basic json support

This includes a generic JSONStream library built on top of Text.JSON
(somewhat hackishly).

It would be possible to stream out a single json document describing
all actions, but it's probably better for consumers if they can expect
one json document per line, so I did it that way instead.

Output from external programs used for transferring files is not
currently hidden when outputting json, which probably makes it not very
useful there. This may be dealt with if there is demand for json
output for --get or --move to be parsable.

The version, status, and find subcommands have hand-crafted output and
don't do json. The whereis subcommand needs to be modified to produce
useful json.

Annex.hs

@@ -64,7 +64,7 @@ data AnnexState = AnnexState
 	, cipher :: Maybe Cipher
 	}
 
-data OutputType = NormalOutput | QuietOutput
+data OutputType = NormalOutput | QuietOutput | JSONOutput
 
 newState :: Git.Repo -> AnnexState
 newState gitrepo = AnnexState

Messages.hs

@@ -5,7 +5,22 @@
  - Licensed under the GNU GPL version 3 or higher.
  -}
 
-module Messages where
+module Messages (
+	showStart,
+	showNote,
+	showAction,
+	showProgress,
+	showSideAction,
+	showOutput,
+	showLongNote,
+	showEndOk,
+	showEndFail,
+	showEndResult,
+	showErr,
+	warning,
+	indent,
+	setupConsole
+) where
 
 import Control.Monad.State (liftIO)
 import System.IO
@@ -13,21 +28,15 @@ import Data.String.Utils
 
 import Types
 import qualified Annex
-
-verbose :: Annex () -> Annex ()
-verbose a = do
-	output <- Annex.getState Annex.output
-	case output of
-		Annex.NormalOutput -> a
-		_ -> return ()
+import qualified Messages.JSON as JSON
 
 showStart :: String -> String -> Annex ()
-showStart command file = verbose $ liftIO $ do
+showStart command file = handle (JSON.start command file) $ do
 	putStr $ command ++ " " ++ file ++ " "
 	hFlush stdout
 
 showNote :: String -> Annex ()
-showNote s = verbose $ liftIO $ do
+showNote s = handle (JSON.note s) $ do
 	putStr $ "(" ++ s ++ ") "
 	hFlush stdout
 
@@ -35,28 +44,31 @@ showAction :: String -> Annex ()
 showAction s = showNote $ s ++ "..."
 
 showProgress :: Annex ()
-showProgress = verbose $ liftIO $ do
+showProgress = handle q $ do
 	putStr "."
 	hFlush stdout
 
 showSideAction :: String -> Annex ()
-showSideAction s = verbose $ liftIO $ putStrLn $ "(" ++ s ++ "...)"
+showSideAction s = handle q $ putStrLn $ "(" ++ s ++ "...)"
 
 showOutput :: Annex ()
-showOutput = verbose $ liftIO $ putStr "\n"
+showOutput = handle q $ putStr "\n"
 
 showLongNote :: String -> Annex ()
-showLongNote s = verbose $ liftIO $ putStr $ '\n' : indent s
+showLongNote s = handle (JSON.note s) $ putStr $ '\n' : indent s
 
 showEndOk :: Annex ()
-showEndOk = verbose $ liftIO $ putStrLn "ok"
+showEndOk = showEndResult True
 
 showEndFail :: Annex ()
-showEndFail = verbose $ liftIO $ putStrLn "failed"
+showEndFail = showEndResult False
 
 showEndResult :: Bool -> Annex ()
-showEndResult True = showEndOk
-showEndResult False = showEndFail
+showEndResult b = handle (JSON.end b) $ putStrLn msg
+	where
+		msg
+			| b = "ok"
+			| otherwise = "failed"
 
 showErr :: (Show a) => a -> Annex ()
 showErr e = liftIO $ do
@@ -65,7 +77,7 @@ showErr e = liftIO $ do
 
 warning :: String -> Annex ()
 warning w = do
-	verbose $ liftIO $ putStr "\n"
+	handle q $ putStr "\n"
 	liftIO $ do
 		hFlush stdout
 		hPutStrLn stderr $ indent w
@@ -85,3 +97,14 @@ setupConsole :: IO ()
 setupConsole = do
 	hSetBinaryMode stdout True
 	hSetBinaryMode stderr True
+
+handle :: IO () -> IO () -> Annex ()
+handle json normal = do
+	output <- Annex.getState Annex.output
+	case output of
+		Annex.NormalOutput -> liftIO normal
+		Annex.QuietOutput -> q
+		Annex.JSONOutput -> liftIO json
+
+q :: Monad m => m ()
+q = return ()

Messages/JSON.hs

@@ -0,0 +1,23 @@
+{- git-annex JSON output
+ -
+ - Copyright 2011 Joey Hess <joey@kitenet.net>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module Messages.JSON (
+	start,
+	end,
+	note
+) where
+
+import qualified Utility.JSONStream as Stream
+
+start :: String -> String -> IO ()
+start command file = putStr $ Stream.start [("command", command), ("file", file)]
+
+end :: Bool -> IO ()
+end b = putStr $ Stream.add [("success", b)] ++ Stream.end
+
+note :: String -> IO ()
+note s = putStr $ Stream.add [("note", s)]

Options.hs

@@ -30,6 +30,8 @@ commonOptions =
 		"avoid verbose output"
 	, Option ['v'] ["verbose"] (NoArg (setoutput Annex.NormalOutput))
 		"allow verbose output (default)"
+	, Option ['j'] ["json"] (NoArg (setoutput Annex.JSONOutput))
+		"enable JSON output"
 	, Option ['d'] ["debug"] (NoArg (setdebug))
 		"show debug messages"
 	, Option ['b'] ["backend"] (ReqArg setforcebackend paramName)

Utility/JSONStream.hs

@@ -0,0 +1,44 @@
+{- Streaming JSON output.
+ -
+ - Copyright 2011 Joey Hess <joey@kitenet.net>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module Utility.JSONStream (
+	start,
+	add,
+	end
+) where
+
+import Text.JSON
+
+{- Text.JSON does not support building up a larger JSON document piece by
+   piece as a stream. To support streaming, a hack. The JSObject is converted
+   to a string with its final "}" is left off, allowing it to be added to
+   later. -}
+start :: JSON a => [(String, a)] -> String
+start l
+	| last s == endchar = take (length s - 1)  s
+	| otherwise = bad s
+	where
+		s = encodeStrict $ toJSObject l
+
+add :: JSON a => [(String, a)] -> String
+add l
+	| head s == startchar = ',' : drop 1 s
+	| otherwise = bad s
+	where
+		s = start l
+
+end :: String
+end = [endchar, '\n']
+
+startchar :: Char
+startchar = '{'
+
+endchar :: Char
+endchar = '}'
+
+bad :: String -> a
+bad s = error $ "Text.JSON returned unexpected string: " ++ s

debian/changelog

@@ -6,6 +6,7 @@ git-annex (3.20110820) UNRELEASED; urgency=low
   * init: Make description an optional parameter.
   * unused, status: Sped up by avoiding unnecessary stats of annexed files.
   * unused --remote: Reduced memory use to 1/4th what was used before.
+  * Add --json switch, to produce machine-consumable output.
 
  -- Joey Hess <joeyh@debian.org>  Tue, 23 Aug 2011 13:41:01 -0400
 

debian/control

@@ -14,6 +14,7 @@ Build-Depends:
 	libghc-hs3-dev (>= 0.5.6),
 	libghc-testpack-dev [any-i386 any-amd64],
 	libghc-monad-control-dev,
+	libghc-json-dev,
 	ikiwiki,
 	perlmagick,
 	git | git-core,

doc/git-annex.mdwn

@@ -337,12 +337,18 @@ Many git-annex commands will stage changes for later `git commit` by you.
 
 * --quiet
 
-  Avoid the default verbose logging of what is done; only show errors
+  Avoid the default verbose display of what is done; only show errors
   and progress displays.
 
 * --verbose
 
-  Enable verbose logging.
+  Enable verbose display.
+
+* --json
+
+  Rather than the normal output, generate JSON. This is intended to be
+  parsed by programs that use git-annex. Each line of output is a JSON
+  object.
 
 * --debug
 

doc/install.mdwn

@@ -28,6 +28,7 @@ To build and use git-annex, you will need:
   * [QuickCheck 2](http://hackage.haskell.org/package/QuickCheck)
   * [HTTP](http://hackage.haskell.org/package/HTTP)
   * [hS3](http://hackage.haskell.org/package/hS3) (optional, but recommended)
+  * [json](http://hackage.haskell.org/package/json)
 * Shell commands
   * [git](http://git-scm.com/)
   * [uuid](http://www.ossp.org/pkg/lib/uuid/)