net: Signal NODE_COMPACT_FILTERS if the block filter index is on.

The node will enable the NODE_COMPACT_FILTERS service flag once the
block filter index catches up to the active chain.

src/index/base.h

@@ -91,6 +91,10 @@ class BaseIndex : public CValidationInterface
     /// Destructor interrupts sync thread if running and blocks until it exits.
     virtual ~BaseIndex();
 
+    /// Returns whether index has completed the initial sync with the active chain.
+    /// After returning true once, this function will return true on all subsequent calls.
+    bool IsSynced() const { return m_synced; }
+
     /// Blocks the current thread until the index is caught up to the current
     /// state of the block chain. This only blocks if the index has gotten in
     /// sync once and only needs to process blocks in the ValidationInterface

src/init.cpp

@@ -1697,6 +1697,13 @@ bool AppInitMain(NodeContext& node)
         GetBlockFilterIndex(filter_type)->Start();
     }
 
+    bool cfilters_enabled = std::find(g_enabled_filter_types.begin(),
+                                      g_enabled_filter_types.end(),
+                                      BlockFilterType::BASIC) != g_enabled_filter_types.end();
+    if (cfilters_enabled) {
+        nLocalServices = ServiceFlags(nLocalServices | NODE_COMPACT_FILTERS);
+    }
+
     // ********************************************************* Step 9: load wallet
     for (const auto& client : node.chain_clients) {
         if (!client->load()) {

src/net.cpp

@@ -10,10 +10,12 @@
 #include <net.h>
 
 #include <banman.h>
+#include <blockfilter.h>
 #include <chainparams.h>
 #include <clientversion.h>
 #include <consensus/consensus.h>
 #include <crypto/sha256.h>
+#include <index/blockfilterindex.h>
 #include <netbase.h>
 #include <net_permissions.h>
 #include <random.h>
@@ -2670,7 +2672,18 @@ uint64_t CConnman::GetTotalBytesSent()
 
 ServiceFlags CConnman::GetLocalServices() const
 {
-    return nLocalServices;
+    uint64_t local_services = nLocalServices;
+    if (local_services & NODE_COMPACT_FILTERS) {
+        BlockFilterIndex* basic_filter_index = GetBlockFilterIndex(BlockFilterType::BASIC);
+        if (!basic_filter_index) {
+            LogPrintf("WARNING: NODE_COMPACT_FILTERS is signaled, but filter index is not available\n");
+        }
+        if (!basic_filter_index || !basic_filter_index->IsSynced()) {
+            // If block filter index is still syncing, do not advertise the service bit.
+            local_services &= ~NODE_COMPACT_FILTERS;
+        }
+    }
+    return ServiceFlags(local_services);
 }
 
 void CConnman::SetBestHeight(int height)

src/protocol.h

@@ -258,6 +258,9 @@ enum ServiceFlags : uint64_t {
     // NODE_WITNESS indicates that a node can be asked for blocks and transactions including
     // witness data.
     NODE_WITNESS = (1 << 3),
+    // NODE_COMPACT_FILTERS means the node will service basic block filter requests.
+    // See BIP157 and BIP158 for details on how this is implemented.
+    NODE_COMPACT_FILTERS = (1 << 6),
     // 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.