Turn the --monitor option to `Volume` into a new plugin `Alsa` instead

See #360.

1 files changed, 149 insertions, 0 deletions

diff --git a/src/Plugins/Monitors/Alsa.hs b/src/Plugins/Monitors/Alsa.hs
new file mode 100644
index 0000000..ba8e100
--- /dev/null
+++ b/src/Plugins/Monitors/Alsa.hs
@@ -0,0 +1,149 @@
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Plugins.Monitors.Alsa
+-- Copyright   :  (c) 2018 Daniel Schüssler
+-- License     :  BSD-style (see LICENSE)
+--
+-- Maintainer  :  Jose A. Ortega Ruiz <jao@gnu.org>
+-- Stability   :  unstable
+-- Portability :  unportable
+--
+-- Event-based variant of the Volume plugin.
+--
+-----------------------------------------------------------------------------
+
+module Plugins.Monitors.Alsa
+  ( startAlsaPlugin
+  , getMonitorWaiter
+  , parseOptsIncludingMonitorArgs
+  , AlsaOpts(aoAlsaCtlPath)
+  ) where
+
+import Control.Concurrent
+import Control.Exception
+import Control.Monad
+import Plugins.Monitors.Common
+import Plugins.Monitors.Volume(volumeConfig, VolumeOpts, runVolumeWith)
+import qualified Plugins.Monitors.Volume as Volume;
+import System.Console.GetOpt
+import System.Directory
+import System.Exit
+import System.IO
+import System.Process
+
+data AlsaOpts = AlsaOpts
+    { aoVolumeOpts :: VolumeOpts
+    , aoAlsaCtlPath :: Maybe FilePath
+    }
+
+defaultOpts :: AlsaOpts
+defaultOpts = AlsaOpts Volume.defaultOpts Nothing
+
+alsaCtlOptionName :: String
+alsaCtlOptionName = "alsactl"
+
+options :: [OptDescr (AlsaOpts -> AlsaOpts)]
+options =
+    Option "" [alsaCtlOptionName] (ReqArg (\x o ->
+       o { aoAlsaCtlPath = Just x }) "") ""
+    : fmap (fmap modifyVolumeOpts) Volume.options
+  where
+    modifyVolumeOpts f o = o { aoVolumeOpts = f (aoVolumeOpts o) }
+
+parseOpts :: [String] -> IO AlsaOpts
+parseOpts argv =
+    case getOpt Permute options argv of
+        (o, _, []) -> return $ foldr id defaultOpts o
+        (_, _, errs) -> ioError . userError $ concat errs
+
+parseOptsIncludingMonitorArgs :: [String] -> IO AlsaOpts
+parseOptsIncludingMonitorArgs args =
+    -- Drop generic Monitor args first
+    case getOpt Permute [] args of
+      (_, args', _) -> parseOpts args'
+
+startAlsaPlugin :: String -> String -> [String] -> (String -> IO ()) -> IO ()
+startAlsaPlugin mixerName controlName args cb = do
+  opts <- parseOptsIncludingMonitorArgs args
+
+  waitFunction <- getMonitorWaiter mixerName (aoAlsaCtlPath opts)
+
+  let run args2 = do
+        -- Replicating the reparsing logic used by other plugins for now,
+        -- but it seems the option parsing could be floated out (actually,
+        -- GHC could in principle do it already since getOpt is pure, but
+        -- it would have to inline 'runMBD', 'doArgs' and 'parseOpts' to see
+        -- it, which probably isn't going to happen with the default
+        -- optimization settings).
+        opts2 <- io $ parseOpts args2
+        runVolumeWith (aoVolumeOpts opts2) mixerName controlName
+
+  runMB args volumeConfig run waitFunction cb
+
+getMonitorWaiter :: String -> Maybe FilePath -> IO (IO ())
+getMonitorWaiter mixerName alsaCtlPath = do
+  mvar <- newMVar Nothing :: IO (MVar (Maybe SomeException))
+
+  forkFinally (readerThread mvar) (putMVar mvar . either Just (const Nothing))
+
+  pure $ do
+    ei <- takeMVar mvar
+    case ei of
+      -- Propagate exceptions from reader thread
+      Just (SomeException ex) -> throwIO ex
+      Nothing -> pure ()
+
+  where
+
+    readerThread mvar = do
+          path <- determineAlsaCtlPath
+          withCreateProcess
+            (proc "stdbuf" ["-oL", path, "monitor", mixerName]) {std_out = CreatePipe}
+            run
+
+      where
+
+        defaultPath = "/usr/sbin/alsactl"
+
+        determineAlsaCtlPath =
+          case alsaCtlPath of
+            Just path -> do
+              found <- doesFileExist path
+              if found
+                then pure path
+                else throwIO . ErrorCall $
+                     "Specified alsactl file " ++ path ++ " does not exist"
+
+            Nothing -> do
+              (ec, path, err) <- readProcessWithExitCode "which" ["alsactl"] ""
+              unless (null err) $ hPutStrLn stderr err
+              case ec of
+                ExitSuccess -> pure $ trimTrailingNewline path
+                ExitFailure _ -> do
+                  found <- doesFileExist defaultPath
+                  if found
+                    then pure defaultPath
+                    else throwIO . ErrorCall $
+                         "alsactl not found in PATH or at " ++
+                         show defaultPath ++
+                         "; please specify with --" ++
+                         alsaCtlOptionName ++ "=/path/to/alsactl"
+
+
+        run _ ~(Just out) _ _ = do
+          hSetBuffering out LineBuffering
+          forever $ do
+            c <- hGetChar out
+            when (c == '\n') $
+              -- This uses 'tryPutMVar' because 'putMVar' would make 'runVolume' run
+              -- once for each event. But we want it to run only once after a burst
+              -- of events.
+              void $ tryPutMVar mvar Nothing
+
+-- This is necessarily very inefficient on 'String's
+trimTrailingNewline :: String -> String
+trimTrailingNewline x =
+  case reverse x of
+    '\n' : '\r' : y -> reverse y
+    '\n' : y -> reverse y
+    _ -> x