improve url download failure display

* When downloading urls fail, explain which urls failed for which
  reasons.
* web: Avoid displaying a warning when downloading one url failed
  but another url later succeeded.

Some other uses of downloadUrl use urls that are effectively internal use,
and should not all be displayed to the user on failure. Eg, Remote.Git
tries different urls where content could be located depending on how the
remote repo is set up. Exposing those urls to the user would lead to wild
goose chases. So had to parameterize it to control whether it displays urls
or not.

A side effect of this change is that when there are some youtube urls
and some regular urls, it will try regular urls first, even if the
youtube urls are listed first. This seems like an improvement if
anything, but in any case there's no defined order of urls that it's
supposed to use.

Sponsored-by: Dartmouth College's Datalad project

Annex/Content.hs

@@ -632,18 +632,20 @@ saveState nocommit = doSideAction $ do
 			Annex.Branch.commit =<< Annex.Branch.commitMessage
 
 {- Downloads content from any of a list of urls, displaying a progress
- - meter. -}
-downloadUrl :: Key -> MeterUpdate -> Maybe IncrementalVerifier -> [Url.URLString] -> FilePath -> Url.UrlOptions -> Annex Bool
-downloadUrl k p iv urls file uo = 
+ - meter.
+ -
+ - Only displays error message if all the urls fail to download.
+ - When listfailedurls is set, lists each url and why it failed.
+ - Otherwise, only displays one error message, from one of the urls
+ - that failed.
+ -}
+downloadUrl :: Bool -> Key -> MeterUpdate -> Maybe IncrementalVerifier -> [Url.URLString] -> FilePath -> Url.UrlOptions -> Annex Bool
+downloadUrl listfailedurls k p iv urls file uo = 
 	-- Poll the file to handle configurations where an external
 	-- download command is used.
-	meteredFile file (Just p) k (go urls Nothing)
+	meteredFile file (Just p) k (go urls [])
   where
-  	-- Display only one error message, if all the urls fail to
-	-- download.
-	go [] (Just err) = warning err >> return False
-	go [] Nothing = return False
-	go (u:us) _ = Url.download' p iv u file uo >>= \case
+	go (u:us) errs = Url.download' p iv u file uo >>= \case
 		Right () -> return True
 		Left err -> do
 			-- If the incremental verifier was fed anything
@@ -655,7 +657,14 @@ downloadUrl k p iv urls file uo =
 					Just n | n > 0 -> unableIncremental iv'
 					_ -> noop
 				Nothing -> noop
-			go us (Just err)
+			go us ((u, err) : errs)
+	go [] [] = return False
+	go [] errs@((_, err):_) = do
+		if listfailedurls
+			then warning $ unlines $ flip map errs $ \(u, err') ->
+				u ++ " " ++ err'
+			else warning err
+		return False
 
 {- Copies a key's content, when present, to a temp file.
  - This is used to speed up some rsyncs. -}

CHANGELOG

@@ -26,6 +26,10 @@ git-annex (8.20210804) UNRELEASED; urgency=medium
     a file's content, and fail with an informative message.
   * Fix support for readonly git remotes.
     (Reversion in version 8.20210621)
+  * When downloading urls fail, explain which urls failed for which
+    reasons.
+  * web: Avoid displaying a warning when downloading one url failed
+    but another url later succeeded.
 
  -- Joey Hess <id@joeyh.name>  Tue, 03 Aug 2021 12:22:45 -0400
 

Command/AddUrl.hs

@@ -314,7 +314,7 @@ downloadWeb addunlockedmatcher o url urlinfo file =
 	go =<< downloadWith' downloader urlkey webUUID url (AssociatedFile (Just file))
   where
 	urlkey = addSizeUrlKey urlinfo $ Backend.URL.fromUrl url Nothing
-	downloader f p = Url.withUrlOptions $ downloadUrl urlkey p Nothing [url] f
+	downloader f p = Url.withUrlOptions $ downloadUrl False urlkey p Nothing [url] f
 	go Nothing = return Nothing
 	go (Just tmp) = ifM (pure (not (rawOption o)) <&&> liftIO (isHtmlFile (fromRawFilePath tmp)))
 		( tryyoutubedl tmp

Remote/External.hs

@@ -810,7 +810,7 @@ checkUrlM external url =
 retrieveUrl :: Retriever
 retrieveUrl = fileRetriever' $ \f k p iv -> do
 	us <- getWebUrls k
-	unlessM (withUrlOptions $ downloadUrl k p iv us (fromRawFilePath f)) $
+	unlessM (withUrlOptions $ downloadUrl True k p iv us (fromRawFilePath f)) $
 		giveup "failed to download content"
 
 checkKeyUrl :: CheckPresent

Remote/Git.hs

@@ -543,7 +543,7 @@ copyFromRemote'' repo forcersync r st@(State connpool _ _ _ _) key file dest met
 		iv <- startVerifyKeyContentIncrementally vc key
 		gc <- Annex.getGitConfig
 		ok <- Url.withUrlOptionsPromptingCreds $
-			Annex.Content.downloadUrl key meterupdate iv (keyUrls gc repo r key) dest
+			Annex.Content.downloadUrl False key meterupdate iv (keyUrls gc repo r key) dest
 		unless ok $
 			giveup "failed to download content"
 		snd <$> finishVerifyKeyContentIncrementally iv

Remote/S3.hs

@@ -414,7 +414,7 @@ retrieve hv r rs c info = fileRetriever' $ \f k p iv -> withS3Handle hv $ \case
 			Left failreason -> do
 				warning failreason
 				giveup "cannot download content"
-			Right us -> unlessM (withUrlOptions $ downloadUrl k p iv us (fromRawFilePath f)) $
+			Right us -> unlessM (withUrlOptions $ downloadUrl False k p iv us (fromRawFilePath f)) $
 				giveup "failed to download content"
 
 retrieveHelper :: S3Info -> S3Handle -> (Either S3.Object S3VersionID) -> FilePath -> MeterUpdate -> Maybe IncrementalVerifier -> Annex ()

Remote/Web.hs

@@ -86,26 +86,30 @@ downloadKey :: Key -> AssociatedFile -> FilePath -> MeterUpdate -> VerifyConfig
 downloadKey key _af dest p vc = go =<< getWebUrls key
   where
 	go [] = giveup "no known url"
-	go urls = getM dl urls >>= \case
+	go urls = dl (partition (not . isyoutube) (map getDownloader urls)) >>= \case
 		Just v -> return v
-		Nothing -> giveup "download failed"
+		Nothing -> giveup $ unwords
+			[ "downloading from all"
+			, show (length urls)
+			, "known url(s) failed"
+			]
 
-	dl u = do
-		let (u', downloader) = getDownloader u
-		case downloader of
-			YoutubeDownloader ->
-				ifM (youtubeDlTo key u' dest p)
-					( return (Just UnVerified)
-					, return Nothing
-					)
-			_ -> do
-				iv <- startVerifyKeyContentIncrementally vc key
-				ifM (Url.withUrlOptions $ downloadUrl key p iv [u'] dest)
-					( finishVerifyKeyContentIncrementally iv >>= \case
-						(True, v) -> return (Just v)
-						(False, _) -> return Nothing
-					, return Nothing
-					)
+	dl ([], ytus) = flip getM (map fst ytus) $ \u ->
+		ifM (youtubeDlTo key u dest p)
+			( return (Just UnVerified)
+			, return Nothing
+			)
+	dl (us, ytus) = do
+		iv <- startVerifyKeyContentIncrementally vc key
+		ifM (Url.withUrlOptions $ downloadUrl True key p iv (map fst us) dest)
+			( finishVerifyKeyContentIncrementally iv >>= \case
+				(True, v) -> return (Just v)
+				(False, _) -> dl ([], ytus)
+			, dl ([], ytus)
+			)
+
+	isyoutube (_, YoutubeDownloader) = True
+	isyoutube _ = False
 
 uploadKey :: Key -> AssociatedFile -> MeterUpdate -> Annex ()
 uploadKey _ _ _ = giveup "upload to web not supported"

doc/todo/get__58___improve_error_reporting_for_failed_attempts.mdwn

@@ -41,3 +41,15 @@ refs in DataLad issues:
 
 - from web remote: ["download failed: Not Found"](https://github.com/datalad/datalad/pull/5936)
 - from ["failed to retrieve content from remote"](https://github.com/datalad/datalad/issues/5750)
+
+> I think this is specific to downloading urls, although it can happen
+> for a few remotes (web, external). There's really no reason to display
+> a download failed message if it successfully downloads a later url.
+> (After all, if it had tried the working url first, it would never display
+> anything about the broken url.)
+> 
+> When all urls fail, it makes sense to display each url and why it failed
+> when using the web (or external) remote, so the user can decide what to
+> do about each of the problems.
+> 
+> [[done]] --[[Joey]]