# This is a Nix flake
# It is written in the Nix expression language
{
  description = "Simple flake for simple libcurl example";
  # nixpkgs is the package repository for the Nix package manager
  inputs.nixpkgs.url = "github:NixOS/nixpkgs";
  outputs = { self, nixpkgs }: let
    # In this simple example we choose to build for "x86_64-linux" only
    pkgs = nixpkgs.legacyPackages.x86_64-linux;
    # Declare our own package as a Nix 'derivation'
    wttr-delft = pkgs.stdenv.mkDerivation rec {
      # Our package name
      name = "wttr-delft";
      # Where the source code lives
      src = builtins.path { path = ../src; name = name; };
      # Dependencies
      buildInputs = [
        pkgs.curl.dev
      ];
      # The source code contains only the C file, so we 'manually' compile
      # Note: If we were using Make/CMake/autoconf, the mkDerivation function
      # could handle those automatically.
      # gcc is available by default in pkgs.stdenv.mkDerivation
      buildPhase = "gcc -lcurl -o wttr-delft ./simple.c";
      # Installing is just copying the executable
      installPhase = "mkdir -p $out/bin; install -t $out/bin wttr-delft";
    };
    # Docker image containing only wttr-delft
    wttr-delft-container = pkgs.dockerTools.buildLayeredImage {
      name = "wttr-delft";
      tag = "nix";
      # created = "now";
      contents = [
        wttr-delft
      ];
      config = {
        Cmd = [
          "${wttr-delft}/bin/wttr-delft"
        ];
        # Needed for curl to work
        Env = [
          "SSL_CERT_FILE=${pkgs.cacert}/etc/ssl/certs/ca-bundle.crt"
        ];
      };
    };
    # Development shell for interacting with containers
    # Based on https://gist.github.com/adisbladis/187204cb772800489ee3dac4acdd9947
    podman-devshell = let
      # Provides a script that copies/creates files that are required for rootless podman
      podmanSetupScript = let
        registriesConf = pkgs.writeText "registries.conf" ''
          [registries.search]
          registries = ['docker.io']
          [registries.block]
          registries = []
        '';
        storageConf = pkgs.writeText "storage.conf" ''
          [storage]
          driver = "overlay"
          # rootless_storage_path="$XDG_DATA_HOME/containers/storage"
        '';
      in pkgs.writeShellScript "podman-setup" ''
        # Dont overwrite customised configuration
        if ! test -f ~/.config/containers/policy.json; then
          echo "Installing missing ~/.config/containers/policy.json"
          install -Dm644 ${pkgs.skopeo.src}/default-policy.json ~/.config/containers/policy.json
        fi
        if ! test -f ~/.config/containers/registries.conf; then
          echo "Installing missing ~/.config/containers/registries.conf"
          install -Dm644 ${registriesConf} ~/.config/containers/registries.conf
        fi
        if ! test -f ~/.config/containers/storage.conf; then
          echo "Installing missing ~/.config/containers/storage.conf"
          install -Dm644 ${storageConf} ~/.config/containers/storage.conf
        fi
      '';
      # Provides a fake "docker" binary mapping to podman
      dockerCompat = pkgs.runCommandNoCC "docker-podman-compat" {} ''
        mkdir -p $out/bin
        ln -s ${pkgs.podman}/bin/podman $out/bin/docker
      '';
    in pkgs.mkShell {
      name = "podman";
      buildInputs = with pkgs; [
        podman          # Manage pods, containers and images
        runc            # Container runtime
        conmon          # Container runtime monitor
        skopeo          # Interact with container registry
        slirp4netns     # User-mode networking for unprivileged namespaces
        fuse-overlayfs  # CoW for images, much faster than default vfs
        dockerCompat    # Aliases for docker / podman
      ];
      shellHook = ''
        # Install configuration required for rootless podman
        ${podmanSetupScript}
        if ! grep -q "^''${USER}:" /etc/subuid; then
          echo "No subuid range defined for user, consider running 'sudo usermod --add-subuids 10000-75535 ''${USER}' to allow rootless podman to work"
        fi
      '';
    };
  in
    # These are the flake outputs, i.e. what we can consume
    {
      packages.x86_64-linux = {
        default = wttr-delft;
        container = wttr-delft-container;
      };
      devShells.x86_64-linux = {
        podman = podman-devshell;
      };
    };
}

{
  "nodes": {
    "nixpkgs": {
      "locked": {
        "lastModified": 1679396235,
        "narHash": "sha256-RjmNVFuZQ2e6u35B98JcY9IzVDtZb3d4QcbtfLtNWkE=",
        "owner": "NixOS",
        "repo": "nixpkgs",
        "rev": "008ce261a7e3c532e792cb8e39482f2cc1b192f5",
        "type": "github"
      },
      "original": {
        "owner": "NixOS",
        "repo": "nixpkgs",
        "type": "github"
      }
    },
    "root": {
      "inputs": {
        "nixpkgs": "nixpkgs"
      }
    }
  },
  "root": "root",
  "version": 7
}

#!/usr/bin/env bash
# shellcheck disable=SC1010,SC2288
set -Eeuo pipefail
dir="$(dirname "${BASH_SOURCE[0]}")"
source "${dir}/../libdemo/libdemo.sh"
h Putting wttr-delft into a container
, Expanding on the previous nix flake makes building a OCI compliant \(Docker\) image easy:
x pygmentize "${dir}/flake.nix"
h We now choose the \'container\' package we defined:
x nix build "${dir}#container" -L -o "${dir}/result-container"
x nix build "${dir}#container" -L -o "${dir}/result-container --rebuild"
x ls -lhH "${dir}/result-container"
x nix develop "${dir}#podman" --command "${dir}/demo-inside-nix-develop.sh"

#!/usr/bin/env bash
set -Eeuo pipefail
dir="$(dirname "${BASH_SOURCE[0]}")"
source "${dir}/../libdemo/libdemo.sh"
h Now we are inside a development shell that has rootless podman.
, We can manipulate containers just like docker could.
n We have added the \'dockerCompat\' package so we can use the \'docker\' command instead of \'podman\'.
h So we start by loading the container we just made into the registry:
x docker load -i ./result-container
h We can see it\'s there:
x docker image ls | grep "wttr-delft\|^REPOSITORY"
h And now we can run it:
x docker run -it localhost/wttr-delft:nix
h The image is very minimal, e.g. there is no interactive shell:
f podman run --entrypoint sh -it localhost/wttr-delft:nix
h We have running containers:
x podman ps --all --storage | grep "wttr-delft\|^CONTAINER ID"
h Let\'s kill them and remove them:
x podman ps --all --storage | tail -n +2 | grep wttr-delft | awk "{print \$1}" | xargs podman rm
x podman image ls | tail -n +2 | grep wttr-delft | awk "{print \$3}" | xargs podman image rm -f