eth: fix #2076, where end of hash query was interpreted number query

eth/handler.go

@@ -372,6 +372,8 @@ func (pm *ProtocolManager) handleMsg(p *peer) error {
 		if err := msg.Decode(&query); err != nil {
 			return errResp(ErrDecode, "%v: %v", msg, err)
 		}
+		hashMode := query.Origin.Hash != (common.Hash{})
+
 		// Gather headers until the fetch or network limits is reached
 		var (
 			bytes   common.StorageSize
@@ -381,7 +383,7 @@ func (pm *ProtocolManager) handleMsg(p *peer) error {
 		for !unknown && len(headers) < int(query.Amount) && bytes < softResponseLimit && len(headers) < downloader.MaxHeaderFetch {
 			// Retrieve the next header satisfying the query
 			var origin *types.Header
-			if query.Origin.Hash != (common.Hash{}) {
+			if hashMode {
 				origin = pm.blockchain.GetHeader(query.Origin.Hash)
 			} else {
 				origin = pm.blockchain.GetHeaderByNumber(query.Origin.Number)

eth/handler_test.go

@@ -301,6 +301,15 @@ func testGetBlockHeaders(t *testing.T, protocol int) {
 				pm.blockchain.GetBlockByNumber(1).Hash(),
 			},
 		},
+		// Check a corner case where requesting more can iterate past the endpoints
+		{
+			&getBlockHeadersData{Origin: hashOrNumber{Number: 2}, Amount: 5, Reverse: true},
+			[]common.Hash{
+				pm.blockchain.GetBlockByNumber(2).Hash(),
+				pm.blockchain.GetBlockByNumber(1).Hash(),
+				pm.blockchain.GetBlockByNumber(0).Hash(),
+			},
+		},
 		// Check that non existing headers aren't returned
 		{
 			&getBlockHeadersData{Origin: hashOrNumber{Hash: unknown}, Amount: 1},
@@ -322,6 +331,17 @@ func testGetBlockHeaders(t *testing.T, protocol int) {
 		if err := p2p.ExpectMsg(peer.app, 0x04, headers); err != nil {
 			t.Errorf("test %d: headers mismatch: %v", i, err)
 		}
+		// If the test used number origins, repeat with hashes as the too
+		if tt.query.Origin.Hash == (common.Hash{}) {
+			if origin := pm.blockchain.GetBlockByNumber(tt.query.Origin.Number); origin != nil {
+				tt.query.Origin.Hash, tt.query.Origin.Number = origin.Hash(), 0
+
+				p2p.Send(peer.app, 0x03, tt.query)
+				if err := p2p.ExpectMsg(peer.app, 0x04, headers); err != nil {
+					t.Errorf("test %d: headers mismatch: %v", i, err)
+				}
+			}
+		}
 	}
 }