Write web applications using your favorite reproducible configuration language.

Flack serves an HTTP server from Nix projects using a Rack-inspired CGI gateway, and provides a web router API written in Nix that works like Express and Sinatra.

It works with both flakes and non-flakes, using idc to load projects that it can't natively load with Nix.

The following example will document options and packages in nixPKCS. Visit http://localhost:2020, click the "Flakes" button, and type "pkcs11" to see module options and packages.

nix run github:numinit/flack -- --flake github:numinit/flack?dir=search \
    --override-input flake github:numinit/nixpkcs

You can override the 'flake' input of the search app to any flake you want.

The first request on each channel may take up to 30 seconds to load as nixpkgs is evaluated (and nixos-search is compiled in the background). Subsequent requests will be fast.

Everything in this repo is subject to change. Don't put it into prod. Nix hasn't had its evaluator threads exposed to the internet before.

Flack will lose its "experimental" status when I get seccomp sandboxing for the evaluator working (and I am comfortable exposing it to the internet even if the eval process gets compromised). Please only run it on localhost for now.

That being said, the module system API for Flack apps is likely fairly consistent.

※ I find documentation applications a bit less technically enjoyable than sandboxing. If you'd like to help with documentation backends, get in touch. Documentation applications will likely be in a separate repo soon.

Here's an example with flakes. Use --flake as your flake ref and (optionally) --dir as the directory to load it from. --dir defaults to ..

# flake.nix
# Run with `nix run github:numinit/flack` and visit http://localhost:2020
{
    inputs.flack.url = "github:numinit/flack";

    outputs = { flack, ... }: {
        flack.apps.default = flack.mkApp {
            route = {
                GET."/" = req: req.res 200 "Hello, Flack!";
            };
        };

        # In case you want `nix run` to work on your local flake, too:
        inherit (flack) apps;
    };
}

For non-flakes, so long as idc can load it and you expose an attribute with a Flack app, it will probably work. Use --import and/or --dir to point Nix at the directory or file to load. This also works fine with flakes.

Check out the example app in apps/default.nix, if you'd like examples of sandboxed CGI scripts, mounts, middlewares, and normal routes.

For a more complicated app implementing a subset of search.nixos.org features, check out the search directory.

• Run it by either:
  • nix run github:numinit/flack -- --flake github:numinit/flack?dir=search --override-input flake github:numinit/flack
  • Cloning, and nix run inside the search directory

Then you can browse to http://localhost:2020 and try an implementation of search.nixos.org in pure Nix.