fixes double lookups when block does not exist (#739)

* fixes double lookups when block does not exist

* handle timeouts on requestBlock

* fix indentation which was causing an integration test to fail

codex/blockexchange/engine/engine.nim

@@ -73,6 +73,7 @@ type
     peersPerRequest: int                          # Max number of peers to request from
     wallet*: WalletRef                            # Nitro wallet for micropayments
     pricing*: ?Pricing                            # Optional bandwidth pricing
+    blockFetchTimeout*: Duration                  # Timeout for fetching blocks over the network
     discovery*: DiscoveryEngine
 
   Pricing* = object
@@ -173,12 +174,10 @@ proc monitorBlockHandle(
 proc requestBlock*(
   b: BlockExcEngine,
   address: BlockAddress,
-  timeout = DefaultBlockTimeout): Future[?!Block] {.async.} =
-  let blockFuture = b.pendingBlocks.getWantHandle(address, timeout)
+): Future[?!Block] {.async.} =
+  let blockFuture = b.pendingBlocks.getWantHandle(address, b.blockFetchTimeout)
 
-  if b.pendingBlocks.isInFlight(address):
-    success await blockFuture
-  else:
+  if not b.pendingBlocks.isInFlight(address):
     let peers = b.peers.selectCheapest(address)
     if peers.len == 0:
       b.discovery.queueFindBlocksReq(@[address.cidOrTreeCid])
@@ -199,12 +198,17 @@ proc requestBlock*(
       await b.sendWantHave(address, @[peer], toSeq(b.peers))
       codex_block_exchange_want_have_lists_sent.inc()
 
+  # Don't let timeouts bubble up. We can't be too broad here or we break
+  # cancellations.
+  try:
     success await blockFuture
+  except AsyncTimeoutError as err:
+    failure err
 
 proc requestBlock*(
   b: BlockExcEngine,
-  cid: Cid,
-  timeout = DefaultBlockTimeout): Future[?!Block] =
+  cid: Cid
+): Future[?!Block] =
   b.requestBlock(BlockAddress.init(cid))
 
 proc blockPresenceHandler*(
@@ -614,7 +618,8 @@ proc new*(
     peerStore: PeerCtxStore,
     pendingBlocks: PendingBlocksManager,
     concurrentTasks = DefaultConcurrentTasks,
-    peersPerRequest = DefaultMaxPeersPerRequest
+    peersPerRequest = DefaultMaxPeersPerRequest,
+    blockFetchTimeout = DefaultBlockTimeout,
 ): BlockExcEngine =
   ## Create new block exchange engine instance
   ##
@@ -629,7 +634,8 @@ proc new*(
       wallet: wallet,
       concurrentTasks: concurrentTasks,
       taskQueue: newAsyncHeapQueue[BlockExcPeerCtx](DefaultTaskQueueSize),
-      discovery: discovery)
+      discovery: discovery,
+      blockFetchTimeout: blockFetchTimeout)
 
   proc peerEventHandler(peerId: PeerId, event: PeerEvent) {.async.} =
     if event.kind == PeerEventKind.Joined:

codex/node.nim

@@ -209,6 +209,62 @@ proc fetchBatched*(
   let iter = Iter.fromSlice(0..<manifest.blocksCount)
   self.fetchBatched(manifest.treeCid, iter, batchSize, onBatch)
 
+proc streamSingleBlock(
+  self: CodexNodeRef,
+  cid: Cid
+): Future[?!LPstream] {.async.} =
+  ## Streams the contents of a single block.
+  ##
+  trace "Streaming single block", cid = cid
+
+  let
+    stream = BufferStream.new()
+
+  without blk =? (await self.networkStore.getBlock(BlockAddress.init(cid))), err:
+    return failure(err)
+
+  proc streamOneBlock(): Future[void] {.async.} =
+    try:
+      await stream.pushData(blk.data)
+    except CatchableError as exc:
+      trace "Unable to send block", cid, exc = exc.msg
+      discard
+    finally:
+      await stream.pushEof()
+
+  asyncSpawn streamOneBlock()
+  LPStream(stream).success
+
+proc streamEntireDataset(
+  self: CodexNodeRef,
+  manifest: Manifest,
+  manifestCid: Cid,
+): ?!LPStream =
+  ## Streams the contents of the entire dataset described by the manifest.
+  ##
+  trace "Retrieving blocks from manifest", manifestCid
+
+  if manifest.protected:
+    # Retrieve, decode and save to the local store all EС groups
+    proc erasureJob(): Future[void] {.async.} =
+      try:
+        # Spawn an erasure decoding job
+        let
+          erasure = Erasure.new(
+            self.networkStore,
+            leoEncoderProvider,
+            leoDecoderProvider)
+        without _ =? (await erasure.decode(manifest)), error:
+          trace "Unable to erasure decode manifest", manifestCid, exc = error.msg
+      except CatchableError as exc:
+        trace "Exception decoding manifest", manifestCid, exc = exc.msg
+
+    asyncSpawn erasureJob()
+
+  # Retrieve all blocks of the dataset sequentially from the local store or network
+  trace "Creating store stream for manifest", manifestCid
+  LPStream(StoreStream.new(self.networkStore, manifest, pad = false)).success
+
 proc retrieve*(
   self: CodexNodeRef,
   cid: Cid,
@@ -219,46 +275,13 @@ proc retrieve*(
   if local and not await (cid in self.networkStore):
     return failure((ref BlockNotFoundError)(msg: "Block not found in local store"))
 
-  if manifest =? (await self.fetchManifest(cid)):
-    trace "Retrieving blocks from manifest", cid
-    if manifest.protected:
-      # Retrieve, decode and save to the local store all EС groups
-      proc erasureJob(): Future[void] {.async.} =
-        try:
-          # Spawn an erasure decoding job
-          let
-            erasure = Erasure.new(
-              self.networkStore,
-              leoEncoderProvider,
-              leoDecoderProvider)
-          without _ =? (await erasure.decode(manifest)), error:
-            trace "Unable to erasure decode manifest", cid, exc = error.msg
-        except CatchableError as exc:
-          trace "Exception decoding manifest", cid, exc = exc.msg
-
-      asyncSpawn erasureJob()
-
-    # Retrieve all blocks of the dataset sequentially from the local store or network
-    trace "Creating store stream for manifest", cid
-    LPStream(StoreStream.new(self.networkStore, manifest, pad = false)).success
-  else:
-    let
-      stream = BufferStream.new()
-
-    without blk =? (await self.networkStore.getBlock(BlockAddress.init(cid))), err:
+  without manifest =? (await self.fetchManifest(cid)), err:
+    if err of AsyncTimeoutError:
       return failure(err)
 
-    proc streamOneBlock(): Future[void] {.async.} =
-      try:
-        await stream.pushData(blk.data)
-      except CatchableError as exc:
-        trace "Unable to send block", cid, exc = exc.msg
-        discard
-      finally:
-        await stream.pushEof()
+    return await self.streamSingleBlock(cid)
 
-    asyncSpawn streamOneBlock()
-    LPStream(stream).success()
+  self.streamEntireDataset(manifest, cid)
 
 proc store*(
   self: CodexNodeRef,

tests/codex/node/helpers.nim

@@ -1,4 +1,4 @@
-
+import std/tables
 import std/times
 
 import pkg/libp2p
@@ -6,10 +6,25 @@ import pkg/chronos
 
 import pkg/codex/codextypes
 import pkg/codex/chunker
+import pkg/codex/stores
 import pkg/codex/slots
 
 import ../../asynctest
 
+type CountingStore* = ref object of NetworkStore
+  lookups*: Table[Cid, int]
+
+proc new*(T: type CountingStore,
+  engine: BlockExcEngine, localStore: BlockStore): CountingStore =
+  # XXX this works cause NetworkStore.new is trivial
+  result = CountingStore(engine: engine, localStore: localStore)
+
+method getBlock*(self: CountingStore,
+  address: BlockAddress): Future[?!Block] {.async.} =
+
+  self.lookups.mgetOrPut(address.cid, 0).inc
+  await procCall getBlock(NetworkStore(self), address)
+
 proc toTimesDuration*(d: chronos.Duration): times.Duration =
   initDuration(seconds = d.seconds)
 

tests/codex/node/testnode.nim

@@ -62,6 +62,21 @@ asyncchecksuite "Test Node - Basic":
     check:
       fetched == manifest
 
+  test "Should not lookup non-existing blocks twice":
+    # https://github.com/codex-storage/nim-codex/issues/699
+    let
+      cstore = CountingStore.new(engine, localStore)
+      node = CodexNodeRef.new(switch, cstore, engine, blockDiscovery)
+      missingCid = Cid.init(
+        "zDvZRwzmCvtiyubW9AecnxgLnXK8GrBvpQJBDzToxmzDN6Nrc2CZ").get()
+
+    engine.blockFetchTimeout = timer.milliseconds(100)
+
+    discard await node.retrieve(missingCid, local = false)
+
+    let lookupCount = cstore.lookups.getOrDefault(missingCid)
+    check lookupCount == 1
+
   test "Block Batching":
     let manifest = await storeDataGetManifest(localStore, chunker)