// Copyright (c) 2024-present 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 <common/pcp.h>

#include <compat/compat.h>

#include <crypto/common.h>

#include <crypto/hex_base.h>

#include <netaddress.h>

#include <netbase.h>

#include <tinyformat.h>

#include <util/check.h>

#include <util/log.h>

#include <util/sock.h>

#include <util/string.h>

#include <util/threadinterrupt.h>

#include <util/time.h>

#include <algorithm>

#include <compare>

#include <cstring>

#include <functional>

#include <map>

#include <memory>

#include <optional>

#include <span>

#include <utility>

#include <vector>

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 not authorized (router doesn't support port mapping).

constexpr uint8_t NATPMP_RESULT_NOT_AUTHORIZED = 2;

//! 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<uint16_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 not authorized (RFC6887 7.4), shared with NAT-PMP.

constexpr uint8_t PCP_RESULT_NOT_AUTHORIZED = NATPMP_RESULT_NOT_AUTHORIZED;

//! 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(uint16_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(std::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(std::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, std::span<const uint8_t> request, int num_tries,

        std::chrono::milliseconds timeout_per_try,

        std::function<bool(std::span<const uint8_t>)> check_packet,

        CThreadInterrupt& interrupt)

{

    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) {

            LogDebug(BCLog::NET, "%s: Retrying (%d)\n", protocol, ntry);

        }

        // Dispatch packet to gateway.

        if (sock.Send(request.data(), request.size(), 0) != static_cast<ssize_t>(request.size())) {

            LogDebug(BCLog::NET, "%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>(MockableSteadyClock::now());

        auto deadline = cur_time + timeout_per_try;

        while ((cur_time = time_point_cast<milliseconds>(MockableSteadyClock::now())) < deadline) {

            if (interrupt) return std::nullopt;

            Sock::Event occurred = 0;

            if (!sock.Wait(deadline - cur_time, Sock::RecvEvent, &occurred)) {

                LogWarning("%s: Could not wait on socket: %s\n", protocol, NetworkErrorString(WSAGetLastError()));

                return std::nullopt; // Network-level error, probably no use retrying.

            }

            if (!occurred) {

                LogDebug(BCLog::NET, "%s: Timeout\n", protocol);

                break; // Retry.

            }

            // Receive response.

            recvsz = sock.Recv(response, sizeof(response), MSG_DONTWAIT);

            if (recvsz < 0) {

                LogDebug(BCLog::NET, "%s: Could not receive response: %s\n", protocol, NetworkErrorString(WSAGetLastError()));

                return std::nullopt; // Network-level error, probably no use retrying.

            }

            LogDebug(BCLog::NET, "%s: Received response of %d bytes: %s\n", protocol, recvsz, HexStr(std::span(response, recvsz)));

            if (check_packet(std::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) {

        LogDebug(BCLog::NET, "%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, CThreadInterrupt& interrupt, int num_tries, std::chrono::milliseconds timeout_per_try)

{

    struct sockaddr_storage dest_addr;

    socklen_t dest_addrlen = sizeof(struct sockaddr_storage);

    LogDebug(BCLog::NET, "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) {

        LogWarning("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) {

        LogWarning("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) {

        LogWarning("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 std::span<const uint8_t> response) -> bool {

            if (response.size() < NATPMP_GETEXTERNAL_RESPONSE_SIZE) {

                LogWarning("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)) {

                LogWarning("natpmp: Response to wrong command\n");

                return false; // Wasn't response to what we expected, try receiving next packet.

            }

            return true;

        },

        interrupt);

    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) {

            LogWarning("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 std::span<const uint8_t> response) -> bool {

            if (response.size() < NATPMP_MAP_RESPONSE_SIZE) {

                LogWarning("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)) {

                LogWarning("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) {

                LogWarning("natpmp: Response port doesn't match request\n");

                return false; // Wasn't response to what we expected, try receiving next packet.

            }

            return true;

        },

        interrupt);

    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) {

            if (result_code == NATPMP_RESULT_NOT_AUTHORIZED) {

                LogWarnThenDebug(BCLog::NET, "natpmp: Port mapping failed with result %s", NATPMPResultString(result_code));

            } else {

                LogWarning("natpmp: Port mapping failed with result %s", 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, CThreadInterrupt& interrupt, 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);

    LogDebug(BCLog::NET, "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) {

        LogWarning("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) {

        LogWarning("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) {

        LogWarning("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) {

        LogWarning("pcp: Could not get sock name: %s\n", NetworkErrorString(WSAGetLastError()));

        return MappingError::NETWORK_ERROR;

    }

    CService internal;

    if (!internal.SetSockAddr((struct sockaddr*)&internal_addr, internal_addrlen)) return MappingError::NETWORK_ERROR;

    LogDebug(BCLog::NET, "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(std::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(std::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 std::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)) {

                LogWarning("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)) {

                LogWarning("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)) {

                LogWarning("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) {

                LogWarning("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;

        },

        interrupt);

    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) {

        if (result_code == PCP_RESULT_NOT_AUTHORIZED) {

            LogWarnThenDebug(BCLog::NET, "pcp: Mapping failed with result %s", PCPResultString(result_code));

        } else {

            LogWarning("pcp: Mapping failed with result %s", 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() const

{

    Assume(version == NATPMP_VERSION || version == PCP_VERSION);

    return strprintf("%s:%s -> %s (for %ds)",

            version == NATPMP_VERSION ? "natpmp" : "pcp",

            external.ToStringAddrPort(),

            internal.ToStringAddrPort(),

            lifetime

        );

}