eth/downloader: dynamically move pivot even during chain sync

eth/downloader/downloader_test.go

@@ -427,11 +427,7 @@ func (dlp *downloadTesterPeer) Head() (common.Hash, *big.Int) {
 // origin; associated with a particular peer in the download tester. The returned
 // function can be used to retrieve batches of headers from the particular peer.
 func (dlp *downloadTesterPeer) RequestHeadersByHash(origin common.Hash, amount int, skip int, reverse bool) error {
-	if reverse {
-		panic("reverse header requests not supported")
-	}
-
-	result := dlp.chain.headersByHash(origin, amount, skip)
+	result := dlp.chain.headersByHash(origin, amount, skip, reverse)
 	go dlp.dl.downloader.DeliverHeaders(dlp.id, result)
 	return nil
 }
@@ -440,11 +436,7 @@ func (dlp *downloadTesterPeer) RequestHeadersByHash(origin common.Hash, amount i
 // origin; associated with a particular peer in the download tester. The returned
 // function can be used to retrieve batches of headers from the particular peer.
 func (dlp *downloadTesterPeer) RequestHeadersByNumber(origin uint64, amount int, skip int, reverse bool) error {
-	if reverse {
-		panic("reverse header requests not supported")
-	}
-
-	result := dlp.chain.headersByNumber(origin, amount, skip)
+	result := dlp.chain.headersByNumber(origin, amount, skip, reverse)
 	go dlp.dl.downloader.DeliverHeaders(dlp.id, result)
 	return nil
 }
@@ -1698,7 +1690,7 @@ func testCheckpointEnforcement(t *testing.T, protocol int, mode SyncMode) {
 	if mode == FastSync || mode == LightSync {
 		expect = errUnsyncedPeer
 	}
-	if err := tester.sync("peer", nil, mode); err != expect {
+	if err := tester.sync("peer", nil, mode); !errors.Is(err, expect) {
 		t.Fatalf("block sync error mismatch: have %v, want %v", err, expect)
 	}
 	if mode == FastSync || mode == LightSync {

eth/downloader/testchain_test.go

@@ -170,18 +170,27 @@ func (tc *testChain) td(hash common.Hash) *big.Int {
 	return tc.tdm[hash]
 }
 
-// headersByHash returns headers in ascending order from the given hash.
-func (tc *testChain) headersByHash(origin common.Hash, amount int, skip int) []*types.Header {
+// headersByHash returns headers in order from the given hash.
+func (tc *testChain) headersByHash(origin common.Hash, amount int, skip int, reverse bool) []*types.Header {
 	num, _ := tc.hashToNumber(origin)
-	return tc.headersByNumber(num, amount, skip)
+	return tc.headersByNumber(num, amount, skip, reverse)
 }
 
-// headersByNumber returns headers in ascending order from the given number.
-func (tc *testChain) headersByNumber(origin uint64, amount int, skip int) []*types.Header {
+// headersByNumber returns headers from the given number.
+func (tc *testChain) headersByNumber(origin uint64, amount int, skip int, reverse bool) []*types.Header {
 	result := make([]*types.Header, 0, amount)
-	for num := origin; num < uint64(len(tc.chain)) && len(result) < amount; num += uint64(skip) + 1 {
-		if header, ok := tc.headerm[tc.chain[int(num)]]; ok {
-			result = append(result, header)
+
+	if !reverse {
+		for num := origin; num < uint64(len(tc.chain)) && len(result) < amount; num += uint64(skip) + 1 {
+			if header, ok := tc.headerm[tc.chain[int(num)]]; ok {
+				result = append(result, header)
+			}
+		}
+	} else {
+		for num := int64(origin); num >= 0 && len(result) < amount; num -= int64(skip) + 1 {
+			if header, ok := tc.headerm[tc.chain[int(num)]]; ok {
+				result = append(result, header)
+			}
 		}
 	}
 	return result