xmrig-hac/src/base/net/stratum/HushClient.cpp

/* XMRig - Hush/DragonX HAC Support
 * Copyright (c) 2024 XMRig       <https://github.com/xmrig>
 *
 *   This program is free software: you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
 *   the Free Software Foundation, either version 3 of the License, or
 *   (at your option) any later version.
 */

#include "base/net/stratum/HushClient.h"
#include "3rdparty/rapidjson/document.h"
#include "3rdparty/rapidjson/error/en.h"
#include "base/io/json/Json.h"
#include "base/io/json/JsonRequest.h"
#include "base/io/log/Log.h"
#include "base/kernel/interfaces/IClientListener.h"
#include "base/net/http/Fetch.h"
#include "base/net/http/HttpData.h"
#include "base/net/http/HttpListener.h"
#include "base/tools/Chrono.h"
#include "base/tools/Cvt.h"
#include "base/tools/Timer.h"
#include "net/JobResult.h"

#include <algorithm>
#include <cinttypes>
#include <cstring>

#ifdef XMRIG_FEATURE_TLS
#   include <openssl/sha.h>
#else
// Standalone SHA-256 for non-TLS builds (Windows cross-compile)
#   ifdef _WIN32
#       include <windows.h>
#       include <bcrypt.h>
static void SHA256(const uint8_t* data, size_t len, uint8_t* out) {
    BCRYPT_ALG_HANDLE hAlg = nullptr;
    BCRYPT_HASH_HANDLE hHash = nullptr;
    BCryptOpenAlgorithmProvider(&hAlg, BCRYPT_SHA256_ALGORITHM, nullptr, 0);
    BCryptCreateHash(hAlg, &hHash, nullptr, 0, nullptr, 0, 0);
    BCryptHashData(hHash, const_cast<PUCHAR>(data), static_cast<ULONG>(len), 0);
    BCryptFinishHash(hHash, out, 32, 0);
    BCryptDestroyHash(hHash);
    BCryptCloseAlgorithmProvider(hAlg, 0);
}
#   else
#       include "crypto/ghostrider/sph_sha2.h"
static void SHA256(const uint8_t* data, size_t len, uint8_t* out) {
    sph_sha256_context ctx;
    sph_sha256_init(&ctx);
    sph_sha256(&ctx, data, len);
    sph_sha256_close(&ctx, out);
}
#   endif
#endif

namespace xmrig {

static const char *kJsonRPC = "/";

// Simple Base64 encoder for HTTP Basic Auth
static std::string toBase64(const std::string &input)
{
    static const char table[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
    std::string encoded;
    encoded.reserve(((input.size() + 2) / 3) * 4);

    unsigned int val = 0;
    int bits = -6;
    for (unsigned char c : input) {
        val = (val << 8) + c;
        bits += 8;
        while (bits >= 0) {
            encoded.push_back(table[(val >> bits) & 0x3F]);
            bits -= 6;
        }
    }
    if (bits > -6) {
        encoded.push_back(table[((val << 8) >> (bits + 8)) & 0x3F]);
    }
    while (encoded.size() % 4) {
        encoded.push_back('=');
    }
    return encoded;
}

// Create JSON-RPC 1.0 request (HAC daemons use 1.0, not 2.0)
static void createRpc10(rapidjson::Document &doc, int64_t id, const char *method, rapidjson::Value &params)
{
    using namespace rapidjson;
    auto &allocator = doc.GetAllocator();

    doc.AddMember("jsonrpc", "1.0", allocator);
    doc.AddMember("id", id, allocator);
    doc.AddMember("method", StringRef(method), allocator);
    doc.AddMember("params", params, allocator);
}

HushClient::HushClient(int id, IClientListener *listener) :
    BaseClient(id, listener)
{
    m_httpListener = std::make_shared<HttpListener>(this);
    m_timer = new Timer(this);
}

HushClient::~HushClient()
{
    delete m_timer;
}

void HushClient::deleteLater()
{
    delete this;
}

bool HushClient::disconnect()
{
    if (m_state != UnconnectedState) {
        setState(UnconnectedState);
    }
    return true;
}

bool HushClient::isTLS() const
{
#ifdef XMRIG_FEATURE_TLS
    return m_pool.isTLS();
#else
    return false;
#endif
}

void HushClient::connect()
{
    if (m_pool.algorithm().family() != Algorithm::RANDOM_X) {
        LOG_ERR("%s " RED("HAC coins require RandomX algorithm"), tag());
        return;
    }

    setState(ConnectingState);
    getBlockTemplate();
}

void HushClient::connect(const Pool &pool)
{
    setPool(pool);
    connect();
}

void HushClient::setPool(const Pool &pool)
{
    BaseClient::setPool(pool);

    // Default to RandomX if not specified
    if (!m_pool.algorithm().isValid()) {
        m_pool.setAlgo(Algorithm::RX_0);
    }
}

int64_t HushClient::submit(const JobResult &result)
{
    if (result.jobId != m_currentJobId) {
        LOG_DEBUG("%s " RED("job ID mismatch"), tag());
        return -1;
    }

    // Get the 32-byte nonce from the solo mining result
    const uint8_t *nonce32 = result.isSoloResult() ? result.soloNonce() : nullptr;
    if (!nonce32) {
        LOG_ERR("%s " RED("submit called without solo nonce"), tag());
        return -1;
    }

    // HAC PoW: RandomX hash becomes nSolution, then SHA256D(header + solution) must be < target
    if (!checkPow(nonce32, result.result())) {
        return -1;
    }

    LOG_INFO("%s " CYAN_BOLD("submitting block at height %u"), tag(), m_height);

    // Build the full block with header + nonce + solution + transactions
    const std::string blockHex = serializeBlockHex(nonce32, result.result());

    return submitBlock(blockHex);
}

void HushClient::onTimer(const Timer *)
{
    if (m_state == ConnectingState) {
        connect();
    }
    else if (m_state == ConnectedState) {
        // Poll for new block template
        getBlockTemplate();
    }
}

void HushClient::onHttpData(const HttpData &data)
{
    if (data.status != 200) {
        LOG_ERR("%s " RED("HTTP error %d"), tag(), data.status);
        return retry();
    }

    m_ip = data.ip().c_str();

#ifdef XMRIG_FEATURE_TLS
    if (data.tlsVersion()) {
        strncpy(m_tlsVersion, data.tlsVersion(), sizeof(m_tlsVersion) - 1);
    }
    if (data.tlsFingerprint()) {
        strncpy(m_tlsFingerprint, data.tlsFingerprint(), sizeof(m_tlsFingerprint) - 1);
    }
#endif

    rapidjson::Document doc;
    if (doc.Parse(data.body.c_str()).HasParseError()) {
        LOG_ERR("%s " RED("JSON parse error: %s"), tag(), rapidjson::GetParseError_En(doc.GetParseError()));
        return retry();
    }

    // Debug: log the raw response for troubleshooting
    LOG_DEBUG("%s RPC response: %.200s", tag(), data.body.c_str());

    const int64_t id = Json::getInt64(doc, "id", -1);
    
    // Handle "result" field which can be object, string, or null depending on RPC method
    const rapidjson::Value *resultPtr = nullptr;
    if (doc.HasMember("result")) {
        resultPtr = &doc["result"];
    }
    static const rapidjson::Value nullValue;
    const auto &result = resultPtr ? *resultPtr : nullValue;
    const auto &error = Json::getObject(doc, "error");

    if (!parseResponse(id, result, error)) {
        retry();
    }
}

int64_t HushClient::getBlockTemplate()
{
    using namespace rapidjson;
    Document doc(kObjectType);
    auto &allocator = doc.GetAllocator();

    // JSON-RPC 1.0 style: params is an array with optional object
    Value params(kArrayType);
    // Empty params array for basic getblocktemplate
    // HAC will return coinbasetxn by default

    createRpc10(doc, m_sequence, "getblocktemplate", params);
    m_pendingRequest = REQ_TEMPLATE;

    return rpcSend(doc);
}

int64_t HushClient::getBlockHash(uint64_t height)
{
    using namespace rapidjson;
    Document doc(kObjectType);
    auto &allocator = doc.GetAllocator();

    Value params(kArrayType);
    params.PushBack(Value(height), allocator);

    createRpc10(doc, m_sequence, "getblockhash", params);
    m_pendingRequest = REQ_KEYHASH;
    m_pendingKeyHeight = height;

    return rpcSend(doc);
}

int64_t HushClient::submitBlock(const std::string &blockHex)
{
    using namespace rapidjson;
    Document doc(kObjectType);
    auto &allocator = doc.GetAllocator();

    Value params(kArrayType);
    params.PushBack(Value(blockHex.c_str(), allocator), allocator);

    createRpc10(doc, m_sequence, "submitblock", params);
    m_pendingRequest = REQ_SUBMIT;

    LOG_INFO("%s " MAGENTA_BOLD("submitting block at height %u"), tag(), m_height);

    return rpcSend(doc);
}

int64_t HushClient::rpcSend(const rapidjson::Document &doc)
{
    FetchRequest req(HTTP_POST, m_pool.host(), m_pool.port(), kJsonRPC, doc, m_pool.isTLS(), isQuiet());

    // HAC daemons require text/plain content-type (override application/json)
    req.headers.erase("Content-Type");
    req.headers.insert({"Content-Type", "text/plain"});

    // Add RPC authentication if configured
    if (!m_pool.user().isEmpty()) {
        std::string auth = m_pool.user().data();
        if (!m_pool.password().isEmpty()) {
            auth += ":";
            auth += m_pool.password().data();
        }
        const std::string encoded = toBase64(auth);
        req.headers.insert({"Authorization", "Basic " + encoded});
    }

    fetch(tag(), std::move(req), m_httpListener);

    return m_sequence++;
}

bool HushClient::parseBlockTemplate(const rapidjson::Value &result)
{
    if (!result.IsObject()) {
        LOG_ERR("%s " RED("invalid block template response"), tag());
        return false;
    }

    // Check if this is the same job (same previous block hash)
    const char *prevHash = Json::getString(result, "previousblockhash");
    if (prevHash && m_prevJobHash == prevHash && m_state == ConnectedState) {
        // Same block, skip duplicate job
        return true;
    }

    // Parse BIP22 block template fields
    m_height = Json::getUint64(result, "height");
    m_curtime = Json::getUint64(result, "curtime");
    m_version = Json::getInt(result, "version", 4);
    m_prevHash = Json::getString(result, "previousblockhash");
    m_saplingRoot = Json::getString(result, "finalsaplingroothash");
    m_target = Json::getString(result, "target");
    m_bits = Json::getString(result, "bits");

    // Parse target into bytes for PoW comparison (32 bytes, big-endian from hex)
    m_targetBytes.resize(32);
    if (m_target.size() == 64) {
        Cvt::fromHex(m_targetBytes.data(), 32, m_target.data(), 64);
    }

    // Coinbase transaction
    const auto &coinbase = result["coinbasetxn"];
    if (!coinbase.IsObject()) {
        LOG_ERR("%s " RED("missing coinbasetxn in template"), tag());
        return false;
    }
    m_coinbaseTx = Json::getString(coinbase, "data");
    m_merkleRoot = Json::getString(coinbase, "hash");

    LOG_DEBUG("%s template: height=%lu bits=%s target=%s", tag(), m_height, m_bits.data(), m_target.data());
    LOG_DEBUG("%s prevHash=%s", tag(), m_prevHash.data());
    LOG_DEBUG("%s merkleRoot=%s", tag(), m_merkleRoot.data());

    // Other transactions (may be empty for low traffic chains)
    m_transactions.clear();
    const auto &txs = result["transactions"];
    if (txs.IsArray()) {
        for (const auto &tx : txs.GetArray()) {
            if (tx.IsObject()) {
                m_transactions.push_back(Json::getString(tx, "data"));
            }
        }
    }

    // Validate required fields
    if (m_height == 0 || m_prevHash.isEmpty() || m_coinbaseTx.isEmpty()) {
        LOG_ERR("%s " RED("incomplete block template"), tag());
        return false;
    }

    // Check if we need to fetch new RandomX key
    const uint64_t keyHeight = getKeyHeight(m_height);
    if (keyHeight != m_keyHeight || m_keyBlockHash.isEmpty()) {
        if (keyHeight == 0) {
            // Use chain-specific initial RandomX key.
            // Daemon computes: sprintf("%08x%s%08x", ASSETCHAINS_MAGIC, SYMBOL, RPCPORT)
            // and passes the raw ASCII bytes to randomx_init_cache().
            // We hex-encode those bytes (zero-padded to 32) for setSeedHash().
            char initialKey[81];
            const uint32_t magic = 2387029918u;  // DRAGONX ASSETCHAINS_MAGIC
            const char* symbol = "DRAGONX";
            const uint16_t rpcPort = 21769;
            snprintf(initialKey, sizeof(initialKey), "%08x%s%08x", magic, symbol, (uint32_t)rpcPort);
            const size_t keyLen = strlen(initialKey);
            // Hex-encode only the actual key bytes (no zero-padding).
            // The daemon passes strlen(initialKey) bytes to randomx_init_cache(),
            // so we must match that exact length.
            char hexBuf[163]; // max 81 bytes * 2 + 1
            for (size_t i = 0; i < keyLen; i++) snprintf(hexBuf + i*2, 3, "%02x", (uint8_t)initialKey[i]);
            hexBuf[keyLen * 2] = '\0';
            m_keyBlockHash = hexBuf;
            m_keyHeight = 0;
            LOG_INFO("%s " CYAN("using initial RandomX key \"%s\" for height %u"), tag(), initialKey, m_height);
        } else {
            LOG_INFO("%s " CYAN("fetching RandomX key block hash at height %u"), tag(), keyHeight);
            getBlockHash(keyHeight);
            return true;  // Will continue after receiving key hash
        }
    }

    // Create the mining job
    Job job(false, m_pool.algorithm(), String());
    job.setHeight(m_height);

    if (!job.setSeedHash(m_keyBlockHash.data())) {
        LOG_ERR("%s " RED("failed to set seed hash: %s (len=%zu)"), tag(), m_keyBlockHash.data(), m_keyBlockHash.size());
        return false;
    }

    // Build 108-byte header for RandomX hashing (nonce bytes 108-139 filled by worker):
    // version(4) + prevHash(32) + merkleRoot(32) + saplingRoot(32) + time(4) + bits(4) = 108
    uint8_t header[108];
    size_t offset = 0;

    // nVersion (4 bytes, little-endian)
    const uint32_t ver = static_cast<uint32_t>(m_version);
    memcpy(header + offset, &ver, 4);
    offset += 4;

    // hashPrevBlock (32 bytes, internal byte order = reversed from display)
    {
        std::vector<uint8_t> tmp(32);
        Cvt::fromHex(tmp.data(), 32, m_prevHash.data(), 64);
        std::reverse(tmp.begin(), tmp.end());
        memcpy(header + offset, tmp.data(), 32);
        // Also store for block submission
        memcpy(m_headerPrevHash, tmp.data(), 32);
    }
    offset += 32;

    // hashMerkleRoot (32 bytes, reversed)
    {
        std::vector<uint8_t> tmp(32);
        Cvt::fromHex(tmp.data(), 32, m_merkleRoot.data(), 64);
        std::reverse(tmp.begin(), tmp.end());
        memcpy(header + offset, tmp.data(), 32);
        memcpy(m_headerMerkleRoot, tmp.data(), 32);
    }
    offset += 32;

    // hashFinalSaplingRoot (32 bytes, reversed)
    {
        std::vector<uint8_t> tmp(32);
        Cvt::fromHex(tmp.data(), 32, m_saplingRoot.data(), 64);
        std::reverse(tmp.begin(), tmp.end());
        memcpy(header + offset, tmp.data(), 32);
        memcpy(m_headerSaplingRoot, tmp.data(), 32);
    }
    offset += 32;

    // nTime (4 bytes, little-endian)
    const uint32_t time32 = static_cast<uint32_t>(m_curtime);
    memcpy(header + offset, &time32, 4);
    m_headerTime = time32;
    offset += 4;

    // nBits (4 bytes) - parse from big-endian hex, store as little-endian uint32
    uint32_t bits = 0;
    if (m_bits.size() == 8) {
        bits = static_cast<uint32_t>(strtoul(m_bits.data(), nullptr, 16));
    }
    memcpy(header + offset, &bits, 4);
    m_headerBits = bits;
    offset += 4;

    // Set the 108-byte header directly into the job blob (worker adds 32-byte nonce at offset 108)
    job.setHushHeader(header);

    // Compute 64-bit target from compact "bits" field (Bitcoin/Zcash format)
    // Top byte = exponent, lower 3 bytes = mantissa
    // Full 256-bit target = mantissa * 2^(8*(exponent-3))
    // xmrig compares: (uint64_t)hash[24..31] < target64
    {
        int exponent = (bits >> 24) & 0xff;
        uint32_t mantissa = bits & 0x007fffff;
        int mantissaPos = exponent - 3;  // Byte position of mantissa's low byte

        uint64_t target64 = 0;

        if (mantissaPos >= 32) {
            target64 = 0xFFFFFFFFFFFFFFFFULL;
        } else if (mantissaPos >= 24) {
            int shift = (mantissaPos - 24) * 8;
            target64 = (uint64_t)mantissa << shift;
            if (mantissaPos > 29) {
                target64 = 0xFFFFFFFFFFFFFFFFULL;
            }
        } else {
            // Mantissa is entirely below byte 24 - extremely high difficulty
            target64 = 0;
        }

        job.setTarget64(target64);
    }

    // Mark as solo mining so workers use 32-byte SoloNonce
    job.setSoloMining(true);

    m_currentJobId = Cvt::toHex(Cvt::randomBytes(4));
    job.setId(m_currentJobId);

    m_job = std::move(job);
    m_prevJobHash = m_prevHash;
    m_jobSteadyMs = Chrono::steadyMSecs();

    if (m_state == ConnectingState) {
        LOG_INFO("%s " GREEN("connected to %s:%d"), tag(), m_pool.host().data(), m_pool.port());
        setState(ConnectedState);
    }

    LOG_INFO("%s " MAGENTA_BOLD("new job") " height: " CYAN_BOLD("%u") " bits: " CYAN_BOLD("0x%08x") " diff: " CYAN_BOLD("%" PRIu64), 
             tag(), m_height, m_headerBits, m_job.diff());

    m_listener->onJobReceived(this, m_job, rapidjson::Value());
    return true;
}

bool HushClient::parseResponse(int64_t id, const rapidjson::Value &result, const rapidjson::Value &error)
{
    // Handle RPC errors
    if (error.IsObject()) {
        const char *message = Json::getString(error, "message", "unknown error");
        const int code = Json::getInt(error, "code", -1);
        LOG_ERR("%s " RED("RPC error %d: \"%s\""), tag(), code, message);
        return false;
    }

    switch (m_pendingRequest) {
    case REQ_TEMPLATE:
        if (parseBlockTemplate(result)) {
            m_timer->start(m_pool.pollInterval(), m_pool.pollInterval());
            return true;
        }
        return m_pendingRequest == REQ_KEYHASH;  // Waiting for key is ok

    case REQ_KEYHASH:
        if (result.IsString()) {
            // getblockhash returns display-order (big-endian) hex, but the daemon
            // passes uint256 internal bytes (little-endian) to randomx_init_cache().
            // Reverse the bytes so setSeedHash() produces the correct LE byte order.
            const char* displayHash = result.GetString();
            std::vector<uint8_t> hashBytes(32);
            Cvt::fromHex(hashBytes.data(), 32, displayHash, 64);
            std::reverse(hashBytes.begin(), hashBytes.end());
            char reversedHex[65];
            for (size_t i = 0; i < 32; i++) snprintf(reversedHex + i*2, 3, "%02x", hashBytes[i]);
            reversedHex[64] = '\0';
            m_keyBlockHash = reversedHex;
            m_keyHeight = m_pendingKeyHeight;
            LOG_INFO("%s " GREEN("RandomX key block %u: %.16s... (reversed to LE)"), 
                     tag(), m_keyHeight, m_keyBlockHash.data());
            // Now get the block template again with the key
            m_pendingRequest = REQ_NONE;
            getBlockTemplate();
            return true;
        }
        LOG_ERR("%s " RED("invalid getblockhash response - expected string, got type %d"), 
                tag(), result.GetType());
        return false;

    case REQ_SUBMIT:
        // submitblock returns null on success
        if (result.IsNull()) {
            LOG_INFO("%s " GREEN_BOLD("BLOCK ACCEPTED!"), tag());
            if (m_results.count(id)) {
                m_listener->onResultAccepted(this, m_results[id], nullptr);
                m_results.erase(id);
            }
        } else if (result.IsString()) {
            const char *msg = result.GetString();
            if (strlen(msg) > 0) {
                LOG_ERR("%s " RED("block rejected: %s"), tag(), msg);
            } else {
                LOG_INFO("%s " GREEN_BOLD("BLOCK ACCEPTED!"), tag());
            }
        }
        // Get new work after submit
        getBlockTemplate();
        return true;

    default:
        return false;
    }
}

void HushClient::retry()
{
    m_failures++;
    m_listener->onClose(this, static_cast<int>(m_failures));

    if (m_state == ConnectedState) {
        setState(ConnectingState);
    }

    m_timer->stop();
    m_timer->start(m_retryPause, 0);
}

void HushClient::setState(SocketState state)
{
    if (m_state == state) {
        return;
    }

    m_state = state;

    switch (state) {
    case ConnectedState:
        m_failures = 0;
        m_listener->onLoginSuccess(this);
        break;

    case UnconnectedState:
        m_timer->stop();
        m_failures = -1;
        m_listener->onClose(this, -1);
        break;

    default:
        break;
    }
}

uint64_t HushClient::getKeyHeight(uint64_t height) const
{
    // RandomX key changes every RANDOMX_INTERVAL blocks with RANDOMX_LAG delay
    if (height < static_cast<uint64_t>(RANDOMX_INTERVAL + RANDOMX_LAG)) {
        return 0;  // Use genesis key
    }
    return ((height - RANDOMX_LAG) / RANDOMX_INTERVAL) * RANDOMX_INTERVAL;
}

std::vector<uint8_t> HushClient::serializeBlock(uint32_t nonce, uint64_t extraNonce) const
{
    std::vector<uint8_t> blob;
    blob.reserve(1024);

    // nVersion (4 bytes, little-endian)
    const uint32_t ver = static_cast<uint32_t>(m_version);
    blob.insert(blob.end(), reinterpret_cast<const uint8_t*>(&ver), 
                reinterpret_cast<const uint8_t*>(&ver) + 4);

    // hashPrevBlock (32 bytes, reversed from hex display)
    std::vector<uint8_t> prevHash(32);
    Cvt::fromHex(prevHash.data(), 32, m_prevHash.data(), 64);
    std::reverse(prevHash.begin(), prevHash.end());
    blob.insert(blob.end(), prevHash.begin(), prevHash.end());

    // hashMerkleRoot (32 bytes, reversed)
    std::vector<uint8_t> merkleRoot(32);
    Cvt::fromHex(merkleRoot.data(), 32, m_merkleRoot.data(), 64);
    std::reverse(merkleRoot.begin(), merkleRoot.end());
    blob.insert(blob.end(), merkleRoot.begin(), merkleRoot.end());

    // hashFinalSaplingRoot (32 bytes, reversed)
    std::vector<uint8_t> saplingRoot(32);
    Cvt::fromHex(saplingRoot.data(), 32, m_saplingRoot.data(), 64);
    std::reverse(saplingRoot.begin(), saplingRoot.end());
    blob.insert(blob.end(), saplingRoot.begin(), saplingRoot.end());

    // nTime (4 bytes, little-endian)
    const uint32_t time32 = static_cast<uint32_t>(m_curtime);
    blob.insert(blob.end(), reinterpret_cast<const uint8_t*>(&time32), 
                reinterpret_cast<const uint8_t*>(&time32) + 4);

    // nBits (4 bytes) - convert from big-endian hex to little-endian binary
    uint32_t bits = 0;
    for (int i = 0; i < 8 && i < static_cast<int>(m_bits.size()); i += 2) {
        uint8_t byte;
        Cvt::fromHex(&byte, 1, m_bits.data() + i, 2);
        bits = (bits << 8) | byte;
    }
    blob.insert(blob.end(), reinterpret_cast<const uint8_t*>(&bits), 
                reinterpret_cast<const uint8_t*>(&bits) + 4);

    // nNonce (32 bytes for Zcash/Hush - uint256)
    std::vector<uint8_t> nonce256(32, 0);
    memcpy(nonce256.data(), &nonce, 4);
    memcpy(nonce256.data() + 4, &extraNonce, sizeof(extraNonce));
    blob.insert(blob.end(), nonce256.begin(), nonce256.end());

    // nSolution placeholder (CompactSize + 32 zeros)
    blob.push_back(32);  // CompactSize for 32 bytes
    blob.insert(blob.end(), 32, 0);

    // Transaction count (CompactSize)
    const size_t txCount = 1 + m_transactions.size();
    if (txCount < 0xFD) {
        blob.push_back(static_cast<uint8_t>(txCount));
    } else {
        blob.push_back(0xFD);
        blob.push_back(txCount & 0xFF);
        blob.push_back((txCount >> 8) & 0xFF);
    }

    // Coinbase transaction
    std::vector<uint8_t> coinbase(m_coinbaseTx.size() / 2);
    Cvt::fromHex(coinbase.data(), coinbase.size(), m_coinbaseTx.data(), m_coinbaseTx.size());
    blob.insert(blob.end(), coinbase.begin(), coinbase.end());

    // Other transactions
    for (const auto &txHex : m_transactions) {
        std::vector<uint8_t> tx(txHex.size() / 2);
        Cvt::fromHex(tx.data(), tx.size(), txHex.data(), txHex.size());
        blob.insert(blob.end(), tx.begin(), tx.end());
    }

    return blob;
}

std::string HushClient::serializeBlockHex(const uint8_t* nonce32, const uint8_t* solution) const
{
    std::vector<uint8_t> blob;
    blob.reserve(1024);

    // Header (140 bytes) using cached binary fields
    // Version (4 bytes LE)
    const uint32_t ver = static_cast<uint32_t>(m_version);
    blob.insert(blob.end(), reinterpret_cast<const uint8_t*>(&ver), 
                reinterpret_cast<const uint8_t*>(&ver) + 4);

    // Previous hash (32 bytes - already in internal order)
    blob.insert(blob.end(), m_headerPrevHash, m_headerPrevHash + 32);

    // Merkle root (32 bytes)
    blob.insert(blob.end(), m_headerMerkleRoot, m_headerMerkleRoot + 32);

    // Sapling root (32 bytes)
    blob.insert(blob.end(), m_headerSaplingRoot, m_headerSaplingRoot + 32);

    // Time (4 bytes LE)
    blob.insert(blob.end(), reinterpret_cast<const uint8_t*>(&m_headerTime), 
                reinterpret_cast<const uint8_t*>(&m_headerTime) + 4);

    // Bits (4 bytes LE)
    blob.insert(blob.end(), reinterpret_cast<const uint8_t*>(&m_headerBits), 
                reinterpret_cast<const uint8_t*>(&m_headerBits) + 4);

    // Nonce (32 bytes from the mining result)
    blob.insert(blob.end(), nonce32, nonce32 + 32);

    // Solution (the RandomX hash - 32 bytes with CompactSize prefix)
    blob.push_back(32);  // CompactSize
    blob.insert(blob.end(), solution, solution + 32);

    // Transactions
    const size_t txCount = 1 + m_transactions.size();
    if (txCount < 0xFD) {
        blob.push_back(static_cast<uint8_t>(txCount));
    } else {
        blob.push_back(0xFD);
        blob.push_back(txCount & 0xFF);
        blob.push_back((txCount >> 8) & 0xFF);
    }

    std::vector<uint8_t> coinbase(m_coinbaseTx.size() / 2);
    Cvt::fromHex(coinbase.data(), coinbase.size(), m_coinbaseTx.data(), m_coinbaseTx.size());
    blob.insert(blob.end(), coinbase.begin(), coinbase.end());

    for (const auto &txHex : m_transactions) {
        std::vector<uint8_t> tx(txHex.size() / 2);
        Cvt::fromHex(tx.data(), tx.size(), txHex.data(), txHex.size());
        blob.insert(blob.end(), tx.begin(), tx.end());
    }

    const String hex = Cvt::toHex(blob.data(), blob.size());
    return std::string(hex.data(), hex.size());
}

void HushClient::sha256d(const uint8_t* data, size_t len, uint8_t* out)
{
    uint8_t hash1[32];
    ::SHA256(data, len, hash1);
    ::SHA256(hash1, 32, out);
}

std::vector<uint8_t> HushClient::serializeHeader(const uint8_t* nonce32, const uint8_t* solution) const
{
    std::vector<uint8_t> header;
    header.reserve(140 + 1 + 32);  // header + compactsize + solution

    // Version (4 bytes LE)
    const uint32_t ver = static_cast<uint32_t>(m_version);
    header.insert(header.end(), reinterpret_cast<const uint8_t*>(&ver), 
                reinterpret_cast<const uint8_t*>(&ver) + 4);

    // Use cached binary header fields (already in internal byte order)
    header.insert(header.end(), m_headerPrevHash, m_headerPrevHash + 32);
    header.insert(header.end(), m_headerMerkleRoot, m_headerMerkleRoot + 32);
    header.insert(header.end(), m_headerSaplingRoot, m_headerSaplingRoot + 32);

    // Time (4 bytes LE)
    header.insert(header.end(), reinterpret_cast<const uint8_t*>(&m_headerTime), 
                reinterpret_cast<const uint8_t*>(&m_headerTime) + 4);

    // Bits (4 bytes LE)
    header.insert(header.end(), reinterpret_cast<const uint8_t*>(&m_headerBits), 
                reinterpret_cast<const uint8_t*>(&m_headerBits) + 4);

    // Nonce (32 bytes)
    header.insert(header.end(), nonce32, nonce32 + 32);

    // nSolution (compactsize + 32 bytes)
    header.push_back(32);  // CompactSize for 32 bytes
    header.insert(header.end(), solution, solution + 32);

    return header;
}

bool HushClient::checkPow(const uint8_t* nonce32, const uint8_t* solution) const
{
    // Build header with solution
    const std::vector<uint8_t> header = serializeHeader(nonce32, solution);
    
    // Compute SHA256D(header)
    uint8_t blockHash[32];
    sha256d(header.data(), header.size(), blockHash);
    
    // Compare blockHash < target (both are 32 bytes, big-endian in target, little-endian in hash)
    // Block hash from SHA256D is little-endian, target from RPC is big-endian
    // We need to compare them byte by byte, reversing the hash for comparison
    for (int i = 0; i < 32; i++) {
        uint8_t hashByte = blockHash[31 - i];  // Reverse hash to big-endian
        uint8_t targetByte = m_targetBytes[i];
        
        if (hashByte < targetByte) {
            LOG_INFO("%s " GREEN_BOLD("PoW check PASSED") " - hash meets target", tag());
            return true;
        }
        if (hashByte > targetByte) {
            return false;
        }
    }
    return true;  // Equal means it passes
}

uint64_t HushClient::targetToDiff(const char *target) const
{
    // Target is 64 hex chars (256-bit big-endian)
    // Find the first non-zero bytes and compute difficulty
    if (!target || strlen(target) < 16) {
        return 1;
    }

    // Parse first 8 bytes as big-endian uint64 for approximation
    uint64_t t = 0;
    for (int i = 0; i < 16; i += 2) {
        uint8_t byte;
        Cvt::fromHex(&byte, 1, target + i, 2);
        t = (t << 8) | byte;
    }

    if (t == 0) {
        return 0xFFFFFFFFFFFFFFFFULL;
    }

    // Rough difficulty approximation
    return 0xFFFFFFFFFFFFFFFFULL / t;
}

} // namespace xmrig