From 948c725b09d4c9f3142674911b6a87c1a2416a66 Mon Sep 17 00:00:00 2001
From: Jean-Paul Calderone <exarkun@twistedmatrix.com>
Date: Fri, 14 Apr 2023 15:28:00 -0400
Subject: [PATCH] Exercise the case where some shares are duplicates
---
src/Tahoe/Download.hs | 9 ++++----
test/Spec.hs | 49 +++++++++++++++++++++++++++++++++++++++++++
2 files changed, 54 insertions(+), 4 deletions(-)
diff --git a/src/Tahoe/Download.hs b/src/Tahoe/Download.hs
index b2b394f..f5a05d6 100644
--- a/src/Tahoe/Download.hs
+++ b/src/Tahoe/Download.hs
@@ -2,6 +2,7 @@ module Tahoe.Download (DownloadError (..), download) where
import qualified Data.ByteString.Lazy as LB
import Data.Either (rights)
+import Data.List (foldl')
import qualified Data.Map.Strict as Map
import qualified Data.Set as Set
import qualified Data.Text as T
@@ -49,13 +50,13 @@ download servers Reader{verifier = Verifier{..}} openServer =
if null discovered
then pure $ Left NoReachableServers
else
- if (fromIntegral required >=) . countShares $ discovered
- then pure $ Left NotEnoughShares{notEnoughSharesNeeded = fromIntegral required, notEnoughSharesFound = countShares discovered}
+ if (fromIntegral required >=) . countDistinctShares $ discovered
+ then pure $ Left NotEnoughShares{notEnoughSharesNeeded = fromIntegral required, notEnoughSharesFound = countDistinctShares discovered}
else pure . Right . LB.fromStrict . encodeUtf8 . T.pack . show $ discovered
where
- -- Figure the total number of shares reported by all of the servers we
+ -- Figure the total number of distinct shares reported by all of the servers we
-- asked.
- countShares = sum . map (Set.size . snd)
+ countDistinctShares = Set.size . foldl' Set.union mempty . map snd
-- Ask one server which shares it has related to the storage index in
-- question.
diff --git a/test/Spec.hs b/test/Spec.hs
index 42c8753..7456668 100644
--- a/test/Spec.hs
+++ b/test/Spec.hs
@@ -73,6 +73,55 @@ tests =
then pure . pure $ server
else pure Nothing
+ -- Try to download the cap which requires three shares to reconstruct.
+ result <- liftIO $ download anns cap openServer
+ assertEqual
+ "download should fail with not enough shares"
+ (Left NotEnoughShares{notEnoughSharesNeeded = 3, notEnoughSharesFound = 2})
+ result
+ , testCase "not enough distinct shares" $ do
+ -- If we can't recover enough *distinct* shares from the
+ -- configured servers then we can't possibly get enough shares to
+ -- recover the application data. Duplicate shares do us no good.
+ let anns =
+ Map.fromList
+ [
+ ( "v0-abc123"
+ , StorageServerAnnouncement
+ { storageServerAnnouncementFURL = Just "somewhere"
+ , storageServerAnnouncementNick = Just "abc123"
+ , storageServerAnnouncementPermutationSeed = Nothing
+ }
+ )
+ ,
+ ( "v0-abc456"
+ , StorageServerAnnouncement
+ { storageServerAnnouncementFURL = Just "elsewhere"
+ , storageServerAnnouncementNick = Just "abc123"
+ , storageServerAnnouncementPermutationSeed = Nothing
+ }
+ )
+ ]
+ cap = trivialCap 3 3
+
+ -- Three shares exist
+ somewhere <- memoryStorageServer
+ let idx = storageIndex . verifier $ cap
+ offset = 0
+ storageServerWrite somewhere idx 0 offset "Hello world"
+ storageServerWrite somewhere idx 1 offset "Hello world"
+ -- But this one is just a duplicate of share 0 on the other
+ -- server.
+ elsewhere <- memoryStorageServer
+ storageServerWrite elsewhere idx 0 offset "Hello world"
+
+ -- Make the server reachable.
+ let openServer furl =
+ pure $ case furl of
+ "somewhere" -> pure somewhere
+ "elsewhere" -> pure elsewhere
+ _ -> Nothing
+
-- Try to download the cap which requires three shares to reconstruct.
result <- liftIO $ download anns cap openServer
assertEqual
--
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