[init] Add -peerblockfilters option

When a node is configured with --blockfilterindex=basic and
-peerblockfilters it can serve compact block filters to its peers.

This commit adds the configuration option handling. Future commits
add compact block serving and service bits signaling.

src/init.cpp

@@ -446,6 +446,7 @@ void SetupServerArgs(NodeContext& node)
     gArgs.AddArg("-onion=<ip:port>", "Use separate SOCKS5 proxy to reach peers via Tor hidden services, set -noonion to disable (default: -proxy)", ArgsManager::ALLOW_ANY, OptionsCategory::CONNECTION);
     gArgs.AddArg("-onlynet=<net>", "Make outgoing connections only through network <net> (ipv4, ipv6 or onion). Incoming connections are not affected by this option. This option can be specified multiple times to allow multiple networks.", ArgsManager::ALLOW_ANY, OptionsCategory::CONNECTION);
     gArgs.AddArg("-peerbloomfilters", strprintf("Support filtering of blocks and transaction with bloom filters (default: %u)", DEFAULT_PEERBLOOMFILTERS), ArgsManager::ALLOW_ANY, OptionsCategory::CONNECTION);
+    gArgs.AddArg("-peerblockfilters", strprintf("Serve compact block filters to peers per BIP 157 (default: %u)", DEFAULT_PEERBLOCKFILTERS), ArgsManager::ALLOW_ANY, OptionsCategory::CONNECTION);
     gArgs.AddArg("-permitbaremultisig", strprintf("Relay non-P2SH multisig (default: %u)", DEFAULT_PERMIT_BAREMULTISIG), ArgsManager::ALLOW_ANY, OptionsCategory::CONNECTION);
     gArgs.AddArg("-port=<port>", strprintf("Listen for connections on <port> (default: %u, testnet: %u, regtest: %u)", defaultChainParams->GetDefaultPort(), testnetChainParams->GetDefaultPort(), regtestChainParams->GetDefaultPort()), ArgsManager::ALLOW_ANY | ArgsManager::NETWORK_ONLY, OptionsCategory::CONNECTION);
     gArgs.AddArg("-proxy=<ip:port>", "Connect through SOCKS5 proxy, set -noproxy to disable (default: disabled)", ArgsManager::ALLOW_ANY, OptionsCategory::CONNECTION);
@@ -993,6 +994,13 @@ 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."));
+    }
+
     // if using block pruning, then disallow txindex
     if (gArgs.GetArg("-prune", 0)) {
         if (gArgs.GetBoolArg("-txindex", DEFAULT_TXINDEX))

src/net_processing.h

@@ -21,6 +21,7 @@ static const unsigned int DEFAULT_MAX_ORPHAN_TRANSACTIONS = 100;
 /** Default number of orphan+recently-replaced txn to keep around for block reconstruction */
 static const unsigned int DEFAULT_BLOCK_RECONSTRUCTION_EXTRA_TXN = 100;
 static const bool DEFAULT_PEERBLOOMFILTERS = false;
+static const bool DEFAULT_PEERBLOCKFILTERS = false;
 
 class PeerLogicValidation final : public CValidationInterface, public NetEventsInterface {
 private: