infra/services/s3-revproxy/default.nix

# Originally written by Jade Lovelace for Lix.
# Adapted for ForkOS.
{ lib, config, ... }:
let
  inherit (lib) mkEnableOption mkIf types mkOption mapAttrs mapAttrs' nameValuePair;
  cfg = config.bagel.services.s3-revproxy;
  s3RevproxyPort = 10652;
  mkTarget = { name, bucket ? name }: {
    mount = {
      host = "${name}.${cfg.domain}";
      path = [ "/" ];
    };
    actions.GET = {
      enabled = true;
      config = {
        # e.g. /2.90 will 404, so it will redirect to /2.90/ if it is a directory
        redirectWithTrailingSlashForNotFoundFile = true;
        indexDocument = "index.html";
      };
    };

    bucket = {
      name = bucket;
      region = "garage";
      s3Endpoint = "https://${cfg.s3.apiUrl}";
      credentials = {
        accessKey.env = "AWS_ACCESS_KEY_ID";
        secretKey.env = "AWS_SECRET_KEY";
      };
    };
  };
  # Makes a subdomain that gets proxied through s3-proxy to provide directory
  # listings and reasonable 404 pages.
  # This is not used on cache, since there a directory listing for cache is a
  # liability at best.
  mkProxiedSubdomain = subdomain: {
    enableACME = true;
    forceSSL = true;
    locations."/" = {
      recommendedProxySettings = true;
      proxyPass = "http://127.0.0.1:${toString s3RevproxyPort}/";
    };
  };
in
{
  options.bagel.services.s3-revproxy = {
    enable = mkEnableOption "a S3 reverse proxy";

    domain = mkOption {
      type = types.str;
    };

    s3 = {
      apiUrl = mkOption {
        type = types.str;
        description = "An URL to the S3 API";
      };
    };

    targets = mkOption {
      type = types.attrsOf types.str;
      description = ''
        A mapping between a nice name and a bucket name.
      '';
    };
  };

  imports = [
    ./module.nix
  ];

  config = mkIf cfg.enable {
    age.secrets.s3-revproxy-api-keys.file = ../../secrets/s3-revproxy-api-keys.age;
    # For each target, generate an entry that passes it to the s3-revproxy.
    services.nginx.virtualHosts = mapAttrs' (subdomain: _: nameValuePair "${subdomain}.${cfg.domain}" (mkProxiedSubdomain subdomain)) cfg.targets;
    # this solves garage supporting neither anonymous access nor automatic
    # directory indexing by simply ignoring garage's web server and replacing it
    # with overengineered golang instead.
    services.s3-revproxy = {
      enable = true;
      settings = {
        templates = {
          helpers = [ ./s3-revproxy-templates/_helpers.tpl ];
          notFoundError = {
            headers = {
              "Content-Type" = "{{ template \"main.headers.contentType\" . }}";
            };
            status = "404";
          };
          folderList = {
            path = ./s3-revproxy-templates/folder-list.tpl;
            headers = {
              "Content-Type" = "{{ template \"main.headers.contentType\" . }}";
            };
            # empty s3 directories are not real and cannot hurt you.
            # due to redirectWithTrailingSlashForNotFoundFile, garbage file names
            # get redirected as folders, which then appear as empty, yielding
            # poor UX.
            status = ''
              {{- if eq (len .Entries) 0 -}}
                404
              {{- else -}}
                200
              {{- end -}}
            '';
          };
        };
        /* For metrics and debugging (e.g. pulling the config)
        internalServer = {
          listenAddr = "127.0.0.1";
          port = 1337;
        };
        */
        server = {
          listenAddr = "127.0.0.1";
          port = s3RevproxyPort;

          # it's going right into nginx, so no point
          compress.enabled = false;
          cors = {
            enabled = true;
            allowMethods = [ "GET" ];
            allowOrigins = [ "*" ];
          };

          cache = {
            noCacheEnabled = false;
            # Taken from the original Perl script.
            # maxage=600: Serve from cache for 5 minutes.
            # stale-while-revaliadate=1800: Serve from cache while updating in the background for 30 minutes.
            # https://web.dev/stale-while-revalidate/
            # https://developer.fastly.com/learning/concepts/cache-freshness/
            cacheControl = "maxage=600,stale-while-revalidate=1800,public";
          };
        };
        targets = mapAttrs (name: bucket: mkTarget { inherit name bucket; }) cfg.targets;
      };
      environmentFile = config.age.secrets.s3-revproxy-api-keys.path;
    };
  };
}