eth, eth/downloader: do async block fetches, add dl tests

eth/downloader/downloader_test.go

@@ -122,7 +122,14 @@ func (dl *downloadTester) insertChain(blocks types.Blocks) (int, error) {
 
 // newPeer registers a new block download source into the downloader.
 func (dl *downloadTester) newPeer(id string, hashes []common.Hash, blocks map[common.Hash]*types.Block) error {
-	err := dl.downloader.RegisterPeer(id, hashes[0], dl.peerGetHashesFn(id), dl.peerGetBlocksFn(id))
+	return dl.newSlowPeer(id, hashes, blocks, 0)
+}
+
+// newSlowPeer registers a new block download source into the downloader, with a
+// specific delay time on processing the network packets sent to it, simulating
+// potentially slow network IO.
+func (dl *downloadTester) newSlowPeer(id string, hashes []common.Hash, blocks map[common.Hash]*types.Block, delay time.Duration) error {
+	err := dl.downloader.RegisterPeer(id, hashes[0], dl.peerGetHashesFn(id, delay), dl.peerGetBlocksFn(id, delay))
 	if err == nil {
 		// Assign the owned hashes and blocks to the peer (deep copy)
 		dl.peerHashes[id] = make([]common.Hash, len(hashes))
@@ -147,8 +154,10 @@ func (dl *downloadTester) dropPeer(id string) {
 // peerGetBlocksFn constructs a getHashes function associated with a particular
 // peer in the download tester. The returned function can be used to retrieve
 // batches of hashes from the particularly requested peer.
-func (dl *downloadTester) peerGetHashesFn(id string) func(head common.Hash) error {
+func (dl *downloadTester) peerGetHashesFn(id string, delay time.Duration) func(head common.Hash) error {
 	return func(head common.Hash) error {
+		time.Sleep(delay)
+
 		limit := MaxHashFetch
 		if dl.maxHashFetch > 0 {
 			limit = dl.maxHashFetch
@@ -178,8 +187,10 @@ func (dl *downloadTester) peerGetHashesFn(id string) func(head common.Hash) erro
 // peerGetBlocksFn constructs a getBlocks function associated with a particular
 // peer in the download tester. The returned function can be used to retrieve
 // batches of blocks from the particularly requested peer.
-func (dl *downloadTester) peerGetBlocksFn(id string) func([]common.Hash) error {
+func (dl *downloadTester) peerGetBlocksFn(id string, delay time.Duration) func([]common.Hash) error {
 	return func(hashes []common.Hash) error {
+		time.Sleep(delay)
+
 		blocks := dl.peerBlocks[id]
 		result := make([]*types.Block, 0, len(hashes))
 		for _, hash := range hashes {
@@ -340,6 +351,37 @@ func TestMultiSynchronisation(t *testing.T) {
 	}
 }
 
+// Tests that synchronising with a peer who's very slow at network IO does not
+// stall the other peers in the system.
+func TestSlowSynchronisation(t *testing.T) {
+	tester := newTester()
+
+	// Create a batch of blocks, with a slow and a full speed peer
+	targetCycles := 2
+	targetBlocks := targetCycles*blockCacheLimit - 15
+	targetIODelay := 500 * time.Millisecond
+
+	hashes := createHashes(targetBlocks, knownHash)
+	blocks := createBlocksFromHashes(hashes)
+
+	tester.newSlowPeer("fast", hashes, blocks, 0)
+	tester.newSlowPeer("slow", hashes, blocks, targetIODelay)
+
+	// Try to sync with the peers (pull hashes from fast)
+	start := time.Now()
+	if err := tester.sync("fast"); err != nil {
+		t.Fatalf("failed to synchronise blocks: %v", err)
+	}
+	if imported := len(tester.ownBlocks); imported != targetBlocks+1 {
+		t.Fatalf("synchronised block mismatch: have %v, want %v", imported, targetBlocks+1)
+	}
+	// Check that the slow peer got hit at most once per block-cache-size import
+	limit := time.Duration(targetCycles+1) * targetIODelay
+	if delay := time.Since(start); delay >= limit {
+		t.Fatalf("synchronisation exceeded delay limit: have %v, want %v", delay, limit)
+	}
+}
+
 // Tests that if a peer returns an invalid chain with a block pointing to a non-
 // existing parent, it is correctly detected and handled.
 func TestNonExistingParentAttack(t *testing.T) {

eth/downloader/peer.go

@@ -74,7 +74,7 @@ func (p *peer) Fetch(request *fetchRequest) error {
 	for hash, _ := range request.Hashes {
 		hashes = append(hashes, hash)
 	}
-	p.getBlocks(hashes)
+	go p.getBlocks(hashes)
 
 	return nil
 }

eth/sync.go

@@ -171,7 +171,7 @@ func (pm *ProtocolManager) fetcher() {
 			// Send out all block requests
 			for peer, hashes := range request {
 				glog.V(logger.Debug).Infof("Explicitly fetching %d blocks from %s", len(hashes), peer.id)
-				peer.requestBlocks(hashes)
+				go peer.requestBlocks(hashes)
 			}
 			request = make(map[*peer][]common.Hash)