Merge #11740: Implement BIP159 NODE_NETWORK_LIMITED (pruned peers) *signaling only*

de74c62 [Doc] Update bip.md, add support for BIP 159 (Jonas Schnelli)
e054d0e [QA] Add node_network_limited test (Jonas Schnelli)
bd09416 Avoid leaking the prune height through getdata (fingerprinting countermeasure) (Jonas Schnelli)
27df193 Always set NODE_NETWORK_LIMITED bit (Jonas Schnelli)
7caba38 Add NODE_NETWORK_LIMITED flags and min block amount constants (Jonas Schnelli)

Pull request description:

  Extracted from #10387.
  Does implement BIP159, but only the signalling part. No connections are made to NODE_NETWORK_LIMITED in this PR.

  The address relay and connection work (the more complicated part) can then be separated (probably in #10387).

Tree-SHA512: e3218eb4789a9320b0f42dc10f62d30c13c49bdef00443fbe653bee22933477adcfc1cf8f6a95269324560b5721203ed41f3c5e2dd8a98ec2791f6a9d8346b1a

4 files changed, 19 insertions, 4 deletions

diff --git a/src/init.cpp b/src/init.cpp
index 871a585267..67e01c9ba9 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -816,7 +816,7 @@ namespace { // Variables internal to initialization process only
 int nMaxConnections;
 int nUserMaxConnections;
 int nFD;
-ServiceFlags nLocalServices = NODE_NETWORK;
+ServiceFlags nLocalServices = ServiceFlags(NODE_NETWORK | NODE_NETWORK_LIMITED);
 
 } // namespace
 
diff --git a/src/net_processing.cpp b/src/net_processing.cpp
index 442cd00c9b..85e6d9c73d 100644
--- a/src/net_processing.cpp
+++ b/src/net_processing.cpp
@@ -1091,6 +1091,16 @@ void static ProcessGetData(CNode* pfrom, const Consensus::Params& consensusParam
                     pfrom->fDisconnect = true;
                     send = false;
                 }
+                // Avoid leaking prune-height by never sending blocks below the NODE_NETWORK_LIMITED threshold
+                if (send && !pfrom->fWhitelisted && (
+                        (((pfrom->GetLocalServices() & NODE_NETWORK_LIMITED) == NODE_NETWORK_LIMITED) && ((pfrom->GetLocalServices() & NODE_NETWORK) != NODE_NETWORK) && (chainActive.Tip()->nHeight - mi->second->nHeight > (int)NODE_NETWORK_LIMITED_MIN_BLOCKS + 2 /* add two blocks buffer extension for possible races */) )
+                   )) {
+                    LogPrint(BCLog::NET, "Ignore block request below NODE_NETWORK_LIMITED threshold from peer=%d\n", pfrom->GetId());
+
+                    //disconnect node and prevent it from stalling (would otherwise wait for the missing block)
+                    pfrom->fDisconnect = true;
+                    send = false;
+                }
                 // Pruned nodes may have deleted the block, so check whether
                 // it's available before trying to send.
                 if (send && (mi->second->nStatus & BLOCK_HAVE_DATA))
diff --git a/src/protocol.h b/src/protocol.h
index bc31434515..cf1d40db77 100644
--- a/src/protocol.h
+++ b/src/protocol.h
@@ -246,9 +246,8 @@ const std::vector<std::string> &getAllNetMessageTypes();
 enum ServiceFlags : uint64_t {
     // Nothing
     NODE_NONE = 0,
-    // NODE_NETWORK means that the node is capable of serving the block chain. It is currently
-    // set by all Bitcoin Core nodes, and is unset by SPV clients or other peers that just want
-    // network services but don't provide them.
+    // NODE_NETWORK means that the node is capable of serving the complete block chain. It is currently
+    // set by all Bitcoin Core non pruned nodes, and is unset by SPV clients or other light clients.
     NODE_NETWORK = (1 << 0),
     // NODE_GETUTXO means the node is capable of responding to the getutxo protocol request.
     // Bitcoin Core does not support this but a patch set called Bitcoin XT does.
@@ -264,6 +263,10 @@ enum ServiceFlags : uint64_t {
     // NODE_XTHIN means the node supports Xtreme Thinblocks
     // If this is turned off then the node will not service nor make xthin requests
     NODE_XTHIN = (1 << 4),
+    // NODE_NETWORK_LIMITED means the same as NODE_NETWORK with the limitation of only
+    // serving the last 288 (2 day) blocks
+    // See BIP159 for details on how this is implemented.
+    NODE_NETWORK_LIMITED = (1 << 10),
 
     // Bits 24-31 are reserved for temporary experiments. Just pick a bit that
     // isn't getting used, or one not being used much, and notify the
diff --git a/src/validation.h b/src/validation.h
index ec17d0d92d..49bff9f30c 100644
--- a/src/validation.h
+++ b/src/validation.h
@@ -203,6 +203,8 @@ extern bool fPruneMode;
 extern uint64_t nPruneTarget;
 /** Block files containing a block-height within MIN_BLOCKS_TO_KEEP of chainActive.Tip() will not be pruned. */
 static const unsigned int MIN_BLOCKS_TO_KEEP = 288;
+/** Minimum blocks required to signal NODE_NETWORK_LIMITED */
+static const unsigned int NODE_NETWORK_LIMITED_MIN_BLOCKS = 288;
 
 static const signed int DEFAULT_CHECKBLOCKS = 6;
 static const unsigned int DEFAULT_CHECKLEVEL = 3;