From 4304f1b6aea19a5c402dc4f9d69aa4ff1c104c9b Mon Sep 17 00:00:00 2001
From: Joey Hess <joeyh@joeyh.name>
Date: Sun, 28 Jul 2024 11:09:07 -0400
Subject: [PATCH] better handling of content not available from cluster

Sending ERROR caused the client to get confused and protocol to freeze.
Better to send empty DATA and indicate it's not valid.

This fixes a hang in git-annex testremote of a cluster accessed via the
http server. That testremote is still failing, for some reason after
storing a test key, the cluster reports it as not present.
---
 P2P/Proxy.hs | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/P2P/Proxy.hs b/P2P/Proxy.hs
index f3f1edcae0..761ced889d 100644
--- a/P2P/Proxy.hs
+++ b/P2P/Proxy.hs
@@ -276,10 +276,7 @@ proxyRequest proxydone proxyparams requestcomplete requestmessage protoerrhandle
 			handleGETTIMESTAMP remotesides
 		GET _ _ k -> proxyGET (proxySelector proxyparams) k >>= \case
 			Just remoteside -> handleGET remoteside requestmessage
-			Nothing -> 
-				protoerrhandler requestcomplete $
-					client $ net $ sendMessage $ 
-						ERROR "content not present"
+			Nothing -> handleGETNoRemoteSide
 		PUT paf k -> do
 			af <- getassociatedfile paf
 			remotesides <- proxyPUT (proxySelector proxyparams) af k
@@ -352,7 +349,7 @@ proxyRequest proxydone proxyparams requestcomplete requestmessage protoerrhandle
 	-- Read a message from one party, send it to the other,
 	-- and then pass the message to the continuation.
 	relayonemessage from to cont =
-		flip protoerrhandler (from $ net $ receiveMessage) $
+		flip protoerrhandler (from $ net receiveMessage) $
 			withresp $ \message ->
 				protoerrhandler (cont message) $
 					to $ net $ sendMessage message
@@ -460,6 +457,15 @@ proxyRequest proxydone proxyparams requestcomplete requestmessage protoerrhandle
 							[] -> FAILURE
 							(err:_) -> ERROR err
 						else FAILURE_PLUS us
+		
+	-- Send an empty DATA and indicate it was invalid.
+	handleGETNoRemoteSide = protoerrhandler requestcomplete $
+		client $ net $ do
+			sendMessage $ DATA (Len 0)
+			sendBytes (Len 0) mempty nullMeterUpdate
+			when (proxyClientProtocolVersion proxyparams /= ProtocolVersion 0) $
+				sendMessage (VALIDITY Invalid)
+			void $ receiveMessage
 
 	handleGET remoteside message = getresponse (runRemoteSide remoteside) message $
 		withDATA (relayGET remoteside) $ \case
@@ -622,7 +628,7 @@ proxyRequest proxydone proxyparams requestcomplete requestmessage protoerrhandle
 		| proxyClientProtocolVersion proxyparams == ProtocolVersion 0 =
 			finish $ net receiveMessage
 		| otherwise =
-			flip protoerrhandler (client $ net $ receiveMessage) $
+			flip protoerrhandler (client $ net receiveMessage) $
 				withresp $ \message ->
 					finish $ do
 						-- Relay VALID or INVALID message