eth/fetcher: if peers never respond, drop them

eth/fetcher/block_fetcher.go

@@ -477,10 +477,21 @@ func (f *BlockFetcher) loop() {
 							}
 							defer req.Close()
 
-							res := <-resCh
-							res.Done <- nil
-
-							f.FilterHeaders(peer, *res.Res.(*eth.BlockHeadersPacket), time.Now().Add(res.Time))
+							timeout := time.NewTimer(2 * fetchTimeout) // 2x leeway before dropping the peer
+							defer timeout.Stop()
+
+							select {
+							case res := <-resCh:
+								res.Done <- nil
+								f.FilterHeaders(peer, *res.Res.(*eth.BlockHeadersPacket), time.Now().Add(res.Time))
+
+							case <-timeout.C:
+								// The peer didn't respond in time. The request
+								// was already rescheduled at this point, we were
+								// waiting for a catchup. With an unresponsive
+								// peer however, it's a protocol violation.
+								f.dropPeer(peer)
+							}
 						}(hash)
 					}
 				}(peer)
@@ -523,11 +534,23 @@ func (f *BlockFetcher) loop() {
 					}
 					defer req.Close()
 
-					res := <-resCh
-					res.Done <- nil
+					timeout := time.NewTimer(2 * fetchTimeout) // 2x leeway before dropping the peer
+					defer timeout.Stop()
+
+					select {
+					case res := <-resCh:
+						res.Done <- nil
 
-					txs, uncles := res.Res.(*eth.BlockBodiesPacket).Unpack()
-					f.FilterBodies(peer, txs, uncles, time.Now())
+						txs, uncles := res.Res.(*eth.BlockBodiesPacket).Unpack()
+						f.FilterBodies(peer, txs, uncles, time.Now())
+
+					case <-timeout.C:
+						// The peer didn't respond in time. The request
+						// was already rescheduled at this point, we were
+						// waiting for a catchup. With an unresponsive
+						// peer however, it's a protocol violation.
+						f.dropPeer(peer)
+					}
 				}(peer, hashes)
 			}
 			// Schedule the next fetch if blocks are still pending