Method GetPubKey

src/script/descriptor.cpp:655–717

    }

    std::optional<CPubKey> GetPubKey(int pos, const SigningProvider& arg, FlatSigningProvider& out, const DescriptorCache* read_cache = nullptr, DescriptorCache* write_cache = nullptr) const override
    {
        FlatSigningProvider dummy;
        // If the participants are not ranged, we can compute and cache the aggregate pubkey by creating a PubkeyProvider for it
        if (!m_aggregate_provider && !m_ranged_participants) {
            // Retrieve the pubkeys from the providers
            std::vector<CPubKey> pubkeys;
            for (const auto& prov : m_participants) {
                std::optional<CPubKey> pubkey = prov->GetPubKey(0, arg, dummy, read_cache, write_cache);
                if (!pubkey.has_value()) {
                    return std::nullopt;
                }
                pubkeys.push_back(pubkey.value());
            }
            std::sort(pubkeys.begin(), pubkeys.end());

            // Aggregate the pubkey
            m_aggregate_pubkey = MuSig2AggregatePubkeys(pubkeys);
            if (!Assume(m_aggregate_pubkey.has_value())) return std::nullopt;

            // Make our pubkey provider
            if (IsRangedDerivation() || !m_path.empty()) {
                // Make the synthetic xpub and construct the BIP32PubkeyProvider
                CExtPubKey extpub = CreateMuSig2SyntheticXpub(m_aggregate_pubkey.value());
                m_aggregate_provider = std::make_unique<BIP32PubkeyProvider>(m_expr_index, extpub, m_path, m_derive, /*apostrophe=*/false);
            } else {
                m_aggregate_provider = std::make_unique<ConstPubkeyProvider>(m_expr_index, m_aggregate_pubkey.value(), /*xonly=*/false);
            }
        }

        // Retrieve all participant pubkeys
        std::vector<CPubKey> pubkeys;
        for (const auto& prov : m_participants) {
            std::optional<CPubKey> pub = prov->GetPubKey(pos, arg, out, read_cache, write_cache);
            if (!pub) return std::nullopt;
            pubkeys.emplace_back(*pub);
        }
        std::sort(pubkeys.begin(), pubkeys.end());

        CPubKey pubout;
        if (m_aggregate_provider) {
            // When we have a cached aggregate key, we are either returning it or deriving from it
            // Either way, we can passthrough to its GetPubKey
            // Use a dummy signing provider as private keys do not exist for the aggregate pubkey
            std::optional<CPubKey> pub = m_aggregate_provider->GetPubKey(pos, dummy, out, read_cache, write_cache);
            if (!pub) return std::nullopt;
            pubout = *pub;
            out.aggregate_pubkeys.emplace(m_aggregate_pubkey.value(), pubkeys);
        } else {
            if (!Assume(m_ranged_participants) || !Assume(m_path.empty())) return std::nullopt;
            // Compute aggregate key from derived participants
            std::optional<CPubKey> aggregate_pubkey = MuSig2AggregatePubkeys(pubkeys);
            if (!aggregate_pubkey) return std::nullopt;
            pubout = *aggregate_pubkey;

            std::unique_ptr<ConstPubkeyProvider> this_agg_provider = std::make_unique<ConstPubkeyProvider>(m_expr_index, aggregate_pubkey.value(), /*xonly=*/false);
            this_agg_provider->GetPubKey(0, dummy, out, read_cache, write_cache);
            out.aggregate_pubkeys.emplace(pubout, pubkeys);