From b02ddbedcba4f9d86b1aabeb71fe18ec03f9a41a Mon Sep 17 00:00:00 2001
From: Matt Corallo <git@bluematt.me>
Date: Sat, 18 Aug 2012 23:45:19 -0400
Subject: [PATCH] Relay CMerkleBlocks when asked for MSG_FILTERED_BLOCK

---
 src/main.cpp     | 26 ++++++++++++++++++++++++--
 src/protocol.cpp |  1 +
 src/protocol.h   |  3 +++
 3 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/src/main.cpp b/src/main.cpp
index bd5b2408..abb0174e 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -3068,7 +3068,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv)
             if (fDebugNet || (vInv.size() == 1))
                 printf("received getdata for: %s\n", inv.ToString().c_str());
 
-            if (inv.type == MSG_BLOCK)
+            if (inv.type == MSG_BLOCK || inv.type == MSG_FILTERED_BLOCK)
             {
                 // Send block from disk
                 map<uint256, CBlockIndex*>::iterator mi = mapBlockIndex.find(inv.hash);
@@ -3076,7 +3076,29 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv)
                 {
                     CBlock block;
                     block.ReadFromDisk((*mi).second);
-                    pfrom->PushMessage("block", block);
+                    if (inv.type == MSG_BLOCK)
+                        pfrom->PushMessage("block", block);
+                    else // MSG_FILTERED_BLOCK)
+                    {
+                        LOCK(pfrom->cs_filter);
+                        if (pfrom->pfilter)
+                        {
+                            CMerkleBlock merkleBlock(block, *pfrom->pfilter);
+                            typedef boost::tuple<unsigned int, uint256, std::vector<uint256> > TupleType;
+                            // CMerkleBlock just contains hashes, so also push any transactions in the block the client did not see 
+                            // This avoids hurting performance by pointlessly requiring a round-trip
+                            // Note that there is currently no way for a node to request any single transactions we didnt send here -
+                            // they must either disconnect and retry or request the full block.
+                            // Thus, the protocol spec specified allows for us to provide duplicate txn here,
+                            // however we MUST always provide at least what the remote peer needs
+                            BOOST_FOREACH(TupleType& tuple, merkleBlock.vtx)
+                                if (!pfrom->setInventoryKnown.count(CInv(MSG_TX, get<1>(tuple))))
+                                    pfrom->PushMessage("tx", block.vtx[get<0>(tuple)]);
+                            pfrom->PushMessage("merkleblock", merkleBlock);
+                        }
+                        // else
+                            // no response
+                    }
 
                     // Trigger them to send a getblocks request for the next batch of inventory
                     if (inv.hash == pfrom->hashContinue)
diff --git a/src/protocol.cpp b/src/protocol.cpp
index 23969e5b..7b42f527 100644
--- a/src/protocol.cpp
+++ b/src/protocol.cpp
@@ -17,6 +17,7 @@ static const char* ppszTypeName[] =
     "ERROR",
     "tx",
     "block",
+    "filtered block"
 };
 
 CMessageHeader::CMessageHeader()
diff --git a/src/protocol.h b/src/protocol.h
index 96fd197e..f5c16205 100644
--- a/src/protocol.h
+++ b/src/protocol.h
@@ -138,6 +138,9 @@ enum
 {
     MSG_TX = 1,
     MSG_BLOCK,
+    // Nodes may always request a MSG_FILTERED_BLOCK in a getdata, however,
+    // MSG_FILTERED_BLOCK should not appear in any invs except as a part of getdata.
+    MSG_FILTERED_BLOCK,
 };
 
 #endif // __INCLUDED_PROTOCOL_H__