eth/downloader: more context in errors (ethereum#21067)

This PR makes use of go 1.13 error handling, wrapping errors and using
errors.Is to check a wrapped root-cause. It also removes the travis
builders for go 1.11 and go 1.12.

.travis.yml

@@ -24,26 +24,6 @@ jobs:
       script:
         - go run build/ci.go lint
 
-    - stage: build
-      os: linux
-      dist: xenial
-      go: 1.11.x
-      env:
-        - GO111MODULE=on
-      script:
-        - go run build/ci.go install
-        - go run build/ci.go test -coverage $TEST_PACKAGES
-
-    - stage: build
-      os: linux
-      dist: xenial
-      go: 1.12.x
-      env:
-        - GO111MODULE=on
-      script:
-        - go run build/ci.go install
-        - go run build/ci.go test -coverage $TEST_PACKAGES
-
     - stage: build
       os: linux
       dist: xenial

eth/downloader/downloader.go

@@ -321,13 +321,28 @@ func (d *Downloader) UnregisterPeer(id string) error {
 // adding various sanity checks as well as wrapping it with various log entries.
 func (d *Downloader) Synchronise(id string, head common.Hash, td *big.Int, mode SyncMode) error {
 	err := d.synchronise(id, head, td, mode)
+
 	switch err {
-	case nil:
-	case errBusy, errCanceled:
+	case nil, errBusy, errCanceled:
+		return err
+	}
 
+	if errors.Is(err, errInvalidChain) {
+		log.Warn("Synchronisation failed, dropping peer", "peer", id, "err", err)
+		if d.dropPeer == nil {
+			// The dropPeer method is nil when `--copydb` is used for a local copy.
+			// Timeouts can occur if e.g. compaction hits at the wrong time, and can be ignored
+			log.Warn("Downloader wants to drop peer, but peerdrop-function is not set", "peer", id)
+		} else {
+			d.dropPeer(id)
+		}
+		return err
+	}
+
+	switch err {
 	case errTimeout, errBadPeer, errStallingPeer, errUnsyncedPeer,
 		errEmptyHeaderSet, errPeersUnavailable, errTooOld,
-		errInvalidAncestor, errInvalidChain:
+		errInvalidAncestor:
 		log.Warn("Synchronisation failed, dropping peer", "peer", id, "err", err)
 		if d.dropPeer == nil {
 			// The dropPeer method is nil when `--copydb` is used for a local copy.
@@ -774,7 +789,7 @@ func (d *Downloader) findAncestor(p *peerConnection, remoteHeader *types.Header)
 				expectNumber := from + int64(i)*int64(skip+1)
 				if number := header.Number.Int64(); number != expectNumber {
 					p.log.Warn("Head headers broke chain ordering", "index", i, "requested", expectNumber, "received", number)
-					return 0, errInvalidChain
+					return 0, fmt.Errorf("%w: %v", errInvalidChain, errors.New("head headers broke chain ordering"))
 				}
 			}
 			// Check if a common ancestor was found
@@ -988,7 +1003,7 @@ func (d *Downloader) fetchHeaders(p *peerConnection, from uint64, pivot uint64)
 				filled, proced, err := d.fillHeaderSkeleton(from, headers)
 				if err != nil {
 					p.log.Debug("Skeleton chain invalid", "err", err)
-					return errInvalidChain
+					return fmt.Errorf("%w: %v", errInvalidChain, err)
 				}
 				headers = filled[proced:]
 				from += uint64(proced)
@@ -1207,13 +1222,13 @@ func (d *Downloader) fetchParts(deliveryCh chan dataPack, deliver func(dataPack)
 			if peer := d.peers.Peer(packet.PeerId()); peer != nil {
 				// Deliver the received chunk of data and check chain validity
 				accepted, err := deliver(packet)
-				if err == errInvalidChain {
+				if errors.Is(err, errInvalidChain) {
 					return err
 				}
 				// Unless a peer delivered something completely else than requested (usually
 				// caused by a timed out request which came through in the end), set it to
 				// idle. If the delivery's stale, the peer should have already been idled.
-				if err != errStaleDelivery {
+				if !errors.Is(err, errStaleDelivery) {
 					setIdle(peer, accepted)
 				}
 				// Issue a log to the user to see what's going on
@@ -1473,7 +1488,7 @@ func (d *Downloader) processHeaders(origin uint64, pivot uint64, td *big.Int) er
 							rollback = append(rollback, chunk[:n]...)
 						}
 						log.Debug("Invalid header encountered", "number", chunk[n].Number, "hash", chunk[n].Hash(), "err", err)
-						return errInvalidChain
+						return fmt.Errorf("%w: %v", errInvalidChain, err)
 					}
 					// All verifications passed, store newly found uncertain headers
 					rollback = append(rollback, unknown...)
@@ -1565,7 +1580,7 @@ func (d *Downloader) importBlockResults(results []*fetchResult) error {
 			// of the blocks delivered from the downloader, and the indexing will be off.
 			log.Debug("Downloaded item processing failed on sidechain import", "index", index, "err", err)
 		}
-		return errInvalidChain
+		return fmt.Errorf("%w: %v", errInvalidChain, err)
 	}
 	return nil
 }
@@ -1706,7 +1721,7 @@ func (d *Downloader) commitFastSyncData(results []*fetchResult, stateSync *state
 	}
 	if index, err := d.blockchain.InsertReceiptChain(blocks, receipts, d.ancientLimit); err != nil {
 		log.Debug("Downloaded item processing failed", "number", results[index].Header.Number, "hash", results[index].Header.Hash(), "err", err)
-		return errInvalidChain
+		return fmt.Errorf("%w: %v", errInvalidChain, err)
 	}
 	return nil
 }

eth/downloader/downloader_test.go

@@ -242,27 +242,32 @@ func (dl *downloadTester) GetTd(hash common.Hash, number uint64) *big.Int {
 func (dl *downloadTester) InsertHeaderChain(headers []*types.Header, checkFreq int) (i int, err error) {
 	dl.lock.Lock()
 	defer dl.lock.Unlock()
-
 	// Do a quick check, as the blockchain.InsertHeaderChain doesn't insert anything in case of errors
 	if _, ok := dl.ownHeaders[headers[0].ParentHash]; !ok {
-		return 0, errors.New("unknown parent")
+		return 0, errors.New("InsertHeaderChain: unknown parent at first position")
 	}
+	var hashes []common.Hash
 	for i := 1; i < len(headers); i++ {
+		hash := headers[i-1].Hash()
 		if headers[i].ParentHash != headers[i-1].Hash() {
-			return i, errors.New("unknown parent")
+			return i, fmt.Errorf("non-contiguous import at position %d", i)
 		}
+		hashes = append(hashes, hash)
 	}
+	hashes = append(hashes, headers[len(headers)-1].Hash())
 	// Do a full insert if pre-checks passed
 	for i, header := range headers {
-		if _, ok := dl.ownHeaders[header.Hash()]; ok {
+		hash := hashes[i]
+		if _, ok := dl.ownHeaders[hash]; ok {
 			continue
 		}
 		if _, ok := dl.ownHeaders[header.ParentHash]; !ok {
-			return i, errors.New("unknown parent")
+			// This _should_ be impossible, due to precheck and induction
+			return i, fmt.Errorf("InsertHeaderChain: unknown parent at position %d", i)
 		}
-		dl.ownHashes = append(dl.ownHashes, header.Hash())
-		dl.ownHeaders[header.Hash()] = header
-		dl.ownChainTd[header.Hash()] = new(big.Int).Add(dl.ownChainTd[header.ParentHash], header.Difficulty)
+		dl.ownHashes = append(dl.ownHashes, hash)
+		dl.ownHeaders[hash] = header
+		dl.ownChainTd[hash] = new(big.Int).Add(dl.ownChainTd[header.ParentHash], header.Difficulty)
 	}
 	return len(headers), nil
 }
@@ -274,9 +279,9 @@ func (dl *downloadTester) InsertChain(blocks types.Blocks) (i int, err error) {
 
 	for i, block := range blocks {
 		if parent, ok := dl.ownBlocks[block.ParentHash()]; !ok {
-			return i, errors.New("unknown parent")
+			return i, fmt.Errorf("InsertChain: unknown parent at position %d / %d", i, len(blocks))
 		} else if _, err := dl.stateDb.Get(parent.Root().Bytes()); err != nil {
-			return i, fmt.Errorf("unknown parent state %x: %v", parent.Root(), err)
+			return i, fmt.Errorf("InsertChain: unknown parent state %x: %v", parent.Root(), err)
 		}
 		if _, ok := dl.ownHeaders[block.Hash()]; !ok {
 			dl.ownHashes = append(dl.ownHashes, block.Hash())
@@ -301,7 +306,7 @@ func (dl *downloadTester) InsertReceiptChain(blocks types.Blocks, receipts []typ
 		}
 		if _, ok := dl.ancientBlocks[blocks[i].ParentHash()]; !ok {
 			if _, ok := dl.ownBlocks[blocks[i].ParentHash()]; !ok {
-				return i, errors.New("unknown parent")
+				return i, errors.New("InsertReceiptChain: unknown parent")
 			}
 		}
 		if blocks[i].NumberU64() <= ancientLimit {

eth/downloader/queue.go

@@ -509,7 +509,7 @@ func (q *queue) reserveHeaders(p *peerConnection, count int, taskPool map[common
 		index := int(header.Number.Int64() - int64(q.resultOffset))
 		if index >= len(q.resultCache) || index < 0 {
 			common.Report("index allocation went beyond available resultCache space")
-			return nil, false, errInvalidChain
+			return nil, false, fmt.Errorf("%w: index allocation went beyond available resultCache space", errInvalidChain)
 		}
 		if q.resultCache[index] == nil {
 			components := 1
@@ -863,14 +863,16 @@ func (q *queue) deliver(id string, taskPool map[common.Hash]*types.Header, taskQ
 		q.active.Signal()
 	}
 	// If none of the data was good, it's a stale delivery
-	switch {
-	case failure == nil || failure == errInvalidChain:
+	if failure == nil {
+		return accepted, nil
+	}
+	if errors.Is(failure, errInvalidChain) {
 		return accepted, failure
-	case useful:
+	}
+	if useful {
 		return accepted, fmt.Errorf("partial failure: %v", failure)
-	default:
-		return accepted, errStaleDelivery
 	}
+	return accepted, fmt.Errorf("%w: %v", failure, errStaleDelivery)
 }
 
 // Prepare configures the result cache to allow accepting and caching inbound