From 4f5b15345282768fe78a8331ac69e6d9d60ad457 Mon Sep 17 00:00:00 2001
From: Gav Wood <i@gavwood.com>
Date: Tue, 7 Oct 2014 16:40:13 +0200
Subject: [PATCH] Better state management.

---
 libethereum/EthereumHost.cpp | 14 ++++++++------
 libethereum/EthereumHost.h   |  2 +-
 libethereum/EthereumPeer.cpp | 25 ++++++++++++++++---------
 libethereum/EthereumPeer.h   |  1 +
 4 files changed, 26 insertions(+), 16 deletions(-)

diff --git a/libethereum/EthereumHost.cpp b/libethereum/EthereumHost.cpp
index 4bd34f201..c5c3e90cd 100644
--- a/libethereum/EthereumHost.cpp
+++ b/libethereum/EthereumHost.cpp
@@ -84,13 +84,15 @@ void EthereumHost::noteNeedsSyncing(EthereumPeer* _who)
 		_who->attemptSync();
 }
 
-void EthereumHost::updateSyncer(EthereumPeer* _syncer)
+void EthereumHost::changeSyncer(EthereumPeer* _syncer)
 {
-	if (_syncer)
+	m_syncer = _syncer;
+	if (isSyncing())
 	{
-		for (auto j: peers())
-			if (j->cap<EthereumPeer>().get() != _syncer && j->cap<EthereumPeer>()->m_asking == Asking::Nothing)
-				j->cap<EthereumPeer>()->transition(Asking::Blocks);
+		if (_syncer->m_asking == Asking::Blocks)
+			for (auto j: peers())
+				if (j->cap<EthereumPeer>().get() != _syncer && j->cap<EthereumPeer>()->m_asking == Asking::Nothing)
+					j->cap<EthereumPeer>()->transition(Asking::Blocks);
 	}
 	else
 	{
@@ -115,7 +117,7 @@ void EthereumHost::noteDoneBlocks(EthereumPeer* _who, bool _clemency)
 		_who->addRating(m_man.chain().size() / 100);
 		m_man.reset();
 	}
-	if (_who->isSyncing())
+	else if (_who->isSyncing())
 	{
 		if (_clemency)
 			clog(NetNote) << "Chain download failed. Aborted while incomplete.";
diff --git a/libethereum/EthereumHost.h b/libethereum/EthereumHost.h
index 2ce5b9971..12ce28f23 100644
--- a/libethereum/EthereumHost.h
+++ b/libethereum/EthereumHost.h
@@ -101,7 +101,7 @@ private:
 	virtual void onStarting() { startWorking(); }
 	virtual void onStopping() { stopWorking(); }
 
-	void updateSyncer(EthereumPeer* _ignore);
+	void changeSyncer(EthereumPeer* _ignore);
 
 	BlockChain const& m_chain;
 	TransactionQueue& m_tq;					///< Maintains a list of incoming transactions not yet in a block on the blockchain.
diff --git a/libethereum/EthereumPeer.cpp b/libethereum/EthereumPeer.cpp
index c80912c30..45e850de6 100644
--- a/libethereum/EthereumPeer.cpp
+++ b/libethereum/EthereumPeer.cpp
@@ -105,7 +105,7 @@ void EthereumPeer::transition(Asking _a, bool _force)
 
 			m_syncingLatestHash = m_latestHash;
 			m_syncingTotalDifficulty = m_totalDifficulty;
-			m_latestHash = h256();
+			resetNeedsSyncing();
 
 			setAsking(_a, true);
 			s.appendList(3) << GetBlockHashesPacket << m_syncingLatestHash << c_maxHashesAsk;
@@ -134,15 +134,14 @@ void EthereumPeer::transition(Asking _a, bool _force)
 			{
 				clog(NetNote) << "Difficulty of hashchain HIGHER. Grabbing" << m_syncingNeededBlocks.size() << "blocks [latest now" << m_syncingLatestHash.abridged() << ", was" << host()->m_latestBlockSent.abridged() << "]";
 
-				m_syncingLatestHash = h256();
-
 				host()->m_man.resetToChain(m_syncingNeededBlocks);
 				host()->m_latestBlockSent = m_syncingLatestHash;
+
 			}
 			else
 			{
 				clog(NetNote) << "Difficulty of hashchain not HIGHER. Ignoring.";
-				m_latestHash = h256();
+				m_syncingLatestHash = h256();
 				setAsking(Asking::Nothing, false);
 				return;
 			}
@@ -151,7 +150,7 @@ void EthereumPeer::transition(Asking _a, bool _force)
 		if (m_asking == Asking::Nothing || m_asking == Asking::Hashes || m_asking == Asking::Blocks)
 		{
 			// Looks like it's the best yet for total difficulty. Set to download.
-			setAsking(Asking::Blocks, true);
+			setAsking(Asking::Blocks, true);		// will kick off other peers to help if available.
 			auto blocks = m_sub.nextFetch(c_maxBlocksAsk);
 			if (blocks.size())
 			{
@@ -202,9 +201,12 @@ void EthereumPeer::transition(Asking _a, bool _force)
 
 void EthereumPeer::setAsking(Asking _a, bool _isSyncing)
 {
+	bool changedAsking = (m_asking != _a);
 	m_asking = _a;
-	if (_isSyncing != (host()->m_syncer == this))
-		host()->updateSyncer(_isSyncing ? this : nullptr);
+
+	if (_isSyncing != (host()->m_syncer == this) || (_isSyncing && changedAsking))
+		host()->changeSyncer(_isSyncing ? this : nullptr);
+
 	if (!_isSyncing)
 	{
 		m_syncingLatestHash = h256();
@@ -221,7 +223,10 @@ void EthereumPeer::setNeedsSyncing(h256 _latestHash, u256 _td)
 	m_latestHash = _latestHash;
 	m_totalDifficulty = _td;
 
-	host()->noteNeedsSyncing(this);
+	if (m_latestHash)
+		host()->noteNeedsSyncing(this);
+
+	session()->addNote("sync", string(isSyncing() ? "ongoing" : "holding") + (needsSyncing() ? " & needed" : ""));
 }
 
 bool EthereumPeer::isSyncing() const
@@ -269,7 +274,7 @@ void EthereumPeer::attemptSync()
 	if (td >= m_totalDifficulty)
 	{
 		clogS(NetAllDetail) << "No. Our chain is better.";
-		m_latestHash = h256();
+		resetNeedsSyncing();
 		transition(Asking::Nothing);
 	}
 	else
@@ -287,6 +292,8 @@ bool EthereumPeer::interpret(RLP const& _r)
 	{
 		m_protocolVersion = _r[1].toInt<unsigned>();
 		m_networkId = _r[2].toInt<u256>();
+
+		// a bit dirty as we're misusing these to communicate the values to transition, but harmless.
 		m_totalDifficulty = _r[3].toInt<u256>();
 		m_latestHash = _r[4].toHash<h256>();
 		auto genesisHash = _r[5].toHash<h256>();
diff --git a/libethereum/EthereumPeer.h b/libethereum/EthereumPeer.h
index 3a625f369..00788d019 100644
--- a/libethereum/EthereumPeer.h
+++ b/libethereum/EthereumPeer.h
@@ -82,6 +82,7 @@ private:
 
 	/// Update our syncing requirements state.
 	void setNeedsSyncing(h256 _latestHash, u256 _td);
+	void resetNeedsSyncing() { setNeedsSyncing(h256(), 0); }
 
 	/// Do we presently need syncing with this peer?
 	bool needsSyncing() const { return !!m_latestHash; }