Add a module for the "id" coreutil

Author: harendra-kumar

src/Streamly/Coreutils/Id.hs

@@ -0,0 +1,143 @@
+-- |
+-- Module      : Streamly.Coreutils.Id
+-- Copyright   : (c) 2022 Composewell Technologies
+-- License     : BSD-3-Clause
+-- Maintainer  : streamly@composewell.com
+-- Stability   : experimental
+-- Portability : GHC
+--
+-- Experimental alternative wrapper API over System.Posix.User.
+--
+-- Shorter names, closer to shell commands.
+-- Int for user-id/group-id for covnenience.
+-- Adds one missing function
+--
+-- Functions to get and set the user and group id of the current process.
+--
+-- Substitutes the functionality of the @id@ and @whoami@ coreutils commands.
+--
+-- This is a Posix only module.
+
+-- TODO: create a portable module with "idNum" and "idName" commands to print
+-- the current user id, name.
+--
+-- Can separate process API and the user DB API.
+
+module Streamly.Coreutils.Id
+    (
+      uid
+    , euid
+    , gid
+    , egid
+    , uid2name
+    , gid2name
+    -- , groups
+    )
+where
+
+import System.Posix (getGroupEntryForID)
+import Prelude hiding (id)
+import qualified System.Posix.User as Posix
+
+------------------------------------------------------
+-- Current process settings
+------------------------------------------------------
+
+-- | Return current process real user id.
+--
+-- id -ru
+uid :: IO Int
+uid = fromIntegral <$> Posix.getRealUserID
+
+-- | Return current process real group id.
+--
+-- id -rg
+gid :: IO Int
+gid = fromIntegral <$> Posix.getRealGroupID
+
+-- | Return current process effective user id.
+--
+-- id -u
+euid :: IO Int
+euid = fromIntegral <$> Posix.getEffectiveUserID
+
+-- | Return current process effective group id.
+--
+-- id -g
+egid :: IO Int
+egid = fromIntegral <$> Posix.getEffectiveGroupID
+
+-- | Get groups associated with the current process.
+--
+-- id -G
+groups :: IO [Int]
+groups = fmap fromIntegral <$> Posix.getGroups
+
+-- | The original login name of the process. Note: the current user name may
+-- change by setuid but login name remains the same.
+logname :: IO String
+logname = Posix.getLoginName
+
+------------------------------------------------------
+-- These should go to user database module?
+------------------------------------------------------
+
+-- XXX We can parse the passwd file ourselves instead of using C code
+-- XXX Use an Compact Array/OsString instead?
+
+{-
+-- getpwuid
+uid2pwent =
+
+-- getgrgid
+gid2grent =
+
+-- getpwnam
+name2pwent =
+
+-- getgrnam
+name2grent =
+
+-- Stream the entries.
+getpwents  =
+-}
+
+-- | Convert numeric user id to user name.
+uid2name :: Int -> IO String
+uid2name i = do
+    -- XXX fromIntegral downcast
+    pw <- Posix.getUserEntryForID (fromIntegral i)
+    return (Posix.userName pw)
+
+-- XXX Use an Compact Array/OsString instead?
+
+-- | Convert numeric group id to group name.
+gid2name :: Int -> IO String
+gid2name i = do
+    -- XXX fromIntegral downcast
+    pw <- Posix.getGroupEntryForID (fromIntegral i)
+    return (Posix.groupName pw)
+
+-- Note there is no uid2groups as anyway the groups file has the user name. We
+-- search by name even if uid is provided. So we can convert uid to name and
+-- then search.
+
+-- | List all the groups in which a uid occurs. Returns (gid, group name).
+--
+-- id -Gn <user>
+user2groups :: Int -> [(Int, String)]
+user2groups = undefined
+
+-- | Current process user name.
+--
+-- id -un
+whoami :: IO String
+whoami = uid >>= uid2name
+
+-- | Current process group names.
+--
+-- id -Gn
+groupNames :: IO [String]
+groupNames = do
+    xs <- Posix.getGroups
+    fmap Posix.groupName <$> mapM getGroupEntryForID xs

streamly-coreutils.cabal

@@ -124,6 +124,7 @@ library
     , Streamly.Coreutils.Directory
     , Streamly.Coreutils.Dirname
     , Streamly.Coreutils.FileTest
+    , Streamly.Coreutils.Id
     , Streamly.Coreutils.Ln
     , Streamly.Coreutils.Cut
     , Streamly.Coreutils.Ls