From 004c903fb417483c492ab4febc921ba83bdd1c30 Mon Sep 17 00:00:00 2001
From: Wei Tang <accounts@that.world>
Date: Sat, 22 Jul 2017 04:06:12 +0800
Subject: [PATCH 1/3] p2p: good will assumption for the DAO fork

Discussion at #309.

After sending a request to check for a particular hash of a hard fork block, allow the peer to claim that it does not know about this block, and then assume the peer is valid, unless it shows it's not so.
---
 eth/handler.go | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/eth/handler.go b/eth/handler.go
index e7e86fd18..cb6e51f9e 100644
--- a/eth/handler.go
+++ b/eth/handler.go
@@ -405,19 +405,21 @@ func (pm *ProtocolManager) handleMsg(p *peer) error {
 			return errResp(ErrDecode, "msg %v: %v", msg, err)
 		}
 		// Filter out any explicitly requested headers, deliver the rest to the downloader
-		isForkCheck := len(headers) == 1
+		isForkCheck := len(headers) == 1 || len(headers) == 0
 		if isForkCheck {
 			if p.timeout != nil {
 				// Disable the fork drop timeout
 				p.timeout.Stop()
 				p.timeout = nil
 			}
-			if err := pm.chainConfig.HeaderCheck(headers[0]); err != nil {
-				pm.removePeer(p.id)
-				return err
+			if len(headers) > 0 {
+				if err := pm.chainConfig.HeaderCheck(headers[0]); err != nil {
+					pm.removePeer(p.id)
+					return err
+				}
+				// Irrelevant of the fork checks, send the header to the fetcher just in case
+				headers = pm.fetcher.FilterHeaders(headers, time.Now())
 			}
-			// Irrelevant of the fork checks, send the header to the fetcher just in case
-			headers = pm.fetcher.FilterHeaders(headers, time.Now())
 		}
 		if len(headers) > 0 || !isForkCheck {
 			err := pm.downloader.DeliverHeaders(p.id, headers)

From 3f09b1f5304914ba6910075aaf2f5831875818ee Mon Sep 17 00:00:00 2001
From: Wei Tang <accounts@that.world>
Date: Sun, 23 Jul 2017 03:37:57 +0800
Subject: [PATCH 2/3] Fix the test failure for the good-will change

---
 eth/handler.go | 20 +++++++++-----------
 1 file changed, 9 insertions(+), 11 deletions(-)

diff --git a/eth/handler.go b/eth/handler.go
index cb6e51f9e..77f8b839f 100644
--- a/eth/handler.go
+++ b/eth/handler.go
@@ -405,23 +405,21 @@ func (pm *ProtocolManager) handleMsg(p *peer) error {
 			return errResp(ErrDecode, "msg %v: %v", msg, err)
 		}
 		// Filter out any explicitly requested headers, deliver the rest to the downloader
-		isForkCheck := len(headers) == 1 || len(headers) == 0
-		if isForkCheck {
+		if len(headers) == 0 || len(headers) == 1 {
 			if p.timeout != nil {
 				// Disable the fork drop timeout
 				p.timeout.Stop()
 				p.timeout = nil
 			}
-			if len(headers) > 0 {
-				if err := pm.chainConfig.HeaderCheck(headers[0]); err != nil {
-					pm.removePeer(p.id)
-					return err
-				}
-				// Irrelevant of the fork checks, send the header to the fetcher just in case
-				headers = pm.fetcher.FilterHeaders(headers, time.Now())
-			}
 		}
-		if len(headers) > 0 || !isForkCheck {
+		if len(headers) == 1 {
+			if err := pm.chainConfig.HeaderCheck(headers[0]); err != nil {
+				pm.removePeer(p.id)
+				return err
+			}
+			// Irrelevant of the fork checks, send the header to the fetcher just in case
+			headers = pm.fetcher.FilterHeaders(headers, time.Now())
+		} else if len(headers) > 0 {
 			err := pm.downloader.DeliverHeaders(p.id, headers)
 			if err != nil {
 				glog.V(logger.Debug).Infoln(err)

From f33d7ade3099162f1c66280cf16d4300af960ba1 Mon Sep 17 00:00:00 2001
From: Wei Tang <accounts@that.world>
Date: Sun, 23 Jul 2017 03:53:35 +0800
Subject: [PATCH 3/3] Problem: wrong logic translation in good-will fix

len(headers) > 0 || !isForkCheck is equivalent to len(headers) > 0 || !(len(headers) == 1), and this is true for len == 0 (!(len(headers) == 1) is true), len == 1 (len(headers > 0) is true, and so on.
---
 eth/handler.go | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/eth/handler.go b/eth/handler.go
index 77f8b839f..8a5887be4 100644
--- a/eth/handler.go
+++ b/eth/handler.go
@@ -419,11 +419,10 @@ func (pm *ProtocolManager) handleMsg(p *peer) error {
 			}
 			// Irrelevant of the fork checks, send the header to the fetcher just in case
 			headers = pm.fetcher.FilterHeaders(headers, time.Now())
-		} else if len(headers) > 0 {
-			err := pm.downloader.DeliverHeaders(p.id, headers)
-			if err != nil {
-				glog.V(logger.Debug).Infoln(err)
-			}
+		}
+		err := pm.downloader.DeliverHeaders(p.id, headers)
+		if err != nil {
+			glog.V(logger.Debug).Infoln(err)
 		}
 
 	case p.version >= eth62 && msg.Code == GetBlockBodiesMsg: