[net] Signal NODE_COMPACT_FILTERS if we're serving compact filters.

If -peerblockfilters is configured, signal the NODE_COMPACT_FILTERS service
bit to indicate that we are able to serve compact block filters, headers
and checkpoints.

src/init.cpp

@@ -996,11 +996,13 @@ bool AppInitParameterInteraction()
         }
     }
 
-    // Basic filters are the only supported filters. The basic filters index must be enabled
-    // to serve compact filters
-    if (gArgs.GetBoolArg("-peerblockfilters", DEFAULT_PEERBLOCKFILTERS) &&
-        g_enabled_filter_types.count(BlockFilterType::BASIC) != 1) {
-        return InitError(_("Cannot set -peerblockfilters without -blockfilterindex."));
+    // Signal NODE_COMPACT_FILTERS if peerblockfilters and basic filters index are both enabled.
+    if (gArgs.GetBoolArg("-peerblockfilters", DEFAULT_PEERBLOCKFILTERS)) {
+        if (g_enabled_filter_types.count(BlockFilterType::BASIC) != 1) {
+            return InitError(_("Cannot set -peerblockfilters without -blockfilterindex."));
+        }
+
+        nLocalServices = ServiceFlags(nLocalServices | NODE_COMPACT_FILTERS);
     }
 
     // if using block pruning, then disallow txindex

src/net_processing.cpp

@@ -2009,7 +2009,7 @@ static bool PrepareBlockFilterRequest(CNode& peer, const CChainParams& chain_par
 {
     const bool supported_filter_type =
         (filter_type == BlockFilterType::BASIC &&
-         gArgs.GetBoolArg("-peerblockfilters", DEFAULT_PEERBLOCKFILTERS));
+         (peer.GetLocalServices() & NODE_COMPACT_FILTERS));
     if (!supported_filter_type) {
         LogPrint(BCLog::NET, "peer %d requested unsupported block filter type: %d\n",
                  peer.GetId(), static_cast<uint8_t>(filter_type));

src/protocol.cpp

@@ -213,6 +213,7 @@ static std::string serviceFlagToStr(size_t bit)
     case NODE_GETUTXO:         return "GETUTXO";
     case NODE_BLOOM:           return "BLOOM";
     case NODE_WITNESS:         return "WITNESS";
+    case NODE_COMPACT_FILTERS: return "COMPACT_FILTERS";
     case NODE_NETWORK_LIMITED: return "NETWORK_LIMITED";
     // Not using default, so we get warned when a case is missing
     }

src/protocol.h

@@ -285,6 +285,9 @@ 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.