github-flakes.nix

{
  lib,
  config,
  nixpkgs,
  ...
}:
let
  pkgs = config.nodes.client.nixpkgs.pkgs;

  # Generate a fake root CA and a fake api.github.com / github.com / channels.nixos.org certificate.
  cert = pkgs.runCommand "cert" { nativeBuildInputs = [ pkgs.openssl ]; } ''
    mkdir -p $out

    openssl genrsa -out ca.key 2048
    openssl req -new -x509 -days 36500 -key ca.key \
      -subj "/C=NL/ST=Denial/L=Springfield/O=Dis/CN=Root CA" -out $out/ca.crt

    openssl req -newkey rsa:2048 -nodes -keyout $out/server.key \
      -subj "/C=CN/ST=Denial/L=Springfield/O=Dis/CN=github.com" -out server.csr
    openssl x509 -req -extfile <(printf "subjectAltName=DNS:api.github.com,DNS:github.com,DNS:channels.nixos.org") \
      -days 36500 -in server.csr -CA $out/ca.crt -CAkey ca.key -CAcreateserial -out $out/server.crt
  '';

  registry = pkgs.writeTextFile {
    name = "registry";
    text = ''
      {
        "flakes": [
          {
            "from": {
              "type": "indirect",
              "id": "nixpkgs"
            },
            "to": {
              "type": "github",
              "owner": "NixOS",
              "repo": "nixpkgs"
            }
          },
          {
            "from": {
              "type": "indirect",
              "id": "private-flake"
            },
            "to": {
              "type": "github",
              "owner": "fancy-enterprise",
              "repo": "private-flake"
            }
          }
        ],
        "version": 2
      }
    '';
    destination = "/flake-registry.json";
  };

  private-flake-rev = "9f1dd0df5b54a7dc75b618034482ed42ce34383d";

  private-flake-api = pkgs.runCommand "private-flake" { } ''
    mkdir -p $out/{commits,tarball}

    # Setup https://docs.github.com/en/rest/commits/commits#get-a-commit
    echo '{"sha": "${private-flake-rev}", "commit": {"tree": {"sha": "ffffffffffffffffffffffffffffffffffffffff"}}}' > $out/commits/HEAD

    # Setup tarball download via API
    dir=private-flake
    mkdir $dir
    echo '{ outputs = {...}: {}; }' > $dir/flake.nix
    tar cfz $out/tarball/${private-flake-rev} $dir --hard-dereference
  '';

  nixpkgs-api = pkgs.runCommand "nixpkgs-flake" { } ''
    mkdir -p $out/commits

    # Setup https://docs.github.com/en/rest/commits/commits#get-a-commit
    echo '{"sha": "${nixpkgs.rev}", "commit": {"tree": {"sha": "ffffffffffffffffffffffffffffffffffffffff"}}}' > $out/commits/HEAD
  '';

  archive = pkgs.runCommand "nixpkgs-flake" { } ''
    mkdir -p $out/archive

    dir=NixOS-nixpkgs-${nixpkgs.shortRev}
    cp -prd ${nixpkgs} $dir
    # Set the correct timestamp in the tarball.
    find $dir -print0 | xargs -0 touch -h -t ${builtins.substring 0 12 nixpkgs.lastModifiedDate}.${
      builtins.substring 12 2 nixpkgs.lastModifiedDate
    } --
    tar cfz $out/archive/${nixpkgs.rev}.tar.gz $dir --hard-dereference
  '';
in

{
  name = "github-flakes";

  nodes = {
    github =
      { config, pkgs, ... }:
      {
        networking.firewall.allowedTCPPorts = [
          80
          443
        ];

        services.httpd.enable = true;
        services.httpd.adminAddr = "foo@example.org";
        services.httpd.extraConfig = ''
          ErrorLog syslog:local6
        '';
        services.httpd.virtualHosts."channels.nixos.org" = {
          forceSSL = true;
          sslServerKey = "${cert}/server.key";
          sslServerCert = "${cert}/server.crt";
          servedDirs = [
            {
              urlPath = "/";
              dir = registry;
            }
          ];
        };
        services.httpd.virtualHosts."api.github.com" = {
          forceSSL = true;
          sslServerKey = "${cert}/server.key";
          sslServerCert = "${cert}/server.crt";
          servedDirs = [
            {
              urlPath = "/repos/NixOS/nixpkgs";
              dir = nixpkgs-api;
            }
            {
              urlPath = "/repos/fancy-enterprise/private-flake";
              dir = private-flake-api;
            }
          ];
        };
        services.httpd.virtualHosts."github.com" = {
          forceSSL = true;
          sslServerKey = "${cert}/server.key";
          sslServerCert = "${cert}/server.crt";
          servedDirs = [
            {
              urlPath = "/NixOS/nixpkgs";
              dir = archive;
            }
          ];
        };
      };

    client =
      {
        config,
        lib,
        pkgs,
        nodes,
        ...
      }:
      {
        virtualisation.writableStore = true;
        virtualisation.diskSize = 2048;
        virtualisation.additionalPaths = [
          pkgs.hello
          pkgs.fuse
        ];
        virtualisation.memorySize = 4096;
        nix.settings.substituters = lib.mkForce [ ];
        nix.extraOptions = "experimental-features = nix-command flakes";
        networking.hosts.${(builtins.head nodes.github.networking.interfaces.eth1.ipv4.addresses).address} =
          [
            "channels.nixos.org"
            "api.github.com"
            "github.com"
          ];
        security.pki.certificateFiles = [ "${cert}/ca.crt" ];
      };
  };

  testScript =
    { nodes }:
    ''
      # fmt: off
      import json
      import time

      start_all()

      def cat_log():
           github.succeed("cat /var/log/httpd/*.log >&2")

      github.wait_for_unit("httpd.service")
      github.wait_for_unit("network-addresses-eth1.service")

      client.wait_for_unit("network-addresses-eth1.service")
      client.succeed("curl -v https://github.com/ >&2")
      out = client.succeed("nix registry list")
      print(out)
      assert "github:NixOS/nixpkgs" in out, "nixpkgs flake not found"
      assert "github:fancy-enterprise/private-flake" in out, "private flake not found"
      cat_log()

      # If no github access token is provided, nix should use the public archive url...
      out = client.succeed("nix flake metadata nixpkgs --json")
      print(out)
      info = json.loads(out)
      assert info["revision"] == "${nixpkgs.rev}", f"revision mismatch: {info['revision']} != ${nixpkgs.rev}"
      cat_log()

      # ... otherwise it should use the API
      out = client.succeed("nix flake metadata private-flake --json --access-tokens github.com=ghp_000000000000000000000000000000000000 --tarball-ttl 0")
      print(out)
      info = json.loads(out)
      assert info["revision"] == "${private-flake-rev}", f"revision mismatch: {info['revision']} != ${private-flake-rev}"
      assert info["fingerprint"]
      cat_log()

      # Fetching with the resolved URL should produce the same result.
      info2 = json.loads(client.succeed(f"nix flake metadata {info['url']} --json --access-tokens github.com=ghp_000000000000000000000000000000000000 --tarball-ttl 0"))
      print(info["fingerprint"], info2["fingerprint"])
      assert info["fingerprint"] == info2["fingerprint"], "fingerprint mismatch"

      client.succeed("nix registry pin nixpkgs")
      client.succeed("nix flake metadata nixpkgs --tarball-ttl 0 >&2")

      # Test fetchTree on a github URL.
      hash = client.succeed(f"nix eval --no-trust-tarballs-from-git-forges --raw --expr '(fetchTree {info['url']}).narHash'")
      assert hash == info['locked']['narHash']

      # Fetching without a narHash should succeed if trust-github is set and fail otherwise.
      client.succeed(f"nix eval --raw --expr 'builtins.fetchTree github:github:fancy-enterprise/private-flake/{info['revision']}'")
      out = client.fail(f"nix eval --no-trust-tarballs-from-git-forges --raw --expr 'builtins.fetchTree github:github:fancy-enterprise/private-flake/{info['revision']}' 2>&1")
      assert "will not fetch unlocked input" in out, "--no-trust-tarballs-from-git-forges did not fail with the expected error"

      # Shut down the web server. The flake should be cached on the client.
      github.succeed("systemctl stop httpd.service")

      info = json.loads(client.succeed("nix flake metadata nixpkgs --json"))
      date = time.strftime("%Y%m%d%H%M%S", time.gmtime(info['lastModified']))
      assert date == "${nixpkgs.lastModifiedDate}", "time mismatch"

      client.succeed("nix build nixpkgs#hello")

      # The build shouldn't fail even with --tarball-ttl 0 (the server
      # being down should not be a fatal error).
      client.succeed("nix build nixpkgs#fuse --tarball-ttl 0")
    '';

}