Reduce getheaders spam by serializing getheader requests per peer

Introduces a counter for getheader requests that have been sent to
a peer but are pending response, reducing the number of parallel
requests a node pushes out to its peers when needing to sync large
amounts of headers. All getheader requests are serialized during
initial sync, except when a non-connecting header is received,
allowing the node to resolve issues with peers sending faulty
blocks using the DoS mechanism, and when we get an inv for a block
that we do not know, because it's possible we're only connected to
legacy nodes that do not implement header announcement properly.

1 files changed, 1 insertions, 0 deletions

diff --git a/src/net.cpp b/src/net.cpp
index e89f1b11d..2117c59fd 100644
--- a/src/net.cpp
+++ b/src/net.cpp
@@ -2704,6 +2704,7 @@ CNode::CNode(NodeId idIn, ServiceFlags nLocalServicesIn, int nMyStartingHeightIn
     fPauseRecv = false;
     fPauseSend = false;
     nProcessQueueSize = 0;
+    nPendingHeaderRequests = 0;
 
     BOOST_FOREACH(const std::string &msg, getAllNetMessageTypes())
         mapRecvBytesPerMsgCmd[msg] = 0;