puppeteer node2nix demonstration

A demonstration of how to work with puppeteer using node2nix.

Steps

1. Add "bin": index.js

In package.json:

{
  // ...
  "bin": "index.js",

2. Run node2nix

You should run node2nix --nodejs-10, since node2nix will use a default of near-EOL NodeJS 8.x.

3. Move default.nix generated by node2nix to something else

I typically use node2nix.nix.

$ mv default.nix node2nix.nix

4. Edit node2nix sources to filter by gitignore (optional)

In node-packages.nix, add gitignoreSource as an argument to the top level so we can filter gitignored sources.

{nodeEnv, fetchurl, fetchgit, globalBuildInputs ? [], gitignoreSource}:

Then go look for the src attribute defined in the args let-binding, and replace the definition.

  args = {
    name = "puppeteer-node2nix";
    packageName = "puppeteer-node2nix";
    version = "1.0.0";
-   src = ./.;
+   src = pkgs.nix-gitignore.gitignoreSource [ ".git" ] ./.;
    dependencies = [

Once these are done, you can add this argument to node2nix.nix

import ./node-packages.nix {
  inherit (pkgs) fetchurl fetchgit;
+ inherit (pkgs.nix-gitignore) gitignoreSource;
  inherit nodeEnv;
}

5. Make a new derivation, e.g. default.nix using the package attribute.

{ pkgs ? import <nixpkgs> {} }:

let
  node2nix = import ./node2nix.nix { inherit pkgs; };

  # note that this derivation does not work because the puppeteer
  # package is not very nice. more details to follow.
  package = node2nix.package;

in pkgs.stdenv.mkDerivation {
  name = "puppeteer-node2nix-demo";

  src = package;

  installPhase = ''
    mkdir -p $out/bin
    ln -s $src/bin/puppeteer-node2nix $out/bin/puppeteer-node2nix
  '';
}

Now you can try to build this package and observe puppeteer doing bad things: nix-build (optionally with -j 10 to give it more jobs)

ERROR: Failed to download Chromium r674921! Set
"PUPPETEER_SKIP_CHROMIUM_DOWNLOAD" env variable to skip download.

6. Set Puppeteer to not download Chrome, as suggested.

- package = node2nix.package;
+ package = node2nix.package.override {
+   preInstallPhases = "skipChromiumDownload";
+   skipChromiumDownload = ''
+     export PUPPETEER_SKIP_CHROMIUM_DOWNLOAD=1
+   '';
+ };

Now you can build this and get a binary. But wait, if you run this, you will just get an error that Chormium is missing.

$ ./result/bin/puppeteer-node2nix

(node:1988) UnhandledPromiseRejectionWarning: Error: Chromium revision is not
downloaded. Run "npm install" or "yarn install"

7. Wrap the program with a Chromium available to it

Of course, you will soon find in the Puppeteer docs that you need to provide the PUPPETEER_EXECUTABLE_PATH environment variable, with a path to the chromium binary. That can be done easily using wrapProgram.

in pkgs.stdenv.mkDerivation {
  name = "puppeteer-node2nix-demo";

  src = package;

+ buildInputs = [ pkgs.makeWrapper ];

  installPhase = ''
    mkdir -p $out/bin
    ln -s $src/bin/puppeteer-node2nix $out/bin/puppeteer-node2nix
+
+   wrapProgram $out/bin/puppeteer-node2nix \
+     --set PUPPETEER_EXECUTABLE_PATH ${pkgs.chromium.outPath}/bin/chromium
  '';
}

Now when we build the derivation, we can see the result that the original puppeteer-node2nix has now been wrapped with a script that will set the PUPPETEER_EXECUTABLE_PATH environment variable:

$ ls -a result/bin/
.  ..  puppeteer-node2nix  .puppeteer-node2nix-wrapped

Contents of puppeteer-node2nix

#! /nix/store/{someSha}-bash-4.4-p23/bin/bash -e
export PUPPETEER_EXECUTABLE_PATH='/nix/store/{someSha}-chromium-76.0.3809.87/bin/chromium'
exec -a "$0" "/nix/store/{someSha}-puppeteer-node2nix-demo/bin/.puppeteer-node2nix-wrapped"  "${extraFlagsArray[@]}" "$@"

Result

We can now run this as expected:

$ ./result/bin/puppeteer-node2nix
navigated to example.com
saved screenshot to example.png

Links

I wrote a blog post about this here: https://github.com/justinwoo/my-blog-posts/blob/master/posts/2019-08-23-using-puppeteer-with-node2nix.md