Method SignTransaction

src/external_signer.cpp:77–124

}

bool ExternalSigner::SignTransaction(PartiallySignedTransaction& psbtx, std::string& error)
{
    // Serialize the PSBT
    DataStream ssTx{};
    ssTx << psbtx;
    // parse ExternalSigner master fingerprint
    std::vector<unsigned char> parsed_m_fingerprint = ParseHex(m_fingerprint);
    // Check if signer fingerprint matches any input master key fingerprint
    auto matches_signer_fingerprint = [&](const PSBTInput& input) {
        for (const auto& entry : input.hd_keypaths) {
            if (std::ranges::equal(parsed_m_fingerprint, entry.second.fingerprint)) return true;
        }
        for (const auto& entry : input.m_tap_bip32_paths) {
            if (std::ranges::equal(parsed_m_fingerprint, entry.second.second.fingerprint)) return true;
        }
        return false;
    };

    if (!std::any_of(psbtx.inputs.begin(), psbtx.inputs.end(), matches_signer_fingerprint)) {
        error = "Signer fingerprint " + m_fingerprint + " does not match any of the inputs:\n" + EncodeBase64(ssTx.str());
        return false;
    }

    const std::vector<std::string> command = Cat(m_command, Cat({"--stdin", "--fingerprint", m_fingerprint}, NetworkArg()));
    const std::string stdinStr = "signtx " + EncodeBase64(ssTx.str());

    const UniValue signer_result = RunCommandParseJSON(command, stdinStr);

    if (signer_result.find_value("error").isStr()) {
        error = signer_result.find_value("error").get_str();
        return false;
    }

    if (!signer_result.find_value("psbt").isStr()) {
        error = "Unexpected result from signer";
        return false;
    }

    util::Result<PartiallySignedTransaction> signer_psbtx = DecodeBase64PSBT(signer_result.find_value("psbt").get_str());
    if (!signer_psbtx) {
        error = strprintf("TX decode failed %s", util::ErrorString(signer_psbtx).original);
        return false;
    }

    psbtx = *signer_psbtx;

    return true;
}