Allow block announcements with headers

This replaces using inv messages to announce new blocks, when a peer requests
(via the new "sendheaders" message) that blocks be announced with headers
instead of inv's.

Since headers-first was introduced, peers send getheaders messages in response
to an inv, which requires generating a block locator that is large compared to
the size of the header being requested, and requires an extra round-trip before
a reorg can be relayed.  Save time by tracking headers that a peer is likely to
know about, and send a headers chain that would connect to a peer's known
headers, unless the chain would be too big, in which case we revert to sending
an inv instead.

Based off of @sipa's commit to announce all blocks in a reorg via inv,
which has been squashed into this commit.

Rebased-by: Pieter Wuille

1 files changed, 4 insertions, 1 deletions

diff --git a/src/version.h b/src/version.h
index 6cdddf9255..f7cf18d0b6 100644
--- a/src/version.h
+++ b/src/version.h
@@ -9,7 +9,7 @@
  * network protocol versioning
  */
 
-static const int PROTOCOL_VERSION = 70011;
+static const int PROTOCOL_VERSION = 70012;
 
 //! initial proto version, to be increased after version/verack negotiation
 static const int INIT_PROTO_VERSION = 209;
@@ -37,4 +37,7 @@ static const int MEMPOOL_GD_VERSION = 60002;
 //! "filter*" commands are disabled without NODE_BLOOM after and including this version
 static const int NO_BLOOM_VERSION = 70011;
 
+//! "sendheaders" command and announcing blocks with headers starts with this version
+static const int SENDHEADERS_VERSION = 70012;
+
 #endif // BITCOIN_VERSION_H