Stub in maximum_history for limiting electrum large address query.

Author: evoskuil

include/bitcoin/server/protocols/protocol_electrum.hpp

@@ -252,7 +252,7 @@ class BCS_API protocol_electrum
     void do_scripthash_subscribe(const hash_digest& hash,
         notify_t type) NOEXCEPT;
     void complete_scripthash_subscribe(const code& ec,
-        hash_digest& status, const hash_digest& hash) NOEXCEPT;
+        const hash_digest& status, const hash_digest& hash) NOEXCEPT;
     void scripthash_unsubscribe(const hash_digest& hash) NOEXCEPT;
     void do_scripthash_unsubscribe(const hash_digest& hash) NOEXCEPT;
     void complete_scripthash_unsubscribe(bool found) NOEXCEPT;
@@ -321,7 +321,7 @@ class BCS_API protocol_electrum
 
     // Status utilities.
     code get_scripthash_status(hash_digest& out, subscription& sub,
-        const hash_digest& hash) NOEXCEPT;
+        const hash_digest& hash, size_t limit=max_size_t) NOEXCEPT;
     bool get_outpoint_statuses(std::vector<interface::object_t>& out,
         const system::chain::point& prevout) const NOEXCEPT;
     bool get_outpoint_status(interface::object_t& out,

include/bitcoin/server/settings.hpp

@@ -94,6 +94,9 @@ class BCS_API settings
         /// Recommended to be a multiple of the difficulty retarget period.
         uint32_t maximum_headers{ 10 * 2016 };
 
+        /// Maximum number of address history entries upon one subscription.
+        uint32_t maximum_history{ 1'000'000 };
+
         /// Maximum cumulative number of address subscriptions per channel.
         uint32_t maximum_subscriptions{ 1'000'000 };
 

src/parser.cpp

@@ -1137,6 +1137,11 @@ options_metadata parser::load_settings() THROWS
         value<uint32_t>(&configured.server.electrum.maximum_headers),
         "The maximum allowed headers returned per request, defaults to '20160'."
     )
+    (
+        "electrum.maximum_history",
+        value<uint32_t>(&configured.server.electrum.maximum_history),
+        "The maximum number of address history entries upon one subscription, defaults to '1000000'."
+    )
     (
         "electrum.maximum_subscriptions",
         value<uint32_t>(&configured.server.electrum.maximum_subscriptions),

src/protocols/electrum/protocol_electrum_scripthash_subscribe.cpp

@@ -91,9 +91,12 @@ void protocol_electrum::do_scripthash_subscribe(const hash_digest& hash,
     hash_digest status{};
     if (address_subscriptions_.size() < options_.maximum_subscriptions)
     {
+        using mid = midstate;
+        const auto limit = options().maximum_history;
+
         // Subscription response is idempotent.
-        auto at = address_subscriptions_.try_emplace(hash, type, midstate{});
-        ec = get_scripthash_status(status, at.first->second, at.first->first);
+        auto& at = *address_subscriptions_.try_emplace(hash, type, mid{}).first;
+        ec = get_scripthash_status(status, at.second, at.first, limit);
         subscribed_address_.store(true, relaxed);
     }
     else
@@ -105,14 +108,15 @@ void protocol_electrum::do_scripthash_subscribe(const hash_digest& hash,
 }
 
 void protocol_electrum::complete_scripthash_subscribe(const code& ec,
-    hash_digest& status, const hash_digest& hash) NOEXCEPT
+    const hash_digest& status, const hash_digest& hash) NOEXCEPT
 {
     BC_ASSERT(stranded());
 
     monitor(false);
     if (stopped())
         return;
 
+    // TODO: map database::error::maximum_depth to server code?
     if (ec)
     {
         send_code(ec);
@@ -281,9 +285,10 @@ hash_digest protocol_electrum::to_status(const histories& histories) NOEXCEPT
 }
 
 code protocol_electrum::get_scripthash_status(hash_digest& out,
-    subscription& /* sub */, const hash_digest& hash) NOEXCEPT
+    subscription& /* sub */, const hash_digest& hash, size_t /* limit */) NOEXCEPT
 {
     // TODO: use cursors and midstate to optimize succesive queries.
+    // TODO: limit first pass query depth.
 
     histories histories{};
     const auto& query = archive();

test/protocols/electrum/electrum.cpp

@@ -57,6 +57,7 @@ electrum_setup_fixture::electrum_setup_fixture(const initializer& setup,
     electrum.banner_message = "banner_message";
     electrum.donation_address = "donation_address";
     electrum.maximum_subscriptions = 3;
+    electrum.maximum_history = 5;
     electrum.maximum_headers = 5;
     electrum.connections = 1;
     database_settings.interval_depth = 2;

test/settings.cpp

@@ -233,6 +233,7 @@ BOOST_AUTO_TEST_CASE(server__electrum_server__defaults__expected)
 
     // electrum_server
     BOOST_REQUIRE_EQUAL(server.maximum_headers, 10u * 2016u);
+    BOOST_REQUIRE_EQUAL(server.maximum_history, 1'000'000u);
     BOOST_REQUIRE_EQUAL(server.maximum_subscriptions, 1'000'000u);
     BOOST_REQUIRE_EQUAL(server.server_name, BC_USER_AGENT);
     BOOST_REQUIRE(server.donation_address.empty());