net: Add PCP and NATPMP implementation

Add a RFC 6886 NATPMP and RFC 6887 Port Control Protocol (PCP)
implementation, to replace libnatpmp.

3 files changed, 593 insertions, 0 deletions

diff --git a/src/util/CMakeLists.txt b/src/util/CMakeLists.txt
index d65e634c57..f4b9b47d10 100644
--- a/src/util/CMakeLists.txt
+++ b/src/util/CMakeLists.txt
@@ -16,6 +16,7 @@ add_library(bitcoin_util STATIC EXCLUDE_FROM_ALL
   hasher.cpp
   moneystr.cpp
   netif.cpp
+  pcp.cpp
   rbf.cpp
   readwritefile.cpp
   serfloat.cpp
diff --git a/src/util/pcp.cpp b/src/util/pcp.cpp
new file mode 100644
index 0000000000..b02568db35
--- /dev/null
+++ b/src/util/pcp.cpp
@@ -0,0 +1,524 @@
+// Copyright (c) 2024 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or https://www.opensource.org/licenses/mit-license.php.
+
+#include <util/pcp.h>
+
+#include <crypto/common.h>
+#include <logging.h>
+#include <netaddress.h>
+#include <netbase.h>
+#include <random.h>
+#include <span.h>
+#include <util/check.h>
+#include <util/netif.h>
+#include <util/readwritefile.h>
+#include <util/sock.h>
+#include <util/strencodings.h>
+
+namespace {
+
+// RFC6886 NAT-PMP and RFC6887 Port Control Protocol (PCP) implementation.
+// NAT-PMP and PCP use network byte order (big-endian).
+
+// NAT-PMP (v0) protocol constants.
+//! NAT-PMP uses a fixed server port number (RFC6887 section 1.1).
+constexpr uint16_t NATPMP_SERVER_PORT = 5351;
+//! Version byte for NATPMP (RFC6886 1.1)
+constexpr uint8_t NATPMP_VERSION = 0;
+//! Request opcode base (RFC6886 3).
+constexpr uint8_t NATPMP_REQUEST = 0x00;
+//! Response opcode base (RFC6886 3).
+constexpr uint8_t NATPMP_RESPONSE = 0x80;
+//! Get external address (RFC6886 3.2)
+constexpr uint8_t NATPMP_OP_GETEXTERNAL = 0x00;
+//! Map TCP port (RFC6886 3.3)
+constexpr uint8_t NATPMP_OP_MAP_TCP = 0x02;
+//! Shared request header size in bytes.
+constexpr size_t NATPMP_REQUEST_HDR_SIZE = 2;
+//! Shared response header (minimum) size in bytes.
+constexpr size_t NATPMP_RESPONSE_HDR_SIZE = 8;
+//! GETEXTERNAL request size in bytes, including header (RFC6886 3.2).
+constexpr size_t NATPMP_GETEXTERNAL_REQUEST_SIZE = NATPMP_REQUEST_HDR_SIZE + 0;
+//! GETEXTERNAL response size in bytes, including header (RFC6886 3.2).
+constexpr size_t NATPMP_GETEXTERNAL_RESPONSE_SIZE = NATPMP_RESPONSE_HDR_SIZE + 4;
+//! MAP request size in bytes, including header (RFC6886 3.3).
+constexpr size_t NATPMP_MAP_REQUEST_SIZE = NATPMP_REQUEST_HDR_SIZE + 10;
+//! MAP response size in bytes, including header (RFC6886 3.3).
+constexpr size_t NATPMP_MAP_RESPONSE_SIZE = NATPMP_RESPONSE_HDR_SIZE + 8;
+
+// Shared header offsets (RFC6886 3.2, 3.3), relative to start of packet.
+//!  Offset of version field in packets.
+constexpr size_t NATPMP_HDR_VERSION_OFS = 0;
+//!  Offset of opcode field in packets
+constexpr size_t NATPMP_HDR_OP_OFS = 1;
+//!  Offset of result code in packets. Result codes are 16 bit in NAT-PMP instead of 8 bit in PCP.
+constexpr size_t NATPMP_RESPONSE_HDR_RESULT_OFS = 2;
+
+// GETEXTERNAL response offsets (RFC6886 3.2), relative to start of packet.
+//!  Returned external address
+constexpr size_t NATPMP_GETEXTERNAL_RESPONSE_IP_OFS = 8;
+
+// MAP request offsets (RFC6886 3.3), relative to start of packet.
+//!  Internal port to be mapped.
+constexpr size_t NATPMP_MAP_REQUEST_INTERNAL_PORT_OFS = 4;
+//!  Suggested external port for mapping.
+constexpr size_t NATPMP_MAP_REQUEST_EXTERNAL_PORT_OFS = 6;
+//!  Requested port mapping lifetime in seconds.
+constexpr size_t NATPMP_MAP_REQUEST_LIFETIME_OFS = 8;
+
+// MAP response offsets (RFC6886 3.3), relative to start of packet.
+//!  Internal port for mapping (will match internal port of request).
+constexpr size_t NATPMP_MAP_RESPONSE_INTERNAL_PORT_OFS = 8;
+//!  External port for mapping.
+constexpr size_t NATPMP_MAP_RESPONSE_EXTERNAL_PORT_OFS = 10;
+//!  Created port mapping lifetime in seconds.
+constexpr size_t NATPMP_MAP_RESPONSE_LIFETIME_OFS = 12;
+
+// Relevant NETPMP result codes (RFC6886 3.5).
+//! Result code representing success status.
+constexpr uint8_t NATPMP_RESULT_SUCCESS = 0;
+//! Result code representing unsupported version.
+constexpr uint8_t NATPMP_RESULT_UNSUPP_VERSION = 1;
+//! Result code representing lack of resources.
+constexpr uint8_t NATPMP_RESULT_NO_RESOURCES = 4;
+
+//! Mapping of NATPMP result code to string (RFC6886 3.5). Result codes <=2 match PCP.
+const std::map<uint8_t, std::string> NATPMP_RESULT_STR{
+    {0,  "SUCCESS"},
+    {1,  "UNSUPP_VERSION"},
+    {2,  "NOT_AUTHORIZED"},
+    {3,  "NETWORK_FAILURE"},
+    {4,  "NO_RESOURCES"},
+    {5,  "UNSUPP_OPCODE"},
+};
+
+// PCP (v2) protocol constants.
+//! Maximum packet size in bytes (RFC6887 section 7).
+constexpr size_t PCP_MAX_SIZE = 1100;
+//! PCP uses a fixed server port number (RFC6887 section 19.1). Shared with NAT-PMP.
+constexpr uint16_t PCP_SERVER_PORT = NATPMP_SERVER_PORT;
+//! Version byte. 0 is NAT-PMP (RFC6886), 1 is forbidden, 2 for PCP (RFC6887).
+constexpr uint8_t PCP_VERSION = 2;
+//! PCP Request Header. See RFC6887 section 7.1. Shared with NAT-PMP.
+constexpr uint8_t PCP_REQUEST = NATPMP_REQUEST; // R = 0
+//! PCP Response Header. See RFC6887 section 7.2. Shared with NAT-PMP.
+constexpr uint8_t PCP_RESPONSE = NATPMP_RESPONSE; // R = 1
+//! Map opcode. See RFC6887 section 19.2
+constexpr uint8_t PCP_OP_MAP = 0x01;
+//! TCP protocol number (IANA).
+constexpr uint16_t PCP_PROTOCOL_TCP = 6;
+//! Request and response header size in bytes (RFC6887 section 7.1).
+constexpr size_t PCP_HDR_SIZE = 24;
+//! Map request and response size in bytes (RFC6887 section 11.1).
+constexpr size_t PCP_MAP_SIZE = 36;
+
+// Header offsets shared between request and responses (RFC6887 7.1, 7.2), relative to start of packet.
+//!  Version field (1 byte).
+constexpr size_t PCP_HDR_VERSION_OFS = NATPMP_HDR_VERSION_OFS;
+//!  Opcode field (1 byte).
+constexpr size_t PCP_HDR_OP_OFS = NATPMP_HDR_OP_OFS;
+//!  Requested lifetime (request), granted lifetime (response) (4 bytes).
+constexpr size_t PCP_HDR_LIFETIME_OFS = 4;
+
+// Request header offsets (RFC6887 7.1), relative to start of packet.
+//!  PCP client's IP address (16 bytes).
+constexpr size_t PCP_REQUEST_HDR_IP_OFS = 8;
+
+// Response header offsets (RFC6887 7.2), relative to start of packet.
+//!  Result code (1 byte).
+constexpr size_t PCP_RESPONSE_HDR_RESULT_OFS = 3;
+
+// MAP request/response offsets (RFC6887 11.1), relative to start of opcode-specific data.
+//!  Mapping nonce (12 bytes).
+constexpr size_t PCP_MAP_NONCE_OFS = 0;
+//!  Protocol (1 byte).
+constexpr size_t PCP_MAP_PROTOCOL_OFS = 12;
+//!  Internal port for mapping (2 bytes).
+constexpr size_t PCP_MAP_INTERNAL_PORT_OFS = 16;
+//!  Suggested external port (request), assigned external port (response) (2 bytes).
+constexpr size_t PCP_MAP_EXTERNAL_PORT_OFS = 18;
+//!  Suggested external IP (request), assigned external IP (response) (16 bytes).
+constexpr size_t PCP_MAP_EXTERNAL_IP_OFS = 20;
+
+//! Result code representing success (RFC6887 7.4), shared with NAT-PMP.
+constexpr uint8_t PCP_RESULT_SUCCESS = NATPMP_RESULT_SUCCESS;
+//! Result code representing lack of resources (RFC6887 7.4).
+constexpr uint8_t PCP_RESULT_NO_RESOURCES = 8;
+
+//! Mapping of PCP result code to string (RFC6887 7.4). Result codes <=2 match NAT-PMP.
+const std::map<uint8_t, std::string> PCP_RESULT_STR{
+    {0,  "SUCCESS"},
+    {1,  "UNSUPP_VERSION"},
+    {2,  "NOT_AUTHORIZED"},
+    {3,  "MALFORMED_REQUEST"},
+    {4,  "UNSUPP_OPCODE"},
+    {5,  "UNSUPP_OPTION"},
+    {6,  "MALFORMED_OPTION"},
+    {7,  "NETWORK_FAILURE"},
+    {8,  "NO_RESOURCES"},
+    {9,  "UNSUPP_PROTOCOL"},
+    {10, "USER_EX_QUOTA"},
+    {11, "CANNOT_PROVIDE_EXTERNAL"},
+    {12, "ADDRESS_MISMATCH"},
+    {13, "EXCESSIVE_REMOTE_PEER"},
+};
+
+//! Return human-readable string from NATPMP result code.
+std::string NATPMPResultString(uint8_t result_code)
+{
+    auto result_i = NATPMP_RESULT_STR.find(result_code);
+    return strprintf("%s (code %d)", result_i == NATPMP_RESULT_STR.end() ? "(unknown)" : result_i->second,  result_code);
+}
+
+//! Return human-readable string from PCP result code.
+std::string PCPResultString(uint8_t result_code)
+{
+    auto result_i = PCP_RESULT_STR.find(result_code);
+    return strprintf("%s (code %d)", result_i == PCP_RESULT_STR.end() ? "(unknown)" : result_i->second,  result_code);
+}
+
+//! Wrap address in IPv6 according to RFC6887. wrapped_addr needs to be able to store 16 bytes.
+[[nodiscard]] bool PCPWrapAddress(Span<uint8_t> wrapped_addr, const CNetAddr &addr)
+{
+    Assume(wrapped_addr.size() == ADDR_IPV6_SIZE);
+    if (addr.IsIPv4()) {
+        struct in_addr addr4;
+        if (!addr.GetInAddr(&addr4)) return false;
+        // Section 5: "When the address field holds an IPv4 address, an IPv4-mapped IPv6 address [RFC4291] is used (::ffff:0:0/96)."
+        std::memcpy(wrapped_addr.data(), IPV4_IN_IPV6_PREFIX.data(), IPV4_IN_IPV6_PREFIX.size());
+        std::memcpy(wrapped_addr.data() + IPV4_IN_IPV6_PREFIX.size(), &addr4, ADDR_IPV4_SIZE);
+        return true;
+    } else if (addr.IsIPv6()) {
+        struct in6_addr addr6;
+        if (!addr.GetIn6Addr(&addr6)) return false;
+        std::memcpy(wrapped_addr.data(), &addr6, ADDR_IPV6_SIZE);
+        return true;
+    } else {
+        return false;
+    }
+}
+
+//! Unwrap PCP-encoded address according to RFC6887.
+CNetAddr PCPUnwrapAddress(Span<const uint8_t> wrapped_addr)
+{
+    Assume(wrapped_addr.size() == ADDR_IPV6_SIZE);
+    if (util::HasPrefix(wrapped_addr, IPV4_IN_IPV6_PREFIX)) {
+        struct in_addr addr4;
+        std::memcpy(&addr4, wrapped_addr.data() + IPV4_IN_IPV6_PREFIX.size(), ADDR_IPV4_SIZE);
+        return CNetAddr(addr4);
+    } else {
+        struct in6_addr addr6;
+        std::memcpy(&addr6, wrapped_addr.data(), ADDR_IPV6_SIZE);
+        return CNetAddr(addr6);
+    }
+}
+
+//! PCP or NAT-PMP send-receive loop.
+std::optional<std::vector<uint8_t>> PCPSendRecv(Sock &sock, const std::string &protocol, Span<const uint8_t> request, int num_tries,
+        std::chrono::milliseconds timeout_per_try,
+        std::function<bool(Span<const uint8_t>)> check_packet)
+{
+    using namespace std::chrono;
+    // UDP is a potentially lossy protocol, so we try to send again a few times.
+    uint8_t response[PCP_MAX_SIZE];
+    bool got_response = false;
+    int recvsz = 0;
+    for (int ntry = 0; !got_response && ntry < num_tries; ++ntry) {
+        if (ntry > 0) {
+            LogPrintLevel(BCLog::NET, BCLog::Level::Debug, "%s: Retrying (%d)\n", protocol, ntry);
+        }
+        // Dispatch packet to gateway.
+        if (sock.Send(request.data(), request.size(), 0) != static_cast<ssize_t>(request.size())) {
+            LogPrintLevel(BCLog::NET, BCLog::Level::Warning, "%s: Could not send request: %s\n", protocol, NetworkErrorString(WSAGetLastError()));
+            return std::nullopt; // Network-level error, probably no use retrying.
+        }
+
+        // Wait for response(s) until we get a valid response, a network error, or time out.
+        auto cur_time = time_point_cast<milliseconds>(steady_clock::now());
+        auto deadline = cur_time + timeout_per_try;
+        while ((cur_time = time_point_cast<milliseconds>(steady_clock::now())) < deadline) {
+            Sock::Event occurred = 0;
+            if (!sock.Wait(deadline - cur_time, Sock::RECV, &occurred)) {
+                LogPrintLevel(BCLog::NET, BCLog::Level::Warning, "%s: Could not wait on socket: %s\n", protocol, NetworkErrorString(WSAGetLastError()));
+                return std::nullopt; // Network-level error, probably no use retrying.
+            }
+            if (!occurred) {
+                LogPrintLevel(BCLog::NET, BCLog::Level::Debug, "%s: Timeout\n", protocol);
+                break; // Retry.
+            }
+
+            // Receive response.
+            recvsz = sock.Recv(response, sizeof(response), MSG_DONTWAIT);
+            if (recvsz < 0) {
+                LogPrintLevel(BCLog::NET, BCLog::Level::Warning, "%s: Could not receive response: %s\n", protocol, NetworkErrorString(WSAGetLastError()));
+                return std::nullopt; // Network-level error, probably no use retrying.
+            }
+            LogPrintLevel(BCLog::NET, BCLog::Level::Debug, "%s: Received response of %d bytes: %s\n", protocol, recvsz, HexStr(Span(response, recvsz)));
+
+            if (check_packet(Span<uint8_t>(response, recvsz))) {
+                got_response = true; // Got expected response, break from receive loop as well as from retry loop.
+                break;
+            }
+        }
+    }
+    if (!got_response) {
+        LogPrintLevel(BCLog::NET, BCLog::Level::Debug, "%s: Giving up after %d tries\n", protocol, num_tries);
+        return std::nullopt;
+    }
+    return std::vector<uint8_t>(response, response + recvsz);
+}
+
+}
+
+std::variant<MappingResult, MappingError> NATPMPRequestPortMap(const CNetAddr &gateway, uint16_t port, uint32_t lifetime, int num_tries, std::chrono::milliseconds timeout_per_try)
+{
+    struct sockaddr_storage dest_addr;
+    socklen_t dest_addrlen = sizeof(struct sockaddr_storage);
+
+    LogPrintLevel(BCLog::NET, BCLog::Level::Debug, "natpmp: Requesting port mapping port %d from gateway %s\n", port, gateway.ToStringAddr());
+
+    // Validate gateway, make sure it's IPv4. NAT-PMP does not support IPv6.
+    if (!CService(gateway, PCP_SERVER_PORT).GetSockAddr((struct sockaddr*)&dest_addr, &dest_addrlen)) return MappingError::NETWORK_ERROR;
+    if (dest_addr.ss_family != AF_INET) return MappingError::NETWORK_ERROR;
+
+    // Create IPv4 UDP socket
+    auto sock{CreateSock(AF_INET, SOCK_DGRAM, IPPROTO_UDP)};
+    if (!sock) {
+        LogPrintLevel(BCLog::NET, BCLog::Level::Warning, "natpmp: Could not create UDP socket: %s\n", NetworkErrorString(WSAGetLastError()));
+        return MappingError::NETWORK_ERROR;
+    }
+
+    // Associate UDP socket to gateway.
+    if (sock->Connect((struct sockaddr*)&dest_addr, dest_addrlen) != 0) {
+        LogPrintLevel(BCLog::NET, BCLog::Level::Warning, "natpmp: Could not connect to gateway: %s\n", NetworkErrorString(WSAGetLastError()));
+        return MappingError::NETWORK_ERROR;
+    }
+
+    // Use getsockname to get the address toward the default gateway (the internal address).
+    struct sockaddr_in internal;
+    socklen_t internal_addrlen = sizeof(struct sockaddr_in);
+    if (sock->GetSockName((struct sockaddr*)&internal, &internal_addrlen) != 0) {
+        LogPrintLevel(BCLog::NET, BCLog::Level::Warning, "natpmp: Could not get sock name: %s\n", NetworkErrorString(WSAGetLastError()));
+        return MappingError::NETWORK_ERROR;
+    }
+
+    // Request external IP address (RFC6886 section 3.2).
+    std::vector<uint8_t> request(NATPMP_GETEXTERNAL_REQUEST_SIZE);
+    request[NATPMP_HDR_VERSION_OFS] = NATPMP_VERSION;
+    request[NATPMP_HDR_OP_OFS] = NATPMP_REQUEST | NATPMP_OP_GETEXTERNAL;
+
+    auto recv_res = PCPSendRecv(*sock, "natpmp", request, num_tries, timeout_per_try,
+        [&](const Span<const uint8_t> response) -> bool {
+            if (response.size() < NATPMP_GETEXTERNAL_RESPONSE_SIZE) {
+                LogPrintLevel(BCLog::NET, BCLog::Level::Warning, "natpmp: Response too small\n");
+                return false; // Wasn't response to what we expected, try receiving next packet.
+            }
+            if (response[NATPMP_HDR_VERSION_OFS] != NATPMP_VERSION || response[NATPMP_HDR_OP_OFS] != (NATPMP_RESPONSE | NATPMP_OP_GETEXTERNAL)) {
+                LogPrintLevel(BCLog::NET, BCLog::Level::Warning, "natpmp: Response to wrong command\n");
+                return false; // Wasn't response to what we expected, try receiving next packet.
+            }
+            return true;
+        });
+
+    struct in_addr external_addr;
+    if (recv_res) {
+        const std::span<const uint8_t> response = *recv_res;
+
+        Assume(response.size() >= NATPMP_GETEXTERNAL_RESPONSE_SIZE);
+        uint16_t result_code = ReadBE16(response.data() + NATPMP_RESPONSE_HDR_RESULT_OFS);
+        if (result_code != NATPMP_RESULT_SUCCESS) {
+            LogPrintLevel(BCLog::NET, BCLog::Level::Warning, "natpmp: Getting external address failed with result %s\n", NATPMPResultString(result_code));
+            return MappingError::PROTOCOL_ERROR;
+        }
+
+        std::memcpy(&external_addr, response.data() + NATPMP_GETEXTERNAL_RESPONSE_IP_OFS, ADDR_IPV4_SIZE);
+    } else {
+        return MappingError::NETWORK_ERROR;
+    }
+
+    // Create TCP mapping request (RFC6886 section 3.3).
+    request = std::vector<uint8_t>(NATPMP_MAP_REQUEST_SIZE);
+    request[NATPMP_HDR_VERSION_OFS] = NATPMP_VERSION;
+    request[NATPMP_HDR_OP_OFS] = NATPMP_REQUEST | NATPMP_OP_MAP_TCP;
+    WriteBE16(request.data() + NATPMP_MAP_REQUEST_INTERNAL_PORT_OFS, port);
+    WriteBE16(request.data() + NATPMP_MAP_REQUEST_EXTERNAL_PORT_OFS, port);
+    WriteBE32(request.data() + NATPMP_MAP_REQUEST_LIFETIME_OFS, lifetime);
+
+    recv_res = PCPSendRecv(*sock, "natpmp", request, num_tries, timeout_per_try,
+        [&](const Span<const uint8_t> response) -> bool {
+            if (response.size() < NATPMP_MAP_RESPONSE_SIZE) {
+                LogPrintLevel(BCLog::NET, BCLog::Level::Warning, "natpmp: Response too small\n");
+                return false; // Wasn't response to what we expected, try receiving next packet.
+            }
+            if (response[0] != NATPMP_VERSION || response[1] != (NATPMP_RESPONSE | NATPMP_OP_MAP_TCP)) {
+                LogPrintLevel(BCLog::NET, BCLog::Level::Warning, "natpmp: Response to wrong command\n");
+                return false; // Wasn't response to what we expected, try receiving next packet.
+            }
+            uint16_t internal_port = ReadBE16(response.data() + NATPMP_MAP_RESPONSE_INTERNAL_PORT_OFS);
+            if (internal_port != port) {
+                LogPrintLevel(BCLog::NET, BCLog::Level::Warning, "natpmp: Response port doesn't match request\n");
+                return false; // Wasn't response to what we expected, try receiving next packet.
+            }
+            return true;
+        });
+
+    if (recv_res) {
+        const std::span<uint8_t> response = *recv_res;
+
+        Assume(response.size() >= NATPMP_MAP_RESPONSE_SIZE);
+        uint16_t result_code = ReadBE16(response.data() + NATPMP_RESPONSE_HDR_RESULT_OFS);
+        if (result_code != NATPMP_RESULT_SUCCESS) {
+            LogPrintLevel(BCLog::NET, BCLog::Level::Warning, "natpmp: Port mapping failed with result %s\n", NATPMPResultString(result_code));
+            if (result_code == NATPMP_RESULT_NO_RESOURCES) {
+                return MappingError::NO_RESOURCES;
+            }
+            return MappingError::PROTOCOL_ERROR;
+        }
+
+        uint32_t lifetime_ret = ReadBE32(response.data() + NATPMP_MAP_RESPONSE_LIFETIME_OFS);
+        uint16_t external_port = ReadBE16(response.data() + NATPMP_MAP_RESPONSE_EXTERNAL_PORT_OFS);
+        return MappingResult(NATPMP_VERSION, CService(internal.sin_addr, port), CService(external_addr, external_port), lifetime_ret);
+    } else {
+        return MappingError::NETWORK_ERROR;
+    }
+}
+
+std::variant<MappingResult, MappingError> PCPRequestPortMap(const PCPMappingNonce &nonce, const CNetAddr &gateway, const CNetAddr &bind, uint16_t port, uint32_t lifetime, int num_tries, std::chrono::milliseconds timeout_per_try)
+{
+    struct sockaddr_storage dest_addr, bind_addr;
+    socklen_t dest_addrlen = sizeof(struct sockaddr_storage), bind_addrlen = sizeof(struct sockaddr_storage);
+
+    LogPrintLevel(BCLog::NET, BCLog::Level::Debug, "pcp: Requesting port mapping for addr %s port %d from gateway %s\n", bind.ToStringAddr(), port, gateway.ToStringAddr());
+
+    // Validate addresses, make sure they're the same network family.
+    if (!CService(gateway, PCP_SERVER_PORT).GetSockAddr((struct sockaddr*)&dest_addr, &dest_addrlen)) return MappingError::NETWORK_ERROR;
+    if (!CService(bind, 0).GetSockAddr((struct sockaddr*)&bind_addr, &bind_addrlen)) return MappingError::NETWORK_ERROR;
+    if (dest_addr.ss_family != bind_addr.ss_family) return MappingError::NETWORK_ERROR;
+
+    // Create UDP socket (IPv4 or IPv6 based on provided gateway).
+    auto sock{CreateSock(dest_addr.ss_family, SOCK_DGRAM, IPPROTO_UDP)};
+    if (!sock) {
+        LogPrintLevel(BCLog::NET, BCLog::Level::Warning, "pcp: Could not create UDP socket: %s\n", NetworkErrorString(WSAGetLastError()));
+        return MappingError::NETWORK_ERROR;
+    }
+
+    // Make sure that we send from requested destination address, anything else will be
+    // rejected by a security-conscious router.
+    if (sock->Bind((struct sockaddr*)&bind_addr, bind_addrlen) != 0) {
+        LogPrintLevel(BCLog::NET, BCLog::Level::Warning, "pcp: Could not bind to address: %s\n", NetworkErrorString(WSAGetLastError()));
+        return MappingError::NETWORK_ERROR;
+    }
+
+    // Associate UDP socket to gateway.
+    if (sock->Connect((struct sockaddr*)&dest_addr, dest_addrlen) != 0) {
+        LogPrintLevel(BCLog::NET, BCLog::Level::Warning, "pcp: Could not connect to gateway: %s\n", NetworkErrorString(WSAGetLastError()));
+        return MappingError::NETWORK_ERROR;
+    }
+
+    // Use getsockname to get the address toward the default gateway (the internal address),
+    // in case we don't know what address to map
+    // (this is only needed if bind is INADDR_ANY, but it doesn't hurt as an extra check).
+    struct sockaddr_storage internal_addr;
+    socklen_t internal_addrlen = sizeof(struct sockaddr_storage);
+    if (sock->GetSockName((struct sockaddr*)&internal_addr, &internal_addrlen) != 0) {
+        LogPrintLevel(BCLog::NET, BCLog::Level::Warning, "pcp: Could not get sock name: %s\n", NetworkErrorString(WSAGetLastError()));
+        return MappingError::NETWORK_ERROR;
+    }
+    CService internal;
+    if (!internal.SetSockAddr((struct sockaddr*)&internal_addr)) return MappingError::NETWORK_ERROR;
+    LogPrintLevel(BCLog::NET, BCLog::Level::Debug, "pcp: Internal address after connect: %s\n", internal.ToStringAddr());
+
+    // Build request packet. Make sure the packet is zeroed so that reserved fields are zero
+    // as required by the spec (and not potentially leak data).
+    // Make sure there's space for the request header and MAP specific request data.
+    std::vector<uint8_t> request(PCP_HDR_SIZE + PCP_MAP_SIZE);
+    // Fill in request header, See RFC6887 Figure 2.
+    size_t ofs = 0;
+    request[ofs + PCP_HDR_VERSION_OFS] = PCP_VERSION;
+    request[ofs + PCP_HDR_OP_OFS] = PCP_REQUEST | PCP_OP_MAP;
+    WriteBE32(request.data() + ofs + PCP_HDR_LIFETIME_OFS, lifetime);
+    if (!PCPWrapAddress(Span(request).subspan(ofs + PCP_REQUEST_HDR_IP_OFS, ADDR_IPV6_SIZE), internal)) return MappingError::NETWORK_ERROR;
+
+    ofs += PCP_HDR_SIZE;
+
+    // Fill in MAP request packet, See RFC6887 Figure 9.
+    // Randomize mapping nonce (this is repeated in the response, to be able to
+    // correlate requests and responses, and used to authenticate changes to the mapping).
+    std::memcpy(request.data() + ofs + PCP_MAP_NONCE_OFS, nonce.data(), PCP_MAP_NONCE_SIZE);
+    request[ofs + PCP_MAP_PROTOCOL_OFS] = PCP_PROTOCOL_TCP;
+    WriteBE16(request.data() + ofs + PCP_MAP_INTERNAL_PORT_OFS, port);
+    WriteBE16(request.data() + ofs + PCP_MAP_EXTERNAL_PORT_OFS, port);
+    if (!PCPWrapAddress(Span(request).subspan(ofs + PCP_MAP_EXTERNAL_IP_OFS, ADDR_IPV6_SIZE), bind)) return MappingError::NETWORK_ERROR;
+
+    ofs += PCP_MAP_SIZE;
+    Assume(ofs == request.size());
+
+    // Receive loop.
+    bool is_natpmp = false;
+    auto recv_res = PCPSendRecv(*sock, "pcp", request, num_tries, timeout_per_try,
+        [&](const Span<const uint8_t> response) -> bool {
+            // Unsupported version according to RFC6887 appendix A and RFC6886 section 3.5, can fall back to NAT-PMP.
+            if (response.size() == NATPMP_RESPONSE_HDR_SIZE && response[PCP_HDR_VERSION_OFS] == NATPMP_VERSION && response[PCP_RESPONSE_HDR_RESULT_OFS] == NATPMP_RESULT_UNSUPP_VERSION) {
+                is_natpmp = true;
+                return true; // Let it through to caller.
+            }
+            if (response.size() < (PCP_HDR_SIZE + PCP_MAP_SIZE)) {
+                LogPrintLevel(BCLog::NET, BCLog::Level::Warning, "pcp: Response too small\n");
+                return false; // Wasn't response to what we expected, try receiving next packet.
+            }
+            if (response[PCP_HDR_VERSION_OFS] != PCP_VERSION || response[PCP_HDR_OP_OFS] != (PCP_RESPONSE | PCP_OP_MAP)) {
+                LogPrintLevel(BCLog::NET, BCLog::Level::Warning, "pcp: Response to wrong command\n");
+                return false; // Wasn't response to what we expected, try receiving next packet.
+            }
+            // Handle MAP opcode response. See RFC6887 Figure 10.
+            // Check that returned mapping nonce matches our request.
+            if (!std::ranges::equal(response.subspan(PCP_HDR_SIZE + PCP_MAP_NONCE_OFS, PCP_MAP_NONCE_SIZE), nonce)) {
+                LogPrintLevel(BCLog::NET, BCLog::Level::Warning, "pcp: Mapping nonce mismatch\n");
+                return false; // Wasn't response to what we expected, try receiving next packet.
+            }
+            uint8_t protocol = response[PCP_HDR_SIZE + 12];
+            uint16_t internal_port = ReadBE16(response.data() + PCP_HDR_SIZE + 16);
+            if (protocol != PCP_PROTOCOL_TCP || internal_port != port) {
+                LogPrintLevel(BCLog::NET, BCLog::Level::Warning, "pcp: Response protocol or port doesn't match request\n");
+                return false; // Wasn't response to what we expected, try receiving next packet.
+            }
+            return true;
+        });
+
+    if (!recv_res) {
+        return MappingError::NETWORK_ERROR;
+    }
+    if (is_natpmp) {
+        return MappingError::UNSUPP_VERSION;
+    }
+
+    const std::span<const uint8_t> response = *recv_res;
+    // If we get here, we got a valid MAP response to our request.
+    // Check to see if we got the result we expected.
+    Assume(response.size() >= (PCP_HDR_SIZE + PCP_MAP_SIZE));
+    uint8_t result_code = response[PCP_RESPONSE_HDR_RESULT_OFS];
+    uint32_t lifetime_ret = ReadBE32(response.data() + PCP_HDR_LIFETIME_OFS);
+    uint16_t external_port = ReadBE16(response.data() + PCP_HDR_SIZE + PCP_MAP_EXTERNAL_PORT_OFS);
+    CNetAddr external_addr{PCPUnwrapAddress(response.subspan(PCP_HDR_SIZE + PCP_MAP_EXTERNAL_IP_OFS, ADDR_IPV6_SIZE))};
+    if (result_code != PCP_RESULT_SUCCESS) {
+        LogPrintLevel(BCLog::NET, BCLog::Level::Warning, "pcp: Mapping failed with result %s\n", PCPResultString(result_code));
+        if (result_code == PCP_RESULT_NO_RESOURCES) {
+            return MappingError::NO_RESOURCES;
+        }
+        return MappingError::PROTOCOL_ERROR;
+    }
+
+    return MappingResult(PCP_VERSION, CService(internal, port), CService(external_addr, external_port), lifetime_ret);
+}
+
+std::string MappingResult::ToString()
+{
+    Assume(version == NATPMP_VERSION || version == PCP_VERSION);
+    return strprintf("%s:%s -> %s (for %ds)",
+            version == NATPMP_VERSION ? "natpmp" : "pcp",
+            external.ToStringAddrPort(),
+            internal.ToStringAddrPort(),
+            lifetime
+        );
+}
diff --git a/src/util/pcp.h b/src/util/pcp.h
new file mode 100644
index 0000000000..0a7955fa57
--- /dev/null
+++ b/src/util/pcp.h
@@ -0,0 +1,68 @@
+// Copyright (c) 2024 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or https://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_UTIL_PCP_H
+#define BITCOIN_UTIL_PCP_H
+
+#include <netaddress.h>
+
+#include <variant>
+
+// RFC6886 NAT-PMP and RFC6887 Port Control Protocol (PCP) implementation.
+// NAT-PMP and PCP use network byte order (big-endian).
+
+//! Mapping nonce size in bytes (see RFC6887 section 11.1).
+constexpr size_t PCP_MAP_NONCE_SIZE = 12;
+
+//! PCP mapping nonce. Arbitrary data chosen by the client to identify a mapping.
+typedef std::array<uint8_t, PCP_MAP_NONCE_SIZE> PCPMappingNonce;
+
+//! Unsuccessful response to a port mapping.
+enum class MappingError {
+    NETWORK_ERROR,  ///< Any kind of network-level error.
+    PROTOCOL_ERROR, ///< Any kind of protocol-level error, except unsupported version or no resources.
+    UNSUPP_VERSION, ///< Unsupported protocol version.
+    NO_RESOURCES,   ///< No resources available (port probably already mapped).
+};
+
+//! Successful response to a port mapping.
+struct MappingResult {
+    MappingResult(uint8_t version, const CService &internal_in, const CService &external_in, uint32_t lifetime_in):
+        version(version), internal(internal_in), external(external_in), lifetime(lifetime_in) {}
+    //! Protocol version, one of NATPMP_VERSION or PCP_VERSION.
+    uint8_t version;
+    //! Internal host:port.
+    CService internal;
+    //! External host:port.
+    CService external;
+    //! Granted lifetime of binding (seconds).
+    uint32_t lifetime;
+
+    //! Format mapping as string for logging.
+    std::string ToString();
+};
+
+//! Try to open a port using RFC 6886 NAT-PMP. IPv4 only.
+//!
+//! * gateway: Destination address for PCP requests (usually the default gateway).
+//! * port: Internal port, and desired external port.
+//! * lifetime: Requested lifetime in seconds for mapping. The server may assign as shorter or longer lifetime. A lifetime of 0 deletes the mapping.
+//! * num_tries: Number of tries in case of no response.
+//!
+//! Returns the external_ip:external_port of the mapping if successful, otherwise a MappingError.
+std::variant<MappingResult, MappingError> NATPMPRequestPortMap(const CNetAddr &gateway, uint16_t port, uint32_t lifetime, int num_tries = 3, std::chrono::milliseconds timeout_per_try = std::chrono::milliseconds(1000));
+
+//! Try to open a port using RFC 6887 Port Control Protocol (PCP). Handles IPv4 and IPv6.
+//!
+//! * nonce: Mapping cookie. Keep this the same over renewals.
+//! * gateway: Destination address for PCP requests (usually the default gateway).
+//! * bind: Specific local bind address for IPv6 pinholing. Set this as INADDR_ANY for IPv4.
+//! * port: Internal port, and desired external port.
+//! * lifetime: Requested lifetime in seconds for mapping. The server may assign as shorter or longer lifetime. A lifetime of 0 deletes the mapping.
+//! * num_tries: Number of tries in case of no response.
+//!
+//! Returns the external_ip:external_port of the mapping if successful, otherwise a MappingError.
+std::variant<MappingResult, MappingError> PCPRequestPortMap(const PCPMappingNonce &nonce, const CNetAddr &gateway, const CNetAddr &bind, uint16_t port, uint32_t lifetime, int num_tries = 3, std::chrono::milliseconds timeout_per_try = std::chrono::milliseconds(1000));
+
+#endif // BITCOIN_UTIL_PCP_H