modules: introduce hostctl (static dns for development)

devshell.toml

@@ -1,5 +1,6 @@
 imports = [
-  "language.go"
+  "language.go",
+  "dns.hostctl"
 ]
 
 [devshell]
@@ -45,3 +46,8 @@ category = "utilites"
 help = "golang linter"
 package = "golangci-lint"
 category = "linters"
+
+[hostctl]
+enable = true
+dns."test.domain.local" = "172.0.0.1"
+dns."shared.domain.link-local" = "169.254.0.5"

extra/dns/hostctl.nix

@@ -0,0 +1,61 @@
+{ lib, pkgs, config, ... }:
+with lib;
+let
+  cfg = config.hostctl;
+  profile = toLower config.devshell.name;
+
+  etcHosts = pkgs.writeText "${profile}-etchosts" (
+    concatStringsSep "\n"
+      (mapAttrsToList (host: ip: ip + " " + host) cfg.dns)
+  );
+
+  # Execute this script to install the project's static dns entries
+  install-hostctl-dns = pkgs.writeShellScriptBin "install-hostctl-dns" ''
+    set -euo pipefail
+    shopt -s nullglob
+
+    log() {
+      IFS=$'\n' loglines=($*)
+      for line in ${"$"}{loglines[@]}; do echo -e "[hostctl] $line" >&2; done
+    }
+
+    # Install local CA into system, java and nss (includes Firefox) trust stores
+    log "Update static dns entries..."
+    sudo -K
+    log $(sudo ${pkgs.hostctl}/bin/hostctl add ${profile} --from ${etcHosts} 2>&1)
+
+    uninstall() {
+      log $(sudo ${pkgs.hostctl}/bin/hostctl remove ${profile} 2>&1)
+    }
+
+    # TODO: Uninstall when leaving the devshell
+    # trap uninstall EXIT
+
+  '';
+in
+{
+  options.hostctl = {
+    enable = mkEnableOption "manage temporary /etc/host entries for development from within the shell";
+
+    dns = mkOption {
+      type = types.attrs;
+      default = {};
+      description = "configure static dns entries";
+      example =
+        {
+          dns."some.host" = "1.2.3.4";
+          dns."another.host" = "4.3.2.1";
+        };
+    };
+  };
+
+  config = mkIf cfg.enable {
+    commands = [ { package = pkgs.hostctl; category = "dns"; } ];
+    devshell = {
+      packages = [ install-hostctl-dns ];
+      startup.install-hostctl-dns.text = "
+        $DEVSHELL_DIR/bin/install-hostctl-dns
+      ";
+    };
+  };
+}