net.cpp

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// Copyright (c) 2009-2010 Satoshi Nakamoto
// Copyright (c) 2009-2019 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
#if defined(HAVE_CONFIG_H)
#include <config/bitcoin-config.h>
#endif
 
#include <net.h>
 
#include <addrdb.h>
#include <addrman.h>
#include <avalanche/avalanche.h>
#include <banman.h>
#include <clientversion.h>
#include <compat.h>
#include <config.h>
#include <consensus/consensus.h>
#include <crypto/sha256.h>
#include <dnsseeds.h>
#include <fs.h>
#include <i2p.h>
#include <netaddress.h>
#include <netbase.h>
#include <node/ui_interface.h>
#include <protocol.h>
#include <random.h>
#include <scheduler.h>
#include <util/sock.h>
#include <util/strencodings.h>
#include <util/system.h>
#include <util/thread.h>
#include <util/trace.h>
#include <util/translation.h>
 
#ifdef WIN32
#include <cstring>
#else
#include <fcntl.h>
#endif
 
#ifdef USE_POLL
#include <poll.h>
#endif
 
#include <algorithm>
#include <array>
#include <cmath>
#include <cstdint>
#include <functional>
#include <limits>
#include <optional>
#include <unordered_map>
 
static constexpr size_t MAX_BLOCK_RELAY_ONLY_ANCHORS = 2;
static_assert(MAX_BLOCK_RELAY_ONLY_ANCHORS <=
                  static_cast<size_t>(MAX_BLOCK_RELAY_ONLY_CONNECTIONS),
              "MAX_BLOCK_RELAY_ONLY_ANCHORS must not exceed "
              "MAX_BLOCK_RELAY_ONLY_CONNECTIONS.");
const char *const ANCHORS_DATABASE_FILENAME = "anchors.dat";
 
// How often to dump addresses to peers.dat
static constexpr std::chrono::minutes DUMP_PEERS_INTERVAL{15};
 
static constexpr int DNSSEEDS_TO_QUERY_AT_ONCE = 3;
 
static constexpr std::chrono::seconds DNSSEEDS_DELAY_FEW_PEERS{11};
static constexpr std::chrono::minutes DNSSEEDS_DELAY_MANY_PEERS{5};
// "many" vs "few" peers
static constexpr int DNSSEEDS_DELAY_PEER_THRESHOLD = 1000;
 
static constexpr std::chrono::seconds MAX_UPLOAD_TIMEFRAME{60 * 60 * 24};
 
// We add a random period time (0 to 1 seconds) to feeler connections to prevent
// synchronization.
#define FEELER_SLEEP_WINDOW 1
 
enum BindFlags {
    BF_NONE = 0,
    BF_EXPLICIT = (1U << 0),
    BF_REPORT_ERROR = (1U << 1),
    BF_DONT_ADVERTISE = (1U << 2),
};
 
// The set of sockets cannot be modified while waiting
// The sleep time needs to be small to avoid new sockets stalling
static const uint64_t SELECT_TIMEOUT_MILLISECONDS = 50;
 
const std::string NET_MESSAGE_COMMAND_OTHER = "*other*";
 
// SHA256("netgroup")[0:8]
static const uint64_t RANDOMIZER_ID_NETGROUP = 0x6c0edd8036ef4036ULL;
// SHA256("localhostnonce")[0:8]
static const uint64_t RANDOMIZER_ID_LOCALHOSTNONCE = 0xd93e69e2bbfa5735ULL;
// SHA256("localhostnonce")[8:16]
static const uint64_t RANDOMIZER_ID_EXTRAENTROPY = 0x94b05d41679a4ff7ULL;
// SHA256("addrcache")[0:8]
static const uint64_t RANDOMIZER_ID_ADDRCACHE = 0x1cf2e4ddd306dda9ULL;
//
// Global state variables
//
bool fDiscover = true;
bool fListen = true;
GlobalMutex g_maplocalhost_mutex;
std::map<CNetAddr, LocalServiceInfo>
    mapLocalHost GUARDED_BY(g_maplocalhost_mutex);
static bool vfLimited[NET_MAX] GUARDED_BY(g_maplocalhost_mutex) = {};
 
void CConnman::AddAddrFetch(const std::string &strDest) {
    LOCK(m_addr_fetches_mutex);
    m_addr_fetches.push_back(strDest);
}
 
uint16_t GetListenPort() {
    // If -bind= is provided with ":port" part, use that (first one if multiple
    // are provided).
    for (const std::string &bind_arg : gArgs.GetArgs("-bind")) {
        CService bind_addr;
        constexpr uint16_t dummy_port = 0;
 
        if (Lookup(bind_arg, bind_addr, dummy_port, /*fAllowLookup=*/false)) {
            if (bind_addr.GetPort() != dummy_port) {
                return bind_addr.GetPort();
            }
        }
    }
 
    // Otherwise, if -whitebind= without NetPermissionFlags::NoBan is provided,
    // use that
    // (-whitebind= is required to have ":port").
    for (const std::string &whitebind_arg : gArgs.GetArgs("-whitebind")) {
        NetWhitebindPermissions whitebind;
        bilingual_str error;
        if (NetWhitebindPermissions::TryParse(whitebind_arg, whitebind,
                                              error)) {
            if (!NetPermissions::HasFlag(whitebind.m_flags,
                                         NetPermissionFlags::NoBan)) {
                return whitebind.m_service.GetPort();
            }
        }
    }
 
    // Otherwise, if -port= is provided, use that. Otherwise use the default
    // port.
    return static_cast<uint16_t>(
        gArgs.GetIntArg("-port", Params().GetDefaultPort()));
}
 
// find 'best' local address for a particular peer
bool GetLocal(CService &addr, const CNetAddr *paddrPeer) {
    if (!fListen) {
        return false;
    }
 
    int nBestScore = -1;
    int nBestReachability = -1;
    {
        LOCK(g_maplocalhost_mutex);
        for (const auto &entry : mapLocalHost) {
            int nScore = entry.second.nScore;
            int nReachability = entry.first.GetReachabilityFrom(paddrPeer);
            if (nReachability > nBestReachability ||
                (nReachability == nBestReachability && nScore > nBestScore)) {
                addr = CService(entry.first, entry.second.nPort);
                nBestReachability = nReachability;
                nBestScore = nScore;
            }
        }
    }
    return nBestScore >= 0;
}
 
static std::vector<CAddress>
convertSeed6(const std::vector<SeedSpec6> &vSeedsIn) {
    // It'll only connect to one or two seed nodes because once it connects,
    // it'll get a pile of addresses with newer timestamps. Seed nodes are given
    // a random 'last seen time' of between one and two weeks ago.
    const auto one_week{7 * 24h};
    std::vector<CAddress> vSeedsOut;
    vSeedsOut.reserve(vSeedsIn.size());
    FastRandomContext rng;
    for (const auto &seed_in : vSeedsIn) {
        struct in6_addr ip;
        memcpy(&ip, seed_in.addr, sizeof(ip));
        CAddress addr(CService(ip, seed_in.port),
                      GetDesirableServiceFlags(NODE_NONE));
        addr.nTime =
            rng.rand_uniform_delay(Now<NodeSeconds>() - one_week, -one_week);
        vSeedsOut.push_back(addr);
    }
    return vSeedsOut;
}
 
// Get best local address for a particular peer as a CService. Otherwise, return
// the unroutable 0.0.0.0 but filled in with the normal parameters, since the IP
// may be changed to a useful one by discovery.
CService GetLocalAddress(const CNetAddr &addrPeer) {
    CService ret{CNetAddr(), GetListenPort()};
    CService addr;
    if (GetLocal(addr, &addrPeer)) {
        ret = CService{addr};
    }
    return ret;
}
 
static int GetnScore(const CService &addr) {
    LOCK(g_maplocalhost_mutex);
    const auto it = mapLocalHost.find(addr);
    return (it != mapLocalHost.end()) ? it->second.nScore : 0;
}
 
// Is our peer's addrLocal potentially useful as an external IP source?
bool IsPeerAddrLocalGood(CNode *pnode) {
    CService addrLocal = pnode->GetAddrLocal();
    return fDiscover && pnode->addr.IsRoutable() && addrLocal.IsRoutable() &&
           IsReachable(addrLocal.GetNetwork());
}
 
std::optional<CService> GetLocalAddrForPeer(CNode &node) {
    CService addrLocal{GetLocalAddress(node.addr)};
    if (gArgs.GetBoolArg("-addrmantest", false)) {
        // use IPv4 loopback during addrmantest
        addrLocal = CService(LookupNumeric("127.0.0.1", GetListenPort()));
    }
    // If discovery is enabled, sometimes give our peer the address it
    // tells us that it sees us as in case it has a better idea of our
    // address than we do.
    FastRandomContext rng;
    if (IsPeerAddrLocalGood(&node) &&
        (!addrLocal.IsRoutable() ||
         rng.randbits((GetnScore(addrLocal) > LOCAL_MANUAL) ? 3 : 1) == 0)) {
        if (node.IsInboundConn()) {
            // For inbound connections, assume both the address and the port
            // as seen from the peer.
            addrLocal = CService{node.GetAddrLocal()};
        } else {
            // For outbound connections, assume just the address as seen from
            // the peer and leave the port in `addrLocal` as returned by
            // `GetLocalAddress()` above. The peer has no way to observe our
            // listening port when we have initiated the connection.
            addrLocal.SetIP(node.GetAddrLocal());
        }
    }
    if (addrLocal.IsRoutable() || gArgs.GetBoolArg("-addrmantest", false)) {
        LogPrint(BCLog::NET, "Advertising address %s to peer=%d\n",
                 addrLocal.ToString(), node.GetId());
        return addrLocal;
    }
    // Address is unroutable. Don't advertise.
    return std::nullopt;
}
 
// Learn a new local address.
bool AddLocal(const CService &addr, int nScore) {
    if (!addr.IsRoutable()) {
        return false;
    }
 
    if (!fDiscover && nScore < LOCAL_MANUAL) {
        return false;
    }
 
    if (!IsReachable(addr)) {
        return false;
    }
 
    LogPrintf("AddLocal(%s,%i)\n", addr.ToString(), nScore);
 
    {
        LOCK(g_maplocalhost_mutex);
        const auto [it, is_newly_added] =
            mapLocalHost.emplace(addr, LocalServiceInfo());
        LocalServiceInfo &info = it->second;
        if (is_newly_added || nScore >= info.nScore) {
            info.nScore = nScore + !is_newly_added;
            info.nPort = addr.GetPort();
        }
    }
 
    return true;
}
 
bool AddLocal(const CNetAddr &addr, int nScore) {
    return AddLocal(CService(addr, GetListenPort()), nScore);
}
 
void RemoveLocal(const CService &addr) {
    LOCK(g_maplocalhost_mutex);
    LogPrintf("RemoveLocal(%s)\n", addr.ToString());
    mapLocalHost.erase(addr);
}
 
void SetReachable(enum Network net, bool reachable) {
    if (net == NET_UNROUTABLE || net == NET_INTERNAL) {
        return;
    }
    LOCK(g_maplocalhost_mutex);
    vfLimited[net] = !reachable;
}
 
bool IsReachable(enum Network net) {
    LOCK(g_maplocalhost_mutex);
    return !vfLimited[net];
}
 
bool IsReachable(const CNetAddr &addr) {
    return IsReachable(addr.GetNetwork());
}
 
bool SeenLocal(const CService &addr) {
    LOCK(g_maplocalhost_mutex);
    const auto it = mapLocalHost.find(addr);
    if (it == mapLocalHost.end()) {
        return false;
    }
    ++it->second.nScore;
    return true;
}
 
bool IsLocal(const CService &addr) {
    LOCK(g_maplocalhost_mutex);
    return mapLocalHost.count(addr) > 0;
}
 
CNode *CConnman::FindNode(const CNetAddr &ip) {
    LOCK(m_nodes_mutex);
    for (CNode *pnode : m_nodes) {
        if (static_cast<CNetAddr>(pnode->addr) == ip) {
            return pnode;
        }
    }
    return nullptr;
}
 
CNode *CConnman::FindNode(const CSubNet &subNet) {
    LOCK(m_nodes_mutex);
    for (CNode *pnode : m_nodes) {
        if (subNet.Match(static_cast<CNetAddr>(pnode->addr))) {
            return pnode;
        }
    }
    return nullptr;
}
 
CNode *CConnman::FindNode(const std::string &addrName) {
    LOCK(m_nodes_mutex);
    for (CNode *pnode : m_nodes) {
        if (pnode->m_addr_name == addrName) {
            return pnode;
        }
    }
    return nullptr;
}
 
CNode *CConnman::FindNode(const CService &addr) {
    LOCK(m_nodes_mutex);
    for (CNode *pnode : m_nodes) {
        if (static_cast<CService>(pnode->addr) == addr) {
            return pnode;
        }
    }
    return nullptr;
}
 
bool CConnman::AlreadyConnectedToAddress(const CAddress &addr) {
    return FindNode(static_cast<CNetAddr>(addr)) ||
           FindNode(addr.ToStringIPPort());
}
 
bool CConnman::CheckIncomingNonce(uint64_t nonce) {
    LOCK(m_nodes_mutex);
    for (const CNode *pnode : m_nodes) {
        if (!pnode->fSuccessfullyConnected && !pnode->IsInboundConn() &&
            pnode->GetLocalNonce() == nonce) {
            return false;
        }
    }
    return true;
}
 
static CAddress GetBindAddress(SOCKET sock) {
    CAddress addr_bind;
    struct sockaddr_storage sockaddr_bind;
    socklen_t sockaddr_bind_len = sizeof(sockaddr_bind);
    if (sock != INVALID_SOCKET) {
        if (!getsockname(sock, (struct sockaddr *)&sockaddr_bind,
                         &sockaddr_bind_len)) {
            addr_bind.SetSockAddr((const struct sockaddr *)&sockaddr_bind);
        } else {
            LogPrint(BCLog::NET, "Warning: getsockname failed\n");
        }
    }
    return addr_bind;
}
 
CNode *CConnman::ConnectNode(CAddress addrConnect, const char *pszDest,
                             bool fCountFailure, ConnectionType conn_type) {
    assert(conn_type != ConnectionType::INBOUND);
 
    if (pszDest == nullptr) {
        if (IsLocal(addrConnect)) {
            return nullptr;
        }
 
        // Look for an existing connection
        CNode *pnode = FindNode(static_cast<CService>(addrConnect));
        if (pnode) {
            LogPrintf("Failed to open new connection, already connected\n");
            return nullptr;
        }
    }
 
    LogPrint(
        BCLog::NET, "trying connection %s lastseen=%.1fhrs\n",
        pszDest ? pszDest : addrConnect.ToString(),
        Ticks<HoursDouble>(pszDest ? 0h : AdjustedTime() - addrConnect.nTime));
 
    // Resolve
    const uint16_t default_port{pszDest != nullptr
                                    ? Params().GetDefaultPort(pszDest)
                                    : Params().GetDefaultPort()};
    if (pszDest) {
        std::vector<CService> resolved;
        if (Lookup(pszDest, resolved, default_port,
                   fNameLookup && !HaveNameProxy(), 256) &&
            !resolved.empty()) {
            addrConnect =
                CAddress(resolved[GetRand(resolved.size())], NODE_NONE);
            if (!addrConnect.IsValid()) {
                LogPrint(BCLog::NET,
                         "Resolver returned invalid address %s for %s\n",
                         addrConnect.ToString(), pszDest);
                return nullptr;
            }
            // It is possible that we already have a connection to the IP/port
            // pszDest resolved to. In that case, drop the connection that was
            // just created.
            LOCK(m_nodes_mutex);
            CNode *pnode = FindNode(static_cast<CService>(addrConnect));
            if (pnode) {
                LogPrintf("Failed to open new connection, already connected\n");
                return nullptr;
            }
        }
    }
 
    // Connect
    bool connected = false;
    std::unique_ptr<Sock> sock;
    proxyType proxy;
    CAddress addr_bind;
    assert(!addr_bind.IsValid());
 
    if (addrConnect.IsValid()) {
        bool proxyConnectionFailed = false;
 
        if (addrConnect.GetNetwork() == NET_I2P &&
            m_i2p_sam_session.get() != nullptr) {
            i2p::Connection conn;
            if (m_i2p_sam_session->Connect(addrConnect, conn,
                                           proxyConnectionFailed)) {
                connected = true;
                sock = std::move(conn.sock);
                addr_bind = CAddress{conn.me, NODE_NONE};
            }
        } else if (GetProxy(addrConnect.GetNetwork(), proxy)) {
            sock = CreateSock(proxy.proxy);
            if (!sock) {
                return nullptr;
            }
            connected = ConnectThroughProxy(
                proxy, addrConnect.ToStringIP(), addrConnect.GetPort(), *sock,
                nConnectTimeout, proxyConnectionFailed);
        } else {
            // no proxy needed (none set for target network)
            sock = CreateSock(addrConnect);
            if (!sock) {
                return nullptr;
            }
            connected =
                ConnectSocketDirectly(addrConnect, *sock, nConnectTimeout,
                                      conn_type == ConnectionType::MANUAL);
        }
        if (!proxyConnectionFailed) {
            // If a connection to the node was attempted, and failure (if any)
            // is not caused by a problem connecting to the proxy, mark this as
            // an attempt.
            addrman.Attempt(addrConnect, fCountFailure);
        }
    } else if (pszDest && GetNameProxy(proxy)) {
        sock = CreateSock(proxy.proxy);
        if (!sock) {
            return nullptr;
        }
        std::string host;
        uint16_t port{default_port};
        SplitHostPort(std::string(pszDest), port, host);
        bool proxyConnectionFailed;
        connected = ConnectThroughProxy(proxy, host, port, *sock,
                                        nConnectTimeout, proxyConnectionFailed);
    }
    if (!connected) {
        return nullptr;
    }
 
    // Add node
    NodeId id = GetNewNodeId();
    uint64_t nonce = GetDeterministicRandomizer(RANDOMIZER_ID_LOCALHOSTNONCE)
                         .Write(id)
                         .Finalize();
    uint64_t extra_entropy =
        GetDeterministicRandomizer(RANDOMIZER_ID_EXTRAENTROPY)
            .Write(id)
            .Finalize();
    if (!addr_bind.IsValid()) {
        addr_bind = GetBindAddress(sock->Get());
    }
    CNode *pnode = new CNode(
        id, sock->Release(), addrConnect, CalculateKeyedNetGroup(addrConnect),
        nonce, extra_entropy, addr_bind, pszDest ? pszDest : "", conn_type,
        /* inbound_onion */ false);
    pnode->AddRef();
 
    // We're making a new connection, harvest entropy from the time (and our
    // peer count)
    RandAddEvent(uint32_t(id));
 
    return pnode;
}
 
void CNode::CloseSocketDisconnect() {
    fDisconnect = true;
    LOCK(cs_hSocket);
    if (hSocket != INVALID_SOCKET) {
        LogPrint(BCLog::NET, "disconnecting peer=%d\n", id);
        CloseSocket(hSocket);
    }
}
 
void CConnman::AddWhitelistPermissionFlags(NetPermissionFlags &flags,
                                           const CNetAddr &addr) const {
    for (const auto &subnet : vWhitelistedRange) {
        if (subnet.m_subnet.Match(addr)) {
            NetPermissions::AddFlag(flags, subnet.m_flags);
        }
    }
}
 
std::string ConnectionTypeAsString(ConnectionType conn_type) {
    switch (conn_type) {
        case ConnectionType::INBOUND:
            return "inbound";
        case ConnectionType::MANUAL:
            return "manual";
        case ConnectionType::FEELER:
            return "feeler";
        case ConnectionType::OUTBOUND_FULL_RELAY:
            return "outbound-full-relay";
        case ConnectionType::BLOCK_RELAY:
            return "block-relay-only";
        case ConnectionType::ADDR_FETCH:
            return "addr-fetch";
        case ConnectionType::AVALANCHE_OUTBOUND:
            return "avalanche";
    } // no default case, so the compiler can warn about missing cases
 
    assert(false);
}
 
CService CNode::GetAddrLocal() const {
    AssertLockNotHeld(m_addr_local_mutex);
    LOCK(m_addr_local_mutex);
    return addrLocal;
}
 
void CNode::SetAddrLocal(const CService &addrLocalIn) {
    AssertLockNotHeld(m_addr_local_mutex);
    LOCK(m_addr_local_mutex);
    if (addrLocal.IsValid()) {
        error("Addr local already set for node: %i. Refusing to change from %s "
              "to %s",
              id, addrLocal.ToString(), addrLocalIn.ToString());
    } else {
        addrLocal = addrLocalIn;
    }
}
 
Network CNode::ConnectedThroughNetwork() const {
    return m_inbound_onion ? NET_ONION : addr.GetNetClass();
}
 
void CNode::copyStats(CNodeStats &stats) {
    stats.nodeid = this->GetId();
    stats.addr = addr;
    stats.addrBind = addrBind;
    stats.m_network = ConnectedThroughNetwork();
    stats.m_last_send = m_last_send;
    stats.m_last_recv = m_last_recv;
    stats.m_last_tx_time = m_last_tx_time;
    stats.m_last_proof_time = m_last_proof_time;
    stats.m_last_block_time = m_last_block_time;
    stats.m_connected = m_connected;
    stats.nTimeOffset = nTimeOffset;
    stats.m_addr_name = m_addr_name;
    stats.nVersion = nVersion;
    {
        LOCK(m_subver_mutex);
        stats.cleanSubVer = cleanSubVer;
    }
    stats.fInbound = IsInboundConn();
    stats.m_bip152_highbandwidth_to = m_bip152_highbandwidth_to;
    stats.m_bip152_highbandwidth_from = m_bip152_highbandwidth_from;
    {
        LOCK(cs_vSend);
        stats.mapSendBytesPerMsgCmd = mapSendBytesPerMsgCmd;
        stats.nSendBytes = nSendBytes;
    }
    {
        LOCK(cs_vRecv);
        stats.mapRecvBytesPerMsgCmd = mapRecvBytesPerMsgCmd;
        stats.nRecvBytes = nRecvBytes;
    }
    stats.m_permissionFlags = m_permissionFlags;
 
    stats.m_last_ping_time = m_last_ping_time;
    stats.m_min_ping_time = m_min_ping_time;
 
    // Leave string empty if addrLocal invalid (not filled in yet)
    CService addrLocalUnlocked = GetAddrLocal();
    stats.addrLocal =
        addrLocalUnlocked.IsValid() ? addrLocalUnlocked.ToString() : "";
 
    stats.m_conn_type = m_conn_type;
 
    stats.m_availabilityScore = m_avalanche_enabled
                                    ? std::make_optional(getAvailabilityScore())
                                    : std::nullopt;
}
 
bool CNode::ReceiveMsgBytes(const Config &config, Span<const uint8_t> msg_bytes,
                            bool &complete) {
    complete = false;
    const auto time = GetTime<std::chrono::microseconds>();
    LOCK(cs_vRecv);
    m_last_recv = std::chrono::duration_cast<std::chrono::seconds>(time);
    nRecvBytes += msg_bytes.size();
    while (msg_bytes.size() > 0) {
        // Absorb network data.
        int handled = m_deserializer->Read(config, msg_bytes);
        if (handled < 0) {
            return false;
        }
 
        if (m_deserializer->Complete()) {
            // decompose a transport agnostic CNetMessage from the deserializer
            CNetMessage msg = m_deserializer->GetMessage(config, time);
 
            // Store received bytes per message command to prevent a memory DOS,
            // only allow valid commands.
            mapMsgCmdSize::iterator i = mapRecvBytesPerMsgCmd.find(msg.m_type);
            if (i == mapRecvBytesPerMsgCmd.end()) {
                i = mapRecvBytesPerMsgCmd.find(NET_MESSAGE_COMMAND_OTHER);
            }
 
            assert(i != mapRecvBytesPerMsgCmd.end());
            i->second += msg.m_raw_message_size;
 
            // push the message to the process queue,
            vRecvMsg.push_back(std::move(msg));
 
            complete = true;
        }
    }
 
    return true;
}
 
int V1TransportDeserializer::readHeader(const Config &config,
                                        Span<const uint8_t> msg_bytes) {
    // copy data to temporary parsing buffer
    uint32_t nRemaining = CMessageHeader::HEADER_SIZE - nHdrPos;
    uint32_t nCopy = std::min<unsigned int>(nRemaining, msg_bytes.size());
 
    memcpy(&hdrbuf[nHdrPos], msg_bytes.data(), nCopy);
    nHdrPos += nCopy;
 
    // if header incomplete, exit
    if (nHdrPos < CMessageHeader::HEADER_SIZE) {
        return nCopy;
    }
 
    // deserialize to CMessageHeader
    try {
        hdrbuf >> hdr;
    } catch (const std::exception &) {
        return -1;
    }
 
    // Reject oversized messages
    if (hdr.IsOversized(config)) {
        LogPrint(BCLog::NET, "Oversized header detected\n");
        return -1;
    }
 
    // switch state to reading message data
    in_data = true;
 
    return nCopy;
}
 
int V1TransportDeserializer::readData(Span<const uint8_t> msg_bytes) {
    unsigned int nRemaining = hdr.nMessageSize - nDataPos;
    unsigned int nCopy = std::min<unsigned int>(nRemaining, msg_bytes.size());
 
    if (vRecv.size() < nDataPos + nCopy) {
        // Allocate up to 256 KiB ahead, but never more than the total message
        // size.
        vRecv.resize(std::min(hdr.nMessageSize, nDataPos + nCopy + 256 * 1024));
    }
 
    hasher.Write(msg_bytes.first(nCopy));
    memcpy(&vRecv[nDataPos], msg_bytes.data(), nCopy);
    nDataPos += nCopy;
 
    return nCopy;
}
 
const uint256 &V1TransportDeserializer::GetMessageHash() const {
    assert(Complete());
    if (data_hash.IsNull()) {
        hasher.Finalize(data_hash);
    }
    return data_hash;
}
 
CNetMessage
V1TransportDeserializer::GetMessage(const Config &config,
                                    const std::chrono::microseconds time) {
    // decompose a single CNetMessage from the TransportDeserializer
    CNetMessage msg(std::move(vRecv));
 
    // store state about valid header, netmagic and checksum
    msg.m_valid_header = hdr.IsValid(config);
    // FIXME Split CheckHeaderMagicAndCommand() into CheckHeaderMagic() and
    // CheckCommand() to prevent the net magic check code duplication.
    msg.m_valid_netmagic =
        (memcmp(std::begin(hdr.pchMessageStart),
                std::begin(config.GetChainParams().NetMagic()),
                CMessageHeader::MESSAGE_START_SIZE) == 0);
    uint256 hash = GetMessageHash();
 
    // store command string, payload size
    msg.m_type = hdr.GetCommand();
    msg.m_message_size = hdr.nMessageSize;
    msg.m_raw_message_size = hdr.nMessageSize + CMessageHeader::HEADER_SIZE;
 
    // We just received a message off the wire, harvest entropy from the time
    // (and the message checksum)
    RandAddEvent(ReadLE32(hash.begin()));
 
    msg.m_valid_checksum = (memcmp(hash.begin(), hdr.pchChecksum,
                                   CMessageHeader::CHECKSUM_SIZE) == 0);
 
    if (!msg.m_valid_checksum) {
        LogPrint(BCLog::NET,
                 "CHECKSUM ERROR (%s, %u bytes), expected %s was %s\n",
                 SanitizeString(msg.m_type), msg.m_message_size,
                 HexStr(Span{hash}.first(CMessageHeader::CHECKSUM_SIZE)),
                 HexStr(hdr.pchChecksum));
    }
 
    // store receive time
    msg.m_time = time;
 
    // reset the network deserializer (prepare for the next message)
    Reset();
    return msg;
}
 
void V1TransportSerializer::prepareForTransport(const Config &config,
                                                CSerializedNetMsg &msg,
                                                std::vector<uint8_t> &header) {
    // create dbl-sha256 checksum
    uint256 hash = Hash(msg.data);
 
    // create header
    CMessageHeader hdr(config.GetChainParams().NetMagic(), msg.m_type.c_str(),
                       msg.data.size());
    memcpy(hdr.pchChecksum, hash.begin(), CMessageHeader::CHECKSUM_SIZE);
 
    // serialize header
    header.reserve(CMessageHeader::HEADER_SIZE);
    CVectorWriter{SER_NETWORK, INIT_PROTO_VERSION, header, 0, hdr};
}
 
size_t CConnman::SocketSendData(CNode &node) const {
    size_t nSentSize = 0;
    size_t nMsgCount = 0;
 
    for (const auto &data : node.vSendMsg) {
        assert(data.size() > node.nSendOffset);
        int nBytes = 0;
 
        {
            LOCK(node.cs_hSocket);
            if (node.hSocket == INVALID_SOCKET) {
                break;
            }
 
            nBytes = send(
                node.hSocket,
                reinterpret_cast<const char *>(data.data()) + node.nSendOffset,
                data.size() - node.nSendOffset, MSG_NOSIGNAL | MSG_DONTWAIT);
        }
 
        if (nBytes == 0) {
            // couldn't send anything at all
            break;
        }
 
        if (nBytes < 0) {
            // error
            int nErr = WSAGetLastError();
            if (nErr != WSAEWOULDBLOCK && nErr != WSAEMSGSIZE &&
                nErr != WSAEINTR && nErr != WSAEINPROGRESS) {
                LogPrint(BCLog::NET, "socket send error for peer=%d: %s\n",
                         node.GetId(), NetworkErrorString(nErr));
                node.CloseSocketDisconnect();
            }
 
            break;
        }
 
        assert(nBytes > 0);
        node.m_last_send = GetTime<std::chrono::seconds>();
        node.nSendBytes += nBytes;
        node.nSendOffset += nBytes;
        nSentSize += nBytes;
        if (node.nSendOffset != data.size()) {
            // could not send full message; stop sending more
            break;
        }
 
        node.nSendOffset = 0;
        node.nSendSize -= data.size();
        node.fPauseSend = node.nSendSize > nSendBufferMaxSize;
        nMsgCount++;
    }
 
    node.vSendMsg.erase(node.vSendMsg.begin(),
                        node.vSendMsg.begin() + nMsgCount);
 
    if (node.vSendMsg.empty()) {
        assert(node.nSendOffset == 0);
        assert(node.nSendSize == 0);
    }
 
    return nSentSize;
}
 
static bool ReverseCompareNodeMinPingTime(const NodeEvictionCandidate &a,
                                          const NodeEvictionCandidate &b) {
    return a.m_min_ping_time > b.m_min_ping_time;
}
 
static bool ReverseCompareNodeTimeConnected(const NodeEvictionCandidate &a,
                                            const NodeEvictionCandidate &b) {
    return a.m_connected > b.m_connected;
}
 
static bool CompareNetGroupKeyed(const NodeEvictionCandidate &a,
                                 const NodeEvictionCandidate &b) {
    return a.nKeyedNetGroup < b.nKeyedNetGroup;
}
 
static bool CompareNodeBlockTime(const NodeEvictionCandidate &a,
                                 const NodeEvictionCandidate &b) {
    // There is a fall-through here because it is common for a node to have many
    // peers which have not yet relayed a block.
    if (a.m_last_block_time != b.m_last_block_time) {
        return a.m_last_block_time < b.m_last_block_time;
    }
 
    if (a.fRelevantServices != b.fRelevantServices) {
        return b.fRelevantServices;
    }
 
    return a.m_connected > b.m_connected;
}
 
static bool CompareNodeTXTime(const NodeEvictionCandidate &a,
                              const NodeEvictionCandidate &b) {
    // There is a fall-through here because it is common for a node to have more
    // than a few peers that have not yet relayed txn.
    if (a.m_last_tx_time != b.m_last_tx_time) {
        return a.m_last_tx_time < b.m_last_tx_time;
    }
 
    if (a.m_relay_txs != b.m_relay_txs) {
        return b.m_relay_txs;
    }
 
    if (a.fBloomFilter != b.fBloomFilter) {
        return a.fBloomFilter;
    }
 
    return a.m_connected > b.m_connected;
}
 
static bool CompareNodeProofTime(const NodeEvictionCandidate &a,
                                 const NodeEvictionCandidate &b) {
    // There is a fall-through here because it is common for a node to have more
    // than a few peers that have not yet relayed proofs. This fallback is also
    // used in the case avalanche is not enabled.
    if (a.m_last_proof_time != b.m_last_proof_time) {
        return a.m_last_proof_time < b.m_last_proof_time;
    }
 
    return a.m_connected > b.m_connected;
}
 
// Pick out the potential block-relay only peers, and sort them by last block
// time.
static bool CompareNodeBlockRelayOnlyTime(const NodeEvictionCandidate &a,
                                          const NodeEvictionCandidate &b) {
    if (a.m_relay_txs != b.m_relay_txs) {
        return a.m_relay_txs;
    }
 
    if (a.m_last_block_time != b.m_last_block_time) {
        return a.m_last_block_time < b.m_last_block_time;
    }
 
    if (a.fRelevantServices != b.fRelevantServices) {
        return b.fRelevantServices;
    }
 
    return a.m_connected > b.m_connected;
}
 
static bool CompareNodeAvailabilityScore(const NodeEvictionCandidate &a,
                                         const NodeEvictionCandidate &b) {
    // Equality can happen if the nodes have no score or it has not been
    // computed yet.
    if (a.availabilityScore != b.availabilityScore) {
        return a.availabilityScore < b.availabilityScore;
    }
 
    return a.m_connected > b.m_connected;
}
 
struct CompareNodeNetworkTime {
    const bool m_is_local;
    const Network m_network;
    CompareNodeNetworkTime(bool is_local, Network network)
        : m_is_local(is_local), m_network(network) {}
    bool operator()(const NodeEvictionCandidate &a,
                    const NodeEvictionCandidate &b) const {
        if (m_is_local && a.m_is_local != b.m_is_local) {
            return b.m_is_local;
        }
        if ((a.m_network == m_network) != (b.m_network == m_network)) {
            return b.m_network == m_network;
        }
        return a.m_connected > b.m_connected;
    };
};
 
template <typename T, typename Comparator>
static void EraseLastKElements(
    std::vector<T> &elements, Comparator comparator, size_t k,
    std::function<bool(const NodeEvictionCandidate &)> predicate =
        [](const NodeEvictionCandidate &n) { return true; }) {
    std::sort(elements.begin(), elements.end(), comparator);
    size_t eraseSize = std::min(k, elements.size());
    elements.erase(
        std::remove_if(elements.end() - eraseSize, elements.end(), predicate),
        elements.end());
}
 
void ProtectEvictionCandidatesByRatio(
    std::vector<NodeEvictionCandidate> &eviction_candidates) {
    // Protect the half of the remaining nodes which have been connected the
    // longest. This replicates the non-eviction implicit behavior, and
    // precludes attacks that start later.
    // To promote the diversity of our peer connections, reserve up to half of
    // these protected spots for Tor/onion, localhost and I2P peers, even if
    // they're not the longest uptime overall. This helps protect these
    // higher-latency peers that tend to be otherwise disadvantaged under our
    // eviction criteria.
    const size_t initial_size = eviction_candidates.size();
    const size_t total_protect_size{initial_size / 2};
 
    // Disadvantaged networks to protect: I2P, localhost and Tor/onion. In case
    // of equal counts, earlier array members have first opportunity to recover
    // unused slots from the previous iteration.
    struct Net {
        bool is_local;
        Network id;
        size_t count;
    };
    std::array<Net, 3> networks{{{false, NET_I2P, 0},
                                 {/* localhost */ true, NET_MAX, 0},
                                 {false, NET_ONION, 0}}};
 
    // Count and store the number of eviction candidates per network.
    for (Net &n : networks) {
        n.count = std::count_if(
            eviction_candidates.cbegin(), eviction_candidates.cend(),
            [&n](const NodeEvictionCandidate &c) {
                return n.is_local ? c.m_is_local : c.m_network == n.id;
            });
    }
    // Sort `networks` by ascending candidate count, to give networks having
    // fewer candidates the first opportunity to recover unused protected slots
    // from the previous iteration.
    std::stable_sort(networks.begin(), networks.end(),
                     [](Net a, Net b) { return a.count < b.count; });
 
    // Protect up to 25% of the eviction candidates by disadvantaged network.
    const size_t max_protect_by_network{total_protect_size / 2};
    size_t num_protected{0};
 
    while (num_protected < max_protect_by_network) {
        // Count the number of disadvantaged networks from which we have peers
        // to protect.
        auto num_networks = std::count_if(networks.begin(), networks.end(),
                                          [](const Net &n) { return n.count; });
        if (num_networks == 0) {
            break;
        }
        const size_t disadvantaged_to_protect{max_protect_by_network -
                                              num_protected};
        const size_t protect_per_network{std::max(
            disadvantaged_to_protect / num_networks, static_cast<size_t>(1))};
 
        // Early exit flag if there are no remaining candidates by disadvantaged
        // network.
        bool protected_at_least_one{false};
 
        for (Net &n : networks) {
            if (n.count == 0) {
                continue;
            }
            const size_t before = eviction_candidates.size();
            EraseLastKElements(
                eviction_candidates, CompareNodeNetworkTime(n.is_local, n.id),
                protect_per_network, [&n](const NodeEvictionCandidate &c) {
                    return n.is_local ? c.m_is_local : c.m_network == n.id;
                });
            const size_t after = eviction_candidates.size();
            if (before > after) {
                protected_at_least_one = true;
                const size_t delta{before - after};
                num_protected += delta;
                if (num_protected >= max_protect_by_network) {
                    break;
                }
                n.count -= delta;
            }
        }
        if (!protected_at_least_one) {
            break;
        }
    }
 
    // Calculate how many we removed, and update our total number of peers that
    // we want to protect based on uptime accordingly.
    assert(num_protected == initial_size - eviction_candidates.size());
    const size_t remaining_to_protect{total_protect_size - num_protected};
    EraseLastKElements(eviction_candidates, ReverseCompareNodeTimeConnected,
                       remaining_to_protect);
}
 
[[nodiscard]] std::optional<NodeId>
SelectNodeToEvict(std::vector<NodeEvictionCandidate> &&vEvictionCandidates) {
    // Protect connections with certain characteristics
 
    // Deterministically select 4 peers to protect by netgroup.
    // An attacker cannot predict which netgroups will be protected
    EraseLastKElements(vEvictionCandidates, CompareNetGroupKeyed, 4);
    // Protect the 8 nodes with the lowest minimum ping time.
    // An attacker cannot manipulate this metric without physically moving nodes
    // closer to the target.
    EraseLastKElements(vEvictionCandidates, ReverseCompareNodeMinPingTime, 8);
    // Protect 4 nodes that most recently sent us novel transactions accepted
    // into our mempool. An attacker cannot manipulate this metric without
    // performing useful work.
    EraseLastKElements(vEvictionCandidates, CompareNodeTXTime, 4);
    // Protect 4 nodes that most recently sent us novel proofs accepted
    // into our proof pool. An attacker cannot manipulate this metric without
    // performing useful work.
    // TODO this filter must happen before the last tx time once avalanche is
    // enabled for pre-consensus.
    EraseLastKElements(vEvictionCandidates, CompareNodeProofTime, 4);
    // Protect up to 8 non-tx-relay peers that have sent us novel blocks.
    EraseLastKElements(vEvictionCandidates, CompareNodeBlockRelayOnlyTime, 8,
                       [](const NodeEvictionCandidate &n) {
                           return !n.m_relay_txs && n.fRelevantServices;
                       });
 
    // Protect 4 nodes that most recently sent us novel blocks.
    // An attacker cannot manipulate this metric without performing useful work.
    EraseLastKElements(vEvictionCandidates, CompareNodeBlockTime, 4);
 
    // Protect up to 128 nodes that have the highest avalanche availability
    // score.
    EraseLastKElements(vEvictionCandidates, CompareNodeAvailabilityScore, 128,
                       [](NodeEvictionCandidate const &n) {
                           return n.availabilityScore > 0.;
                       });
 
    // Protect some of the remaining eviction candidates by ratios of desirable
    // or disadvantaged characteristics.
    ProtectEvictionCandidatesByRatio(vEvictionCandidates);
 
    if (vEvictionCandidates.empty()) {
        return std::nullopt;
    }
 
    // If any remaining peers are preferred for eviction consider only them.
    // This happens after the other preferences since if a peer is really the
    // best by other criteria (esp relaying blocks)
    // then we probably don't want to evict it no matter what.
    if (std::any_of(
            vEvictionCandidates.begin(), vEvictionCandidates.end(),
            [](NodeEvictionCandidate const &n) { return n.prefer_evict; })) {
        vEvictionCandidates.erase(
            std::remove_if(
                vEvictionCandidates.begin(), vEvictionCandidates.end(),
                [](NodeEvictionCandidate const &n) { return !n.prefer_evict; }),
            vEvictionCandidates.end());
    }
 
    // Identify the network group with the most connections and youngest member.
    // (vEvictionCandidates is already sorted by reverse connect time)
    uint64_t naMostConnections;
    unsigned int nMostConnections = 0;
    std::chrono::seconds nMostConnectionsTime{0};
    std::map<uint64_t, std::vector<NodeEvictionCandidate>> mapNetGroupNodes;
    for (const NodeEvictionCandidate &node : vEvictionCandidates) {
        std::vector<NodeEvictionCandidate> &group =
            mapNetGroupNodes[node.nKeyedNetGroup];
        group.push_back(node);
        const auto grouptime{group[0].m_connected};
        size_t group_size = group.size();
        if (group_size > nMostConnections ||
            (group_size == nMostConnections &&
             grouptime > nMostConnectionsTime)) {
            nMostConnections = group_size;
            nMostConnectionsTime = grouptime;
            naMostConnections = node.nKeyedNetGroup;
        }
    }
 
    // Reduce to the network group with the most connections
    vEvictionCandidates = std::move(mapNetGroupNodes[naMostConnections]);
 
    // Disconnect from the network group with the most connections
    return vEvictionCandidates.front().id;
}
 
bool CConnman::AttemptToEvictConnection() {
    std::vector<NodeEvictionCandidate> vEvictionCandidates;
    {
        LOCK(m_nodes_mutex);
        for (const CNode *node : m_nodes) {
            if (node->HasPermission(NetPermissionFlags::NoBan)) {
                continue;
            }
            if (!node->IsInboundConn()) {
                continue;
            }
            if (node->fDisconnect) {
                continue;
            }
 
            NodeEvictionCandidate candidate = {
                node->GetId(),
                node->m_connected,
                node->m_min_ping_time,
                node->m_last_block_time,
                node->m_last_proof_time,
                node->m_last_tx_time,
                node->m_has_all_wanted_services,
                node->m_relays_txs.load(),
                node->m_bloom_filter_loaded.load(),
                node->nKeyedNetGroup,
                node->m_prefer_evict,
                node->addr.IsLocal(),
                node->ConnectedThroughNetwork(),
                node->m_avalanche_enabled
                    ? node->getAvailabilityScore()
                    : -std::numeric_limits<double>::infinity()};
            vEvictionCandidates.push_back(candidate);
        }
    }
    const std::optional<NodeId> node_id_to_evict =
        SelectNodeToEvict(std::move(vEvictionCandidates));
    if (!node_id_to_evict) {
        return false;
    }
    LOCK(m_nodes_mutex);
    for (CNode *pnode : m_nodes) {
        if (pnode->GetId() == *node_id_to_evict) {
            LogPrint(
                BCLog::NET,
                "selected %s connection for eviction peer=%d; disconnecting\n",
                pnode->ConnectionTypeAsString(), pnode->GetId());
            pnode->fDisconnect = true;
            return true;
        }
    }
    return false;
}
 
void CConnman::AcceptConnection(const ListenSocket &hListenSocket) {
    struct sockaddr_storage sockaddr;
    socklen_t len = sizeof(sockaddr);
    SOCKET hSocket =
        accept(hListenSocket.socket, (struct sockaddr *)&sockaddr, &len);
    CAddress addr;
 
    if (hSocket == INVALID_SOCKET) {
        const int nErr = WSAGetLastError();
        if (nErr != WSAEWOULDBLOCK) {
            LogPrintf("socket error accept failed: %s\n",
                      NetworkErrorString(nErr));
        }
        return;
    }
 
    if (!addr.SetSockAddr((const struct sockaddr *)&sockaddr)) {
        LogPrintf("Warning: Unknown socket family\n");
    }
 
    const CAddress addr_bind = GetBindAddress(hSocket);
 
    NetPermissionFlags permissionFlags = NetPermissionFlags::None;
    hListenSocket.AddSocketPermissionFlags(permissionFlags);
 
    CreateNodeFromAcceptedSocket(hSocket, permissionFlags, addr_bind, addr);
}
 
void CConnman::CreateNodeFromAcceptedSocket(SOCKET hSocket,
                                            NetPermissionFlags permissionFlags,
                                            const CAddress &addr_bind,
                                            const CAddress &addr) {
    int nInbound = 0;
    int nMaxInbound = nMaxConnections - m_max_outbound;
 
    AddWhitelistPermissionFlags(permissionFlags, addr);
    if (NetPermissions::HasFlag(permissionFlags,
                                NetPermissionFlags::Implicit)) {
        NetPermissions::ClearFlag(permissionFlags,
                                  NetPermissionFlags::Implicit);
        if (gArgs.GetBoolArg("-whitelistforcerelay",
                             DEFAULT_WHITELISTFORCERELAY)) {
            NetPermissions::AddFlag(permissionFlags,
                                    NetPermissionFlags::ForceRelay);
        }
        if (gArgs.GetBoolArg("-whitelistrelay", DEFAULT_WHITELISTRELAY)) {
            NetPermissions::AddFlag(permissionFlags, NetPermissionFlags::Relay);
        }
        NetPermissions::AddFlag(permissionFlags, NetPermissionFlags::Mempool);
        NetPermissions::AddFlag(permissionFlags, NetPermissionFlags::NoBan);
    }
 
    {
        LOCK(m_nodes_mutex);
        for (const CNode *pnode : m_nodes) {
            if (pnode->IsInboundConn()) {
                nInbound++;
            }
        }
    }
 
    if (!fNetworkActive) {
        LogPrint(BCLog::NET,
                 "connection from %s dropped: not accepting new connections\n",
                 addr.ToString());
        CloseSocket(hSocket);
        return;
    }
 
    if (!IsSelectableSocket(hSocket)) {
        LogPrintf("connection from %s dropped: non-selectable socket\n",
                  addr.ToString());
        CloseSocket(hSocket);
        return;
    }
 
    // According to the internet TCP_NODELAY is not carried into accepted
    // sockets on all platforms.  Set it again here just to be sure.
    SetSocketNoDelay(hSocket);
 
    // Don't accept connections from banned peers.
    bool banned = m_banman && m_banman->IsBanned(addr);
    if (!NetPermissions::HasFlag(permissionFlags, NetPermissionFlags::NoBan) &&
        banned) {
        LogPrint(BCLog::NET, "connection from %s dropped (banned)\n",
                 addr.ToString());
        CloseSocket(hSocket);
        return;
    }
 
    // Only accept connections from discouraged peers if our inbound slots
    // aren't (almost) full.
    bool discouraged = m_banman && m_banman->IsDiscouraged(addr);
    if (!NetPermissions::HasFlag(permissionFlags, NetPermissionFlags::NoBan) &&
        nInbound + 1 >= nMaxInbound && discouraged) {
        LogPrint(BCLog::NET, "connection from %s dropped (discouraged)\n",
                 addr.ToString());
        CloseSocket(hSocket);
        return;
    }
 
    if (nInbound >= nMaxInbound) {
        if (!AttemptToEvictConnection()) {
            // No connection to evict, disconnect the new connection
            LogPrint(BCLog::NET, "failed to find an eviction candidate - "
                                 "connection dropped (full)\n");
            CloseSocket(hSocket);
            return;
        }
    }
 
    NodeId id = GetNewNodeId();
    uint64_t nonce = GetDeterministicRandomizer(RANDOMIZER_ID_LOCALHOSTNONCE)
                         .Write(id)
                         .Finalize();
    uint64_t extra_entropy =
        GetDeterministicRandomizer(RANDOMIZER_ID_EXTRAENTROPY)
            .Write(id)
            .Finalize();
 
    ServiceFlags nodeServices = nLocalServices;
    if (NetPermissions::HasFlag(permissionFlags,
                                NetPermissionFlags::BloomFilter)) {
        nodeServices = static_cast<ServiceFlags>(nodeServices | NODE_BLOOM);
    }
 
    const bool inbound_onion =
        std::find(m_onion_binds.begin(), m_onion_binds.end(), addr_bind) !=
        m_onion_binds.end();
    CNode *pnode = new CNode(id, hSocket, addr, CalculateKeyedNetGroup(addr),
                             nonce, extra_entropy, addr_bind, "",
                             ConnectionType::INBOUND, inbound_onion);
    pnode->AddRef();
    pnode->m_permissionFlags = permissionFlags;
    pnode->m_prefer_evict = discouraged;
    for (auto interface : m_msgproc) {
        interface->InitializeNode(*config, *pnode, nodeServices);
    }
 
    LogPrint(BCLog::NET, "connection from %s accepted\n", addr.ToString());
 
    {
        LOCK(m_nodes_mutex);
        m_nodes.push_back(pnode);
    }
 
    // We received a new connection, harvest entropy from the time (and our peer
    // count)
    RandAddEvent(uint32_t(id));
}
 
bool CConnman::AddConnection(const std::string &address,
                             ConnectionType conn_type) {
    std::optional<int> max_connections;
    switch (conn_type) {
        case ConnectionType::INBOUND:
        case ConnectionType::MANUAL:
            return false;
        case ConnectionType::OUTBOUND_FULL_RELAY:
            max_connections = m_max_outbound_full_relay;
            break;
        case ConnectionType::BLOCK_RELAY:
            max_connections = m_max_outbound_block_relay;
            break;
        // no limit for ADDR_FETCH because -seednode has no limit either
        case ConnectionType::ADDR_FETCH:
            break;
        // no limit for FEELER connections since they're short-lived
        case ConnectionType::FEELER:
            break;
        case ConnectionType::AVALANCHE_OUTBOUND:
            max_connections = m_max_avalanche_outbound;
            break;
    } // no default case, so the compiler can warn about missing cases
 
    // Count existing connections
    int existing_connections =
        WITH_LOCK(m_nodes_mutex,
                  return std::count_if(
                      m_nodes.begin(), m_nodes.end(), [conn_type](CNode *node) {
                          return node->m_conn_type == conn_type;
                      }););
 
    // Max connections of specified type already exist
    if (max_connections != std::nullopt &&
        existing_connections >= max_connections) {
        return false;
    }
 
    // Max total outbound connections already exist
    CSemaphoreGrant grant(*semOutbound, true);
    if (!grant) {
        return false;
    }
 
    OpenNetworkConnection(CAddress(), false, &grant, address.c_str(),
                          conn_type);
    return true;
}
 
void CConnman::DisconnectNodes() {
    {
        LOCK(m_nodes_mutex);
 
        if (!fNetworkActive) {
            // Disconnect any connected nodes
            for (CNode *pnode : m_nodes) {
                if (!pnode->fDisconnect) {
                    LogPrint(BCLog::NET,
                             "Network not active, dropping peer=%d\n",
                             pnode->GetId());
                    pnode->fDisconnect = true;
                }
            }
        }
 
        // Disconnect unused nodes
        std::vector<CNode *> nodes_copy = m_nodes;
        for (CNode *pnode : nodes_copy) {
            if (pnode->fDisconnect) {
                // remove from m_nodes
                m_nodes.erase(remove(m_nodes.begin(), m_nodes.end(), pnode),
                              m_nodes.end());
 
                // release outbound grant (if any)
                pnode->grantOutbound.Release();
 
                // close socket and cleanup
                pnode->CloseSocketDisconnect();
 
                // hold in disconnected pool until all refs are released
                pnode->Release();
                m_nodes_disconnected.push_back(pnode);
            }
        }
    }
    {
        // Delete disconnected nodes
        std::list<CNode *> nodes_disconnected_copy = m_nodes_disconnected;
        for (CNode *pnode : nodes_disconnected_copy) {
            // Destroy the object only after other threads have stopped using
            // it.
            if (pnode->GetRefCount() <= 0) {
                m_nodes_disconnected.remove(pnode);
                DeleteNode(pnode);
            }
        }
    }
}
 
void CConnman::NotifyNumConnectionsChanged() {
    size_t nodes_size;
    {
        LOCK(m_nodes_mutex);
        nodes_size = m_nodes.size();
    }
    if (nodes_size != nPrevNodeCount) {
        nPrevNodeCount = nodes_size;
        if (m_client_interface) {
            m_client_interface->NotifyNumConnectionsChanged(nodes_size);
        }
    }
}
 
bool CConnman::ShouldRunInactivityChecks(const CNode &node,
                                         std::chrono::seconds now) const {
    return node.m_connected + m_peer_connect_timeout < now;
}
 
bool CConnman::InactivityCheck(const CNode &node) const {
    // Tests that see disconnects after using mocktime can start nodes with a
    // large timeout. For example, -peertimeout=999999999.
    const auto now{GetTime<std::chrono::seconds>()};
    const auto last_send{node.m_last_send.load()};
    const auto last_recv{node.m_last_recv.load()};
 
    if (!ShouldRunInactivityChecks(node, now)) {
        return false;
    }
 
    if (last_recv.count() == 0 || last_send.count() == 0) {
        LogPrint(BCLog::NET,
                 "socket no message in first %i seconds, %d %d peer=%d\n",
                 count_seconds(m_peer_connect_timeout), last_recv.count() != 0,
                 last_send.count() != 0, node.GetId());
        return true;
    }
 
    if (now > last_send + TIMEOUT_INTERVAL) {
        LogPrint(BCLog::NET, "socket sending timeout: %is peer=%d\n",
                 count_seconds(now - last_send), node.GetId());
        return true;
    }
 
    if (now > last_recv + TIMEOUT_INTERVAL) {
        LogPrint(BCLog::NET, "socket receive timeout: %is peer=%d\n",
                 count_seconds(now - last_recv), node.GetId());
        return true;
    }
 
    if (!node.fSuccessfullyConnected) {
        LogPrint(BCLog::NET, "version handshake timeout peer=%d\n",
                 node.GetId());
        return true;
    }
 
    return false;
}
 
bool CConnman::GenerateSelectSet(std::set<SOCKET> &recv_set,
                                 std::set<SOCKET> &send_set,
                                 std::set<SOCKET> &error_set) {
    for (const ListenSocket &hListenSocket : vhListenSocket) {
        recv_set.insert(hListenSocket.socket);
    }
 
    {
        LOCK(m_nodes_mutex);
        for (CNode *pnode : m_nodes) {
            // Implement the following logic:
            // * If there is data to send, select() for sending data. As this
            //   only happens when optimistic write failed, we choose to first
            //   drain the write buffer in this case before receiving more. This
            //   avoids needlessly queueing received data, if the remote peer is
            //   not themselves receiving data. This means properly utilizing
            //   TCP flow control signalling.
            // * Otherwise, if there is space left in the receive buffer,
            //   select() for receiving data.
            // * Hand off all complete messages to the processor, to be handled
            //   without blocking here.
 
            bool select_recv = !pnode->fPauseRecv;
            bool select_send;
            {
                LOCK(pnode->cs_vSend);
                select_send = !pnode->vSendMsg.empty();
            }
 
            LOCK(pnode->cs_hSocket);
            if (pnode->hSocket == INVALID_SOCKET) {
                continue;
            }
 
            error_set.insert(pnode->hSocket);
            if (select_send) {
                send_set.insert(pnode->hSocket);
                continue;
            }
            if (select_recv) {
                recv_set.insert(pnode->hSocket);
            }
        }
    }
 
    return !recv_set.empty() || !send_set.empty() || !error_set.empty();
}
 
#ifdef USE_POLL
void CConnman::SocketEvents(std::set<SOCKET> &recv_set,
                            std::set<SOCKET> &send_set,
                            std::set<SOCKET> &error_set) {
    std::set<SOCKET> recv_select_set, send_select_set, error_select_set;
    if (!GenerateSelectSet(recv_select_set, send_select_set,
                           error_select_set)) {
        interruptNet.sleep_for(
            std::chrono::milliseconds(SELECT_TIMEOUT_MILLISECONDS));
        return;
    }
 
    std::unordered_map<SOCKET, struct pollfd> pollfds;
    for (SOCKET socket_id : recv_select_set) {
        pollfds[socket_id].fd = socket_id;
        pollfds[socket_id].events |= POLLIN;
    }
 
    for (SOCKET socket_id : send_select_set) {
        pollfds[socket_id].fd = socket_id;
        pollfds[socket_id].events |= POLLOUT;
    }
 
    for (SOCKET socket_id : error_select_set) {
        pollfds[socket_id].fd = socket_id;
        // These flags are ignored, but we set them for clarity
        pollfds[socket_id].events |= POLLERR | POLLHUP;
    }
 
    std::vector<struct pollfd> vpollfds;
    vpollfds.reserve(pollfds.size());
    for (auto it : pollfds) {
        vpollfds.push_back(std::move(it.second));
    }
 
    if (poll(vpollfds.data(), vpollfds.size(), SELECT_TIMEOUT_MILLISECONDS) <
        0) {
        return;
    }
 
    if (interruptNet) {
        return;
    }
 
    for (struct pollfd pollfd_entry : vpollfds) {
        if (pollfd_entry.revents & POLLIN) {
            recv_set.insert(pollfd_entry.fd);
        }
        if (pollfd_entry.revents & POLLOUT) {
            send_set.insert(pollfd_entry.fd);
        }
        if (pollfd_entry.revents & (POLLERR | POLLHUP)) {
            error_set.insert(pollfd_entry.fd);
        }
    }
}
#else
void CConnman::SocketEvents(std::set<SOCKET> &recv_set,
                            std::set<SOCKET> &send_set,
                            std::set<SOCKET> &error_set) {
    std::set<SOCKET> recv_select_set, send_select_set, error_select_set;
    if (!GenerateSelectSet(recv_select_set, send_select_set,
                           error_select_set)) {
        interruptNet.sleep_for(
            std::chrono::milliseconds(SELECT_TIMEOUT_MILLISECONDS));
        return;
    }
 
    //
    // Find which sockets have data to receive
    //
    struct timeval timeout;
    timeout.tv_sec = 0;
    // frequency to poll pnode->vSend
    timeout.tv_usec = SELECT_TIMEOUT_MILLISECONDS * 1000;
 
    fd_set fdsetRecv;
    fd_set fdsetSend;
    fd_set fdsetError;
    FD_ZERO(&fdsetRecv);
    FD_ZERO(&fdsetSend);
    FD_ZERO(&fdsetError);
    SOCKET hSocketMax = 0;
 
    for (SOCKET hSocket : recv_select_set) {
        FD_SET(hSocket, &fdsetRecv);
        hSocketMax = std::max(hSocketMax, hSocket);
    }
 
    for (SOCKET hSocket : send_select_set) {
        FD_SET(hSocket, &fdsetSend);
        hSocketMax = std::max(hSocketMax, hSocket);
    }
 
    for (SOCKET hSocket : error_select_set) {
        FD_SET(hSocket, &fdsetError);
        hSocketMax = std::max(hSocketMax, hSocket);
    }
 
    int nSelect =
        select(hSocketMax + 1, &fdsetRecv, &fdsetSend, &fdsetError, &timeout);
 
    if (interruptNet) {
        return;
    }
 
    if (nSelect == SOCKET_ERROR) {
        int nErr = WSAGetLastError();
        LogPrintf("socket select error %s\n", NetworkErrorString(nErr));
        for (unsigned int i = 0; i <= hSocketMax; i++) {
            FD_SET(i, &fdsetRecv);
        }
        FD_ZERO(&fdsetSend);
        FD_ZERO(&fdsetError);
        if (!interruptNet.sleep_for(
                std::chrono::milliseconds(SELECT_TIMEOUT_MILLISECONDS))) {
            return;
        }
    }
 
    for (SOCKET hSocket : recv_select_set) {
        if (FD_ISSET(hSocket, &fdsetRecv)) {
            recv_set.insert(hSocket);
        }
    }
 
    for (SOCKET hSocket : send_select_set) {
        if (FD_ISSET(hSocket, &fdsetSend)) {
            send_set.insert(hSocket);
        }
    }
 
    for (SOCKET hSocket : error_select_set) {
        if (FD_ISSET(hSocket, &fdsetError)) {
            error_set.insert(hSocket);
        }
    }
}
#endif
 
void CConnman::SocketHandler() {
    std::set<SOCKET> recv_set, send_set, error_set;
    SocketEvents(recv_set, send_set, error_set);
 
    if (interruptNet) {
        return;
    }
 
    //
    // Accept new connections
    //
    for (const ListenSocket &hListenSocket : vhListenSocket) {
        if (hListenSocket.socket != INVALID_SOCKET &&
            recv_set.count(hListenSocket.socket) > 0) {
            AcceptConnection(hListenSocket);
        }
    }
 
    //
    // Service each socket
    //
    std::vector<CNode *> nodes_copy;
    {
        LOCK(m_nodes_mutex);
        nodes_copy = m_nodes;
        for (CNode *pnode : nodes_copy) {
            pnode->AddRef();
        }
    }
    for (CNode *pnode : nodes_copy) {
        if (interruptNet) {
            return;
        }
 
        //
        // Receive
        //
        bool recvSet = false;
        bool sendSet = false;
        bool errorSet = false;
        {
            LOCK(pnode->cs_hSocket);
            if (pnode->hSocket == INVALID_SOCKET) {
                continue;
            }
            recvSet = recv_set.count(pnode->hSocket) > 0;
            sendSet = send_set.count(pnode->hSocket) > 0;
            errorSet = error_set.count(pnode->hSocket) > 0;
        }
        if (recvSet || errorSet) {
            // typical socket buffer is 8K-64K
            uint8_t pchBuf[0x10000];
            int32_t nBytes = 0;
            {
                LOCK(pnode->cs_hSocket);
                if (pnode->hSocket == INVALID_SOCKET) {
                    continue;
                }
                nBytes = recv(pnode->hSocket, (char *)pchBuf, sizeof(pchBuf),
                              MSG_DONTWAIT);
            }
            if (nBytes > 0) {
                bool notify = false;
                if (!pnode->ReceiveMsgBytes(*config, {pchBuf, (size_t)nBytes},
                                            notify)) {
                    pnode->CloseSocketDisconnect();
                }
                RecordBytesRecv(nBytes);
                if (notify) {
                    size_t nSizeAdded = 0;
                    auto it(pnode->vRecvMsg.begin());
                    for (; it != pnode->vRecvMsg.end(); ++it) {
                        // vRecvMsg contains only completed CNetMessage
                        // the single possible partially deserialized message
                        // are held by TransportDeserializer
                        nSizeAdded += it->m_raw_message_size;
                    }
                    {
                        LOCK(pnode->cs_vProcessMsg);
                        pnode->vProcessMsg.splice(pnode->vProcessMsg.end(),
                                                  pnode->vRecvMsg,
                                                  pnode->vRecvMsg.begin(), it);
                        pnode->nProcessQueueSize += nSizeAdded;
                        pnode->fPauseRecv =
                            pnode->nProcessQueueSize > nReceiveFloodSize;
                    }
                    WakeMessageHandler();
                }
            } else if (nBytes == 0) {
                // socket closed gracefully
                if (!pnode->fDisconnect) {
                    LogPrint(BCLog::NET, "socket closed for peer=%d\n",
                             pnode->GetId());
                }
                pnode->CloseSocketDisconnect();
            } else if (nBytes < 0) {
                // error
                int nErr = WSAGetLastError();
                if (nErr != WSAEWOULDBLOCK && nErr != WSAEMSGSIZE &&
                    nErr != WSAEINTR && nErr != WSAEINPROGRESS) {
                    if (!pnode->fDisconnect) {
                        LogPrint(BCLog::NET,
                                 "socket recv error for peer=%d: %s\n",
                                 pnode->GetId(), NetworkErrorString(nErr));
                    }
                    pnode->CloseSocketDisconnect();
                }
            }
        }
 
        if (sendSet) {
            // Send data
            size_t bytes_sent =
                WITH_LOCK(pnode->cs_vSend, return SocketSendData(*pnode));
            if (bytes_sent) {
                RecordBytesSent(bytes_sent);
            }
        }
 
        if (InactivityCheck(*pnode)) {
            pnode->fDisconnect = true;
        }
    }
    {
        LOCK(m_nodes_mutex);
        for (CNode *pnode : nodes_copy) {
            pnode->Release();
        }
    }
}
 
void CConnman::ThreadSocketHandler() {
    while (!interruptNet) {
        DisconnectNodes();
        NotifyNumConnectionsChanged();
        SocketHandler();
    }
}
 
void CConnman::WakeMessageHandler() {
    {
        LOCK(mutexMsgProc);
        fMsgProcWake = true;
    }
    condMsgProc.notify_one();
}
 
void CConnman::ThreadDNSAddressSeed() {
    FastRandomContext rng;
    std::vector<std::string> seeds =
        GetRandomizedDNSSeeds(config->GetChainParams());
    // Number of seeds left before testing if we have enough connections
    int seeds_right_now = 0;
    int found = 0;
 
    if (gArgs.GetBoolArg("-forcednsseed", DEFAULT_FORCEDNSSEED)) {
        // When -forcednsseed is provided, query all.
        seeds_right_now = seeds.size();
    } else if (addrman.size() == 0) {
        // If we have no known peers, query all.
        // This will occur on the first run, or if peers.dat has been
        // deleted.
        seeds_right_now = seeds.size();
    }
 
    // goal: only query DNS seed if address need is acute
    // * If we have a reasonable number of peers in addrman, spend
    //   some time trying them first. This improves user privacy by
    //   creating fewer identifying DNS requests, reduces trust by
    //   giving seeds less influence on the network topology, and
    //   reduces traffic to the seeds.
    // * When querying DNS seeds query a few at once, this ensures
    //   that we don't give DNS seeds the ability to eclipse nodes
    //   that query them.
    // * If we continue having problems, eventually query all the
    //   DNS seeds, and if that fails too, also try the fixed seeds.
    //   (done in ThreadOpenConnections)
    const std::chrono::seconds seeds_wait_time =
        (addrman.size() >= DNSSEEDS_DELAY_PEER_THRESHOLD
             ? DNSSEEDS_DELAY_MANY_PEERS
             : DNSSEEDS_DELAY_FEW_PEERS);
 
    for (const std::string &seed : seeds) {
        if (seeds_right_now == 0) {
            seeds_right_now += DNSSEEDS_TO_QUERY_AT_ONCE;
 
            if (addrman.size() > 0) {
                LogPrintf("Waiting %d seconds before querying DNS seeds.\n",
                          seeds_wait_time.count());
                std::chrono::seconds to_wait = seeds_wait_time;
                while (to_wait.count() > 0) {
                    // if sleeping for the MANY_PEERS interval, wake up
                    // early to see if we have enough peers and can stop
                    // this thread entirely freeing up its resources
                    std::chrono::seconds w =
                        std::min(DNSSEEDS_DELAY_FEW_PEERS, to_wait);
                    if (!interruptNet.sleep_for(w)) {
                        return;
                    }
                    to_wait -= w;
 
                    int nRelevant = 0;
                    {
                        LOCK(m_nodes_mutex);
                        for (const CNode *pnode : m_nodes) {
                            if (pnode->fSuccessfullyConnected &&
                                pnode->IsFullOutboundConn()) {
                                ++nRelevant;
                            }
                        }
                    }
                    if (nRelevant >= 2) {
                        if (found > 0) {
                            LogPrintf("%d addresses found from DNS seeds\n",
                                      found);
                            LogPrintf(
                                "P2P peers available. Finished DNS seeding.\n");
                        } else {
                            LogPrintf(
                                "P2P peers available. Skipped DNS seeding.\n");
                        }
                        return;
                    }
                }
            }
        }
 
        if (interruptNet) {
            return;
        }
 
        // hold off on querying seeds if P2P network deactivated
        if (!fNetworkActive) {
            LogPrintf("Waiting for network to be reactivated before querying "
                      "DNS seeds.\n");
            do {
                if (!interruptNet.sleep_for(std::chrono::seconds{1})) {
                    return;
                }
            } while (!fNetworkActive);
        }
 
        LogPrintf("Loading addresses from DNS seed %s\n", seed);
        if (HaveNameProxy()) {
            AddAddrFetch(seed);
        } else {
            std::vector<CNetAddr> vIPs;
            std::vector<CAddress> vAdd;
            ServiceFlags requiredServiceBits =
                GetDesirableServiceFlags(NODE_NONE);
            std::string host = strprintf("x%x.%s", requiredServiceBits, seed);
            CNetAddr resolveSource;
            if (!resolveSource.SetInternal(host)) {
                continue;
            }
 
            // Limits number of IPs learned from a DNS seed
            unsigned int nMaxIPs = 256;
            if (LookupHost(host, vIPs, nMaxIPs, true)) {
                for (const CNetAddr &ip : vIPs) {
                    CAddress addr = CAddress(
                        CService(ip, config->GetChainParams().GetDefaultPort()),
                        requiredServiceBits);
                    // Use a random age between 3 and 7 days old.
                    addr.nTime = rng.rand_uniform_delay(
                        Now<NodeSeconds>() - 3 * 24h, -4 * 24h);
                    vAdd.push_back(addr);
                    found++;
                }
                addrman.Add(vAdd, resolveSource);
            } else {
                // We now avoid directly using results from DNS Seeds which do
                // not support service bit filtering, instead using them as a
                // addrfetch to get nodes with our desired service bits.
                AddAddrFetch(seed);
            }
        }
        --seeds_right_now;
    }
    LogPrintf("%d addresses found from DNS seeds\n", found);
}
 
void CConnman::DumpAddresses() {
    int64_t nStart = GetTimeMillis();
 
    DumpPeerAddresses(config->GetChainParams(), ::gArgs, addrman);
 
    LogPrint(BCLog::NET, "Flushed %d addresses to peers.dat  %dms\n",
             addrman.size(), GetTimeMillis() - nStart);
}
 
void CConnman::ProcessAddrFetch() {
    std::string strDest;
    {
        LOCK(m_addr_fetches_mutex);
        if (m_addr_fetches.empty()) {
            return;
        }
        strDest = m_addr_fetches.front();
        m_addr_fetches.pop_front();
    }
    CAddress addr;
    CSemaphoreGrant grant(*semOutbound, true);
    if (grant) {
        OpenNetworkConnection(addr, false, &grant, strDest.c_str(),
                              ConnectionType::ADDR_FETCH);
    }
}
 
bool CConnman::GetTryNewOutboundPeer() const {
    return m_try_another_outbound_peer;
}
 
void CConnman::SetTryNewOutboundPeer(bool flag) {
    m_try_another_outbound_peer = flag;
    LogPrint(BCLog::NET, "net: setting try another outbound peer=%s\n",
             flag ? "true" : "false");
}
 
// Return the number of peers we have over our outbound connection limit.
// Exclude peers that are marked for disconnect, or are going to be disconnected
// soon (eg ADDR_FETCH and FEELER).
// Also exclude peers that haven't finished initial connection handshake yet (so
// that we don't decide we're over our desired connection limit, and then evict
// some peer that has finished the handshake).
int CConnman::GetExtraFullOutboundCount() const {
    int full_outbound_peers = 0;
    {
        LOCK(m_nodes_mutex);
        for (const CNode *pnode : m_nodes) {
            if (pnode->fSuccessfullyConnected && !pnode->fDisconnect &&
                pnode->IsFullOutboundConn()) {
                ++full_outbound_peers;
            }
        }
    }
    return std::max(full_outbound_peers - m_max_outbound_full_relay -
                        m_max_avalanche_outbound,
                    0);
}
 
int CConnman::GetExtraBlockRelayCount() const {
    int block_relay_peers = 0;
    {
        LOCK(m_nodes_mutex);
        for (const CNode *pnode : m_nodes) {
            if (pnode->fSuccessfullyConnected && !pnode->fDisconnect &&
                pnode->IsBlockOnlyConn()) {
                ++block_relay_peers;
            }
        }
    }
    return std::max(block_relay_peers - m_max_outbound_block_relay, 0);
}
 
void CConnman::ThreadOpenConnections(
    const std::vector<std::string> connect,
    std::function<void(const CAddress &, ConnectionType)> mockOpenConnection) {
    // Connect to specific addresses
    if (!connect.empty()) {
        for (int64_t nLoop = 0;; nLoop++) {
            ProcessAddrFetch();
            for (const std::string &strAddr : connect) {
                CAddress addr(CService(), NODE_NONE);
                OpenNetworkConnection(addr, false, nullptr, strAddr.c_str(),
                                      ConnectionType::MANUAL);
                for (int i = 0; i < 10 && i < nLoop; i++) {
                    if (!interruptNet.sleep_for(
                            std::chrono::milliseconds(500))) {
                        return;
                    }
                }
            }
            if (!interruptNet.sleep_for(std::chrono::milliseconds(500))) {
                return;
            }
        }
    }
 
    // Initiate network connections
    auto start = GetTime<std::chrono::microseconds>();
 
    // Minimum time before next feeler connection (in microseconds).
    auto next_feeler = GetExponentialRand(start, FEELER_INTERVAL);
    auto next_extra_block_relay =
        GetExponentialRand(start, EXTRA_BLOCK_RELAY_ONLY_PEER_INTERVAL);
    const bool dnsseed = gArgs.GetBoolArg("-dnsseed", DEFAULT_DNSSEED);
    bool add_fixed_seeds = gArgs.GetBoolArg("-fixedseeds", DEFAULT_FIXEDSEEDS);
 
    if (!add_fixed_seeds) {
        LogPrintf("Fixed seeds are disabled\n");
    }
 
    while (!interruptNet) {
        ProcessAddrFetch();
 
        // No need to sleep the thread if we are mocking the network connection
        if (!mockOpenConnection &&
            !interruptNet.sleep_for(std::chrono::milliseconds(500))) {
            return;
        }
 
        CSemaphoreGrant grant(*semOutbound);
        if (interruptNet) {
            return;
        }
 
        if (add_fixed_seeds && addrman.size() == 0) {
            // When the node starts with an empty peers.dat, there are a few
            // other sources of peers before we fallback on to fixed seeds:
            // -dnsseed, -seednode, -addnode If none of those are available, we
            // fallback on to fixed seeds immediately, else we allow 60 seconds
            // for any of those sources to populate addrman.
            bool add_fixed_seeds_now = false;
            // It is cheapest to check if enough time has passed first.
            if (GetTime<std::chrono::seconds>() >
                start + std::chrono::minutes{1}) {
                add_fixed_seeds_now = true;
                LogPrintf("Adding fixed seeds as 60 seconds have passed and "
                          "addrman is empty\n");
            }
 
            // Checking !dnsseed is cheaper before locking 2 mutexes.
            if (!add_fixed_seeds_now && !dnsseed) {
                LOCK2(m_addr_fetches_mutex, m_added_nodes_mutex);
                if (m_addr_fetches.empty() && m_added_nodes.empty()) {
                    add_fixed_seeds_now = true;
                    LogPrintf(
                        "Adding fixed seeds as -dnsseed=0, -addnode is not "
                        "provided and all -seednode(s) attempted\n");
                }
            }
 
            if (add_fixed_seeds_now) {
                CNetAddr local;
                local.SetInternal("fixedseeds");
                addrman.Add(convertSeed6(config->GetChainParams().FixedSeeds()),
                            local);
                add_fixed_seeds = false;
            }
        }
 
        //
        // Choose an address to connect to based on most recently seen
        //
        CAddress addrConnect;
 
        // Only connect out to one peer per network group (/16 for IPv4).
        int nOutboundFullRelay = 0;
        int nOutboundBlockRelay = 0;
        int nOutboundAvalanche = 0;
        std::set<std::vector<uint8_t>> setConnected;
 
        {
            LOCK(m_nodes_mutex);
            for (const CNode *pnode : m_nodes) {
                if (pnode->IsAvalancheOutboundConnection()) {
                    nOutboundAvalanche++;
                } else if (pnode->IsFullOutboundConn()) {
                    nOutboundFullRelay++;
                } else if (pnode->IsBlockOnlyConn()) {
                    nOutboundBlockRelay++;
                }
 
                // Netgroups for inbound and manual peers are not excluded
                // because our goal here is to not use multiple of our
                // limited outbound slots on a single netgroup but inbound
                // and manual peers do not use our outbound slots. Inbound
                // peers also have the added issue that they could be attacker
                // controlled and could be used to prevent us from connecting
                // to particular hosts if we used them here.
                switch (pnode->m_conn_type) {
                    case ConnectionType::INBOUND:
                    case ConnectionType::MANUAL:
                        break;
                    case ConnectionType::AVALANCHE_OUTBOUND:
                    case ConnectionType::OUTBOUND_FULL_RELAY:
                    case ConnectionType::BLOCK_RELAY:
                    case ConnectionType::ADDR_FETCH:
                    case ConnectionType::FEELER:
                        setConnected.insert(
                            pnode->addr.GetGroup(addrman.GetAsmap()));
                } // no default case, so the compiler can warn about missing
                  // cases
            }
        }
 
        ConnectionType conn_type = ConnectionType::OUTBOUND_FULL_RELAY;
        auto now = GetTime<std::chrono::microseconds>();
        bool anchor = false;
        bool fFeeler = false;
 
        // Determine what type of connection to open. Opening
        // BLOCK_RELAY connections to addresses from anchors.dat gets the
        // highest priority. Then we open AVALANCHE_OUTBOUND connection until we
        // hit our avalanche outbound peer limit, which is 0 if avalanche is not
        // enabled. We fallback after 50 retries to OUTBOUND_FULL_RELAY if the
        // peer is not avalanche capable until we meet our full-relay capacity.
        // Then we open BLOCK_RELAY connection until we hit our block-relay-only
        // peer limit.
        // GetTryNewOutboundPeer() gets set when a stale tip is detected, so we
        // try opening an additional OUTBOUND_FULL_RELAY connection. If none of
        // these conditions are met, check to see if it's time to try an extra
        // block-relay-only peer (to confirm our tip is current, see below) or
        // the next_feeler timer to decide if we should open a FEELER.
 
        if (!m_anchors.empty() &&
            (nOutboundBlockRelay < m_max_outbound_block_relay)) {
            conn_type = ConnectionType::BLOCK_RELAY;
            anchor = true;
        } else if (g_avalanche &&
                   (nOutboundAvalanche < m_max_avalanche_outbound)) {
            conn_type = ConnectionType::AVALANCHE_OUTBOUND;
        } else if (nOutboundFullRelay < m_max_outbound_full_relay) {
            // OUTBOUND_FULL_RELAY
        } else if (nOutboundBlockRelay < m_max_outbound_block_relay) {
            conn_type = ConnectionType::BLOCK_RELAY;
        } else if (GetTryNewOutboundPeer()) {
            // OUTBOUND_FULL_RELAY
        } else if (now > next_extra_block_relay &&
                   m_start_extra_block_relay_peers) {
            // Periodically connect to a peer (using regular outbound selection
            // methodology from addrman) and stay connected long enough to sync
            // headers, but not much else.
            //
            // Then disconnect the peer, if we haven't learned anything new.
            //
            // The idea is to make eclipse attacks very difficult to pull off,
            // because every few minutes we're finding a new peer to learn
            // headers from.
            //
            // This is similar to the logic for trying extra outbound
            // (full-relay) peers, except:
            // - we do this all the time on an exponential timer, rather than
            //   just  when our tip is stale
            // - we potentially disconnect our next-youngest block-relay-only
            //   peer, if our newest block-relay-only peer delivers a block more
            //   recently.
            //   See the eviction logic in net_processing.cpp.
            //
            // Because we can promote these connections to block-relay-only
            // connections, they do not get their own ConnectionType enum
            // (similar to how we deal with extra outbound peers).
            next_extra_block_relay =
                GetExponentialRand(now, EXTRA_BLOCK_RELAY_ONLY_PEER_INTERVAL);
            conn_type = ConnectionType::BLOCK_RELAY;
        } else if (now > next_feeler) {
            next_feeler = GetExponentialRand(now, FEELER_INTERVAL);
            conn_type = ConnectionType::FEELER;
            fFeeler = true;
        } else {
            // skip to next iteration of while loop
            continue;
        }
 
        addrman.ResolveCollisions();
 
        const auto nANow{AdjustedTime()};
        int nTries = 0;
        while (!interruptNet) {
            if (anchor && !m_anchors.empty()) {
                const CAddress addr = m_anchors.back();
                m_anchors.pop_back();
                if (!addr.IsValid() || IsLocal(addr) || !IsReachable(addr) ||
                    !HasAllDesirableServiceFlags(addr.nServices) ||
                    setConnected.count(addr.GetGroup(addrman.GetAsmap()))) {
                    continue;
                }
                addrConnect = addr;
                LogPrint(BCLog::NET,
                         "Trying to make an anchor connection to %s\n",
                         addrConnect.ToString());
                break;
            }
            // If we didn't find an appropriate destination after trying 100
            // addresses fetched from addrman, stop this loop, and let the outer
            // loop run again (which sleeps, adds seed nodes, recalculates
            // already-connected network ranges, ...) before trying new addrman
            // addresses.
            nTries++;
            if (nTries > 100) {
                break;
            }
 
            CAddress addr;
            NodeSeconds addr_last_try{0s};
 
            if (fFeeler) {
                // First, try to get a tried table collision address. This
                // returns an empty (invalid) address if there are no collisions
                // to try.
                std::tie(addr, addr_last_try) = addrman.SelectTriedCollision();
 
                if (!addr.IsValid()) {
                    // No tried table collisions. Select a new table address
                    // for our feeler.
                    std::tie(addr, addr_last_try) = addrman.Select(true);
                } else if (AlreadyConnectedToAddress(addr)) {
                    // If test-before-evict logic would have us connect to a
                    // peer that we're already connected to, just mark that
                    // address as Good(). We won't be able to initiate the
                    // connection anyway, so this avoids inadvertently evicting
                    // a currently-connected peer.
                    addrman.Good(addr);
                    // Select a new table address for our feeler instead.
                    std::tie(addr, addr_last_try) = addrman.Select(true);
                }
            } else {
                // Not a feeler
                std::tie(addr, addr_last_try) = addrman.Select();
            }
 
            // Require outbound connections, other than feelers and avalanche,
            // to be to distinct network groups
            if (!fFeeler && conn_type != ConnectionType::AVALANCHE_OUTBOUND &&
                setConnected.count(addr.GetGroup(addrman.GetAsmap()))) {
                break;
            }
 
            // if we selected an invalid or local address, restart
            if (!addr.IsValid() || IsLocal(addr)) {
                break;
            }
 
            if (!IsReachable(addr)) {
                continue;
            }
 
            // only consider very recently tried nodes after 30 failed attempts
            if (nANow - addr_last_try < 10min && nTries < 30) {
                continue;
            }
 
            // for non-feelers, require all the services we'll want,
            // for feelers, only require they be a full node (only because most
            // SPV clients don't have a good address DB available)
            if (!fFeeler && !HasAllDesirableServiceFlags(addr.nServices)) {
                continue;
            }
 
            if (fFeeler && !MayHaveUsefulAddressDB(addr.nServices)) {
                continue;
            }
 
            // Do not connect to bad ports, unless 50 invalid addresses have
            // been selected already.
            if (nTries < 50 && (addr.IsIPv4() || addr.IsIPv6()) &&
                IsBadPort(addr.GetPort())) {
                continue;
            }
 
            // For avalanche peers, check they have the avalanche service bit
            // set.
            if (conn_type == ConnectionType::AVALANCHE_OUTBOUND &&
                !(addr.nServices & NODE_AVALANCHE)) {
                // If this peer is not suitable as an avalanche one and we tried
                // over 20 addresses already, see if we can fallback to a non
                // avalanche full outbound.
                if (nTries < 20 ||
                    nOutboundFullRelay >= m_max_outbound_full_relay ||
                    setConnected.count(addr.GetGroup(addrman.GetAsmap()))) {
                    // Fallback is not desirable or possible, try another one
                    continue;
                }
 
                // Fallback is possible, update the connection type accordingly
                conn_type = ConnectionType::OUTBOUND_FULL_RELAY;
            }
 
            addrConnect = addr;
            break;
        }
 
        if (addrConnect.IsValid()) {
            if (fFeeler) {
                // Add small amount of random noise before connection to avoid
                // synchronization.
                int randsleep = GetRand<int>(FEELER_SLEEP_WINDOW * 1000);
                if (!interruptNet.sleep_for(
                        std::chrono::milliseconds(randsleep))) {
                    return;
                }
                LogPrint(BCLog::NET, "Making feeler connection to %s\n",
                         addrConnect.ToString());
            }
 
            // This mock is for testing purpose only. It prevents the thread
            // from attempting the connection which is useful for testing.
            if (mockOpenConnection) {
                mockOpenConnection(addrConnect, conn_type);
            } else {
                OpenNetworkConnection(addrConnect,
                                      int(setConnected.size()) >=
                                          std::min(nMaxConnections - 1, 2),
                                      &grant, nullptr, conn_type);
            }
        }
    }
}
 
std::vector<CAddress> CConnman::GetCurrentBlockRelayOnlyConns() const {
    std::vector<CAddress> ret;
    LOCK(m_nodes_mutex);
    for (const CNode *pnode : m_nodes) {
        if (pnode->IsBlockOnlyConn()) {
            ret.push_back(pnode->addr);
        }
    }
 
    return ret;
}
 
std::vector<AddedNodeInfo> CConnman::GetAddedNodeInfo() const {
    std::vector<AddedNodeInfo> ret;
 
    std::list<std::string> lAddresses(0);
    {
        LOCK(m_added_nodes_mutex);
        ret.reserve(m_added_nodes.size());
        std::copy(m_added_nodes.cbegin(), m_added_nodes.cend(),
                  std::back_inserter(lAddresses));
    }
 
    // Build a map of all already connected addresses (by IP:port and by name)
    // to inbound/outbound and resolved CService
    std::map<CService, bool> mapConnected;
    std::map<std::string, std::pair<bool, CService>> mapConnectedByName;
    {
        LOCK(m_nodes_mutex);
        for (const CNode *pnode : m_nodes) {
            if (pnode->addr.IsValid()) {
                mapConnected[pnode->addr] = pnode->IsInboundConn();
            }
            std::string addrName{pnode->m_addr_name};
            if (!addrName.empty()) {
                mapConnectedByName[std::move(addrName)] =
                    std::make_pair(pnode->IsInboundConn(),
                                   static_cast<const CService &>(pnode->addr));
            }
        }
    }
 
    for (const std::string &strAddNode : lAddresses) {
        CService service(
            LookupNumeric(strAddNode, Params().GetDefaultPort(strAddNode)));
        AddedNodeInfo addedNode{strAddNode, CService(), false, false};
        if (service.IsValid()) {
            // strAddNode is an IP:port
            auto it = mapConnected.find(service);
            if (it != mapConnected.end()) {
                addedNode.resolvedAddress = service;
                addedNode.fConnected = true;
                addedNode.fInbound = it->second;
            }
        } else {
            // strAddNode is a name
            auto it = mapConnectedByName.find(strAddNode);
            if (it != mapConnectedByName.end()) {
                addedNode.resolvedAddress = it->second.second;
                addedNode.fConnected = true;
                addedNode.fInbound = it->second.first;
            }
        }
        ret.emplace_back(std::move(addedNode));
    }
 
    return ret;
}
 
void CConnman::ThreadOpenAddedConnections() {
    while (true) {
        CSemaphoreGrant grant(*semAddnode);
        std::vector<AddedNodeInfo> vInfo = GetAddedNodeInfo();
        bool tried = false;
        for (const AddedNodeInfo &info : vInfo) {
            if (!info.fConnected) {
                if (!grant.TryAcquire()) {
                    // If we've used up our semaphore and need a new one, let's
                    // not wait here since while we are waiting the
                    // addednodeinfo state might change.
                    break;
                }
                tried = true;
                CAddress addr(CService(), NODE_NONE);
                OpenNetworkConnection(addr, false, &grant,
                                      info.strAddedNode.c_str(),
                                      ConnectionType::MANUAL);
                if (!interruptNet.sleep_for(std::chrono::milliseconds(500))) {
                    return;
                }
            }
        }
        // Retry every 60 seconds if a connection was attempted, otherwise two
        // seconds.
        if (!interruptNet.sleep_for(std::chrono::seconds(tried ? 60 : 2))) {
            return;
        }
    }
}
 
// If successful, this moves the passed grant to the constructed node.
void CConnman::OpenNetworkConnection(const CAddress &addrConnect,
                                     bool fCountFailure,
                                     CSemaphoreGrant *grantOutbound,
                                     const char *pszDest,
                                     ConnectionType conn_type) {
    assert(conn_type != ConnectionType::INBOUND);
 
    //
    // Initiate outbound network connection
    //
    if (interruptNet) {
        return;
    }
    if (!fNetworkActive) {
        return;
    }
    if (!pszDest) {
        bool banned_or_discouraged =
            m_banman && (m_banman->IsDiscouraged(addrConnect) ||
                         m_banman->IsBanned(addrConnect));
        if (IsLocal(addrConnect) || banned_or_discouraged ||
            AlreadyConnectedToAddress(addrConnect)) {
            return;
        }
    } else if (FindNode(std::string(pszDest))) {
        return;
    }
 
    CNode *pnode = ConnectNode(addrConnect, pszDest, fCountFailure, conn_type);
 
    if (!pnode) {
        return;
    }
    if (grantOutbound) {
        grantOutbound->MoveTo(pnode->grantOutbound);
    }
 
    for (auto interface : m_msgproc) {
        interface->InitializeNode(*config, *pnode, nLocalServices);
    }
 
    {
        LOCK(m_nodes_mutex);
        m_nodes.push_back(pnode);
    }
}
 
Mutex NetEventsInterface::g_msgproc_mutex;
 
void CConnman::ThreadMessageHandler() {
    LOCK(NetEventsInterface::g_msgproc_mutex);
 
    FastRandomContext rng;
    while (!flagInterruptMsgProc) {
        std::vector<CNode *> nodes_copy;
        {
            LOCK(m_nodes_mutex);
            nodes_copy = m_nodes;
            for (CNode *pnode : nodes_copy) {
                pnode->AddRef();
            }
        }
 
        bool fMoreWork = false;
 
        // Randomize the order in which we process messages from/to our peers.
        // This prevents attacks in which an attacker exploits having multiple
        // consecutive connections in the m_nodes list.
        Shuffle(nodes_copy.begin(), nodes_copy.end(), rng);
 
        for (CNode *pnode : nodes_copy) {
            if (pnode->fDisconnect) {
                continue;
            }
 
            bool fMoreNodeWork = false;
            // Receive messages
            for (auto interface : m_msgproc) {
                fMoreNodeWork |= interface->ProcessMessages(
                    *config, pnode, flagInterruptMsgProc);
            }
            fMoreWork |= (fMoreNodeWork && !pnode->fPauseSend);
            if (flagInterruptMsgProc) {
                return;
            }
 
            // Send messages
            for (auto interface : m_msgproc) {
                interface->SendMessages(*config, pnode);
            }
 
            if (flagInterruptMsgProc) {
                return;
            }
        }
 
        {
            LOCK(m_nodes_mutex);
            for (CNode *pnode : nodes_copy) {
                pnode->Release();
            }
        }
 
        WAIT_LOCK(mutexMsgProc, lock);
        if (!fMoreWork) {
            condMsgProc.wait_until(lock,
                                   std::chrono::steady_clock::now() +
                                       std::chrono::milliseconds(100),
                                   [this]() EXCLUSIVE_LOCKS_REQUIRED(
                                       mutexMsgProc) { return fMsgProcWake; });
        }
        fMsgProcWake = false;
    }
}
 
void CConnman::ThreadI2PAcceptIncoming() {
    static constexpr auto err_wait_begin = 1s;
    static constexpr auto err_wait_cap = 5min;
    auto err_wait = err_wait_begin;
 
    bool advertising_listen_addr = false;
    i2p::Connection conn;
 
    while (!interruptNet) {
        if (!m_i2p_sam_session->Listen(conn)) {
            if (advertising_listen_addr && conn.me.IsValid()) {
                RemoveLocal(conn.me);
                advertising_listen_addr = false;
            }
 
            interruptNet.sleep_for(err_wait);
            if (err_wait < err_wait_cap) {
                err_wait *= 2;
            }
 
            continue;
        }
 
        if (!advertising_listen_addr) {
            AddLocal(conn.me, LOCAL_MANUAL);
            advertising_listen_addr = true;
        }
 
        if (!m_i2p_sam_session->Accept(conn)) {
            continue;
        }
 
        CreateNodeFromAcceptedSocket(
            conn.sock->Release(), NetPermissionFlags::None,
            CAddress{conn.me, NODE_NONE}, CAddress{conn.peer, NODE_NONE});
    }
}
 
bool CConnman::BindListenPort(const CService &addrBind, bilingual_str &strError,
                              NetPermissionFlags permissions) {
    int nOne = 1;
 
    // Create socket for listening for incoming connections
    struct sockaddr_storage sockaddr;
    socklen_t len = sizeof(sockaddr);
    if (!addrBind.GetSockAddr((struct sockaddr *)&sockaddr, &len)) {
        strError = strprintf(
            Untranslated("Error: Bind address family for %s not supported"),
            addrBind.ToString());
        LogPrintf("%s\n", strError.original);
        return false;
    }
 
    std::unique_ptr<Sock> sock = CreateSock(addrBind);
    if (!sock) {
        strError =
            strprintf(Untranslated("Error: Couldn't open socket for incoming "
                                   "connections (socket returned error %s)"),
                      NetworkErrorString(WSAGetLastError()));
        LogPrintf("%s\n", strError.original);
        return false;
    }
 
    // Allow binding if the port is still in TIME_WAIT state after
    // the program was closed and restarted.
    setsockopt(sock->Get(), SOL_SOCKET, SO_REUSEADDR, (sockopt_arg_type)&nOne,
               sizeof(int));
 
    // Some systems don't have IPV6_V6ONLY but are always v6only; others do have
    // the option and enable it by default or not. Try to enable it, if
    // possible.
    if (addrBind.IsIPv6()) {
#ifdef IPV6_V6ONLY
        setsockopt(sock->Get(), IPPROTO_IPV6, IPV6_V6ONLY,
                   (sockopt_arg_type)&nOne, sizeof(int));
#endif
#ifdef WIN32
        int nProtLevel = PROTECTION_LEVEL_UNRESTRICTED;
        setsockopt(sock->Get(), IPPROTO_IPV6, IPV6_PROTECTION_LEVEL,
                   (sockopt_arg_type)&nProtLevel, sizeof(int));
#endif
    }
 
    if (::bind(sock->Get(), (struct sockaddr *)&sockaddr, len) ==
        SOCKET_ERROR) {
        int nErr = WSAGetLastError();
        if (nErr == WSAEADDRINUSE) {
            strError = strprintf(_("Unable to bind to %s on this computer. %s "
                                   "is probably already running."),
                                 addrBind.ToString(), PACKAGE_NAME);
        } else {
            strError = strprintf(_("Unable to bind to %s on this computer "
                                   "(bind returned error %s)"),
                                 addrBind.ToString(), NetworkErrorString(nErr));
        }
        LogPrintf("%s\n", strError.original);
        return false;
    }
    LogPrintf("Bound to %s\n", addrBind.ToString());
 
    // Listen for incoming connections
    if (listen(sock->Get(), SOMAXCONN) == SOCKET_ERROR) {
        strError = strprintf(_("Error: Listening for incoming connections "
                               "failed (listen returned error %s)"),
                             NetworkErrorString(WSAGetLastError()));
        LogPrintf("%s\n", strError.original);
        return false;
    }
 
    vhListenSocket.push_back(ListenSocket(sock->Release(), permissions));
    return true;
}
 
void Discover() {
    if (!fDiscover) {
        return;
    }
 
#ifdef WIN32
    // Get local host IP
    char pszHostName[256] = "";
    if (gethostname(pszHostName, sizeof(pszHostName)) != SOCKET_ERROR) {
        std::vector<CNetAddr> vaddr;
        if (LookupHost(pszHostName, vaddr, 0, true)) {
            for (const CNetAddr &addr : vaddr) {
                if (AddLocal(addr, LOCAL_IF)) {
                    LogPrintf("%s: %s - %s\n", __func__, pszHostName,
                              addr.ToString());
                }
            }
        }
    }
#elif (HAVE_DECL_GETIFADDRS && HAVE_DECL_FREEIFADDRS)
    // Get local host ip
    struct ifaddrs *myaddrs;
    if (getifaddrs(&myaddrs) == 0) {
        for (struct ifaddrs *ifa = myaddrs; ifa != nullptr;
             ifa = ifa->ifa_next) {
            if (ifa->ifa_addr == nullptr || (ifa->ifa_flags & IFF_UP) == 0 ||
                strcmp(ifa->ifa_name, "lo") == 0 ||
                strcmp(ifa->ifa_name, "lo0") == 0) {
                continue;
            }
            if (ifa->ifa_addr->sa_family == AF_INET) {
                struct sockaddr_in *s4 =
                    reinterpret_cast<struct sockaddr_in *>(ifa->ifa_addr);
                CNetAddr addr(s4->sin_addr);
                if (AddLocal(addr, LOCAL_IF)) {
                    LogPrintf("%s: IPv4 %s: %s\n", __func__, ifa->ifa_name,
                              addr.ToString());
                }
            } else if (ifa->ifa_addr->sa_family == AF_INET6) {
                struct sockaddr_in6 *s6 =
                    reinterpret_cast<struct sockaddr_in6 *>(ifa->ifa_addr);
                CNetAddr addr(s6->sin6_addr);
                if (AddLocal(addr, LOCAL_IF)) {
                    LogPrintf("%s: IPv6 %s: %s\n", __func__, ifa->ifa_name,
                              addr.ToString());
                }
            }
        }
        freeifaddrs(myaddrs);
    }
#endif
}
 
void CConnman::SetNetworkActive(bool active) {
    LogPrintf("%s: %s\n", __func__, active);
 
    if (fNetworkActive == active) {
        return;
    }
 
    fNetworkActive = active;
 
    if (m_client_interface) {
        m_client_interface->NotifyNetworkActiveChanged(fNetworkActive);
    }
}
 
CConnman::CConnman(const Config &configIn, uint64_t nSeed0In, uint64_t nSeed1In,
                   AddrMan &addrmanIn, bool network_active)
    : config(&configIn), addrman(addrmanIn), nSeed0(nSeed0In),
      nSeed1(nSeed1In) {
    SetTryNewOutboundPeer(false);
 
    Options connOptions;
    Init(connOptions);
    SetNetworkActive(network_active);
}
 
NodeId CConnman::GetNewNodeId() {
    return nLastNodeId.fetch_add(1);
}
 
bool CConnman::Bind(const CService &addr, unsigned int flags,
                    NetPermissionFlags permissions) {
    if (!(flags & BF_EXPLICIT) && !IsReachable(addr)) {
        return false;
    }
    bilingual_str strError;
    if (!BindListenPort(addr, strError, permissions)) {
        if ((flags & BF_REPORT_ERROR) && m_client_interface) {
            m_client_interface->ThreadSafeMessageBox(
                strError, "", CClientUIInterface::MSG_ERROR);
        }
        return false;
    }
 
    if (addr.IsRoutable() && fDiscover && !(flags & BF_DONT_ADVERTISE) &&
        !NetPermissions::HasFlag(permissions, NetPermissionFlags::NoBan)) {
        AddLocal(addr, LOCAL_BIND);
    }
 
    return true;
}
 
bool CConnman::InitBinds(const Options &options) {
    bool fBound = false;
    for (const auto &addrBind : options.vBinds) {
        fBound |= Bind(addrBind, (BF_EXPLICIT | BF_REPORT_ERROR),
                       NetPermissionFlags::None);
    }
    for (const auto &addrBind : options.vWhiteBinds) {
        fBound |= Bind(addrBind.m_service, (BF_EXPLICIT | BF_REPORT_ERROR),
                       addrBind.m_flags);
    }
    for (const auto &addr_bind : options.onion_binds) {
        fBound |= Bind(addr_bind, BF_EXPLICIT | BF_DONT_ADVERTISE,
                       NetPermissionFlags::None);
    }
    if (options.bind_on_any) {
        struct in_addr inaddr_any;
        inaddr_any.s_addr = htonl(INADDR_ANY);
        struct in6_addr inaddr6_any = IN6ADDR_ANY_INIT;
        fBound |= Bind(CService(inaddr6_any, GetListenPort()), BF_NONE,
                       NetPermissionFlags::None);
        fBound |=
            Bind(CService(inaddr_any, GetListenPort()),
                 !fBound ? BF_REPORT_ERROR : BF_NONE, NetPermissionFlags::None);
    }
    return fBound;
}
 
bool CConnman::Start(CScheduler &scheduler, const Options &connOptions) {
    Init(connOptions);
 
    if (fListen && !InitBinds(connOptions)) {
        if (m_client_interface) {
            m_client_interface->ThreadSafeMessageBox(
                _("Failed to listen on any port. Use -listen=0 if you want "
                  "this."),
                "", CClientUIInterface::MSG_ERROR);
        }
        return false;
    }
 
    proxyType i2p_sam;
    if (GetProxy(NET_I2P, i2p_sam)) {
        m_i2p_sam_session = std::make_unique<i2p::sam::Session>(
            gArgs.GetDataDirNet() / "i2p_private_key", i2p_sam.proxy,
            &interruptNet);
    }
 
    for (const auto &strDest : connOptions.vSeedNodes) {
        AddAddrFetch(strDest);
    }
 
    if (m_use_addrman_outgoing) {
        // Load addresses from anchors.dat
        m_anchors =
            ReadAnchors(config->GetChainParams(),
                        gArgs.GetDataDirNet() / ANCHORS_DATABASE_FILENAME);
        if (m_anchors.size() > MAX_BLOCK_RELAY_ONLY_ANCHORS) {
            m_anchors.resize(MAX_BLOCK_RELAY_ONLY_ANCHORS);
        }
        LogPrintf(
            "%i block-relay-only anchors will be tried for connections.\n",
            m_anchors.size());
    }
 
    if (m_client_interface) {
        m_client_interface->InitMessage(
            _("Starting network threads...").translated);
    }
 
    fAddressesInitialized = true;
 
    if (semOutbound == nullptr) {
        // initialize semaphore
        semOutbound = std::make_unique<CSemaphore>(
            std::min(m_max_outbound, nMaxConnections));
    }
    if (semAddnode == nullptr) {
        // initialize semaphore
        semAddnode = std::make_unique<CSemaphore>(nMaxAddnode);
    }
 
    //
    // Start threads
    //
    assert(m_msgproc.size() > 0);
    InterruptSocks5(false);
    interruptNet.reset();
    flagInterruptMsgProc = false;
 
    {
        LOCK(mutexMsgProc);
        fMsgProcWake = false;
    }
 
    // Send and receive from sockets, accept connections
    threadSocketHandler = std::thread(&util::TraceThread, "net",
                                      [this] { ThreadSocketHandler(); });
 
    if (!gArgs.GetBoolArg("-dnsseed", DEFAULT_DNSSEED)) {
        LogPrintf("DNS seeding disabled\n");
    } else {
        threadDNSAddressSeed = std::thread(&util::TraceThread, "dnsseed",
                                           [this] { ThreadDNSAddressSeed(); });
    }
 
    // Initiate manual connections
    threadOpenAddedConnections = std::thread(
        &util::TraceThread, "addcon", [this] { ThreadOpenAddedConnections(); });
 
    if (connOptions.m_use_addrman_outgoing &&
        !connOptions.m_specified_outgoing.empty()) {
        if (m_client_interface) {
            m_client_interface->ThreadSafeMessageBox(
                _("Cannot provide specific connections and have addrman find "
                  "outgoing connections at the same."),
                "", CClientUIInterface::MSG_ERROR);
        }
        return false;
    }
    if (connOptions.m_use_addrman_outgoing ||
        !connOptions.m_specified_outgoing.empty()) {
        threadOpenConnections =
            std::thread(&util::TraceThread, "opencon",
                        [this, connect = connOptions.m_specified_outgoing] {
                            ThreadOpenConnections(connect, nullptr);
                        });
    }
 
    // Process messages
    threadMessageHandler = std::thread(&util::TraceThread, "msghand",
                                       [this] { ThreadMessageHandler(); });
 
    if (connOptions.m_i2p_accept_incoming &&
        m_i2p_sam_session.get() != nullptr) {
        threadI2PAcceptIncoming =
            std::thread(&util::TraceThread, "i2paccept",
                        [this] { ThreadI2PAcceptIncoming(); });
    }
 
    // Dump network addresses
    scheduler.scheduleEvery(
        [this]() {
            this->DumpAddresses();
            return true;
        },
        DUMP_PEERS_INTERVAL);
 
    return true;
}
 
class CNetCleanup {
public:
    CNetCleanup() {}
 
    ~CNetCleanup() {
#ifdef WIN32
        // Shutdown Windows Sockets
        WSACleanup();
#endif
    }
};
static CNetCleanup instance_of_cnetcleanup;
 
void CConnman::Interrupt() {
    {
        LOCK(mutexMsgProc);
        flagInterruptMsgProc = true;
    }
    condMsgProc.notify_all();
 
    interruptNet();
    InterruptSocks5(true);
 
    if (semOutbound) {
        for (int i = 0; i < m_max_outbound; i++) {
            semOutbound->post();
        }
    }
 
    if (semAddnode) {
        for (int i = 0; i < nMaxAddnode; i++) {
            semAddnode->post();
        }
    }
}
 
void CConnman::StopThreads() {
    if (threadI2PAcceptIncoming.joinable()) {
        threadI2PAcceptIncoming.join();
    }
    if (threadMessageHandler.joinable()) {
        threadMessageHandler.join();
    }
    if (threadOpenConnections.joinable()) {
        threadOpenConnections.join();
    }
    if (threadOpenAddedConnections.joinable()) {
        threadOpenAddedConnections.join();
    }
    if (threadDNSAddressSeed.joinable()) {
        threadDNSAddressSeed.join();
    }
    if (threadSocketHandler.joinable()) {
        threadSocketHandler.join();
    }
}
 
void CConnman::StopNodes() {
    if (fAddressesInitialized) {
        DumpAddresses();
        fAddressesInitialized = false;
 
        if (m_use_addrman_outgoing) {
            // Anchor connections are only dumped during clean shutdown.
            std::vector<CAddress> anchors_to_dump =
                GetCurrentBlockRelayOnlyConns();
            if (anchors_to_dump.size() > MAX_BLOCK_RELAY_ONLY_ANCHORS) {
                anchors_to_dump.resize(MAX_BLOCK_RELAY_ONLY_ANCHORS);
            }
            DumpAnchors(config->GetChainParams(),
                        gArgs.GetDataDirNet() / ANCHORS_DATABASE_FILENAME,
                        anchors_to_dump);
        }
    }
 
    // Delete peer connections.
    std::vector<CNode *> nodes;
    WITH_LOCK(m_nodes_mutex, nodes.swap(m_nodes));
    for (CNode *pnode : nodes) {
        pnode->CloseSocketDisconnect();
        DeleteNode(pnode);
    }
 
    // Close listening sockets.
    for (ListenSocket &hListenSocket : vhListenSocket) {
        if (hListenSocket.socket != INVALID_SOCKET) {
            if (!CloseSocket(hListenSocket.socket)) {
                LogPrintf("CloseSocket(hListenSocket) failed with error %s\n",
                          NetworkErrorString(WSAGetLastError()));
            }
        }
    }
 
    for (CNode *pnode : m_nodes_disconnected) {
        DeleteNode(pnode);
    }
    m_nodes_disconnected.clear();
    vhListenSocket.clear();
    semOutbound.reset();
    semAddnode.reset();
}
 
void CConnman::DeleteNode(CNode *pnode) {
    assert(pnode);
    for (auto interface : m_msgproc) {
        interface->FinalizeNode(*config, *pnode);
    }
    delete pnode;
}
 
CConnman::~CConnman() {
    Interrupt();
    Stop();
}
 
std::vector<CAddress>
CConnman::GetAddresses(size_t max_addresses, size_t max_pct,
                       std::optional<Network> network) const {
    std::vector<CAddress> addresses =
        addrman.GetAddr(max_addresses, max_pct, network);
    if (m_banman) {
        addresses.erase(std::remove_if(addresses.begin(), addresses.end(),
                                       [this](const CAddress &addr) {
                                           return m_banman->IsDiscouraged(
                                                      addr) ||
                                                  m_banman->IsBanned(addr);
                                       }),
                        addresses.end());
    }
    return addresses;
}
 
std::vector<CAddress>
CConnman::GetAddresses(CNode &requestor, size_t max_addresses, size_t max_pct) {
    auto local_socket_bytes = requestor.addrBind.GetAddrBytes();
    uint64_t cache_id =
        GetDeterministicRandomizer(RANDOMIZER_ID_ADDRCACHE)
            .Write(requestor.addr.GetNetwork())
            .Write(local_socket_bytes.data(), local_socket_bytes.size())
            .Finalize();
    const auto current_time = GetTime<std::chrono::microseconds>();
    auto r = m_addr_response_caches.emplace(cache_id, CachedAddrResponse{});
    CachedAddrResponse &cache_entry = r.first->second;
    // New CachedAddrResponse have expiration 0.
    if (cache_entry.m_cache_entry_expiration < current_time) {
        cache_entry.m_addrs_response_cache =
            GetAddresses(max_addresses, max_pct, /* network */ std::nullopt);
        // Choosing a proper cache lifetime is a trade-off between the privacy
        // leak minimization and the usefulness of ADDR responses to honest
        // users.
        //
        // Longer cache lifetime makes it more difficult for an attacker to
        // scrape enough AddrMan data to maliciously infer something useful. By
        // the time an attacker scraped enough AddrMan records, most of the
        // records should be old enough to not leak topology info by e.g.
        // analyzing real-time changes in timestamps.
        //
        // It takes only several hundred requests to scrape everything from an
        // AddrMan containing 100,000 nodes, so ~24 hours of cache lifetime
        // indeed makes the data less inferable by the time most of it could be
        // scraped (considering that timestamps are updated via ADDR
        // self-announcements and when nodes communicate). We also should be
        // robust to those attacks which may not require scraping *full*
        // victim's AddrMan (because even several timestamps of the same handful
        // of nodes may leak privacy).
        //
        // On the other hand, longer cache lifetime makes ADDR responses
        // outdated and less useful for an honest requestor, e.g. if most nodes
        // in the ADDR response are no longer active.
        //
        // However, the churn in the network is known to be rather low. Since we
        // consider nodes to be "terrible" (see IsTerrible()) if the timestamps
        // are older than 30 days, max. 24 hours of "penalty" due to cache
        // shouldn't make any meaningful difference in terms of the freshness of
        // the response.
        cache_entry.m_cache_entry_expiration =
            current_time + std::chrono::hours(21) +
            GetRandMillis(std::chrono::hours(6));
    }
    return cache_entry.m_addrs_response_cache;
}
 
bool CConnman::AddNode(const std::string &strNode) {
    LOCK(m_added_nodes_mutex);
    for (const std::string &it : m_added_nodes) {
        if (strNode == it) {
            return false;
        }
    }
 
    m_added_nodes.push_back(strNode);
    return true;
}
 
bool CConnman::RemoveAddedNode(const std::string &strNode) {
    LOCK(m_added_nodes_mutex);
    for (std::vector<std::string>::iterator it = m_added_nodes.begin();
         it != m_added_nodes.end(); ++it) {
        if (strNode == *it) {
            m_added_nodes.erase(it);
            return true;
        }
    }
    return false;
}
 
size_t CConnman::GetNodeCount(NumConnections flags) const {
    LOCK(m_nodes_mutex);
    // Shortcut if we want total
    if (flags == CConnman::CONNECTIONS_ALL) {
        return m_nodes.size();
    }
 
    int nNum = 0;
    for (const auto &pnode : m_nodes) {
        if (flags &
            (pnode->IsInboundConn() ? CONNECTIONS_IN : CONNECTIONS_OUT)) {
            nNum++;
        }
    }
 
    return nNum;
}
 
void CConnman::GetNodeStats(std::vector<CNodeStats> &vstats) const {
    vstats.clear();
    LOCK(m_nodes_mutex);
    vstats.reserve(m_nodes.size());
    for (CNode *pnode : m_nodes) {
        vstats.emplace_back();
        pnode->copyStats(vstats.back());
        vstats.back().m_mapped_as = pnode->addr.GetMappedAS(addrman.GetAsmap());
    }
}
 
bool CConnman::DisconnectNode(const std::string &strNode) {
    LOCK(m_nodes_mutex);
    if (CNode *pnode = FindNode(strNode)) {
        LogPrint(BCLog::NET,
                 "disconnect by address%s matched peer=%d; disconnecting\n",
                 (fLogIPs ? strprintf("=%s", strNode) : ""), pnode->GetId());
        pnode->fDisconnect = true;
        return true;
    }
    return false;
}
 
bool CConnman::DisconnectNode(const CSubNet &subnet) {
    bool disconnected = false;
    LOCK(m_nodes_mutex);
    for (CNode *pnode : m_nodes) {
        if (subnet.Match(pnode->addr)) {
            LogPrint(BCLog::NET,
                     "disconnect by subnet%s matched peer=%d; disconnecting\n",
                     (fLogIPs ? strprintf("=%s", subnet.ToString()) : ""),
                     pnode->GetId());
            pnode->fDisconnect = true;
            disconnected = true;
        }
    }
    return disconnected;
}
 
bool CConnman::DisconnectNode(const CNetAddr &addr) {
    return DisconnectNode(CSubNet(addr));
}
 
bool CConnman::DisconnectNode(NodeId id) {
    LOCK(m_nodes_mutex);
    for (CNode *pnode : m_nodes) {
        if (id == pnode->GetId()) {
            LogPrint(BCLog::NET, "disconnect by id peer=%d; disconnecting\n",
                     pnode->GetId());
            pnode->fDisconnect = true;
            return true;
        }
    }
    return false;
}
 
void CConnman::RecordBytesRecv(uint64_t bytes) {
    nTotalBytesRecv += bytes;
}
 
void CConnman::RecordBytesSent(uint64_t bytes) {
    LOCK(cs_totalBytesSent);
    nTotalBytesSent += bytes;
 
    const auto now = GetTime<std::chrono::seconds>();
    if (nMaxOutboundCycleStartTime + MAX_UPLOAD_TIMEFRAME < now) {
        // timeframe expired, reset cycle
        nMaxOutboundCycleStartTime = now;
        nMaxOutboundTotalBytesSentInCycle = 0;
    }
 
    // TODO, exclude peers with download permission
    nMaxOutboundTotalBytesSentInCycle += bytes;
}
 
uint64_t CConnman::GetMaxOutboundTarget() const {
    LOCK(cs_totalBytesSent);
    return nMaxOutboundLimit;
}
 
std::chrono::seconds CConnman::GetMaxOutboundTimeframe() const {
    return MAX_UPLOAD_TIMEFRAME;
}
 
std::chrono::seconds CConnman::GetMaxOutboundTimeLeftInCycle() const {
    LOCK(cs_totalBytesSent);
    if (nMaxOutboundLimit == 0) {
        return 0s;
    }
 
    if (nMaxOutboundCycleStartTime.count() == 0) {
        return MAX_UPLOAD_TIMEFRAME;
    }
 
    const std::chrono::seconds cycleEndTime =
        nMaxOutboundCycleStartTime + MAX_UPLOAD_TIMEFRAME;
    const auto now = GetTime<std::chrono::seconds>();
    return (cycleEndTime < now) ? 0s : cycleEndTime - now;
}
 
bool CConnman::OutboundTargetReached(bool historicalBlockServingLimit) const {
    LOCK(cs_totalBytesSent);
    if (nMaxOutboundLimit == 0) {
        return false;
    }
 
    if (historicalBlockServingLimit) {
        // keep a large enough buffer to at least relay each block once.
        const std::chrono::seconds timeLeftInCycle =
            GetMaxOutboundTimeLeftInCycle();
        const uint64_t buffer =
            timeLeftInCycle / std::chrono::minutes{10} * ONE_MEGABYTE;
        if (buffer >= nMaxOutboundLimit ||
            nMaxOutboundTotalBytesSentInCycle >= nMaxOutboundLimit - buffer) {
            return true;
        }
    } else if (nMaxOutboundTotalBytesSentInCycle >= nMaxOutboundLimit) {
        return true;
    }
 
    return false;
}
 
uint64_t CConnman::GetOutboundTargetBytesLeft() const {
    LOCK(cs_totalBytesSent);
    if (nMaxOutboundLimit == 0) {
        return 0;
    }
 
    return (nMaxOutboundTotalBytesSentInCycle >= nMaxOutboundLimit)
               ? 0
               : nMaxOutboundLimit - nMaxOutboundTotalBytesSentInCycle;
}
 
uint64_t CConnman::GetTotalBytesRecv() const {
    return nTotalBytesRecv;
}
 
uint64_t CConnman::GetTotalBytesSent() const {
    LOCK(cs_totalBytesSent);
    return nTotalBytesSent;
}
 
ServiceFlags CConnman::GetLocalServices() const {
    return nLocalServices;
}
 
unsigned int CConnman::GetReceiveFloodSize() const {
    return nReceiveFloodSize;
}
 
void CNode::invsPolled(uint32_t count) {
    invCounters += count;
}
 
void CNode::invsVoted(uint32_t count) {
    invCounters += uint64_t(count) << 32;
}
 
void CNode::updateAvailabilityScore(double decayFactor) {
    if (!m_avalanche_enabled) {
        return;
    }
 
    uint64_t windowInvCounters = invCounters.exchange(0);
    double previousScore = availabilityScore;
 
    int64_t polls = windowInvCounters & std::numeric_limits<uint32_t>::max();
    int64_t votes = windowInvCounters >> 32;
 
    availabilityScore =
        decayFactor * (2 * votes - polls) + (1. - decayFactor) * previousScore;
}
 
double CNode::getAvailabilityScore() const {
    // The score is set atomically so there is no need to lock the statistics
    // when reading.
    return availabilityScore;
}
 
CNode::CNode(NodeId idIn, SOCKET hSocketIn, const CAddress &addrIn,
             uint64_t nKeyedNetGroupIn, uint64_t nLocalHostNonceIn,
             uint64_t nLocalExtraEntropyIn, const CAddress &addrBindIn,
             const std::string &addrNameIn, ConnectionType conn_type_in,
             bool inbound_onion)
    : m_connected(GetTime<std::chrono::seconds>()), addr(addrIn),
      addrBind(addrBindIn), m_addr_name{addrNameIn.empty()
                                            ? addr.ToStringIPPort()
                                            : addrNameIn},
      m_inbound_onion(inbound_onion), nKeyedNetGroup(nKeyedNetGroupIn),
      // Don't relay addr messages to peers that we connect to as
      // block-relay-only peers (to prevent adversaries from inferring these
      // links from addr traffic).
      id(idIn), nLocalHostNonce(nLocalHostNonceIn),
      nLocalExtraEntropy(nLocalExtraEntropyIn), m_conn_type(conn_type_in) {
    if (inbound_onion) {
        assert(conn_type_in == ConnectionType::INBOUND);
    }
    hSocket = hSocketIn;
 
    for (const std::string &msg : getAllNetMessageTypes()) {
        mapRecvBytesPerMsgCmd[msg] = 0;
    }
    mapRecvBytesPerMsgCmd[NET_MESSAGE_COMMAND_OTHER] = 0;
 
    if (fLogIPs) {
        LogPrint(BCLog::NET, "Added connection to %s peer=%d\n", m_addr_name,
                 id);
    } else {
        LogPrint(BCLog::NET, "Added connection peer=%d\n", id);
    }
 
    m_deserializer = std::make_unique<V1TransportDeserializer>(
        V1TransportDeserializer(GetConfig().GetChainParams().NetMagic(),
                                SER_NETWORK, INIT_PROTO_VERSION));
    m_serializer =
        std::make_unique<V1TransportSerializer>(V1TransportSerializer());
}
 
CNode::~CNode() {
    CloseSocket(hSocket);
}
 
bool CConnman::NodeFullyConnected(const CNode *pnode) {
    return pnode && pnode->fSuccessfullyConnected && !pnode->fDisconnect;
}
 
void CConnman::PushMessage(CNode *pnode, CSerializedNetMsg &&msg) {
    size_t nMessageSize = msg.data.size();
    LogPrint(BCLog::NETDEBUG, "sending %s (%d bytes) peer=%d\n", msg.m_type,
             nMessageSize, pnode->GetId());
    if (gArgs.GetBoolArg("-capturemessages", false)) {
        CaptureMessage(pnode->addr, msg.m_type, msg.data,
                       /*is_incoming=*/false);
    }
 
    TRACE6(net, outbound_message, pnode->GetId(), pnode->m_addr_name.c_str(),
           pnode->ConnectionTypeAsString().c_str(), msg.m_type.c_str(),
           msg.data.size(), msg.data.data());
 
    // make sure we use the appropriate network transport format
    std::vector<uint8_t> serializedHeader;
    pnode->m_serializer->prepareForTransport(*config, msg, serializedHeader);
    size_t nTotalSize = nMessageSize + serializedHeader.size();
 
    size_t nBytesSent = 0;
    {
        LOCK(pnode->cs_vSend);
        bool optimisticSend(pnode->vSendMsg.empty());
 
        // log total amount of bytes per message type
        pnode->mapSendBytesPerMsgCmd[msg.m_type] += nTotalSize;
        pnode->nSendSize += nTotalSize;
 
        if (pnode->nSendSize > nSendBufferMaxSize) {
            pnode->fPauseSend = true;
        }
        pnode->vSendMsg.push_back(std::move(serializedHeader));
        if (nMessageSize) {
            pnode->vSendMsg.push_back(std::move(msg.data));
        }
 
        // If write queue empty, attempt "optimistic write"
        if (optimisticSend == true) {
            nBytesSent = SocketSendData(*pnode);
        }
    }
    if (nBytesSent) {
        RecordBytesSent(nBytesSent);
    }
}
 
bool CConnman::ForNode(NodeId id, std::function<bool(CNode *pnode)> func) {
    CNode *found = nullptr;
    LOCK(m_nodes_mutex);
    for (auto &&pnode : m_nodes) {
        if (pnode->GetId() == id) {
            found = pnode;
            break;
        }
    }
    return found != nullptr && NodeFullyConnected(found) && func(found);
}
 
CSipHasher CConnman::GetDeterministicRandomizer(uint64_t id) const {
    return CSipHasher(nSeed0, nSeed1).Write(id);
}
 
uint64_t CConnman::CalculateKeyedNetGroup(const CAddress &ad) const {
    std::vector<uint8_t> vchNetGroup(ad.GetGroup(addrman.GetAsmap()));
 
    return GetDeterministicRandomizer(RANDOMIZER_ID_NETGROUP)
        .Write(vchNetGroup.data(), vchNetGroup.size())
        .Finalize();
}
 
std::string getSubVersionEB(uint64_t MaxBlockSize) {
    // Prepare EB string we are going to add to SubVer:
    // 1) translate from byte to MB and convert to string
    // 2) limit the EB string to the first decimal digit (floored)
    std::stringstream ebMBs;
    ebMBs << (MaxBlockSize / (ONE_MEGABYTE / 10));
    std::string eb = ebMBs.str();
    eb.insert(eb.size() - 1, ".", 1);
    if (eb.substr(0, 1) == ".") {
        eb = "0" + eb;
    }
    return eb;
}
 
std::string userAgent(const Config &config) {
    // format excessive blocksize value
    std::string eb = getSubVersionEB(config.GetMaxBlockSize());
    std::vector<std::string> uacomments;
    uacomments.push_back("EB" + eb);
 
    // Comments are checked for char compliance at startup, it is safe to add
    // them to the user agent string
    for (const std::string &cmt : gArgs.GetArgs("-uacomment")) {
        uacomments.push_back(cmt);
    }
 
    const std::string client_name = gArgs.GetArg("-uaclientname", CLIENT_NAME);
    const std::string client_version =
        gArgs.GetArg("-uaclientversion", FormatVersion(CLIENT_VERSION));
 
    // Size compliance is checked at startup, it is safe to not check it again
    return FormatUserAgent(client_name, client_version, uacomments);
}
 
void CaptureMessageToFile(const CAddress &addr, const std::string &msg_type,
                          Span<const uint8_t> data, bool is_incoming) {
    // Note: This function captures the message at the time of processing,
    // not at socket receive/send time.
    // This ensures that the messages are always in order from an application
    // layer (processing) perspective.
    auto now = GetTime<std::chrono::microseconds>();
 
    // Windows folder names can not include a colon
    std::string clean_addr = addr.ToString();
    std::replace(clean_addr.begin(), clean_addr.end(), ':', '_');
 
    fs::path base_path = gArgs.GetDataDirNet() / "message_capture" / clean_addr;
    fs::create_directories(base_path);
 
    fs::path path =
        base_path / (is_incoming ? "msgs_recv.dat" : "msgs_sent.dat");
    AutoFile f{fsbridge::fopen(path, "ab")};
 
    ser_writedata64(f, now.count());
    f.write(MakeByteSpan(msg_type));
    for (auto i = msg_type.length(); i < CMessageHeader::COMMAND_SIZE; ++i) {
        f << uint8_t{'\0'};
    }
    uint32_t size = data.size();
    ser_writedata32(f, size);
    f.write(AsBytes(data));
}
 
std::function<void(const CAddress &addr, const std::string &msg_type,
                   Span<const uint8_t> data, bool is_incoming)>
    CaptureMessage = CaptureMessageToFile;