modules/environment.nix: support etc

Signed-off-by: magic_rb <magic_rb@redalder.org>

Author: MagicRB

modules/environment.hs

@@ -0,0 +1,53 @@
+{-# LANGUAGE ImportQualifiedPost, DeriveAnyClass, BlockArguments, ViewPatterns #-}
+
+module Main where
+
+import Data.Aeson qualified as A
+import GHC.Generics (Generic)
+import System.Environment (getArgs)
+import Data.HashMap.Strict as HMS
+import Data.HashMap.Strict (HashMap)
+import System.Exit (ExitCode(..))
+import Control.Monad (forM_)
+import System.Directory (createDirectoryIfMissing)
+import System.Posix.Files (createSymbolicLink)
+import System.Exit (exitWith)
+import System.FilePath.Posix (takeDirectory, (</>))
+
+data EtcEntry
+  = EtcEntry
+  { enable :: Bool
+  , target :: String
+  , source :: String
+  , mode :: String
+  , user :: String
+  , group :: String
+  , uid :: String
+  , gid :: String
+  }
+  deriving (Show, Generic, A.FromJSON)
+
+etcDirectory :: FilePath
+etcDirectory = "/etc"
+
+main :: IO ()
+main = do
+  args <- getArgs
+  let
+    etcFile = args !! 0
+  etcs' :: Maybe (HashMap String EtcEntry) <- A.decodeFileStrict etcFile
+
+  case etcs' of
+    Nothing -> do
+      putStrLn $ "Unable to deserialize " <> etcFile
+      exitWith (ExitFailure 1)
+    Just (HMS.elems -> etcs) -> forM_ etcs \etc ->
+      let
+        subdir = takeDirectory (target etc)
+        exactTarget = etcDirectory </> (target etc)
+      in
+        if mode etc == "symlink" then do
+          createDirectoryIfMissing True (etcDirectory </> subdir)
+          createSymbolicLink (source etc) exactTarget
+        else do
+          putStrLn $ "Other modes than symlink are not supported"

modules/environment.nix

@@ -15,6 +15,83 @@
 }:
 let
   cfg = config.environment;
+
+  etcEntry =
+    { name, ... }:
+    {
+      options = {
+        enable = lib.mkOption {
+          type = lib.types.bool;
+          description = ''
+            Whether this /etc file should be generated. This option allows specific /etc files to be disabled.
+          '';
+          default = true;
+        };
+
+        source = lib.mkOption {
+          type = lib.types.path;
+          description = ''
+            Path of the source file.
+          '';
+        };
+
+        target = lib.mkOption {
+          type = lib.types.str;
+          description = ''
+            Name of symlink (relative to `/etc`). Defaults to the attribute name.
+          '';
+          default = name;
+        };
+
+        mode = lib.mkOption {
+          type = lib.types.str;
+          description = ''
+            If set to something else than symlink, the file is copied instead of symlinked, with the given file mode.
+          '';
+          default = "symlink";
+        };
+
+        user = lib.mkOption {
+          type = lib.types.str;
+          description = ''
+            User name of file owner.
+
+            Only takes effect when the file is copied (that is, the mode is not symlink).
+
+            When services.userborn.enable, this option has no effect. You have to assign a uid instead. Otherwise this option takes precedence over uid.
+          '';
+          default = "+0";
+        };
+
+        group = lib.mkOption {
+          type = lib.types.str;
+          description = ''
+            Group name of file owner.
+
+            Only takes effect when the file is copied (that is, the mode is not symlink).
+
+            When services.userborn.enable, this option has no effect. You have to assign a gid instead. Otherwise this option takes precedence over gid.
+          '';
+          default = "+0";
+        };
+
+        uid = lib.mkOption {
+          type = lib.types.str;
+          description = ''
+            UID of created file. Only takes effect when the file is copied (that is, the mode is not 'symlink').
+          '';
+          default = "0";
+        };
+
+        gid = lib.mkOption {
+          type = lib.types.str;
+          description = ''
+            GID of created file. Only takes effect when the file is copied (that is, the mode is not ‘symlink’).
+          '';
+          default = "0";
+        };
+      };
+    };
 in
 {
   options.environment = {
@@ -64,6 +141,11 @@ in
       default = [ ];
       type = with lib.types; listOf package;
     };
+
+    etc = lib.mkOption {
+      type = lib.types.attrsOf (lib.types.submodule etcEntry);
+      default = { };
+    };
   };
 
   config = {
@@ -105,5 +187,22 @@ in
         mkdir -pm 0555 /var/empty
       ''
     );
+
+    init.services.environment-etc = {
+      enabled = true;
+      execStart =
+        let
+          start = pkgs.writers.writeHaskell "environment-etc-start" {
+            libraries = with pkgs.haskellPackages; [
+              unix
+              directory
+              filepath
+              aeson
+              unordered-containers
+            ];
+          } (builtins.readFile ./environment.hs);
+        in
+        "${start} ${pkgs.writers.writeJSON "environment-etc.json" cfg.etc}";
+    };
   };
 }