}

With the above wrapper expression, we can deploy a wrapped dnschain (that is able to find the openssl executable), by running:

$ nix-build override.nix -A dnschain

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 refers to 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.

Furtheremore, you can provide specific versions of supplemental packages. Here is example of supplement.json with grunt-cli version 1.2.0:

[
  {
    "grunt-cli": "1.2.0"
  }
]

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

In some development projects, it may be desired to deploy private Git repositories as dependencies. The fetchgit {} function in Nixpkgs, however, only supports public repositories.

It is also possible to instruct the generator to use the fetchgitPrivate {} function, that adds support for private repositories that can be reached with SSH:

$ node2nix --use-fetchgit-private

Before running the node2nix command shown above, you probably want to set up ssh-agent first and use ssh-add to add a private key to the keychain to prevent the generator from asking for passphrases.

When deploying a project or package, you need to pass an additional parameter that provides an SSH configuration file with a reference to an identify file. The following SSH config file (e.g. ~/ssh_config) suffices for me:

StrictHostKeyChecking=no
UserKnownHostsFile /dev/null
IdentityFile ~/id_rsa

When deploying a package with Nix, you must propagate the location of the SSH config file as a parameter:

$ nix-build -A package -I ssh-config-file=~/ssh_config

It is also possible to provide the location of the config file by adapting the NIX_PATH environment variable, as opposed to using the -I parameter:

$ export NIX_PATH=ssh-config-file=~/ssh_config:$NIX_PATH

The above approach also makes it possible to deploy a NPM package with private dependencies as part of a NixOS, NixOps or Disnix configuration.

In a Nix builder environment, the NPM packages cache is empty and NPM does not seem to trust dependencies that are already stored in the bundled node_modules/ folder, because they lack the meta data that can be used for integrity checks.

By default, node2nix bypasses the cache by augmenting package configuration files with these mandatory meta data fields.

If older versions of NPM are used (any version before 5.x), this meta information is not required. Bypassing the cache can be disabled by providing the --no-bypass-cache parameter.

This section contains some troubleshooting information for common problems.

In NPM version 2.x and older, peer dependencies were automatically deployed if they were not declared as regular dependencies. In newer versions of NPM, this behaviour has changed -- peer dependencies are only used for version checks, but NPM no longer installs them.

Some package deployments may still rely on the old behaviour and will fail to deploy. To generate expressions that install peer dependencies, you can add the --include-peer-dependencies parameter:

$ node2nix --include-peer-dependencies

When NPM packages with optional dependencies are published to the NPM registry, the optional dependencies become regular runtime dependencies. As a result, when deploying a package with a broken "integrated" optional dependency, the deployment with fail, unlike pure optional dependencies that are allowed to fail.

To fix these package deployments, it is possible to strip the optional dependencies from packages installed from the NPM registry:

$ node2nix --strip-optional-dependencies

When deploying projects that provide a package-lock.json file, node2nix deployments will typically fail if the corresponding package.json configuration has changed after the generation of the lock file, because the dependency tree in the lock file may be incomplete.

To fix this problem, npm install must be executed again so that the missing or changed dependencies are updated in the lock file.

In Nix shell sessions, that can be started with nix-shell -A shell, conventional Node.js projects will typically work, because there is a NODE_PATH environment variable that refers to a Nix store path that provides all the dependencies that the project needs.

However, there are also a variety of Node.js/NPM-based build tools available, such as Grunt, Gulp, Babel or ESLint, that work with plugins that are stored in the node_modules/ folder of the project.

Unfortunately, these tools do not respect the NODE_PATH environment variable and, as a result, fail to work in a Nix shell session.

As a workaround, you can create a symlink in the project's root folder to allow these tools to find their dependencies:

$ ln -s $NODE_PATH node_modules

Keep in mind that the symlink needs to be removed again if you want to deploy the package with nix-build or nix-env.

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. 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 {
    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.

This package includes API documentation, which can be generated with JSDoc.

The contents of this package is available under the MIT license

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