Fixed race condition with mainchain prefetch on startup, Version-gated checkpoint exchange for backward compatibility, Version bump to v4.13 with protocol 1.5, Added CAP exchange protocol (CHECKPOINT_REQUEST/CHECKPOINT_RESPONSE)

src/p2p_server.cpp

@@ -2661,9 +2661,11 @@ void P2PServer::P2PClient::on_after_handshake(uint8_t* &p)
 	}
 
 	// Request checkpoints from peer (CAP exchange)
-	// TODO: Only send to peers with compatible protocol version to avoid disconnects
-	// LOGINFO(5, "sending CHECKPOINT_REQUEST to " << static_cast<char*>(m_addrString));
-	// *(p++) = static_cast<uint8_t>(MessageId::CHECKPOINT_REQUEST);
+	// Only send to peers with protocol 1.5+ to avoid disconnects with older nodes
+	if (m_protocolVersion >= PROTOCOL_VERSION_1_5) {
+		LOGINFO(5, "sending CHECKPOINT_REQUEST to " << static_cast<char*>(m_addrString));
+		*(p++) = static_cast<uint8_t>(MessageId::CHECKPOINT_REQUEST);
+	}
 }
 
 bool P2PServer::P2PClient::on_listen_port(const uint8_t* buf)

src/p2p_server.h

@@ -43,8 +43,9 @@ static constexpr uint32_t PROTOCOL_VERSION_1_1 = 0x00010001UL;
 static constexpr uint32_t PROTOCOL_VERSION_1_2 = 0x00010002UL;
 static constexpr uint32_t PROTOCOL_VERSION_1_3 = 0x00010003UL;
 static constexpr uint32_t PROTOCOL_VERSION_1_4 = 0x00010004UL;
+static constexpr uint32_t PROTOCOL_VERSION_1_5 = 0x00010005UL;
 
-static constexpr uint32_t SUPPORTED_PROTOCOL_VERSION = PROTOCOL_VERSION_1_4;
+static constexpr uint32_t SUPPORTED_PROTOCOL_VERSION = PROTOCOL_VERSION_1_5;
 
 class P2PServer : public TCPServer
 {

src/p2pool.cpp

@@ -1461,6 +1461,9 @@ void p2pool::download_block_headers4(uint64_t start_height, uint64_t current_hei
 					}
 #endif
 
+					// Pre-fetch recent mainchain blocks to populate cache before sidechain sync
+					prefetch_mainchain_blocks(current_height);
+
 					api_update_network_stats();
 					get_miner_data();
 
@@ -1949,6 +1952,46 @@ uint32_t p2pool::parse_block_headers_range(const char* data, size_t size)
 	return num_headers_parsed;
 }
 
+void p2pool::prefetch_mainchain_blocks(uint64_t current_height)
+{
+	// Pre-fetch recent mainchain blocks to populate cache before sidechain sync
+	// This prevents the race condition where cached sidechain blocks need mainchain data
+	// that hasn't arrived via ZMQ yet
+	constexpr uint64_t PREFETCH_DEPTH = 300;
+
+	if (current_height < PREFETCH_DEPTH) {
+		return;
+	}
+
+	const uint64_t start_height = current_height - PREFETCH_DEPTH;
+
+	LOGINFO(1, "Pre-fetching mainchain blocks " << start_height << " - " << current_height << " to populate cache");
+
+	char buf[log::Stream::BUF_SIZE + 1] = {};
+	log::Stream s(buf);
+
+	const Params::Host& host = current_host();
+
+	s.m_pos = 0;
+	s << "{\"jsonrpc\":\"2.0\",\"id\":\"0\",\"method\":\"get_block_headers_range\",\"params\":{\"start_height\":" << start_height << ",\"end_height\":" << current_height << "}}" << '\0';
+
+	JSONRPCRequest::call(host.m_address, host.m_rpcPort, buf, host.m_rpcLogin, m_params->m_socks5Proxy, host.m_rpcSSL, host.m_rpcSSL_Fingerprint,
+		[this, start_height, current_height](const char* data, size_t size, double) {
+			const uint32_t parsed = parse_block_headers_range(data, size);
+			if (parsed > 0) {
+				LOGINFO(1, "Pre-fetched " << parsed << " mainchain blocks into cache");
+			} else {
+				LOGWARN(1, "Failed to pre-fetch mainchain blocks, will rely on ZMQ");
+			}
+		},
+		[this](const char* data, size_t size, double) {
+			if (size > 0) {
+				LOGWARN(1, "Failed to pre-fetch mainchain blocks: " << log::const_buf(data, size));
+			}
+		}
+	);
+}
+
 void p2pool::api_update_network_stats()
 {
 	if (!m_api || m_stopped) {

src/p2pool.h

@@ -119,6 +119,7 @@ public:
 	void download_block_headers2(uint64_t current_height);
 	void download_block_headers3(uint64_t start_height, uint64_t current_height);
 	void download_block_headers4(uint64_t start_height, uint64_t current_height);
+	void prefetch_mainchain_blocks(uint64_t current_height);
 
 	bool chainmain_get_by_hash(const hash& id, ChainMain& data) const;
 

src/util.h

@@ -35,7 +35,7 @@
 namespace p2pool {
 
 #define P2POOL_VERSION_MAJOR 4
-#define P2POOL_VERSION_MINOR 12
+#define P2POOL_VERSION_MINOR 13
 #define P2POOL_VERSION_PATCH 0
 
 constexpr uint32_t P2POOL_VERSION = (P2POOL_VERSION_MAJOR << 16) | (P2POOL_VERSION_MINOR << 8) | P2POOL_VERSION_PATCH;