decorate openTempFile errors with the template name

This is to track down what file in .git/annex/ is being written to via a
temp file when the repository is read-only.

Sponsored-by: Dartmouth College's Datalad project

Annex/Branch.hs

@@ -84,6 +84,7 @@ import Annex.Branch.Transitions
 import qualified Annex
 import Annex.Hook
 import Utility.Directory.Stream
+import Utility.Tmp
 import qualified Utility.RawFilePath as R
 
 {- Name of the branch that is used to store git-annex's information. -}
@@ -596,7 +597,7 @@ stageJournal jl commitindex = withIndex $ withOtherTmp $ \tmpdir -> do
 		mapM_ (removeFile . (dir </>)) stagedfs
 		hClose jlogh
 		removeWhenExistsWith (R.removeLink) (toRawFilePath jlogf)
-	openjlog tmpdir = liftIO $ openTempFile tmpdir "jlog"
+	openjlog tmpdir = liftIO $ openTmpFileIn tmpdir "jlog"
 
 {- This is run after the refs have been merged into the index,
  - but before the result is committed to the branch.

Annex/Ingest.hs

@@ -110,7 +110,7 @@ lockDown' cfg file = tryNonAsync $ ifM crippledFileSystem
 	withhardlink tmpdir = do
 		setperms
 		withTSDelta $ \delta -> liftIO $ do
-			(tmpfile, h) <- openTempFile (fromRawFilePath tmpdir) $
+			(tmpfile, h) <- openTmpFileIn (fromRawFilePath tmpdir) $
 				relatedTemplate $ "ingest-" ++ takeFileName file
 			hClose h
 			removeWhenExistsWith R.removeLink (toRawFilePath tmpfile)

Utility/LockFile/PidLock.hs

@@ -33,6 +33,7 @@ import Utility.Hash
 import Utility.FileSystemEncoding
 import Utility.Env
 import Utility.Env.Set
+import Utility.Tmp
 import qualified Utility.LockFile.Posix as Posix
 
 import System.IO
@@ -143,7 +144,7 @@ tryLock lockfile = do
   where
 	go abslockfile sidelock = do
 		let abslockfile' = fromRawFilePath abslockfile
-		(tmp, h) <- openTempFile (takeDirectory abslockfile') "locktmp"
+		(tmp, h) <- openTmpFileIn (takeDirectory abslockfile') "locktmp"
 		let tmp' = toRawFilePath tmp
 		setFileMode tmp' (combineModes readModes)
 		hPutStr h . show =<< mkPidLock

Utility/Tmp.hs

@@ -14,6 +14,7 @@ module Utility.Tmp (
 	withTmpFile,
 	withTmpFileIn,
 	relatedTemplate,
+	openTmpFileIn,
 ) where
 
 import System.IO
@@ -21,6 +22,7 @@ import System.FilePath
 import System.Directory
 import Control.Monad.IO.Class
 import System.PosixCompat.Files hiding (removeLink)
+import System.IO.Error
 
 import Utility.Exception
 import Utility.FileSystemEncoding
@@ -28,6 +30,18 @@ import Utility.FileMode
 
 type Template = String
 
+{- This is the same as openTempFile, except when there is an
+ - error, it displays the template as well as the directory,
+ - to help identify what call was responsible.
+ -}
+openTmpFileIn :: FilePath -> String -> IO (FilePath, Handle)
+openTmpFileIn dir template = openTempFile dir template
+	`catchIO` decoraterrror
+  where
+	decoraterrror e = throwM $
+		let loc = ioeGetLocation e ++ " template " ++ template
+		in annotateIOError e loc Nothing Nothing
+
 {- Runs an action like writeFile, writing to a temp file first and
  - then moving it into place. The temp file is stored in the same
  - directory as the final file to avoid cross-device renames.
@@ -43,7 +57,7 @@ viaTmp a file content = bracketIO setup cleanup use
 	template = relatedTemplate (base ++ ".tmp")
 	setup = do
 		createDirectoryIfMissing True dir
-		openTempFile dir template
+		openTmpFileIn dir template
 	cleanup (tmpfile, h) = do
 		_ <- tryIO $ hClose h
 		tryIO $ removeFile tmpfile
@@ -73,7 +87,7 @@ withTmpFile template a = do
 withTmpFileIn :: (MonadIO m, MonadMask m) => FilePath -> Template -> (FilePath -> Handle -> m a) -> m a
 withTmpFileIn tmpdir template a = bracket create remove use
   where
-	create = liftIO $ openTempFile tmpdir template
+	create = liftIO $ openTmpFileIn tmpdir template
 	remove (name, h) = liftIO $ do
 		hClose h
 		catchBoolIO (removeFile name >> return True)

doc/bugs/unable_to_get_content_via_ssh_without_write_perms/comment_3_a4f9bb23f0682a66e951b96aed6ae214._comment

@@ -3,11 +3,18 @@
  subject="""comment 3"""
  date="2021-08-30T16:24:52Z"
  content="""
-reversion in [[!commit f46e4c9b7c]], which reversed some logic and made
+keysdb error was a reversion in [[!commit f46e4c9b7c]], which reversed some
-database reads be treated as database writes, so they failed on permission
+logic and made database reads be treated as database writes, so it failed
-denied, rather than the right behavior of returning DbUnavailable. Fixed that. 
+on permission denied, rather than the right behavior of returning
+DbUnavailable when it cannot read or the database does not exist yet. 
+
+Fixed that. It seems to work for me now, both get and drop, and over ssh or
+direct access to the readonly repository.
 
 I have not been able to reproduce the other error involving
 opening a temp file. All I can tell from the message is that it's writing
-to some file in .git/annex via a temp file in the same directory.
+to some file in .git/annex via a temp file in the same directory, but
+I don't know what file it is trying to write. I've made a change that
+will include more information in that error message. So either update
+your build of git-annex, or find a better reproduction recipe for that..
 """]]